Evolution and Distribution 

of the Genus My a, and 

Tertiary Migrations 

of Mollusca

GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G

Evolution and Distribution 

of the Genus My a, and 

Tertiary Migrations 

of Mollusca

By F. STEARNS MACNEIL

CONTRIBUTIONS TO PALEONTOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G

Known first in the early Tertiary of Japan, the 

genus Mya migrated to western North America, 

the Arctic Ocean, and to both the European and 

the American sides of the North Atlantic

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

The U.S. Geological Survey Library has cataloged this publication as follows :

MacNeil, Francis Stearns, 1909-

Evolution and distribution of the genus Mya and Tertiary 

migrations of Mollusca. Washington, U.S. Govt. Print. Off., 

1964.

iv. 51 p. illus., map, diagrs. 30 cm. (U.S. Geological Survey. 

Professional Paper 483-G) 

Contributions to paleontology. 

Bibliography: p. 45-47.

1. Mollusks. 2. Paleontology Tertiary. I. Title. (Series)

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C , 20402 - Price 65 cents (paper cover)
CONTENTS

Abstract. __________________________________________

Introduction _______________________________________

Migrations of Pacific and Atlantic Ocean mollusks______

Biological and temporal aspects of migration.______

Migration and dispersaL-____________________

Migration and ecology.._____________________

Migration and specific variability.____________

Migration and evolution.____________________

Migration and correlation.___________________

Tertiary paleogeography of the Arctic and the boreal 

regions._____________________________________

Arctic climate and its effect on organisms__________

Periods and routes of migration __________________

Phylogeny and distribution of species________________

Identity of Mya japonica Jay-.___________________

Mya crassa Grewingk, Mya elegans (Eichwald), and 

Mya intermedia Dall__________________________

Ancestry of Mya______________________________

Indigenous Atlantic species Mya producta Conrad _ 

Early Pacific species---__________________________

Mya arenaria group_____________________________

Mya elegans group______________________________

Mya truncata group_____________________________

Morphologic characters._________________________

Shell thickness.___________________________

Shell shape_______________________________

Variability of form._________________________

Sculpture._________________________________

Pallial line and pallial sinus__________________

Muscle scars.______________________________

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Phylogeny and distribution of species Continued 

Morphologic characters Continued

Ligament.________-___________---___---____ G21

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Spoon.________-____-_-___-_-_----_

Ligamental callus___________________

Subumbonal solution._______________

Systematic paleontology.__-________--_----__

Genus Mya Linne", 1758________________

Subgenus Arenomya Winckworth, 1930____

Mya (?Arenomya) producta Conrad__ 

M. (1A.) ezoensis Nagao and Inoue..__ 

M. (?A) kusiroensis Nagao and Inoue. 

M. (1A.) grewingki Makiyama________

M. (?A) grewingki haboroensis Fujie__ 

M. (?A) dickersoni Clark___________-

M. (?A) elegans (Eichwald)________

M. (Arenomya) fujiei MacNeil, n. sp__ 

M. (A.) arrosis MacNeil, n. sp________

M. (A.) japonica Jay________________

M. (A.) arenaria Linne.____-----____

Subgenus Mya Linne".-_________-----____

Mya (Mya) salmonensis Clark._______

M. (M.) cuneiformis (Bohm)_________

M. (M.) pseudoarenaria Schlesch_.____

M. (M.) truncata Linne--------------

M. (M.) priapus Tilesius-__________

M. (M.) pullus Sowerby_____________

Localities. _______________-__-_-_-_-------_-

Bibliography.______________________________

Index.__________________________________ 

ILLUSTRATIONS

[Plates follow Index] 

PLATES 1-11. Mya from the 

1. Choptank Formation (Maryland), the Poul Creek Formation (Alaska), and the Acila shumardi zone, Popof 

Island (Alaska).

2. Briones and Neroly Formations (California), Pliocene beds, Chignik Bay (Alaska), Pleistocene beds, St. Paul 

Island (Alaska), Recent (Alaska).

3. Briones, Cierbo, and Neroly Formations (California), Pleistocene beds, Cape Kruzenstern (Alaska), and 

Recent (Alaska).

4. Pleistocene beds, Nome (Alaska), and Recent (Japan and Alaska).

5. Briones, Cierbo, Etchegoin, and San Joaquin Formations (California), and the Yorktown Formation (Virginia).

6. Red Crag and Icenian Crag (England), Pleistocene beds, Nome (Alaska), and Recent (Denmark and British Columbia.

7. Poul Creek and Yakataga Formations (Alaska), middle Miocene beds (Sakhalin and Kodiak Island), Pleistocene 

beds, Yenisey River (Russia), and Recent (Alaska).

8. Yakataga Formation (Alaska), the Icenian Crag (England), the Clyde Beds (Scotland), Pleistocene beds, 

Nome (Alaska), and Recent (Alaska).

9. Icenian Crag (England), Pliocene beds, Tugidak Island (Alaska), postglacial beds, Juneau (Alaska), and Recent 

(Greenland and Alaska).

10. Recent (Kamchatka and Alaska).

11. Red Crag (England), Pleistocene beds, Wingham Island (Alaska), postglacial beds, Kachemak Bay (Alaska), 

and Recent (Alaska).

in
IV CONTENTS

Page 

FIGURE 1. Most probable late Tertiary and Quaternary migration routes between eastern Asia and western North America

and between the North Pacific Ocean and the North Atlantic Ocean.___________________________________ Gil

2. Diagram showing terminology of parts of spoon. Upper, Mya (Arenomya); lower, Mya (Mya). From Fujie

(1957)_.___._-__-_-_-_____________-._____. . ___._____._____--.....__._--_--____-_---.----..-_--- 22

3. Phylogeny of myarian subgenera and species, showing distribution of the two types of ligamental callus.______ 23
CONTRIBUTIONS TO PALEONTOLOGY

EVOLUTION AND DISTRIBUTION OF THE GENUS MY A, AND TERTIARY

MIGRATIONS OF MOLLUSCA

By F. STEARNS

ABSTRACT

Two genera, Mya, a pelecypod, and Neptunea, a gastropod, 

were selected as vehicles for a study of late Tertiary to Recent 

faunal migrations from the Pacific to the Atlantic Ocean by way 

of the Arctic Ocean because they are mollusks of large size, and 

because they have unlike larval stages; Mya has small currentborne pelagic larvae, and Neptunea has large bottom-crawling 

benthonic larvae. This report considers chiefly the genus Mya 

but also includes a general discussion of Arctic faunal migrations 

and its bearing on Tertiary paleogeography of the Arctic. Available evidence suggests that during early Tertiary time the 

Arctic regions either had greatly reduced marine embayments, 

or they were entirely land. The earliest known marine 

Tertiary deposits in the high Arctic, found in northern Alaska 

and Spitzbergen, are of middle or late Miocene age. The 

first boreal species of Pacific origin to be found in Atlantic 

Ocean deposits is in the Yorktown Formation of Virginia. 

The Yorktown Formation is currently assigned to the Pontian 

(late Miocene) Stage.

All known species of the genus Mya are defined and delimited, 

and an attempt is made to resolve the synonymy of Japanese 

and American and Pacific and Atlantic species. American, 

Arctic, and European species are illustrated; Japanese species 

have been illustrated elsewhere.

The geographical distribution of Mya is treated from an 

evolutionary and migrational standpoint. The genus is restricted to the Northern Hemisphere. Its ancestry is unknown, 

but it may stem from temperate or subtropical early Eocene 

forms currently assigned to the genus Sphenia. The earliest 

known species of Mya occurs in late Eocene or early Oligocene 

beds of Japan. One indigenous Atlantic species is known. The 

remaining 16 recognizable taxa are indigenous to the North 

Pacific. Three, and possibly four, of the Pacific species 

migrated subsequently by way of the Arctic Ocean to northern 

Europe and the American Atlantic coast.

Nomenclatural and synonymic revisions in this paper include: suppression of the name Mya grewingki nagaoi Oyama 

and Mizuno as a synonym of M. salmonensis Clark; recognition of M. kusiroensis Nagao and Inoue, M. grewingki Makiyama, and M. cuneiformis (Bohm) in Alaska; acceptance of 

the name M. japonica Jay in preference to M. oonogai Makiyania for the species occurring in southern Japan; recognition 

of the name M. elegans (Eichwald) as the valid name for 

M. crassa Grewingk M. intermedia Dall, and M. profunnior 

Grant and Gale; recognition of the name M. priapus Tilesius 

as the valid name for the North Pacific and Bering Sea species 

identified by most modern Japanese authors as If. japonica 

Jay; recognition of M. dic-Jcersoni Clark as a close relative of 

M. elegans; and the recognition of If. pullus Sowerby as a 

valid species probably most closely related to M. priapus.

Two new species are described: Mya fujiei MacNeil, based 

on M. japonica oonogai Fujie (1957, pi. 2. figs, la-b) from the 

Takinoue Formation (early middle Miocene) of Hokkaido, 

and M. arrosis MacNeil, based on specimens in the collections 

of the University of California from the Cierbo Sandstone 

(middle late Miocene) of the San Pablo Group, Contra Costa 

County, Calif.

INTRODUCTION

The genus Mya,, by virtue of both its morphological 

peculiarities and its heavy commercial harvest, should 

be one of the best understood mollusks. Instead, its 

comparatively few species, comparatively simple evolution, and comparatively restricted geographical occurrence involve subtleties that evade and confuse paleontologists and malacologists alike. Besides, there are 

still sizable gaps in our knowledge of phylogenetic 

lines.

Numerous attempts have been made to resolve the 

systematics of Mya,. Until recently the most careful 

studies were by European and American workers 

whose main interest was in Atlantic and Arctic 

species, and who were dealing literally with the outermost fringes of the problem. In the last three decades, 

however, several important studies have been made by 

Japanese paleontologists. These studies show conclusively that the greater part of the genus evolved in 

East Asia, although its place of origin remains unknown. It remained for knowledge of the Japanese 

Tertiary species to be reasonably complete before any 

clear picture of the evolution of the genus as a whole 

could be had. Much of the basic study of the Japanese 

species was performed by Makiyama (1935), Nagao 

and Inoue (1941), and Minato, Matsui, and Uozumi 

(1950).

Fujie (1957 and 1962) further segregated some of the 

fossil forms, brought together the age, formational occurrence, and geographical distribution of the different 

species, pointed out the morphological details by which 

they can be distinguished, and he showed by differences 

in their chondrophores that they constitute two species 

groups. Unfortunately, Fujie had access to very little 

extra Japanese material, and most of his treatment of 

foreign species is based on literature that too often does

Gl
G2 CONTRIBUTIONS TO PALEONTOLOGY

not describe or illustrate clearly the details he sought. 

Nevertheless, Fujie's work on the Japanese species contains the information necessary to a clear understanding of the origin and relationships of most myarian 

species, and it is unlikely that the present study could 

have been made without it.

If a genus so small, so clearly delimited, and so obviously isolated biologically from its closest relatives can 

pose such baffling problems, it can serve only to point 

up the complexity of organic evolution. It serves to 

show also how multiplied the problems can be in large 

multilinear groups in which separate lines of descent 

are morphologically parallel, less clearly marked, and 

complicated, moreover, by crisscrossing routes of migration. At least in the genus My a the picture is not complicated by uncertainties in generic or subgeneric assignment, or by homeomorphy in lineages that have been 

distinct phylogenetically since Eocene time.

The present study has been carried on concurrently 

with a similar study of the gastropod genus Neptunea, 

a much more complex group. Comparable studies of 

Neptunea and Mya, with emphasis on migration, provide a comparison of the distribution pattern of a genus 

having small pelagic larvae with a genus having large 

benthonic larvae.

All photographs used in this paper were taken by 

Mr. Kenji Sakamoto, of the U.S. Geological Survey, 

Menlo Park, Calif. Mr. Sakamoto also translated the 

paper by Minato, Matsui, and Uozumi, as well as 

numerous other short passages from Japanese.

I am indebted to Dr. A. Andersson of the Naturhistoriska Riksmuseet, Stockholm, for permission to figure 

a specimen from the Nordensiold Yenisey Expedition 

collections, and to Dr. G. Spaink of the Netherlands 

Geological Survey for the loan of specimens from 

Pleistocene deposits of the Netherlands. Drs. G. A. 

Cooper and H. A. Render of the U.S. National Museum 

both loaned specimens for figuring. Considerable use 

was made of the collections of the University of California, Berkeley, The California Academy of Sciences, 

San Francisco, and Stanford University, Palo Alto, 

and I gratefully acknowledge the assistance of Dr. J. 

Wyatt Durham, Dr. Leo. G. Hertlein, and Dr. A. Myra 

Keen of these institutions, respectively, for permission 

to publish on specimens in their collections, and for 

critical reading of the manuscript.

MIGRATIONS OF PACIFIC AND ATLANTIC OCEAN 

MOLLUSKS

Next to Neptunea, Mya is the most conspicious of 

those modern North Atlantic mollusks that clearly are 

immigrants from the Pacific. Because they are also

transArctic migrants, an understanding of Arctic 

migrations is a most important part of an understanding of myarian distribution.

Few genera have been the subject of worldwide 

monographic treatment, and even fewer of those monographed have been treated from the standpoint of evolution and migration. Such studies are not only the 

most reliable means of dealing with their taxonomy, 

but they have bearing on practically every phase of 

their geologic history. Many genera probably will be 

found to have nearly identical distribution patterns.

Migration studies would also aid materially in the 

solution of many stratigraphic and climatologic problems. Inasmuch as the temperature preference of 

many species is confined to fairly narrow limits, the 

species participating in Arctic migrations would reveal 

much concerning both the actual climate of each migration period and the relative amelioration of the polar 

climate for different periods. Two-way migrations 

give the greatest promise for accurate correlation of 

beds of departure with beds of arrival inasmuch as they 

can be checked both ways. A more detailed knowledge 

of paleogeography and of the time of opening of 

waterways would result.

BIOLOGICAL AND TEMPORAL ASPECTS OF 

MIGRATION

MIGRATION AN1> DISPERSAL

Migration can be defined as either an extension of the 

living area of an organism, or the complete abandonment of an area in favor of another. Dispersal can 

best be defined as the enlargement of the geographical 

distribution of an organism during any stage of its life, 

or death, by whatever means. Thus, migration can be 

accomplished by the dispersal of pelagic larvae by 

currents, but the most widespread dispersal of larvae 

cannot be construed as migration if the larvae are 

unable to establish themselves in new areas. The wide 

current dispersal of nautiloids, and probably ammonites, as gas-filled moribund individuals or floating 

dead shells is not migration.

MIGRATION AND ECOLOGY

It is impossible to lay down strictly geographical 

rules for the migration of species. Some elements of a 

fauna may migrate to a new area while other elements 

remain behind; still other elements may migrate to 

entirely different areas. Often it is difficult to see why 

a species does not occupy an area that seems open to it.

Viewed in the aggregate, migrations seem fortuitous. 

More probably, very careful selections of bottom, 

salinity, temperature, and other conditions are made.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G3

In some molluscan migrations depth seems unimportant. 

In Mya it may be a limiting factor inasmuch as the , 

genus is most prolific in very shallow water. Living 

specimens of both M, arenaria and M. truncata have 

been obtained as deep as 40 fathoms, but they are of 

small size and may not propagate at that depth.

The burrowing habit of Mya arenaria virtually 

restricts it to muddy and sandy bottoms. Its restriction to these substrata, however, does not necessarily 

restrict its migration because its larvae are pelagic. 

The stretch of unsuitable bottom the larvae could bypass would be limited, of course, to the duration of the 

larval period. According to Turner (1948), the length 

of the larval period of M. arenaria varies with temperature. Thorson (1950) stated that more than 70 percent of the Recent marine invertebrates have pelagic 

larvae, and that the larval period ranges from 2 to 4 

weeks for those breeding in summer, and from 1 to 3 

months for those breeding in winter. He also stated 

that up to 85 percent of the tropical species and up to 

65 percent of the boreal species have pelagic larvae, 

but that such larvae are rare in the Arctic. Considering the number of species that have made successful 

transarctic migrations in the past, there must have been 

considerably warmer temperatures in the Arctic than 

the present temperature.

Cahn (1951, p. 86) quoted Yoshida (1938) as saying 

that bottom fixation takes place in Mya japonica before 

metamorphosis is completed, generally when the 

swimming larvae are from 0.24 to 0.30 mm long. At the 

end of metamorphosis the larger individuals may 'be as 

much as 3.2 mm long. Turner (1949) said that M. 

arenaria attaches to sand grains following metamorphosis by means of a byssus, and that until the tiny 

clams are about 25 mm long they remain exposed. 

After that they burrow into the substratum.

Mya arenaria is most common in bays and estuaries, 

and it may form dense colonies in the inner parts of 

estuaries where the salinity is reduced. Minato, 

Matsui, andUozumi (1950, p. 1) qualified this by saying 

that Mya can live in brackish water provided there is 

sufficient salt in the substratum. Newcombe and Kessler (1936) showed that M. arenaria develops a heavier 

shell in water of high salinity. Merrill (1959) described 

specimens of M. arenaria attached to a buoy in the open 

sea that grew in iy2 years to the size reached by specimens in the normal bottom habitat in 2^ years.

Spawning temperatures probably are a more important factor in Arctic migrations than adult survival 

temperatures. Mya arenaria certainly can survive in 

bottom sands in areas where sea water freezes in winter, 

and Gunter (1957, p. 163) gives its lethal maximum

temperature as 40.6°C. This range might enable it to 

survive almost anywhere. According to Merrill (1959, 

p. 40), spawning begins before May in Wickford 

Harbor, R.I., but not until August at Malpeque, Prince 

Edward Island.

A detailed comparison of the migration patterns of 

Mya and Neptunea is deferred until the study of 

Neptunea is completed. Several seemingly important 

differences, however, have been determined thus far 

in the study that lead to the following generalizations.

Temperature is by far the most important factor in 

determining the global distribution of a species. Other 

factors, such as salinity and bottom conditions, are of 

local importance only; they may make areas within 

the preferred temperature range uninhabitable. Bathymetric preference is subsidiary to temperature 

preference. The spawning temperature is more critical 

than maturation or adult survival temperature. The 

isothermal boundaries of the spawning area, therefore, 

largely determine the geographical distribution of 

species. Pelagic larvae might mature outside the 

spawning area, and free-crawling adults may invade 

marginal areas, or areas well outside the spawning 

area.

The shape of a spawning area is determined by latitudinal isotherms and currents. Currents indent and 

extend the marginal configuration of the spawning 

area. A boreal breeding ground begins where incoming 

warm currents become sufficiently cool, and it ends 

where outgoing currents become too cold. The converse 

is true of cold currents. A species may or may not 

inhabit all of a possible spawning area, but migration 

is possible only within the thermogeographic limits of 

spawning.

The path and the direction of migration of species 

having pelagic larvae are controlled exclusively by 

currents. Benthonic organisms, on the other hand, can 

migrate with or against currents. They are confined 

to currents only if adjacent water is outside their temperature tolerance.

A cooling trend that makes the Arctic region too cold 

for spawning will, conversely, cause a shift in the 

spawning area to more southerly latitudes. The role 

currents play in determining the spawning area of 

species is fully as important as their role in transporting larvae. A species that spawns normally in boreal 

regions will follow warm currents into Arctic regions, 

and it will follow cold currents into temperate or subtropical regions.

Several apparently cool periods are indicated by the 

presence of cold-water species in beds of late Tertiary 

and Quaternary age in southern California. Un-
G4 CONTRIBUTIONS TO PALEONTOLOGY

doubtedly these reflect cooling in Arctic regions. The 

occurrence, however, of mollusks now restricted to 

boreal regions at the latitude of Los Angeles, or farther 

south, does not indicate, necessarily, that boreal conditions existed at the time in southern California. They 

may indicate merely that a cool current flowed farther 

south than usual.

Arctic temperature changes seem to have caused 

greater advances and retreats of molluscan species on 

the American side of the Pacific than on the Asiatic 

side. Current distribution appears to minimize a cooling trend on the Asiatic side and exaggerate it on the 

American side.

Mya truncata, for instance, lives now as far south as 

southern Hokkaido and Puget Sound. It is a known 

fossil in beds of middle Miocene to Pleistocene age in 

Japan, but it is not known south of northern Honshu in 

beds of any age. It is found, however, in deposits of 

early Pliocene and early Pleistocene age as far south as 

Los Angeles on the American coast, a latitude more than 

a thousand miles south of its present southern limit.

Probably the boundary between warmer and colder 

water is more permanently located in East Asia where 

it marks the point of departure from the coast of the 

warm Kuro Shio current. The Kuro Shio feeds the 

Japan Current that flows eastward across the northern 

Pacific. The Japan Current divides near the American shore into northward and southward flowing 

branches. Throughout its transit across the northern 

Pacific the Japan Current is cooled by intermingling 

with the counterclockwise flowing Subarctic Current 

to the north. The Japan Current remains sufficiently 

warm for its northward flowing branch to have a 

moderating effect on the Gulf of Alaska, but it is 

cooled sufficiently for its southward flowing branch, 

the California Current, to have a cooling effect on the 

California coast. The degree to which the Japan Current is cooled by the Subarctic Current depends, in 

turn, on Arctic temperatures, and it has a major effect 

on the temperature of the California Current and its 

molluscan faunas from Canada to Mexico. The temperature of the California Current in its southern 

reaches, however, could be out of all proportion to 

adjacent land temperatures, and the mollusks it brings 

with it could at times be much colder types than those 

of adjacent estuarine faunas.

The Asiatic coast might be little affected by the same 

cooling trend that greatly reduces the temperature of 

California coastal waters, probably because of the less 

variable departure point of the Kuro Shio. Reduced 

Arctic temperatures might have a profound effect on 

the area from Hokkaido northward where water temperatures are controlled by the Oya Shio, the southward flowing cold current of East Asia. The Japan 

Sea and the western side of Japan might also be cooled 

by a lowering of the temperature of the Oya Shio. 

It probably would not, however, displace the course of 

the Kuro Shio appreciably, nor would it cause an appreciable shift in the boundary between warm water 

and cold water faunas along eastern Japan.

MIGRATION AND SPECIFIC VARIABILITY

A factor that seems important to both ecology and 

the distribution of organisms is the nature of, and the 

reason for, specific variability. In particular, how do 

we determine whether local differences within greater 

populations are due to (1) differences in the substratum, salinity, light, available oxygen, temperature 

or current intensity, or (2) to genetics, or (3) to differences in the distribution of older populations? 

How can we tell an adaptation from a genetic innovation or a relict ?

The thinking of marine biologists in general, whether 

in connection with studies of adjacent habitats of unlike nature, or of experimental transplants of organisms from one environment or another, seems to be 

that (1) a given variant results from an organism 

having entered, or having been left stranded in a given 

environment, (2) that the variant is specific to that 

environment, and (3) that the morphological response 

to the new environment is both immediate and reversible.

From the standpoint of both taxomony and geologic 

history, it is important to know, for instance, whether 

a Neptunea living in a chilled fiord is merely a temperature variant of a species living in a warmer current 

flowing by its mouth (Golikov, 1960), or whether it is 

a relict of a stock that had a wider distribution in 

Pleistocene time. It is important to know whether 

the supposed intergradation with the species outside 

is a complete morphological gradation, or whether it 

is merely a progressive shift in the relative percentages 

of two discrete forms. Even in the former instance 

it would not be clear whether the morphological gradation was a response to temperature or other conditions, 

or whether it was an example of interbreeding between 

a species following the warm current and a relict stock 

in the fiord.

Soot-Eyen (1951, p. 2) discussed the relict character 

of faunas in Norwegian fiords. He pointed out that 

the warm Norwegian Current, which flows along the 

western side of Norway and rounds North Cape to 

flow thence along the Murman coast, virtually isolates 

the very cold water species in the fiords; there are sufficiently high thresholds to prevent warm water from
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G5

entering. He described Porsanger Fiord, near North 

Cape, as being the only real Arctic fiord in Norway, 

and only the innermost part, called 0sterbotten, contains a completely Arctic fauna. Several species now 

widespread in the Arctic, but confined to fiords in 

Norway, ranged as far south as England during the 

Pleistocene. This would suggest that generally lower 

temperatures and a different terminal distribution of 

Atlantic currents existed during at least some stages 

of the Pleistocene.

The final answer to this problem could not be forthcoming without a knowledge of the Pleistocene species 

and subspecies and at least the major aspects of their 

distribution and migrations. If, for instance, the variants in fiords, the White Sea, or within the influence 

of the Labrador Current are a response to low temperature, it is a most important ecologic fact. If they are 

not, the assumption that they are cancels out one of the 

most important clues to past climate, evolution, migration routes, and Pleistocene history that we could ever 

hope to have. Furthermore, if they are attributed incorrectly to temperature, we are led to some entirely 

erroneous taxonomy. If any conclusion involving biology is based on a presumed knowledge of taxonomy, it 

is doubly important that the taxonomy be correct.

There certainly are some well-documented examples 

of physical change in organisms under different conditions of turbulence. The same coral species can be 

branching in quiet water and encrusting in turbulent 

water, and oysters tend to be more elongate in running 

water than in still water. There is danger of oversimplification, however, if all variants are regarded as the 

result of environment. If supposed environmental 

changes are used to interpret either geologic or Eecent 

events, some entirely false conclusions can result. The 

great difficulty lies in being able to sort out the differences due to environment from those due to genetics, 

mutation, and hybridization. In all probability organisms respond morphologically to turbulence, but they 

select their temperature. If forced into an unfavorable 

temperature environment, they either adjust to it or 

perish. There is no incontrovertible evidence, however, 

that temperature alone can cause a mollusk to change 

morphologically.

MIGRATION AND EVOLUTION

Mya, as far as is known, reached the Atlantic coast 

of America and Europe well before Neptune a, and, 

moreover, the Atlantic representatives of Mya are less 

changed from their parent Pacific stock than are the 

first of the Neptunea found in Europe. This could well

be a function of both the means and the rapidity of 

their migration. Mya, which has pelagic larvae, probably is able to migrate rather rapidly, and because its 

larvae are current borne, probably all or most of its 

phenotypic forms go together. This would tend to 

maintain a uniformity in the varietal range of the 

migrating stock. Neptunea, on the other hand^ has 

large benthonic larvae, and it has literally to crawl 

every inch of the way. There is a much greater chance 

for some variants to go astray and, in this sense, for the 

stock to evolve enroute. Time favors the possibility 

of mutational change as well.

In general, organisms that are pelagic during some 

stage of their life history are most apt to be distributed 

widely and with the least change. Wholly benthonic 

organisms change the most during migration; they take 

longer to migrate, and they are less indicative of temporal equivalence.

I am convinced that minor changes in genetic composition take place in migrating stocks along the entire 

route of migration. I am convinced, also, that a succession of intergrading variants can be taken as the 

trace of a migration route. The more distant representatives of a species may show significant and 

consistent differences. Possibly a genetic change due 

to the chance elimination of some of the variant types 

enroute is responsible. Only personal opinion, or the 

sentimentality inherent in nomenclature, can determine whether a species leaving the Pacific is the same 

species on arrival in Europe. Generally, however, 

there is no difficulty in identifying the Pacific stock 

from which it came; and if the distribution of the 

variants in the Pacific is well-enough known, there is 

no doubt as to which part of the Pacific it came.

MIGRATION AND CORRELiATION

Ever since Huxley (1862; see Smith, 1904, p. 232) 

questioned the simultaneous occurrence of similar 

faunas in widely separated regions, there have been 

arguments as to whether such faunas were prima-facie 

evidence of temporal equivalence, or prima-facie evidence of an 'age difference owing to migrational lag. 

In all probability there is no universal rule. The 

answer would depend on the individual traits of each 

species or genus. The life history of each organism 

would have to be known before any positive statement 

could be made about the effect of migration on its 

evolution, or about the relative age of the beds in which 

it occurs.

It is hardly necessary to point out that the Eecent 

fauna is not homogeneous throughout the world. 

There are important differences in the faunas of the
G6 CONTRIBUTIONS TO PALEONTOLOGY

Caribbean, the Mediterranean, South Africa, Australia, 

Japan, and the west coast of the Americas. The faunas 

are not alike now, and there is no reason to suppose they 

were the same at any period in the past. Correlation 

of far-flung fossil faunas is tenuous and is based, 

usually, on intermediate correlations and on stratigraphic succession within units of epoch magnitude 

rather than on the identity of species.

Some genera are decidedly provincial and they appear not to have left the area in which they originated. 

Others, particularly in the Tethyan sea, have migrated 

to the opposite side of the world. It would be a mistake, however, to assume the occurrence of the same 

species to be synchronous everywhere.

TEETIAEY PALEOGEOGEAPHY OF THE AECTIC AND 

THE BOEEAL EEGIONS

Marine Paleocene deposits are known as far north as 

the Nugassuaq Peninsula in western Greenland at lat 

TO^ 0 N. The Midway sea of the American gulf coast 

extended as far north as North Dakota where there is a 

disconnected remnant of it known as the Cannonball 

Member of the Fort Union Formation. If there was a 

more northward extension of the Cannonball Member, 

or any kind of a connection between it and the Paleocene of Greenland by a Canadian passage, no geologic 

evidence for such a passage has been found to date. 

Identification of Paleocene beds in Alaska is still tentative, but even those that might be of this age are nonmarine. In Europe the northernmost marine Paleocene beds known are in Denmark and southern Sweden.

Marine middle Eocene and Oligocene deposits are 

known from the northern Gulf of Alaska region at just 

past 60° north, and middle and late Eocene and Oligocene deposits are known in the Alaskan Peninsula below 

56° north. There are marine Eocene and Oligocene 

beds in Kamchatka on the Asiatic side of the North 

Pacific. Marine Eocene deposits are known on the 

Atlantic coast of North America as far north as New 

Jersey, although they may be present below sea level 

farther north. In Europe the northernmost Marine 

Eocene and Oligocene deposits are found in southern 

England and Denmark.

In at least four areas in the high Arctic, northeastern 

Alaska (MacNeil and others, 1961, p. 1807, 17c), St. 

Lawrence Island in northern Bering Sea (ibid., 15), the 

Canadian Archipelago (Fortier, 1957, p. 437), and 

Spitzbergen (Schloemer-Jager, 1958), early Tertiary 

beds are landlaid and, in part, coalbearing. Probably 

this area includes all or most of the present Bering Sea. 

The evidence available suggests, therefore, that more 

of the polar region was land than at present.

The probability that a continuous shoreline extended 

from eastern Asia to western North America close to 

the present southern margin of Bering Sea during the 

Oligocene is indicated both by the fact that the Oligocene fauna of the Alaskan Peninsula is predominantly 

Asiatic, most of the species having been described from 

Hokkaido, Sakhalin, and Kamchatka, and by the presence in the Oligocene strata of beds containing such 

large-sized Asiatic fresh-water mollusks as Cipangopaludina sp. and Lanceolaria pisciformis (Yokoyama). 

It would not be too surprising to find Asiatic marine 

mollusks in the Alaskan Peninsula inasmuch as their 

distribution might be controlled by currents, but the 

Asiatic fresh-water mollusks would be difficult to explain except by a continuous landmass. The large 

fresh-water pelecypod Batissa, which is found in the 

Puget Group (Eocene and Oligocene?) of Washington, 

and which is otherwise unknown except in eastern and 

southeastern Asia and in nearby Pacific islands within 

the sial line, probably reached America by the same 

land route.

A more nearly continuous shoreline also seems to 

have existed between Europe and North America 

throughout Eocene, Oligocene, and into Miocene time. 

Stage for stage throughout the Eocene and Oligocene 

there are both closely related and identical shallowwater species in Europe and the southeastern United 

States. Some nearly identical forms go under different names, largely because they were described in different continents rather than because of significant morphological differences. Some stocks that seem to have 

been peculiar to one continent or the other for several 

stages suddenly become very abundant and appear in 

the other continent. Such occurrences could be interpreted as a single coastal proliferation, because the 

mollusks are types that hardly could be expected to 

bridge an abyssal gap like the existing North Atlantic.

The Nuwok Formation of Dall (1919, p. 26A) in the 

vicinity of Camden Bay, northern Alaska, is the oldest 

known marine Tertiary in the American Arctic. The 

oldest fossiliferous part of the formation appears to be 

of Miocene age, either middle or late, and it contains 

several genera of Atlantic origin (Arctica and Palliolum} that, as far as is known, have never been in the 

Pacific. One of the genera present (Subemarginula] 

is found subsequently in the Pacific.

The Nuwok Formation may represent much more 

than an invasion of the Arctic Ocean by an Atlantic 

fauna. It may well represent the first marine invasion 

of the high Arctic in Tertiary time; the beginning of 

the Arctic Ocean. The oldest fossiliferous marine 

Tertiary beds in Spitzbergen are of about the same age
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G7

(Hagg, 1927). Eavn (1922) regarded these beds as 

being of Paleocene age. The oldest fossiliferous beds 

contain species of Arctica and Cyrtodaria that strongly 

resemble species of these genera in the Nuwok Formation. Younger beds have yielded Thyasira bisecta 

Conrad, a species known from Oligocene to Eecent in 

the Pacific and otherwise known only in the Pacific 

Ocean area. In my opinion the oldest fossiliferous 

marine Tertiary beds of Spitzbergen are not older than 

middle Miocene, and the Thyasira 5we<?ta-bearing beds 

are younger; it hardly seems possible that they could 

antedate the first escape of Pacific species into the Arctic 

Ocean. (See p. G8.) Other lines of research that 

suggest a youthful age for the Arctic Ocean were 

reviewed by Pushcharovskiy (1960, p. 19).

The complete lack of marine Tertiary or Quaternary 

beds, except of very late glacial or postglacial age, in 

the Canadian Archipelago makes it unlikely that the 

Nuwok invasion was through that area. The presence 

of similar species of similar age in Spitzbergen, however, suggests that the invasion came from the region of 

the extreme North Atlantic Ocean and Barents Sea. 

The first faunal migrations probably were counterclockwise as in the existing Arctic Ocean. (See 

p. G9.)

The assumption that there was no Arctic Ocean, or at 

least a greatly reduced one in the form of epicontinental seas in areas such as the Laurentian and Angara 

basins, during the early and middle Tertiary could be 

of importance to supposed migrations of land mammals. No Tertiary land mammals of any kind have 

been found in Alaska, in spite of the insistence of 

vertebrate paleontologists that American-Asiatic and 

American-European migrations were commonplace. 

Even though Tertiary land mammals may be found 

eventually in Alaska, there probably were many alternate migration routes if much of the Arctic was land.

ARCTIC CLIMATE AND ITS EFFECT ON ORGANISMS

The northernmost Paleocene and Eocene faunas 

indicate a tropical or subtropical climate by modern 

standards. Certainly the most outstanding climatic 

event in the northern region from Oligocene to Recent 

time, however, has been a progressive deterioration of 

the polar climate. Northern mollusks had to adapt to 

a cold environment, and this resulted in a progressive 

differentiation of the mollusks into typically warmwater and typically cold-water forms. The change 

from south to north is gradational.

If, as seems to be indicated, there was no polar connection between the Atlantic and Pacific Oceans during

the early and middle Tertiary, even to the extent that 

the Arctic Ocean did not exist at that time, the net 

result seems to have been that mollusks characteristic 

of cold water were trapped in the northern parts of the 

two oceans. Once having become adjusted to cold 

water, they were incapable of migrating southward except by following cold water to ever-increasing depths, 

and those that may have ranged to the subtropics at 

depth were not able to gain access to the shallow waterways between the Pacific and the Caribbean.

With the gradual cooling of the polar regions during 

the Tertiary, some genera became characteristic of 

temperate and cold water and such genera are more apt 

to be restricted to the North Atlantic and North Pacific 

regions. Genera that are known as early as Eocene are 

more apt to have separate and indigenous Atlantic and 

Pacific species, but genera that did not become well 

defined until the middle Tertiary are apt to be restricted 

to one ocean or the other. Some of the cold-water 

genera peculiar to the North Pacific seem to be most 

closely related to warm-water stocks in the IndoPacific region, and they appear either to have invaded 

cold water successfully, or they were aible to adapt to 

it after having been left stranded in it.

The apparent geographic differentiation of mollusks 

into warm- and cold-water species may, however, be 

subject to other interpretations. Probably there was a 

thermobathymetric gradation during Eocene time when 

surface layers seem to have been so universally warm. 

The cooling of polar waters may have caused normally 

cool, deepwater forms to invade shallow water in the 

Arctic regions, whereas the normally warm, shallowwater forms withdrew to shallow waters of the tropics. 

This interpretation would explain the apparent derivation of some Arctic genera from early Tertiary genera 

in tropical latitudes.

The presence of palms, ExflabeUaria groenlandica 

(Heer) (LaMotte, 1952, p. 159), in the high Arctic 

during the Paleocene seems to indicate that the progressive cooling of the northern oceans during the Tertiary 

was due to more than the probable birth of the Arctic 

Ocean as a source of cold currents. Arctic land at that 

time was definitely warm. It was able to hold the insolation it received.

In general, shallow seas during the Eocene were more 

uniformly warm; tropical and subtropical genera are 

found as far north as Eocene deposits are known. 

Families and genera that were more universal during 

the Eocene are more apt to be restricted to subtropical 

regions at present, and they may be distributed in all 

warm seas.
G8 CONTRIBUTIONS TO PALEONTOLOGY

PERIODS AND ROUTES OF MIGRATION

It has been recognized for a long while that the 

Tertiary to Recent distribution of molluscan genera 

indicates intermittent exchange of rnollusks between 

Atlantic and Pacific waters in the near equatorial latitudes throughout most of Tertiary time. At far 

northern latitudes, however, there seems to have been 

exchange only in very late Tertiary to Recent time.

Probably the largest exchanges took place across 

northern South America in the early Tertiary, 

although there were lesser exchanges during the Miocene both there and possibly across Central America.

All these southern areas lie within the tropical and 

subtropical zones, a fact in keeping with the similarity 

of many Caribbean and tropical west American species. 

The existence of some nearly identical mollusks and 

echinoids in the Tamiami Formation (late Miocene 

and possibly including Pliocene) and in the Caloosahatchee Formation (regarded by most past authors as 

Pliocene but now known to contain Equus, a genus 

supposedly restricted to the Pleistocene) of Florida and 

in the Imperial Formation (late Miocene or early 

Pliocene) of southern California attests some kind 

of exchange not earlier than middle Miocene time 

and possibly later.

In the far north, there seems to have been no early 

or even middle Tertiary exchange of genera between the 

Atlantic and Pacific Oceans. By contrast, the late 

Miocene, Pliocene, and Pleistocene seem to have been 

periods of frequent exchanges of fauna. Many genera 

that underwent most of their evolution in the North 

Pacific, and that have a long Tertiary history there, 

appear suddenly on the Atlantic coast of North America and in northern Europe. At the same time, a few 

typically North Atlantic genera and species appear 

for the first time in the Pacific. In all probability 

the climate was warmer when the north passage was 

first opened than it was during the interglacial stages, 

or even at the present time.

The far greater number of Pacific migrants to the 

Atlantic than Atlantic migrants to the Pacific probably can be explained as due to the fact that most of the 

flow of water through Bering Strait is northward and 

to the fact that the passage between the Arctic and 

Atlantic Oceans is very large. Any Atlantic forms 

that entered the Pacific had first to find the comparatively narrow entrance through Bering Strait and then 

had to advance against outward flowing currents, or to 

find smaller counter currents, to enter the Pacific. In 

other words, Pacific species entering the Arctic Ocean 

found it easy to gain access to the Atlantic, but only

a few of the Atlantic species entering the Arctic ever 

found the entrance to the Pacific.

The earliest clear recorded occurrence of a Pacific 

boreal stock in the Tertiary sequence of the Atlantic 

coast is in the Yorktown Formation (late Miocene) of 

Virginia. Here Mya arenaria, a member of a species 

group that extends back to the late Eocene or early 

Oligocene of Japan, makes its first appearance in Atlantic waters. Plaaopecten clintonius (Say) may also 

have come from the Pacific. The earliest known 

occurrence of M. a-renaria in Europe is in the Red 

Crag (early Pleistocene) of England. Another Pacific migrant, M, truncata, was reported by Wood 

from the Coralline Crag (late Pliocene) of England, 

but a specimen from the Coralline Crag in the Ipswich 

Museum is, in my opinion, M. pseudoarenaria, another 

Pacific derivative. At any rate, M. truncata occurs 

with certainty in the Norwich Stage of the Icenian 

Crag (late early Pleistocene) to which the specimen 

figured by Wood (1857, pi. 29, fig. 1) was reassigned 

by Chatwin (1961, fig. 24, no. 13).

Only one pre-Yorktown Mya M. producta Conrad, 

is known from the Atlantic. It occurs in the Choptank Formation (early middle Miocene) of Maryland 

and in equivalent beds in New Jersey. This species is 

unrelated to M. arenaria, or to any known Pacific 

species, and, presumably, it belongs to an indigenous 

Atlantic stock.

The first appearance of species of Atlantic origin in 

the Pacific Tertiary is in the Yakataga Formation 

(Miocene and Pliocene) along the northern coast of 

the Gulf of Alaska. About 8,000 feet above the base 

of the formation, and at a horizon believed to be either 

very late Miocene or very early Pliocene, there are 

found for the first time, Astarte alaskensis Dall 

(= elliptica Brown) and Hm-tella arctica (Linne).

From Yorktown and mid-Yakataga time to the 

present time, migrations from one ocean to another 

are common. Siliqua appears in the Pacific, and a large 

number of Pacific genera and species appear in the 

Atlantic, among them Acila, Neptunea, Thais, Boreoscala, Panomya, and Macoma calcarea (Gmelin).

Different stocks appear to have migrated to the Atlantic at different times and along different routes. 

Some, such as the stock of Spisula voyi (Gabb) 

(= alaskana Dall) are found only in postglacial 

deposits and living along the North American coast of 

the Atlantic where there is a species known as Splsula 

polynyma Stimpson. Others seem to have migrated to 

northern Europe directly by way of the western edge 

of the Canadian Archipelago, but they did not reach 

the American Atlantic coast.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G9

Boreal and north-temperate mollusks also passed 

freely from the Pacific to the Atlantic during the 

Pleistocene, but the more southern forms apparently 

made the trip only during interglaciations that were 

even warmer than the present period. Although Arctic species now extend into boreal regions, there are 

boreal species common to both the North Atlantic and 

the North Pacific that do not live in the Arctic now.

A few boreal or cool-temperate species, having a 

Pacific origin and even more southerly habits, are now 

common to both oceans. Perhaps the most conspicuous 

of these is Neptunea decemcostata (Say). This species 

was described from the North Atlantic coast of the 

United States, where it lives from Grand Banks southward to Massachusetts. It is indistinguishable, except 

for a whiter shell and a more purplish coloring of the 

spiral ribs, from a form living around Kodiak Island. 

Neptunea decemcostata is a comparatively young 

species in the Gulf of Alaska, and its evolution there 

during the Pliocene and Pleistocene is well shown by 

specimens in the Geological Survey collections. This 

species appears to have been on the Atlantic coast, only 

in Recent and sub-Recent time.

Many of the molluscan genera represented in both 

oceans have species groups that are typically Atlantic 

and typically Pacific. Probably they owe these differences to the fact that they were mutually isolated for a 

part of Tertiary time. Because of the late Tertiary 

and Quaternary migrations by way of the Arctic, however, the distribution pattern in Recent seas has been 

most confusing. Many of the independently derived 

pairs, or groups of species, are now circumarctic, with 

derivatives of both oceans inhabiting virtually the same 

areas. Because the species are congeneric, there have 

been suggestions that they are merely varieties of the 

same species.

Two such species are Hiatella arctica and H. pholadis. H. arctica has a long history in the Atlantic and 

clearly traces its origin to a form in the Oligocene of 

the Netherlands. The H. pTwladis group, on the other 

hand, is known in the Pacific at least as far back as the 

Echinophoria apt a zone of the Oligocene and Miocene 

on Sitkinak Island just south of Kodiak in the western 

Gulf of Alaska and in the Poul Creek Formation of the 

Yakataga district. This may be H. saJchalinensis 

(Takeda), a species described from the Maoka Group 

(Oligocene and Miocene) of Sakhalin. Because of the 

fact that adults of H. arctica often lose their bicarinate 

posterior ridge and become rounded, it is difficult to tell 

them from H. pholadis, particularly when they occur 

together.

732-763 O 64 2

Another peculiarity of Arctic distribution is the 

occurrence of Pacific species along the Arctic coast of 

western Siberia but not along the Arctic coast of eastern 

Siberia. In other instances the variants found west of 

the Taymir Peninsula are more like the variants found 

along the Arctic coast of Alaska than they are like 

the variants found along the coast of intervening 

eastern Sibera. Both pelecypods, which are current 

borne, and some species of Neptunea, which are wholly 

benthonic, are so distributed. On the other hand, both 

Neptunea berlngiana and N. ventricosa have migrated 

westward along the Arctic coast at least as far as 

Wrangel Island. This suggests that even though some 

benthonic species may have migrated westward from 

Bering Strait, others migrated eastward and reached 

western Siberia by way of Spitzbergen, from whence 

they migrated eastward along the Siberian Arctic coast. 

For such species the East Siberian Sea is a province remote from the Bering Sea, inasmuch as they reached 

there by a counterclockwise migration all the way 

around the Arctic Ocean. Long shore currents along 

both the Siberian and Alaskan Arctic coasts flow eastward, a factor contributing to a counterclockwise migration pattern. The distribution of Arctic brachiopods leads to a similar conclusion (Elliot, 1956, p. 280).

This circumstance may also be a factor in the predominance of Pacific to Atlantic migrants over Atlantic 

to Pacific migrants. Those leaving the Pacific met 

currents that carried them along the Alaskan Arctic 

coast, the west side of the Canadian Archipelago, and 

thence around northern Greenland to the Atlantic entrance. Thyasira ~bwecta. Conrad, which occurs in late 

Tertiary beds of Spitzbergen, probably represents one 

of the earliest of such migrations. Atlantic species 

entering the Arctic, however, were carried eastward 

along the much longer Norwegian and Russian coasts. 

As shown by Lavrova and Troitskey (1960, fig. 1), 

different Atlantic mollusks migrating eastward during 

the Pleistocene Boreal transgression (post-Riss; 

Sangamon) penetrated the Arctic coast unequal distances. Lines can be drawn showing where, first, 

Cardium edule, then Pholas crispatus, and finally Arctica islandica dropped out. Thus some Atlantic species, 

not, only did not enter Bering Strait; they did not reach 

Bering Strait.

Although such genera as Arctica, and Palliolum 

reached northern Alaska in Nuwok time (middle or 

late Miocene and Pliocene), subsequent migrations did 

not extend that far. In the Pleistocene, Arctica got 

only as far as the Yenisey-Dudypta valley region in 

the Pechora Basin. Both Soot-Ryen (1932, p. 20) and 

MacNeil (1957, p. 104) discussed the occurrence of
G10 CONTRIBUTIONS TO PALEONTOLOGY

Palliolum groenlandicum in the Eecent fauna as far 

east as the East Siberian Sea; it does not live now in 

either the Chukchi or Beaufort Seas.

Migrations within the Pacific Ocean area seem to 

have been predominantly from west to east. Of the 

many species common to American and Asiatic waters, 

almost all have a known older history on the Asiatic 

side. There probably are genera with benthonic larvae 

that originated along the American coast and migrated 

westward along the northern fringes of the Pacific. 

Fusitriton, for instance, is known in middle Miocene 

beds in Alaska, but I can find no recorded occurrence of 

it in Japan before Pliocene time. Its range extends 

along the west coast of South America to Cape Horn 

and thence northward along the Atlantic coast to 

Brazil. It has not been found in the Caribbean, possibly because it is confined to deep water in tropical 

latitudes water deeper than the isthmian straits.

Many eastern Asiatic species, on the other hand, have 

moved eastward along the Asiatic coast, some to enter 

Chukchi Sea and thence eastward along the Alaskan 

Arctic coast and others to migrate southward along the 

American coast as far as California and Baja California. Some of the best American index fossils, such 

as Acila shumardi and Acila gettysburgensis, are 

Asiatic species that made abrupt and temporary appearances in western North America. They belong to 

longer ranging Asiatic stocks. These species are not as 

critical for dating in East Asia where there are closely 

related earlier and later species. Species entering the 

Pacific from the Arctic seem to have favored the American side. A few, however, such as Hiatella arctica 

and Astarte elliptica, appear to have migrated westward to Japan.

Figure 1 shows what is probably the main path of 

migration for species having pelagic larvae during late 

Tertiary and Quaternary time. Owing to the fact that 

the main course and terminal distribution of currents 

may have varied from time to time with both climate 

and basinal configuration and as they are complicated, 

moreover, by countercurrents and eddies, the paths so 

indicated are not presumed to indicate the exact location of currents. They are presumed to indicate 

merely the origin, direction, and termination of species 

migrations.

The general pattern of Arctic faunal migrations is 

beginning to emerge more clearly, and the history of 

the study makes it obvious why they were recognized 

sooner by the workers in some areas than in others. 

Scandinavians have long recognized that many elements of their modern fauna are of northern Pacific 

origin. British workers of the last century stressed

the fact that many species "came down from the north.'" 

Western American workers (see Smith, 1904; Keen, 

1940) have long been cognizant of the influx of Asiatic 

species to western America, but the idea of two way 

transarctic migrations has not been strongly put forth. 

Species or closely related species in the North Atlantic 

and North Pacific Oceans were regarded primarily as 

Arctic species that extended into the boreal parts of 

both oceans; periodic abandonments of the Arctic and 

reinvasions of the Arctic were believed to coincide with 

climatic changes.

Japanese workers have been preoccupied, and justifiably so, with the tremendously rich warm-water element of their modern fauna. New additions to the 

warm-water fauna came largely from the Tethys. 

They seem to have been the least aware, therefore, that 

the northern fauna, including that of the Kuril Islands, 

the Sea of Okhotsk, and Kamchatka, was the source of 

many elements of the western American and northern 

Atlantic faunas. Many Alaskan Tertiary fossils are 

now identified as Asiatic species. Further critical 

comparisons of American and Asiatic species may show 

much less endemism in East Asia than the current 

nomenclature suggests.

Although the main pattern of Pacific-Atlantic migrations is becoming clearer, many details remain to be 

worked out. Different species appear to have migrated 

during different preglacial periods in the late Tertiary 

and during different interglacial periods. Accurate 

determination of these species and of the time each 

species migrated would do much towards more accurate 

stage assignment of Arctic and boreal marine Pleistocene deposits, particularly those bordering the North 

Pacific which are farther removed from Europe and 

where more information is needed. A situation so 

complex and which at first glance might seem so completely hopeless, could, if completely understood, prove 

to be an extremely delicate tool in solving many of the 

temporal and climatic problems of the Pleistocene.

PHYLOGENY AND DISTRIBUTION OF SPECIES 

IDENTITY OF MYA JAPONICA JAY

It would be extremely cumbersome to discuss or compare the various Pacific species of Mya without first 

clarifying the identity of M. japonlca. Previous 

authors have interpreted this species differently, so that 

comparisons with "Mya japonica" by name are most 

confusing.

There are three Recent species of Mya in Japan. 

One is M. tmmcata. Another species lives from 

Hokkaido southward; a third species lives from Hokkaido northward. The southern species is closely re-
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA Gil

FIGURE 1. Most probable late Tertiary and Quaternary migration routes between eastern Asia and western North America, and between the North Pacific Ocean and North Atlantic Ocean.
G12 CONTRIBUTIONS TO PALEONTOLOGY

lated to M. arenaria. The northern species belongs to 

the M. truncata group.

Prior to 1931 most authors seem to have associated 

My a, japonica with M. arenaria. It was regarded, 

therefore, as being the southern species. Grant and Gale 

(1931, p. 412), on the other hand, used the name for the 

northern species. Makiyama (1934, 1935) and, as far 

as I can see, most subsequent Japanese authors also have 

applied the name japonica to the northern species. 

Makiyama (1935) proposed the name M. oonogai for 

the southern species. Whether Makiyama's action 

reflects Grant and Gale's opinion, or whether it is 

because the northern species is the common Mya in 

Uchiura-wan, Hokkaido (the "Volcano Bay, Yeddo" 

of Jay) is not clear. According to Fujie (1962, p. 400), 

however, M. oonogai also inhabits Uchiura-wan.

Grant and Gale's concept of M. japonica may very 

well have been based on Ball's identification of some 

very well preserved specimens from postglacial beds 

on Cottonwood Creek, Kachemak Bay, Alaska (Dall, in 

Martin and others, 1915, p. 92). Some of these specimens are figured in this report (pi. 11, figs. 1-3, 10, 

13,14). _

Jay did not figure the spoon of his species, and his 

remarks are not sufficient to identify it beyond all question. His figures (Jay, 1856, pi. 1, fig. 7, 10; also 

Slodkewitsch, 1938, pi. 102, fig. 2), however, show it has 

the outline of Mya oonogai, and, more important, its 

pallial sinus is completely detached from the pallial line 

except at the posterior juncture. In the northern 

species, the lower leg of the pallial sinus coincides with 

the pallial line. The character alone indicates that 

M. japonica could only be the form Makiyama named 

M. oonogai and the form Fujie treated as M. japonica 

oonogai Makiyama.

Fujie recognized the possibility that M. oonogai and 

M. arenaria might be the same species, but his conviction was not strong enough to make him adopt Linne's 

name. Instead, he accepted it as a subspecies of the 

northern Japanese species to which it is only distantly 

related.

The name Mya japonica would not have priority for 

the northern Japanese species in any event. The 

species ranges from Hokkaido to northern Bering Sea 

and eastward to Cook Inlet, Alaska. There is no doubt 

in my mind that it is the species for which Steller prepared a description in 1743 from a live specimen from 

southern Kamchatka. The description and an illustration prepared under Steller's direction was salvaged 

and published by Tilesius in 1822 as M. priapus.

MYA GRASS A GREWINGK, MYA ELEGANS (EICHWALD), AND MYA INTERMEDIA DALL

I have been informed by Dr. O. A. Scarlato (written 

comm., Aug. 31,1960) of the Zoological Institute, Academy of Science, Leningrad, that Grewingk's collection 

cannot be found; at least at this date none of the specimens he handled can be identified. This being so, we 

can judge his species only by his remarks and figures 

and by an attempt to reidentify his species.

Grewingk listed three species of Mya: M. crassa 

Grewingk, M. arenaria Linne, and M. arenarm var. 

The last is stated to have cardinal teeth and an external 

ligament and probably is a Macoina.

Mya crassa Grewingk and the form he identified as 

M. arenaria are fossils. The worst- snarl in myarian 

taxonomy has developed from the fact that he thought 

these were different species, and both Dall, and Grant 

and Gale, although they expressed doubts, accepted 

them as such. Neither Dall, nor Grant and Gale, knew 

Grewingk's species except from his figures. In 1960, 

however, a large suite of Mya was collected from a 

locality in the Alaskan Peninsula northwest of Chignik 

Bay by the Gulf Oil Co. These fossils, which are 

now in the collections of the U.S. Geological Survey, 

compare perfectly with Grewingk's figures and they 

show, moreover, that both of Grewingk's forms are 

the same species. The range of variation within this 

suite, due both to individual variation and differential 

deformation, is even greater than indicated by Grewingk's figures. Furthermore, I can see no way in 

which the fossils can be differentiated from the large 

thick-shelled species now living in southeastern Bering 

Sea and on the south side of the Alaskan Peninsula.

Mya crassa is twice a homonym (Vallot, 1801; Wood, 

1815). Grant and Gale (1931, p. 414) proposed M. 

profundior as a substitute name for M. crassa, and, in 

a footnote inserted in page proof, they called attention 

to Anatina elegans Eichwald as a possible earlier name. 

Anatina elegans Eichwald was proposed for Grewingk's 

second species, his M. arenaria Linne. The fact that 

both Grewingk's species are one makes the acceptance of 

this name unavoidable, but it is with the utmost reluctance that I accept a name so incorrect as to generic 

assignment and presumed age; Eichwald thought all 

Grewingk's fossils were of Turonian (Cretaceous) age! 

Dall (1898, p. 857) suggested that Grewingk's M. 

arenaria might be called M. intermedia. At the same 

time, he said the shell grows to a very large size in the 

Alaskan Peninsula, indicating that he regarded it as the 

large Kecent species. He also said, "Mya crassa, from 

the Miocene of Alaska, appears from the figures to be
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G13

distinct from My a intermedia" Ball (1904, p. 117) 

expressed the opinion, however, that the two might be 

mutations of the same species.

Grewingk mentioned My a intermedia Sowerby (a 

Panope)m connection with M. crassa. It seems improbable that Dall, who was entirely familiar with 

Grewingk's work, could have overlooked the earlier 

M. intermedia Sowerby. Possibly his original intention was that one of Grewingk's species might be assigned to M. intermedia Sowerby. Later, and possibly 

forgetfully, Dall (1921, p. 52, pi. 4) used the name "Mya 

intermedia Dall" for the large Alaskan Peninsula 

species, and according to MacGinitie (1959, p. 187, pi. 

19, fig. 6), he purified the species by selecting a "lectotype" from Chignik Bay, Alaska. The selection of a 

lectotype must be in the form of a label in the U.S. 

National Museum.

Grant and Gale recognized Mya profundior (M. 

crassa} only as a fossil. The large Kecent species (as 

M. intermedia Dall, a homonym) they placed in the 

synonymy of the northern species that they wrongly 

interpreted as M. japonica Jay (here interpreted as 

M. priapus}. In their discussion of M. profundior, 

however, they said, "This may be but an unusual 

variation of the form for which Dall used the preoccupied name intermedia; and if it is decided to separate 

the latter from japonica [meaning priapus} and dickersoni, it may be possible to use this name for it." 

Thus they conditionally suggested the use of the name 

profundior for the large Recent species that Dall had 

called M. intermedia.

MacGinitie (1959), like Grant and Gale, realized 

that Mya intermedia was a homonym, and she said, 

"Since the name intermedia is unavailable, the figured 

shell [pi. 19, fig. 6] can undoubtedly be assigned to 

M. japonica Jay." Her M. japonica, however, was 

the southern Japanese species, the true M. japonica, 

rather than the northern species (= M. priapus} to 

which Grant and Gale applied the name.

MacGinitie (1959, p. 188) further pointed out that 

Dall (1924, p. 31, 32) identified specimens from two 

localities on the Arctic coast of Canada as Mya intermedia, and that these really belong to M. pseudoarenaria Schlesch. It is not clear what Fujie had in 

mind when he said, M. japonica (meaning priapus}, 

M. intermedia (meaning elegants'*, or perhaps DalFs 

Canadian Arctic species), and M. pseud oarenaria were 

all one species; at least he seems to have regarded 

priapus and pseudoarenaria as one species.

Any further discussion of the subtleties involved, 

however, are immaterial to the nomenclature at this 

date, because M. crassa, M. profundior, M. arenaria, of

Grewingk, and M. intermedia of Dall are the same 

species, and M. elegans (Eichwald) is the earliest valid 

name for it. I do not believe the Recent representatives of this species are sufficiently distinct to justify 

even a subspecific name.

ANCESTRY OF MYA

The predecessor of Mya is at present unknown. 

Either the ancestor of Mya is an East Asian form as 

yet undiscovered, or it is some earlier non-Asian genus 

as yet unidentified. Both Bicorbula from the Eocene 

of Java and Raetomya from the Eocene of Egypt and 

Nigeria have been mentioned as possible antecedents, 

but, if so, there is a wide morphological gap between 

them.

In all probability the ancestor of Mya had a ligament 

that was more symmetrical dorsoventrally, and its ligament was almost certainly partly internal. One possible ancestor is Sphenial minor Forbes (Wood, 1877, 

p. 23, pi. B, figs. 16a, b) from the British early Eocene.

INDIGENOUS ATLANTIC SPECIES MYA PRODUCTA 

CONRAD

Of the known species of Mya, all but one can be 

interpreted on the basis of morphology and distribution as belonging to a group that underwent the greater 

part of its evolution in the North Pacific. The exception is Mya producta from the Choptank Formation 

of Maryland and the Kirkwood Formation of New 

Jersey, both middle Miocene.

This species is not only dissimilar in shape to other 

myarian species, but it is not related with certainty to 

any known Pacific species. As far as is known, Mya 

producta enjoyed only a brief existence in the western 

Atlantic, and it is clearly unrelated to M. arenaria, a 

species found on the Atlantic seaboard for the first time 

in the Yorktown Formation (late Miocene) of Virginia.

Mya producta is undoubtedly a true Mya, but its 

peculiarities suggest only that it probably had a common origin with the earliest of the Pacific species. If 

true, where or when the stock existed previously is not 

known.1

EARLY PACIFIC SPECIES

The earliest known species of Mya, is M. ezoensix 

Nagao and Inoue from the Wakkanabe Formation

1 Since this paper was written, Mr. Druid Wilson, of the U.S. Geolosical Survey, has called my attention to an unidentified small Mya 

from beds of probable early Miocene age in North Carolina. The 

species has a pallial sinus like that of M. producta, but its shell is 

small, has crude concentric undulations, and some specimens are much 

distorted. Shells were found in holes in the upper surface of a bed 

of limestone, suggesting that it is a borer or, possibly, a nestler. The 

species is not related to any known Pacific species.
G14 CONTRIBUTIONS TO PALEONTOLOGY

(late Eocene or early Oligocene) of the lower part of 

the Ishikari Group of Hokkaido, Japan.

Mya e^ensis probably gave rise directly to M. kusiroensis Nagao and Inoue, a species found in the Shitakara Formation (middle Oligocene) of the Urohoro 

Group of Hokkaido. The Urohoro Group is correlated 

with the upper part of the Ishikari Group. The earliest known Mya in America is found in the upper part 

of the Acila shumardi zone (middle Oligocene) of 

Popof Island in the Shumagin Islands, located south 

of the Alaskan Peninsula. This same species occurs 

in the basal part of the Poul Creek Formation in the 

Yakataga district along the northern side of the Gulf 

of Alaska; the lowermost part of the Poul Creek Formation as currently defined may also fall within the 

upper part of the Acila shumardi zone. The Alaskan 

species matches perfectly the available figures of M. 

kusiroensis, and it occurs in beds of about the same age.

The common Mya in the middle and upper part of the 

Poul Creek Formation (late Oligocene and early Miocene) is M. salmonensis Clark. M. salmonensis appears 

to be identical with M. grewingki elongata Nagao and 

Inoue (not Brocchi, 1814; renamed M. nagaoi Oyama 

and Mizuno) from the Poronai Series 2 (Oligocene and 

Miocene; generally considered to be equivalent to the 

Poul Creek Formation and the Blakely Formation of 

Washington) of Hokkaido.

Occurring with Mya salmonensis in the Poronai 

series of Hokkaido and in equivalent beds of Sakhalin 

is another species, M. grewingki Makiyama. One 

specimen from the Poul Creek Formation of Alaska is 

identified tentatively as this species. I do not regard 

either salmonensis or grewingki as being a subspecies of 

the other, but both probably are derived from M. 

kusiroensis. On the basis of its spoon, M. salmonensis 

is ancestral to M. cuneiformis and in turn to other 

members of the M. truncata group. M. grewingki, on 

the other hand, is related to M. elegans and M. arenaria.

Fujie stated that M. grewingki persisted until middle 

Miocene time in Hokkaido where it occurs in both the 

Horoshin and Chikubetsu Formations. I am not

2 Japanese stratigraphic names used in this paper are cited as In the 

source references, and no attempt is made to make them conform to the 

American Stratigraphic Code. Hatai and Nlslyama (1952, p. 5), said, 

"Until comparatively recently in Japan little attention was paid to the 

use of uniform stratigraphic terms, and different authors changed the 

names of formations at will. Little or no distinction was made between terms used for lithologic units, time-rock terms, and divisions 

of geologic time."

Japanese stratigraphers do not regard the geographic component of 

a name as preempted by usage in a higher category. Thus, there may 

be the Takikawa Formation of the Takikawa Stage of the Takikawa 

Series. Series and group may be used interchangeably, although in 

recent years group has replaced series. Stage appears to be used most 

widely as a biostratigraphic zone.

entirely convinced that M. grewingki survived the early 

Miocene in Japan. Fujie (1957, p. 392, pi. 5, figs. 1-4) 

described a supposed "variety" from the Chikubetsu 

Formation as M. grewingki var. haboroensis. As discussed later, this form is very closely related to M. 

dickersoni Clark from the late Miocene of California, 

and it could be regarded as a subspecies of M, dickersoni. I am following Fujie, however, in regarding it 

as a subspecies of grewingki. M. dickersoni belongs to 

the M. elegans group. The specimen from the Horoshin Formation figured by Fujie (1957, pi. 5, fig. 7) 

also seems to be more like M. elegans. Except for M. 

grewingki haboroensis, I can find no recorded occurrence of M. grewingki in postearly Miocene beds of 

Japan or Alaska.

MYA ARENARIA GROUP

The different types of spoons in the two coexisting 

species, M. grewingki and M. salmonensis, suggests 

that the primary differentiation of the spoon into more 

rounded and more triangular types took place in an 

ancestor of both species, either in M. kusiroensis or in 

M. ezoensis-kusiroensis intermediates. The more archaic type of spoon in M. ezoensis is broader anteriorly and has a moderately strong indentation or 

concavity along its ventral margin opposite the boundary between the laminum attachment and the fibrum 

receptacle. This ventral marginal concavity persists 

in Mya (Mya}, but in Mya (Arenomya) the ventral 

margin of the spoon is convex; in M. elegans the greatest marginal convexity is located at about the same 

position as the concavity in M. ezoensis.

The early history of M. arenaria and its precise 

origin has been anything but clear. Fujie (1962, p. 

401) thought M. arenaria and M. japonica (as M. 

japonica oonogai) might be conspecific, but he had no 

specimens of M. arenaria for comparison and he 

hesitated to combine them. He thought M. japonica 

oonogai could be traced back to the Takinoue Formation (early middle Miocene) (1957, pi. 2, figs, la^-b, 2 

of Hokkaido; however, he said there is no record of 

the species from younger Miocene deposits of Japan. 

He recorded four occurrences of M. japonica oonogai 

from Pliocene beds of Honshu (Fujie, 1962, p. 405). 

In my opinion the form in the Takinoue Formation is 

a new species, and it may be identical with the oldest 

of the forms that have been included in M. dickersoni 

in California. I am naming this species M. fujiei.

Mya dickersoni has been identified in the past from 

the Briones, Cierbo, and Neroly Formations of the 

San Pablo Group (late Miocene) of California. The 

spoon of M. dickersoni has never been figured, and
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G15

neither the illustrations of the exterior nor the published remarks give much clue to its actual relationships. A study of the spoon and other characters, 

both in topotypes and in other specimens contained in 

the collections of the University of California, suggests 

that four possible taxa have been included in M. dickersoni. These are: M. dickersoni (closely related to 

M. grewingki haboroensis] , M. arrosis n. sp., M. cf. 

M. fujiei n. sp. (as the paratype of M. dickersoni), 

and M. arenaria. The first belongs to the M. elegans 

group; the second may be ancestral to M. japonica; the 

last two belong to the M. arenaria group.

Clark figured two distinct species under Mya, dickersoul The holotype (Clark, 1915, pi. 63, fig. 3) came 

from the Neroly Formation (late late Miocene), the 

youngest formational unit of the San Pablo Group of 

central California. The paratype (Clark, 1915, pi. 63, 

fig. 4) came from J. C. Merriam's locality 197 from 

"near the base of the Contra Costa Miocene" on the 

west limb of the Pacheco syncline. A late notation in 

an unknown hand in the University of California 

locality catalog says, "Sobrante." However, I can 

find no other record of a Mya from the Sobrante Sandstone, the oldest formational unit referred to the Monterey Group (Miocene) in Contra Costa County, Calif. 

Weaver (1953, p. 68) listed M. dickersoni from the 

Briones Sandstone at a locality close to or identical 

with Merriam's locality 197 but none from the Sobrante 

Sandstone in the same area.

In all probability the paratype of Mya dickersoni is 

from the Briones Sandstone. Fujie (1957, p. 410) expressed the opinion that the holotype and paratype of 

M. dickersoni were different species, but he could not 

possibly have been aware of an age difference. He 

suggested the holotype might be related to M. cuneiformis. As discussed on page G17, typical M. dickersoni belongs to the M. elegans group. The paratype 

appears to be closely related to M. fujiei from the middle 

Miocene of Japan, and it may connect that species with 

M. arenaria, a species first recognized in the Cierbo 

Sandstone; the spoon of the paratype is unknown.

The Briones Sandstone (early late Miocene) appears, 

therefore, to be the earliest known occurrence of Mya 

in western North America, south of Alaska.

The University of California collections contain another species from the San Pablo Group of central 

California that is here described as Mya arrosis. This 

species has appeared in past check lists as M. dickersoni. 

A large specimen of M. arrosis from the Briones Sandstone is here figured (pi. 2, fig. 9; pi. 3, fig. 3). The 

holotype of M. arrosis comes from the Cierbo Sandstone. 

The species is present also in the Neroly Formation

where it occurs with M. dickersoni at the type locality 

of the latter.

M-ya arrosis is a very variable species. It ranges 

from heavier individuals that are much more tumid 

anteriorly and very acuminate posteriorly, such specimens strongly resembling M. cuneiformis in shape, to 

less carinate, more elongate, thinner shelled individuals 

that are surprisingly like M. japonica.

I do not agree with Fujie that the form he figured 

from the Takinoue Formation (early middle Miocene) 

of Hokkaido as Mya japonica oonogai (Fujie, 1957, pi. 

2, figs, la-b) is conspecific with M. japonica Jay. I am 

renaming this form M. fujiei, and I believe it is the immediate ancestor of M. arenaria. I regard M. japonica 

as descended also from M. fujiei but through the intermediate species, M. arrosis. It must be admitted, however, that the fossil record at this stage of evolution is 

scanty and a much better knowledge of it will be necessary before the matter can be settled to everyone's 

satisfaction. M. japonica could be interpreted as a relatively recent offshoot from typical M. arenaria. M. japonica is known for certain only in late Pleistocene beds 

and Kecent. The more crudely sculptured M. arenaria 

appears to be the older of the two forms.

Mya japonica is more attenuated posteriorly and more 

inflated anteriorly than M. arenaria. Its shell is thinner 

and less crudely sculptured. The spoon of M. japonica 

is tilted downwards anteriorly, whereas in M. arenaria 

it is more horizontal. M. japonica has a longer posterior ridge and a more elongate posterior furrow, 

making the posterior side of the spoon more alate. 

Nevertheless, the two species have a striking morphological similarity. Most workers in the past have regarded M. japonica either a synonym or a subspecies of 

M. arenaria. In spite of the subtle differences, I do not 

believe there is any difficulty in telling them apart, and 

in my opinion they are distinct species.

Mya japonica is known from late Pleistocene beds 

near Lake Abashiri, Kitami province, in northern Hokkaido (Fujie, 1957, pi. 2, figs. 6a-c). The species made 

an invasion of the American coast during the late 

Pleistocene. It is found in lagoon deposits near Nome 

on Norton Sound, Alaska, and in terrace deposits near 

Cape Kruzenstern, north of Bering Strait. Both these 

occurrences are, in my opinion, of middle Wisconsin 

age. Apparently the species still lives in the area. A 

large left valve and several live juveniles were collected 

from the present beach at Safety Spit near Nome. Several unworn shells were discovered in 1962 on the beach 

behind Sheshalik Spit in northern Kotzebue Sound. 

Another juvenile was found at Deering.
G16 CONTRIBUTIONS TO PALEONTOLOGY

The species also made a deep southward penetration 

of the American coast during the Pleistocene. It is 

found in Pleistocene beds near Vancouver, British Columbia (Lamplugh, 1886; Wagner, 1959, pi. 1, figs. 

19a-b; as My a arenaria). Oklroyd (192-i, p. 198), in 

a statement that has been challenged, said M. arenaria, 

is found in Indian mounds on Vancouver Island. This 

may refer to M. japonica in the Pleistocene deposits.

The late Pleistocene migration that brought Mya japonica to the vicinity of Bering Strait, as well as to the 

Vancouver area, is the only undoubted establishment 

of the species, to my knowledge, on the American coast. 

It is of interest to note that Protothaca adamsi (Eeeve), 

another Asiatic species, accompanied it to both areas. It 

has been found with M. japonica at both Cape Kruzenstern and Nome, and it probably is the species reported 

by Frizzell (1931, p. 321) from Pleistocene beds at Port 

Blakely, Wash. A Eecent form was described by Frizzell (1930, p. 120) as Paphia restorationensis and later 

(1931, p. 321) reassigned to Venerupis (Protothaca) 

restorationensis.

Mya japonica is the more southerly of the modern 

Japanese species. It ranges southward to Amakusa 

Island south of Nagasaki in western Kyushu and to the 

Gulf of Chihli near Tientsin on the China coast. It 

has been assumed by most Japanese authors that the 

species does not live north of southern Hokkaido. As 

already stated, however, the species may be living in 

Kotzebue Sound and Norton Sound, Alaska. Middendorff (1849, pi. 20, figs. 1-3) figured a malformed specimen (as M. arenaria) that is very similar to a malformed specimen from late Pleistocene beds near Nome, 

Alaska. No locality is given by Middendorff for his 

specimen, but of the localities he listed for the species, 

the most likely seems to 'be the Okhotsk Sea; the Arctic 

Ocean localities probably are of M. pseudoarenaria. 

Kotaka (1962, pi. 35, figs. 22-25) figured two very young 

specimens from the Okhotsk Sea as M. arenaria.

Some other poorly preserved internal molds from the 

Briones Sandstone (early late Miocene) have been 

identified as Mya dickersoni, but they may be more 

closely related to M. arenaria. A somewhat less tumid 

form is known from the Cierbo Sandstone (middle late 

Miocene) of central California. This form is referable 

to M. arenaria, and it is the earliest occurrence of the 

species I can find in the Pacific Ocean area. The Cierbo 

form may be derived directly from M. fujiei. If M. 

arenaria originated on the American side of the Pacific 

during the Miocene, it is an exception to the general 

rule that transpacific migrations, particularly of species 

having pelagic larvae, were from the Asiatic to the 

American side. I suspect it will be found eventually

that M. arenaria originated in Japan in middle Miocene 

time.

Four possible Pliocene occurrences of Mya arenaria 

(as M. japonica oonogai) in Honshu were recorded by 

Fujie. I believe the species in the Toshima Sand 

(Pleistocene) of the Atsumi Peninsula, east-central 

Honshu (Hayasaka, 1961, p. 64, pi. 8, figs. lOa, b; as M. 

japonica oonogai) is also M. arenaria.

The Etchegoin Formation (Pliocene) and the San 

Joaquin Formation (late Pliocene) of the central valley 

of California and the upper part of the Merced Formation (late Pliocene and early Pleistocene?) near San 

Francisco (Glen, 1959, p. 176, pi. 16, fig. 2) contain a 

form that must certainly be referred to typical Mya 

arenaria. Most authors in the past have identified the 

Etchegoin and San Joaquin species as M. japonica, but 

it was reidentified by Woodring and Stewart (in Woodring and others, 1940, p. 95) as M. cf. M. dickersoni 

Clark. Apparently Woodring and Stewart accepted 

Grant and Gale's interpretation of M. japonica (as 

being the M. priapus as here delimited). The Etchegoin and San Joaquin form undoubtedly is descended 

from the early variant of M. arenaria in the Cierbo 

sandstone, which at the the time of Woodring and Stewart's writing was included in M. dickersoni; probably 

specimens of this form were the basis for their identification. The holotype of M. dickersoni is believed to 

be more closely related to M. elegans.

The Etchegoin and San Joaquin specimens have a 

more deeply incised pallial line and pallial sinus than 

is common for Mya arenaria. However, a nearly identical heavy-shelled Recent specimen from Long Island 

Sound is in the collection of Stanford University. This 

specimen was mentioned by Grant and Gale (1931, p. 

411).

Most authors, with the exception of those who follow 

Grant and Gale's synonymy, seem to have taken for 

granted that Mya japonica is a synonym of M. arenaria, 

or at best a subspecies of it. Both of these species 

belong to the phylogenetic segment of Mya- that have a 

large spatulate ligamental callus and a detached pallial 

sinus. However, in my opinion, their lineages have 

been distinct since Miocene time.

As I trace the history of Mya arenaria in the Pacific, 

therefore, it is descended from M. fujiei which is 

known from the Takinoue Formation (early middle 

Miocene) of Japan and possibly from the Briones 

Sandstone (early late Miocene) of California. An 

early form of M. arenaria, possibly a subspecies, occurs 

in the Cierbo Sandstone (middle late Miocene) of California. A later form of the species occurs in the Etchegoin Formation (Pliocene) of California and pos-
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G17

sibly in the Pliocene of Japan. The last undoubted 

occurrences are in the San Joaquin Formation (late 

Pliocene), in the upper part of the Merced Formation 

(late Pliocene or early Pleistocene) of California, and 

possibly the Toshima Sand (Pleistocene) of Japan.

The question of whether Mya arenaria survived until Recent time in the Pacific has been much discussed. 

No specimens from post-San Joaquin or post-Merced 

beds of western North America are referable to M. 

arena/rid., and the species has not been seen from beds 

of any age in Alaska.

The known evidence suggests that Mya arenaria became extinct in the Pacific during early Pleistocene 

time and that Recent representatives of the species on 

the Pacific coast are derived from transplants brought 

from the Atlantic coast to San Francisco Bay about 

1865. The species now lives from Monterey, Calif., 

to southeastern Alaska. Recent representatives of this 

species at Vancouver are not to be confused with M. 

japonica in late Pleistocene deposits in the Vancouver 

area (see p. G33), and around Willapa Bay in western 

Washington.

The migration that brought Mya arenaria to the Atlantic seems without doubt to have taken place in late 

Miocene time. Of all the known variants of Mya 

arenaria in the Pacific, the form, in the Cierbo Sandstone of California is most like the form found in the 

Yorktown Formation of Virginia. M. arenaria is 

not known in the Alaskan Tertiary, either in the Alaskan Peninsula-Gulf of Alaska region or in the Nuwok 

Formation of Dall (1919) on the Arctic coast. It is 

difficult to see how it could have reached Virginia except by way of the Arctic; no Mya of any kind or any 

age is known from the West Indian-Gulf of Mexico 

region. I am inclined to believe that there was an 

Asiatic representative of the species corresponding to 

the Cierbo form, but to date it is not known. The first 

migration to the Arctic in late Miocene time probably 

was confined to the Asiatic coast of the Pacific.

Mya arenaria probably has persisted in the western 

Atlantic since Yorktown time. It is found at least as 

far south as Wilmington, N.C., in beds that are of late 

Miocene or Pliocene age.

No Mya is known from the Caloosahatchee Formation of Florida, nor has the genus been found in equivalent beds near Myrtle Beach, S.C. (Mansfield and 

MacNeil, 1937, p. 7, bed 1). No fossiliferous marine 

early or middle Pleistocene is known farther north, 

unless the Croatan Sand along the Neuse River, N.C., 

is of that age. Even so, this formation has not 

yielded Mya.

Mya arenaria is common in the Pamlico Formation 

(late Pleistocene; Sangamon or middle Wisconsin) of 

Maryland, and in the equivalent Jacob Sand of Long 

Island. It occurs from Hudson Bay and Labrador to 

Younges Island, S.C., in beds of late Pleistocene or postPleistocene age.

In Europe, Mya arenaria first appears in the Newbournian Stage of the Red Crag (early Pleistocene) of 

England and in possibly equivalent Merxemian beds of 

Belgium. It may have persisted until postglacial time 

in northern Europe where it is a common fossil in the 

sub-Recent "Mya banks'' around Oslo Fiord.

In Europe, as in the Pacific, however, it has been believed by some workers that Mya arenaria became extinct in early glacial time, long before the "Mya banks" 

were deposited. Hessland (1946) believed it was reintroduced accidentally in the 16th or 17th century by 

sailing vessels and since that time has become distributed widely. Thus, it seems probable that the M. arenaria in both Europe and the west coast of North America were introduced by man from the last natural stand 

in the western Atlantic.

MYA ELEGANS GROUP

Mya elegans (Eichwald), which species must include 

both M. crassa and "M. arenaria^ of Grewingk, is fairly 

closely related to M. arenaria. It might, however, with 

M. dickersoni, be made to constitute a group intermediate between the M. arenaria and M. truncata groups.

Mya elegans appears to stem from M. grewingki by 

way of the late Miocene species M. dickersoni. Typical 

specimens of M. dickersoni occur in the Neroly Formation (late late Miocene) of California, but there are no 

known earlier American occurrences. An earlier and 

presumably ancestral form, M. greioingki haboroensis, 

occurs in the Chikubetsu Formation (middle Miocene) 

of Hokkaido. This subspecies, which I regard as the 

earliest member of the M. elegans group, probably diverged from typical M. grewingki in early Miocene 

time, and probably the divergence took place in Japanese waters.

There is no recorded occurrence of this group in late 

Miocene deposits in East Asia, but in my opinion the 

Mya cuneiformis forma a of Fujie (1957, pi. 3, figs. 

5a, b) from the Honbetsu Formation (Pliocene) of 

Hokkaido belongs to it; I refer this form to M. elegans, 

tentatively.

Grewingk's Mya crassa (not Vallot, 1801) appears to 

have been a fossil. He stated that it came from near 

Pavlof, a now-abandoned village near Settlement Point 

on the east side of Pavlof Bay in the Alaskan Peninsula.
G18 CONTRIBUTIONS TO PALEONTOLOGY

I know of no beds in that immediate area from which 

it might have come; beds in that area are of Eocene age. 

It does occur, however, along with Glycymeris aleuticus 

Grewingk in beds of late Miocene or Pliocene age east 

of Yellow Bluff Creek, northwest of Chignik Bay. 

These beds were referred erroneously to the Meshik Formation by MacNeil, Wolf, Miller, and Hopkins (1961, 

p. 1802,3a of fig. 1.). M. C. Lachenbruch (written communication, Mar. 25,1963) told me that his field assignment of these beds to the Meshik Formation appears to 

have been incorrect; the type Meshik Formation is 

therefore still regarded as of Oligocene or Miocene age. 

I am now inclined to regard the J/ya-bearing beds as 

being of Pliocene age.

Aside from its occurrence in late Tertiary beds in the 

Alaskan Peninsula, M. elegans is known from Pleistocene beds on St. Paul Island in the Pribiloffs. I can see 

no way to distinguish any of the fossils from the large 

species still living in the area. As such it still lives in 

the Pribiloffs, in Kuskokwim Bay, at several places 

around Bristol Bay, and it lives for certain in Chignik 

Bay on the south side of the Alaskan Peninsula. M. 

elegans may occur elsewhere along the Alaskan Peninsula.

In spite of the poor understanding various workers 

have had of this species owing to its relative geographic 

obscurity, M. elegans is one of the really distinctive 

species of My a. It grows to a larger size than any other 

species of the genus.

MYA TRUNCATA GROUP

Like the Mya arenaria group, the M. tnmcata group 

also appears to stem from M. kusiroensis, a species 

found in the Oligocene of Alaska and Japan. The earliest clearly differentiated member of the M. tnmcata 

group is M. cuneiformis (Bohm), a species first known 

in the (middle?) Miocene of Japan. Fujie recognized 

that in Miocene time the geographical range of M. cuneiformis probably extended beyond the northern limit 

of occurrences known to him. This is borne out by the 

fact that it is a common fossil in the lower part of the 

Yakataga Formation (Miocene and Pliocene) of the 

northern part of the Gulf of Alaska. The Poul Creek 

Formation (late Oligocene and early Miocene) of the 

Yakataga district contains a different species, M. salmonensis Clark, that appears to be identical with the 

form in the Poronai Group, E. grewingki elongata 

Nagao and Inoue. M. cuneifarmis occurs in beds of 

middle Miocene age on Kodiak Island in association 

with Mytilus middendorffi Grewingk.

It is not clear just how, or in what order, the subsequent species of the Mya tnmcata group arose. These

are M. tnmcata Linne, M. ps&wdoarenaria Schlesch, M. 

priapus Tilesius, and ?M. pullm Sowerby.

The earliest occurrence of Mya truncata in Japan is 

in the Takinoue Formation of the Kawabata Series 

(Fujie, 1957, p. 412; Uozumi, 1962, table 2). Japanese 

geologists assign this stage to the early Miocene; however, it is post-Poronai (the Poronai Series is correlated 

with the Poul Creek Formation of Alaska and the 

Blakeley Formation of Washington), and according to 

American standards it would be late early Miocene or 

early middle Miocene. The oldest specimens of M. 

tmncata from Alaska in the Geological Survey collections are from about 700 feet above the base of the Yakataga Formation, which formation overlies conformably 

the Poul Creek Formation. The first appearance of 

M. tnmcata appears, therefore, to be nearly synchronous in Japan and Alaska, and probably it originated 

along a continuous coast connecting the two areas.

Mya tnmcata has lived continuously from middle 

Miocene to Kecent time in the northern Pacific. Its 

southern limit in Japan has been at about the latitude 

of northern Honshu and southern Hokkaido at all times. 

M. tnmcata made at least one advance southward along 

the American coast in the early Pliocene as evidenced 

by its occurrence in the Coos Conglomerate at Coos Bay, 

Oreg., and in the Towsley Formation (late Miocene and 

early Pliocene) at Elsmere Canyon in the Ventura 

Basin, Los Angeles County, Calif. I am inclined to 

believe Reagan (1909) was correct in identifying a 

specimen from his Quillayute Formation (Pliocene) of 

Washington as this species, although Ball (1922, p. 312) 

reidentified it as M. intermedia Dall (= elegans (Eichwald)), and both Grant and Gale (1931, p. 412) and 

Weaver (1942, p. 254) reidentified it as M. arenaria japonica (in which they included both elegans and 

priapus).

In the early Pleistocene, Mya truncata again extended 

its range to southern California where it is found in 

both the "Upper Pico" (Waterfall, 1929, table, p. 78) 

of Ventura County and in the Timms Point Silt Member of the San Pedro Formation of the Palos Verdes 

Hills, Los Angeles (Woodring and others, 1946, p. 85).

Mya truncata is now one of the most widespread 

Arctic and boreal species. According to Soot-Ryen 

(1932, p. 21), it does not occur in the East Siberian Sea 

so that it is not truly circumarctic, but it extends f ram 

the Arctic Ocean to Hokkaido and Puget Sound in the 

Pacific and to Cape Cod and the Bay of Biscay in the 

Atlantic.

A puzzling fact regarding the distribution of Mya 

truncata and M. arenaria, if existing records are anywhere near complete, is that although M. truncata is
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G19

the more northern of the two species, it was preceded in 

the Atlantic by M. arenaria. M. arenaria is known in 

the Yorktown Formation (late Miocene) of Virginia, 

whereas the earliest recorded occurrence of M. truncata 

from the Atlantic is either in the Coralline Crag (late 

Pliocene) or in the Norwich Stage of the Icenian Crag 

(early Pleistocene), depending on the identity of the 

species in the Coralline Crag. It occurs unquestionably 

in the Norwich Stage. In my opinion, the species in 

the Coralline Crag, and possibly the one in the equivalent Sables de Kattendijk and Luchtbal of Belgium, 

is M. pseudoarenaria.

Mya truncata migrated as far south as Italy during 

the early Pleistocene where it occurs in upper beds of 

the Calabrian Stage in Sicily, Calabria, and Tuscany. 

Specimens have been reported from early Pleistocene 

beds of Iceland, but a specimen from there figured 

by Schlesch (1924, pi. 6, fig. 1), was identified as M. 

truncata ovata Jensen (=M. pseudoarenaria Schlesch).

In all probability, Mya truncata lived in northern 

European waters throughout the glacial Pleistocene. 

I can find no reference to its having invaded the Arctic 

coast of Siberia until the middle glacial Pleistocene. 

If current identifications and age assignments are correct, it occurs in Taymyr in beds beneath the drift of 

the "Maximum glaciation" (Riss); these beds are assigned to the Q2 stage of Russian usage.

The fossil distribution of Mya truncata in eastern 

North America is similar to its Recent distribution. 

It has not been on the Atlantic coast very long, all 

its occurrences being postglacial, or mid-Wisconsin at 

the oldest. It is known as a fossil from near 

Thule, Greenland, and Hudson and James Bays to 

Massachusetts.

How Mya tnmcata reached eastern North America 

is not definitely known, but it certainly was in Europe 

previously. Soot-Ryen (1932, p. 29) discussed the 

much-debated occurrence of this and many other shallow-water forms strewn over the sea floor of the North 

Atlantic between Greenland, Iceland, and Jan Mayen 

at a depth of 1,300 fathoms. The maximum natural 

depth for any of the species found is about 600-700 

meters, and they are rare at that depth. He quoted 

Jensen (1899) as saying that these shells were not 

transported by ice rafting. It is possible that shallower water existed between Greenland and the Barents 

Sea in late Pleistocene time and that M. truncata 

reached eastern North America by that route.

The range of Mya priapus (M. japonica of Fujie) 

is much less extensive than that of M. truncata. Fujie 

(1962, p. 400) combined M. priapus (his japonica} and 

M. pseudoarenaria. The geographic range Fujie gave

for M. pivapus (the range he gave for M. japonica) is 

much greater, therefore, than it would be if these were 

regarded as distinct forms. Likewise, MacGinitie 

(1959, p. 188), who recognized M. pseudoarenaria as 

distinct, hesitated to give its exact geographic range 

"until collections are reexamined with a view to separating M. japonica and M. pseudoarenaria" MacGinitie used M. japonica in the sense I use it, and apparently the distinction was not being drawn between 

two members of the M. truncata group but between two 

species resembling M. arenaria.

Possibly both Mya priapus and M. pseudoarenaria 

are derived from M. cuneiformis, but, if so, I am inclined to believe they are coderivatives. If anything, 

the spoon of M. pseudoarenaria is more like that of M. 

salmonensis. At present, however, M. priapus is confined mainly to the North Pacific and Bering Sea, extending possibly to Wainwright, Alaska, whereas M. 

pseudoarenaria is mainly if not exclusively Arctic.

According to Fujie (1957, p. 412), M. priapus (as 

japonica) is known in the Togeshita Formation (late 

Miocene) of Hokkaido. It is known again in the 

Setana Formation (late Pliocene or early Pleistocene) 

of Hokkaido, and apparently it existed continuously in 

that area until the present day.

The species appears to be present in beds referred to 

the Pliocene about 4% miles south of the entrance to 

Lituya Bay along the east side of the Gulf of Alaska. 

In my opinion, this is the most southern recorded occurrence of any age for the species from America.

During the Pleistocene, Mya priapm ranged at least 

as far north as the Chukotsk Peninsula where it occurs 

in post-Riss beds (Merklin and others, 1962, pi. 9, fig. 

7; as M. arenaria) and to the area between the Kukpowruk and Kuk Rivers, Alaska. Specimens from Wingham Island, Controller Bay, Alaska, probably are this 

species (Dall, in Martin, 1908, p. 46; as "Mya near 

arenaria"). One of these specimens is figured in this 

report (pi. 11, fig. 8). The species occurs in very late 

Pleistocene beds at the mouth of Cottonwood Creek 

on the north shore of Kachemak Bay (Dall, in Martin 

and others, 1915, p. 92; as Mya japonica).

Mya priapus now lives from Hokkaido to northern 

Bering Sea, Chuckchi Sea at Point Lay, and east to 

Cook Inlet. It is the most abundant species in a large 

collection of Recent shells from St. Lawrence Island in 

the collections of the Geological Survey. Fujie (1962, 

p. 412) stated that the species (his japonica) ranges 

southward to Bellingham, Wash., but I have not seen a 

Recent specimen of M. priapus from east of Cook Inlet 

nor a fossil from south of the Lituya Bay district. 

Probably the occurrence to which Fujie referred comes
G20 CONTRIBUTIONS TO PALEONTOLOGY

from MacGinitie's (1959, p. 188) statement regarding 

M. japonica (presumably typical) and M. pseudoarenaria. I am inclined to believe, however, that the 

species actually involved in both statements is M. 

arenaria. Neither M. priapus nor M. pseudoarenaria 

is present in the very fossiliferous postglacial deposits 

near Juneau, Alaska. M. truncata, which is very abundant, is the only My a present.

Shells from north of Point Lay that appear most like 

My a priapus are thinner, more attenuated posteriorly, 

and their spoon has a narrower more elongate posterior 

furrow than M. priapus. The outline of the shell is 

more like that of M. arenaria. The beaks are more 

twisted and the greatest inflation is along the anterior 

truncation; M. arenaria has less twisted beaks and the 

shell is more evenly inflated. As recognized by SootEyen (1951, p. 3) and MacGinitie (1959, p. 186), this is 

M. pseudoarenaria Schlesch (new name for M. truncata 

forma ovata Jensen (not Donovan, 1802)). A fossil? 

specimen from West Greenland figured by Jensen (1899, 

p. 139, fig. 3) is the type.

Specimens from Point Barrow have a spoon much 

more like that of specimens of Mya cuneiformis from 

the Yakataga Formation than like that of M. priapus 

from northern Bering Sea; they resemble M. salmonensis even more closely. Probably, therefore, M. pseudoarenaria is a distinct species. It is related to M. priapus 

but probably not derived from it and it may have lived 

in the Pacific as a species distinct from M. cuneiformis at 

one time. I have seen no Kecent specimens from either 

the Bering Sea or the Pacific Ocean, however, that can 

be considered to be M. pseudoarenaria. The species is 

now widespread throughout the Arctic. In my opinion, 

the species in the Coralline Crag (late Pliocene) of 

England is M. pseudoarenaria. It probably is present 

both in the Red Crag (early Pleistocene) of England 

and in the Cardium groenlandicum zone of the Icelandic 

Crag (early Pleistocene) of Iceland. Schlesch (1931, 

p. 136) had a "subfossil" specimen from Hunafloi Bay, 

northern Iceland that presumably came from some part 

of the Icelandic Crag.

Mya pseudoarenaria occurs in Pleistocene beds in 

Spitzbergen and in beds of the Boreal Transgression 

(post-Kiss; Sangamon) at Gostinoj on the Yenisey 

Kiver in the Pechora Basin, northern Kussia. It probably occurs in late glacial or postglacial deposits of 

western Greenland, and possibly some recorded occurrences of Mya truncata in very young beds elsewhere in 

eastern North America are this species.

Mya pseud'Oarenfirm is known to be living in northern 

Norway, Iceland, Greenland, Spitzbergen, northern 

Canada, and Point Barrow, Alaska. According to

Laursen (1944, p. 63), the species lives only on the western side of Greenland.

MORPHOLOGIC CHARACTERS 

SHELL THICKNESS

The shell of Mya ranges from almost paper thin to 

very thick. The thickness of the shell in a given species 

may range within certain limits, depending on the 

physicochemical environment, particularly in open 

water as opposed to bays and in Arctic waters as opposed to warm boreal waters. The intraspecific differ: 

ences are not as great, generally, as those found between 

normally thick shelled and normally thin shelled species.

SHELL SHAPE

The shell ranges from oval to elongate and from moderately sharp posteriorly, on the one hand, to very short 

and nearly straight posteriorly, on the other hand. The 

beaks are nearly central in the oval species. In the 

posteriorly pointed species the beaks are relatively more 

anterior, whereas in the posteriorly truncated species 

the beaks are more posterior. The shell may be either 

evenly inflated or more inflated anteriorly. Shells that 

are very inflated anteriorly generally are truncated 

along a line extending from the beak to the anteroventral margin. This anterior truncation is often accentuated by lateral crushing in fossils. The greatest height 

is generally either central or just anterior of center. 

Mya product®, Conrad from the Miocene of Maryland is 

unique in having a broad median sulcus, making both 

its anterior and posterior areas higher and more inflated 

than the central area.

VARIABILITY OF FORM

It is difficult to make definite statements regarding 

the variability of a burrowing mollusk inasmuch as it 

may be influenced by the texture of the substratum. 

Some species such as M. japonica Jay seem to be much 

more uniform in shape than the closely related M. 

arenaria Linne, or the more distantly related M. truncata Linne. Whether this is an inherent character, or 

due to the fact that one lives mostly in a uniform substratum, whereas the other lives in a less sorted substratum is not known.

SCULPTURE

The sculpture of Mya consists of concentric growth 

lines. Random wrinkles are common on some species, 

notably M. truncata, and they probably reflect in the 

shell the coarse fleshy wrinkles of the tough siphonal 

sheath. The concentric sculpture is finer and more 

regular on some species than on others.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G21

PAXiLIAL LINE AND PALLIAI; SINUS

The pallial line ranges from very broad to thin; it 

may be continuous, or it may consist of disconnected 

segments; and it may be either deeply incised, or so 

nearly flush with adjoining areas as to make it indistinguishable except as a slightly smoother area.

The pallial sinus, both in its location, size, and shape 

and in the way it connects with the pallial line, is one 

of the most important species characters. It ranges in 

different species from (1) very short and high with its 

posterior side descending almost vertically to the pallial 

line (Mya truncata] ; to (2) more elongate with a sloping posterior margin and having a broad common boundary with the pallial line that generally is wider than 

the pallial line beyond the sinus (M. pria,pus) ; to (3) 

very long and subparallel with the pallial line but narrowly disconnected from it. for nearly its entire length 

(M. elegrans) ; to (4) moderately long and bluntly 

pointed and lying well above the pallial line, the space 

between the pallial line and the sinus being nearly as 

broad as the sinus itself (M. a/rencvria).

MUSCU3 SCARS

The posterior adductor scar of Mya is the smaller and 

is located just under the dorsal shelving. In the shorter 

posteriorly truncated shells (M: tru/ncata var. uddevalensis) the posterior scar lies in the posterodorsal corner, 

but in posteriorly attenuated shells (M. praducta] it 

lies at more nearly the midpoint of the posterior dorsal 

margin.

The anterior adductor soar is narrower and more elongate, often tear shaped. The anterior adductor scar 

may be as dorsal as the posterior scar, and rarely it is 

more dorsal (M. elegans). More commonly at least part 

of the anterior adductor scar is more ventral than 

the posterior scar, and in M. truncata, in which it is 

narrowest and most elongate, the anterior scar extends 

well below the middle of the shell.

MGAMENT

The myarian ligament is one of the most peculiar 

adaptations among the many completely dissimilar 

structural and mechanical devices developed in the 

pelecypods. The ligament is completely internal and 

assymetrical anteroposteriorly. It is sharply inclined 

dorsoventrally so that it lies wholly within the right 

valve. The chondropliore of the right valve lines the 

umbonal cavity, whereas the chondrophore of the left 

valve (the spoon) projects into the umbonal cavity of 

the right valve.

The ligament of Mya retains all three of the primary 

layers, the outer noncalcareous, the inner noncalcar732-763 0 64 3

eous, and the calcareous (fibrous or spicular) layers. 

These are here named, the elasticum, laminum, and 

fibrum, respectively. The outer noncalcareous layer 

(elasticum), which often is detached from the other 

two layers and may be partly concealed by an overlapping fold of shell (Solemya, TTiracia, Periploma), 

is vestigial in Mya and is present in the spoon only in 

very young shells. It attached to a groove along the 

posterior side of the main chondrophore in the right 

valve and to the posterior side of the posterior ridge 

of the spoon of the left valve. In adults the elasticum 

appears to withdraw from the spoon to reinforce the underside of the intervalve periostracum connection centrally. The thick central part of the intervalve connections consists of two layers, a thin amber-colored 

outer layer (periostracum) and a thick black innner 

layer (elasticum?). The inner black layer thins and 

disappears both anteriorly and posteriorly; the terminal parts of the intervalve connection consist only of 

the outer amber layer the true periostracum.

In adults, the spoon retains only the inner noncalcareous and calcareous layers. The inner noncalcareous layer (laminum) serves as an intervalve connection, and the calcareous layer (fibrum), as always, is 

the shell-opening mechanism, which, by resisting compression, operates in opposition to the adductor 

muscles.

The posterior ridge, which probably arose as the attachment or concealing fold for the outer noncalcareous 

layer (elasticum), continues to grow after the abortion 

of the outer noncalcareous layer and becomes a stabilizing mechanism. It is in contact with and articulates 

with a crude buttress along the posterior side of the 

chondrophore in the right valve; probably it is the 

articulation point for a twisting of the valves along a 

dorsoventral axis, allowing either end to gap more or 

to be drawn more tightly together (Trueman, 1954, p. 

291).

The noncalcareous layers can be observed only on 

Kecent specimens, but the calcareous spicules of the 

fibrous layer are preserved in many fossils. No specific 

differences are accompanied in Mya by modifications in 

the position of the ligament layers, but there are differences in the concavity or convexity of their attachment surfaces. An understanding of the location of the 

ligament layers is essential to an understanding of 

the significance and terminology of parts of the 

chondrophore.

SPOON

The most detailed terminology proposed thus far for 

the parts of the spoon (the chondrophore of the left 

valve) is that of Fujie (1957, p. 391). Fujie does not
G22 CONTRIBUTIONS TO PALEONTOLOGY

distinguish between the ligamental and nonligamental 

parts of the spoon, nor does he identify any of the 

named segments within the ligamental area with particular layers of the ligament. Fujie's diagram is reproduced in figure 2.

6

FIGURE 2. Diagram showing terminology of parts of spoon, 

figure is My a (Arenomya), and the lower figure is My a 

From Fujie (1957).

This report Fujie

1. Beak or umbo______________. Beak.

2. Anterior leg__-______________ Leg.

3. Anterior ridge________________

4. Ventral margin________________

5. Fibrum receptacle______________

6. Laminum attachment__________

7. Posterior ridge- ______________

8. Posterior furrow__________ 

SB. Anterior subumbonal groove____

Upper

Anterior ridge.

Outer margin.

Sculpture.

Undulated part.

Posterior ridge.

Furrow.

Subumbonal excavation.

The terminology adopted here for the parts of the 

spoon is given as follows with Fujie's terms in parentheses. 

The extraligamental parts of the spoon are:

2. The anterior leg (the leg) a line or ridge, often 

undercut, marking the edge of the live mantle. 

The periostracum-elasticum connection between the 

two valves attaches to it.

3. The anterior ridge (the anterior ridge) the anterior 

confining wall of the ligament receptacle. It may 

be narrow and overturned, or broad and flat. The 

dorsal part ranges from narrow to very wide.

7. The posterior ridge (the posterior ridge) the posterior confining wall of the ligament. In adults 

its point of contact with a buttress in the right

valve forms an articulation or rocking point for 

the valves along a dorsoventral axis. In juveniles 

it is the attachment or concealing fold for the 

outermost of the two noncalcareous or conchiolin 

elements of the ligament (elasticum). 

8. The posterior furrow (the furrow) an excavated 

area occupied by mantle. The outermost border 

marks the edge of the live mantle; the innermost 

border is the posterior ridge.

SE. The anterior subumbonal groove (the subumbonal 

excavation) a grooved area radiating from the 

beak and marking the outer edge of the intervalve periostracum-elasticum connection and 

thus properly a part of the exterior of the shell; 

this is found only in the Mya truncata group. 

The ligamental parts of the spoon are as follows: 

6. The laminum attachment (the undulated part) 

the attachment or insertion of the laminated and 

innermost of the two noncalcareous or conchiolin 

elements of the ligament (laminum). 

5. The fibrum receptacle (the sculpture) the receptacle or attachment of the calcareous (fibrous or 

spicular) element of the ligament (fibrum).

LIGAMENTAL CALLUS

Another very important feature of the myrian chondrophore has gone almost unnoticed by authors. It is 

here named the ligamental callus. Wood (1856, p. 280) 

was almost certainly referring to this structure in Mya 

arenaria from the Red Crag in his statement, "It was 

furnished with a large and strong ligament, or rather 

cartilage, the greater part of which is preserved in most 

fossil specimens." Woodring and Stewart (in Woodring and others, 1940, p. 95) observed it on specimens 

of M. arenaria (as Mya cf. dickersoni Clark) from 

the San Joaquin Formation (late Pliocene) of the 

Kettleman Hills, Calif. They commented that the San 

Joaquin species had "a more prominent deposit of callus 

on the middle of the chondrophore than that on Recent 

specimens" (of M. priapus; as M. japonica). The ligamental callus is shown very well on a specimen of M. 

japonica (as M. oonogai) from alluvial deposits around 

Lake Abashiri, Hokkaido, figured by Fujie (1957, pi. 

2, fig. 6c), but he does not mention it.

The ligamental callus is best developed in Mya, 

arenaria and M. japonica in which it is long and spatulate. M. priapus often has a callus, but in this species 

it is short and often has a comblike lower edge. A 

callus is much less frequent in M. truncata, and when 

present, it is very small and restricted to the upper 

anterior side of the ligament pit.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G23

A diagram (fig. 3) shows the supposed phylogeny 

of myarian species and the distribution of the ligamental callus in the different species groups.

The ligamental callus does not appear to have been 

deposited during normal ligament growth. Its lowest 

extremity is well back from the edge of the chondrophore where ligament growth takes place. The callus seems, however, to be continuous with the last increment of shell deposited on the surface of the anterior 

ridge. A lobe of the mantle seems to have extended 

from the dorsal part of the anterior ridge into the ligament pit and downwards under the fibrous ligament, 

which at that stage was detached from the surface of the 

spoon. Apparently the ligament of Mya is so constructed that it cannot remain functional throughout 

its length for the life of the individual, a condition that 

is true particularly for the species having a high overturned anterior ridge such as M. arenaria. Stresses 

cause the oldest part of the fibrous ligament to be torn 

away from its attachment, and, inasmuch as the intervalve periostracum elasticum connection is above the

Recent Mya (Mya>

o Middle "to

JJ

o_

Early

Late

<v

c

o Middle 

o

K

Early

Late

<v

g Middle

o

^

Early

Late

<v

c

o Middle 

o

Dp

O

Early

Middle

Early

spoon, a lobe of the mantle is free to invade the cavity 

and deposit a callus. It is not uncommon in pelecypods 

with a cardinal gape for the fibrum to be severed continuously with growth, but Mya is the only pelecypod 

known to me in which fibrum severance takes place 

in a wholly internal ligament. The ligamental callus 

is peculiar to the left valve.

The ligamental callus in Mya arenaria generally covers about two-thirds to three-quarters of the dorsal part 

of the fibrum receptacle. It does not cover any of the 

laminum attachment; this shows that the laminum does 

not become detached as does the fibrum. There is no 

ligamental callus in the right-valve chondrophore, 

showing that the fibrum becomes detached only from 

the spoon of the left valve.

Specimens of Mya arenaria from the Red Crag, a 

formation taking its name from the color imparted by 

large amounts of iron oxide, indicate that the ligamental callus is crystallographically different from 

other parts of the shell. In most specimens the ligamental callus is very dark brown, whereas the reMya (Arenomya)

<roducta

? Sphenia dubia

Spatulate, ribbed callus

Narrow dashed track indicates 

reduced size or infrequent 

occurrence.

FIGURE 3. Phylogeny of myarian subgenera and species, showing distribution of the two types of ligamental callus.
G24 CONTRIBUTIONS TO PALEONTOLOGY

mainder of the spoon and shell are a pale yellowish 

brown. Some specimens show the impregnation of iron 

oxide to begin as rosettes with dark centers fading 

toward the edge; these enlarge and coalese until the 

whole callus is stained dark brown.

SUBTJMBONAL. SOLUTION

Mya, arenaria almost always shows a considerable 

amount of solution under the umbo of the left valve. 

It is less frequent in the right valve and, when present, 

is restricted to a narrow area along the margin immediately behind the umbo. This condition is found 

also in M. japonica, M. elegans, M. grewingki, and to 

a lesser extent in M. producta, but it is unknown in the 

M. truncata group. It thus seems to be characteristic 

of Mya (Arenomya) but not of Mya (Mya) . Recent 

shells of M. arena/rid show both that the solution cavity 

is lined with secondary conchiolin, probably elasticum, 

and that solution progresses in the shell behind the 

secondary seal.

Very young shells (18-25.mm) of Mya japonica 

from Nome, Alaska, have a thin but well-formed ligamental callus. At this stage there is no subumbonal 

solution. In shells 30 mm in length, however, there is 

a small solution cavity under the umbo of the left valve. 

The cavity clearly begins along the margin of the valve 

where the intervalve periostracum-elasticum connection 

attaches and not at the umbo where it might be expected 

if it started at a point of abrasion between the two 

valves.

Some species (M. arenaria and M. japonica) have 

both a ligamental callus and a large amount of subumbonal solution. Some species ( M. producta and M. 

elegans) have subumbonal solution and no callus, 

whereas other species (M. priapus and M. truncata} 

may have a small callus but no solution in the left, 

valve; some specimens of M. priapus may have a small 

solution pit at the top of the chondrophore of the right 

valve (pi. 11, fig. 15).

Structural weakness seems to be the only factor relating solution and callus. In all species, there seems to 

be a tendency for the fibrum to be pulled away from the 

dorsal part of the spoon. The mantle tends to heal the 

void with a deposit of callus. The same stresses that 

tear the fibrum from the spoon also cause a rupture of 

the intervalve periostracum-elasticum connection, and 

most commonly the rupture takes place where the intervalve connection attaches to the left valve above the 

spoon.

According to Trueman (1954, p. 291), Mya arenaria 

not only opens and closes its valves along the hinge axis, 

but it twists its valves on a dorsoventral axis, allowing

either end to gape more or to be drawn more tightly 

together. This motion could also be a factor in the 

rupture of both the fibrum and the intervalve connection.

The narrow slit of shell exposed by the periostracum-elasticum rupture is open to attack by sea 

water. The mantle, which becomes exposed, is able to 

seal itself off with a secondary deposit of elasticum. 

The secondary elasticum is fixed to the shell along the 

lower edge of the area of active solution, confining the 

solution, in effect, to the exterior of the shell. However, 

it is not able to permanently arrest solution. As the 

solution cavity enlarges, the secondary seal retreats to 

now positions. Its line of connection thus keeps enlarging in circumference, and the elasticum seal becomes a balloonlike sac filling most of the solution 

cavity.

A further relation between subumbonal solution and 

the ligamental callus can be seen in a few specimens of 

Mya arenaria. The dorsal end of the callus is enlarged 

or bulbous on some specimens and expands into the 

solution cavity where it is deposited on the surface 

already pitted by solution. In such specimens it may 

partly refill the solution cavity with a secondary deposit. If solution continues, however, it may in turn 

attack the callus. Several specimens examined showed 

a young solution pit cutting callus and original shell 

alike. Post-callus solution always seems to have taken 

place from the posterior dorsal side of the callus.

Either slight differences in the shape of the shell in 

Mya (Mya) andJ/ya (Arenomya) provide for different 

mechanical stresses in these two groups, or the intervalve periostracum-elasticum connection in Mya (Mya) 

is much stronger. Specimens of M. priapus in which 

the intervalve connection is preserved show that it forms 

a thick bundle below and anterior to the beaks. The 

subumbonal groove appears to mark the outer edge of 

the periostracum-elasticum bundle. In addition, the 

right valve of Mya (Mya) has a broad projecting spur 

along the anterior border of the chondrophore (pi. 8, 

figs. 2, 3). The outer edge of the spur inserts along 

the posterior side of the anterior ridge of the left valve. 

The dorsal surface of the spur serves as the attachment 

for the intervalve periostracum-elasticum connection at 

the apex of the chondrophore. This relatively broad 

attachment area makes possible the thick periostracumelasticum bundle that in Mya (Mya) prevents subumbonal solution.

There is no broad projecting spur in the right valve 

of Mya (Arenomya) ; rather, there is a sharp narrow 

point (pi. 6, fig. 16) alined with the dorsal margin of 

the shell. A relatively narrow intervalve connection of
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G25

periostracum and elasticum attaches to its thin dorsal 

edge.

The protruding spoon of Mya is the chondrophore 

of the left valve. The corresponding chondrophore of 

the right valve lines the umbonal cavity beneath the 

umbo. Differences corresponding to those in the left 

valve can be seen in the right valve, but owing to the 

prominence of the spoon, the left valve is the more 

definitive valve. Because of its more protected position, 

the spoon is more apt to be preserved in fossils that have 

paired valves. In fossils, the spoon is certainly easier 

to prepare. I have never seen any indication of a ligamental callus in a right-valve chondrophore. This fact 

seems to indicate that the fibrous ligament remains 

attached to the right valve when it tears away from the 

spoon. Consequently, only left valves and spoons are 

figured in this paper, and all discussions of relationship are in terms of the left valve.

SYSTEMATIC PALEONTOLOGY

Genus MYA Linne, 1758

Mya Linn6, Systema naturae, ed. 10, p. 670, 1758.

Type. ('by subsequent designation, Children, 1822) : 

Mya truncata Linne. Recent, North Atlantic, Pacific, 

and Arctic Oceans. Linne's specimen is from Europe.

Mya was added to the Official List of Generic Names 

in Opinion 94 of the International Commission on Zoological Nomenclature.

Hiatula Modeer, 1793, and Myarius Froriep, 1806, 

have the same type species.

Winckworth (1930, p. 15) attempted to restrict the 

genus by proposing the genus Arenomya (type, by mono typy, Mya arenaria Linne). His only justification 

was in the statement, "The marked conchological differences between adult Arenomya and Mya (type 

truncata L.) seem sufficient reason for giving this name." 

Arenomya has been accepted as a subgenus by several 

modern Japanese authors (Habe, 1952), and it is so regarded here. Most authors, however, have regarded 

Arenomya as superfluous; no one to my knowledge has 

followed Winckworth in recognizing it as a genus.

Mya (Mya} has an anterior subumbonal groove, and 

the ventral leg of its pallial sinus is confluent with the 

pallial line. The ligamental callus, when present, is 

small and lacks a radial ridge. There is no subumbonal 

solution in the left valve, although M. priapus often 

has a solution pit at the top of the chondrophore of the 

right valve.

Mya (Arenomya} has no anterior subumbonal 

groove, and the pallial sinus is detached. The ligamental callus is spatulate and generally has a radial

ridge posterior of its center. The left valve always 

has a subumbonal solution pit.

In addition, there are species ancestral to, and coexistent with, these subgenera that either are peculiar in 

some way, or they combine characters of both of the 

above subgenera. In general they seem to be more 

closely related to M. (Arenomya} ; this residue of 

species is here treated as M. (1 Arenomya).

These species have no anterior subumbonal groove, 

and they all have a subumbonal solution cavity in the 

left valve. They may or may not have a ligamental 

callus, but when present it is like that of M. arenaria. 

The pallial sinus ranges from detached to confluent ventrally with the pallial line.

The exact time of origin of the ligamental callus is 

not known. There is reason to believe that it is not a 

genetic character. Rather, it seems to be a repair of 

a structural weakness, and in this sense it is analogous 

to subumbonal solution and to the balloonlike sac of 

elasticum that forms in the solution pit. I can find no 

indication of a callus in Mya producta. A thin callus 

may be present in a specimen from Alaska here referred to M. kusiroensis. M. grewingki appears from 

the available illustrations to have a callus. The only 

known spoon of M. salmonensis had a moderately large 

callus but it crumbled, along with part of the surface 

of the fibrum receptacle, in preparation.

Some species of both Mya (Mya} and Mya (Arenomya} have a callus, whereas other species have it only 

occasionally; in other species it appears to have become 

obsolete. Where found, the calluses of Mya (Mya} 

and Mya (Arenomya} have a different shape. In Mya 

(Mya} the callus is short, conforms more to the contour of the ligament pit, and in some specimens it has 

teeth or spurs along its ventral margin. In Mya (Arenomya) the callus is long and spatulate, and generally 

it has a rib or ridge near its posterior border.

The callus is largest in the Mya arenaria group, but 

it does not occur in M. elegans. M. dickersoni has variants with a small callus or no callus; M. elegans may 

have descended from the variant of M. dickersoni with 

no callus.

The callus is less common in the Mya truncata group. 

It is largest in M. priapus, and this seems to be the only 

species of the group in which it is always present. 

It is less frequent and smaller in M. truncata. Only a 

few specimens of M. pseudoarenaria have a callus, and 

when present it is restricted to the extreme dorsal end 

of the fibrum receptacle.

The emphasis in the following systematic treatment 

is on species outside Japan. An attempt is made to 

point out the apparent synonymy of American and
G26 CONTRIBUTIONS TO PALEONTOLOGY

Japanese species. Mya has been a common mollusk in 

Japanese waters since Eocene time. Both Myd (Mya) 

and Mya (Arenomya} are represented in the Japanese 

Tertiary. Numerous species, subspecies, and varieties 

belonging to both subgenera have been described. Unfortunately, much of the fossil material is poorly preserved. Consequently, there are named forms that 

cannot be recognized with certainty, and it has been 

difficult for Japanese workers to obtain and prepare 

specimens of all recognizable species for adequate illustration. My concept of the Japanese species is mainly 

that of Fujie, and the synonymy expressed is modified 

from Fujie's work and the work of other recent Japanese authors. Without access to specimens, it would be 

impossible to form an opinion on the more dubious 

forms described from Japan.

Japanese workers seem to have accepted Grant and 

Gale's interpretation of Mya japonica, an interpretation 

that is in complete disagreement with that of most 

previous and subsequent American authors. In my 

opinion, Grant and Gale's interpretation is incorrect. 

The nomenclature used for the Recent Japanese species 

in this paper is not in accord, therefore, with recent 

Japanese usage.

Subgenus ARENOMYA Winckworth, 1930 

Arenomya Winckworth, Malacological Soc. London Proc., v. 19,

p. 15, 1930.

Type. (by monotypy) : Mya arenaria Linne. Recent, North Atlantic coast of North America, northern 

Europe, and the west coast of the United States from 

Monterey to southeastern Alaska. Both the European 

and the western American representatives are said to 

be introduced; Linne's specimen came from the North 

Sea.

 Mya (?Arenomya) producta Conrad

Plate 1, figures 1-4, 7

Mya producta Conrad, Fossils of the medial Tertiary, p. 1, pi. 1,

fig. 1, 1838.

Dall, Wagner Free Inst. Sci. Trans., v. 3, pt. 4, p. 858, 1898. 

Glenn, Maryland Geol. Survey, Miocene, p. 283, pi. 68, figs.

la, b, 2,1904. 

Richards and Harbison, Acad. Nat. Sci. Philadelphia Proc.,

v. 94, p. 202, pi. 16, figs. 11,12,1942.

Mya producta is one of the most peculiar species of 

Mya. It has no anterior subumbonal groove. The anterior ridge of the spoon is very short and weakly overturned. There is a very pronounced dorsal broadening, 

but it is produced anteriorly along the hinge axis rather 

than ventrally towards the end of the ridge; the ventral 

part of the anterior ridge is, in fact, quite narrow. The 

posterior ridge is nearly twice as long as the anterior

ridge. The spoon is broad and has a strongly rounded 

outer margin. The fibrum receptacle is rather deep and 

concave, and the angle it forms probably is the largest 

for any species of the genus. There is a flattening or 

even a slight convexity along the laminum attachment.

The shell is lower and longer than in any other Mya, 

and in this respect it resembles a Panope. The beak is 

slightly anterior of center, which makes the shell 

slightly longer posteriorly. There is a weak broad medial sulcus that becomes stronger in large shells and 

which tends to make the ventral margin nearly straight.

The pallial sinus of this species is very deep and 

broad, and its lower leg is confluent with the pallial line 

except for a slight recurving at the anterior end. This 

type of sinus is characteristic of the Mya trwncata 

group.

Large specimens of Myd producta show a moderate 

amount of subumbonal solution in the left valve, a condition characteristic of the M. arenaria group and 

unknown in the M. truncata group. The anterior leg is 

more like that of M. arenaria, whereas the posterior part 

of the spoon is more like that of M. pseudoa^enaria of 

the M. truncata group. It would seem, therefore, that 

among three distinct myarian groups M. producta and 

the groups of M. arenaria and M. truncata different 

single characters are peculiar to different combinations 

of two groups but not the odd group. This would be 

difficult to explain except as a differential survival of 

primitive characters in different phylogenetic lines.

If the pallial sinus of Mya ezoensis is found to be confluent with the pallial line, it would be a further indication that this type of sinus is the more primitive, and it 

would strengthen my contention that M. producta and 

the large Pacific complex of species are related through 

some Eocene species as yet unknown.

The holotype (according to Moore, 1962, p. 89) may 

be in the collection of the Wagner Free Institute of 

Science. The specimen figured by Glenn (1904) measures 123 nun in length, about 50 nun in height; convexity is 14 nun. The specimen figured here is numbered USNM 146004.

Occurrence: Maryland, Choptank Formation (middle Miocene), USGS 2451; New Jersey, Kirkwood Formation (middle 

Miocene).

Mya (?Arenomya) ezoensis Nagao and Inoue

Mya ezoensis Nagao and Inoue, Hokkaido Imp. Univ. Fac. Sci.

Jour., v. 6, no. 273, p. 145, pi. 34, figs. 2, 7-9, 1941. 

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu (Studdies of the Cenozoic), no. 7, p. Ill, pi. 10, figs. 75, 78, 79', 

81,1950 (in Japanese).

Mya ezoensis var. sagittaria Minato and Uozumi, Shinseidai-noKenkyu, no. 7, p. 107, pi. 10, figs. 76, 77, 80, 83, 1950.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G27

Mya ezoensis Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9,

no. 4, p. 383, pi. 8, figs. 1-10,1957. 

Oyama, Mizuno, and Sakamoto, Illustrated handbook of

Japanese Paleogene molluscs; Japan Geol. Survey, p. 209,

pi. 64, figs, la-b, 2a-f, 1960. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 11, no. 3, p.

403, 1962.

The known specimens of this species are poorly preserved. Fujie (1957, pi. 8, fig. 5) gave one photograph 

of its spoon, and he also included a drawing of it in his 

diagram of spoon types (1957, p. 391, fig. 2, A). It has 

no anterior subumbonal groove. Fujie's photograph 

shows the anterior ridge to be narrow ventrally and 

short. This character places it closer morphologically 

to Ar&nomya, than to typical Mya. Judging from 

Fujie's photograph, there is a moderately strong convexity along the ventral margin of the spoon opposite 

the anterior margin of the laminum attachment, a 

character more typical of Mya (Mya).

Apparently the pallial impressions are obscure on 

known specimens of the species and no one, unfortunately, has observed them. Nagao and Inoue describe 

the dorsal margin as nearly horizontal (straight?), a 

condition more typical of Mya producta than any 

known Pacific species.

This is the oldest known species of Mya. No Mya resembling this species, or of this age, is known from the 

American side of the Pacific.

Lectotype: Univ. Hokkaido Reg. 8997; selected by Hatai and 

Nisiyama, 1952. Measures 42 mm in length, 20.5 mm in height; 

convexity is 13 mm. The maximum length given for the species 

is 56.8 mm.

Occurrence: Wakkanabe Formation of the Ishikari Group, 

Hokkaido. Fujie gave the age as "probably Eocene." Oyama, 

Mizuno, and Sakamoto assign the Wakkanabe Formation to 

the early Oligocene.

Mya (?Arenomya) kusiroensis Nagao and Inoue

Plate 1, figures 5, 6, 8-10

Mya grewingki var. Jcusiroensis Nagao and Inoue, Hokkaido Imp.

Univ. Fac. Sci. Jour., ser. 4, v. 6, no. 2, p. 150, pi. 32, figs.

2-6,1941.

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu [Studies of the Cenozoic], no. 7, p. 3, pi. 10, figs. 84-86, 1950. 

Mya grewingki var. elongata Fujie, Hokkaido Univ. Fac. Sci.

Jour., ser. 4, v. 9, no. 4, p. 389, pi. 7, figs. 3, 4, 8, 9, 1957

[in part]. 

Mya grewingki kusiroensis Oyama, Mizuno, and Sakamoto,

Illustrated handbook of Japanese Paleogene molluscs;

Japan Geol. Survey, p. 211, pi. 65, figs, la-e, 1960.

The spoon of this species has not been illustrated previously. The rubber cast figured here (pi. 1, fig. 5), 

taken from the internal mold of a specimen from the 

basal part of the Poul Creek Formation of Alaska, 

shows that the spoon is rounded anteriorly and has a

moderately strong slightly overturned anterior ridge. 

The laminum attachment and the fibmm receptacle 

together form a surface that is weakly and evenly convex. The spoon appears to have a thin ligament al callus, 

although it is difficult to recognize a callus with certainty from a rubber cast; the cast shows only the surface contour and not the callus layer. The spoon of 

this species is closer to that of Mya (Arenomya) . At 

the same time, the species is closely related to M. salmonesis, the probable prototype of Mya (My\a].

The shell of this species is moderately attenuated 

posteriorly. The anterior part is strongly inflated and 

evenly rounded, but the posterior part is very weakly 

inflated. The left valve has somewhat the shape and 

proportions of a right valve of Macoma nasuta Conrad.

This is the earliest known Mya in America. Its earliest occurrence is in the upper part of the Actta shumardi 

zone (probably equivalent to the type Lincoln Formation of Weaver, 1912, p. 10-22). This zone is of approximately the same age as the Shitakara Formation of the 

Urohoro Group of Hokkaido, the only known occurence 

for M. kusiroensis in Japan.

Lectotype: Univ. Hokkaido Reg. 8268; selected by Hatai and 

Nisiyama, 1952: Measures 31 mm in length, 19 mm in height. 

Figured specimen USNM 644267 measures 60 mm in length and 

38 mm in height; double convexity of internal mold is 20 mm.

Occurrence: Shitakara Formation, Urohoro Group (late middle Oligocene), Hokkaido, Japan. In Alaska it occurs in the 

upper part of the Acila shumardi zone (late middle Oligocene) 

on the north side of Popof Island, USGS M-1164, M-1655, in 

beds of middle Oligocene age (basal part of the Poul Creek 

Formation or the underlying Kulthieth Formation) near Hanna 

Lake in the Yakataga district, USGS 16864, 16891, and possibly 

in the middle part of the Poul Creek Formation (1,800 ft above 

the base of the formation) on the Kulthieth River, Yakataga 

district, USGS 16899.

Mya (?Arenomya) grewingki Makiyama 

Plate 1, figure 11

Mya crassa Jimbo, Geol. Soc. Tokyo Jour., v. 5, no. 54, p. 227,

pi. 1, fig. 3,1887. 

Makiyama, Geol. Soc. Tokyo Jour., v. 28, no. 334, p. 301,

1921. 

Yokoyama, Tokyo Imp. Univ. Coll. Sci. Jour., v. 45, art. 3,

p. 12, pi. 1, figs. 11-16,1924.

Mya (Arenomya) grewingki Makiyama, Kyoto Imp.- Univ. Coll.

Sci. Jour., ser. B, v. 10, no. 2, p. 156, pi. 7, figs. 50-52, 1934.

Mya grewingki Nagao and Inoue, Hokkaido Imp. Univ. Fac.

Sci. Jour., ser. 4, v. 6, no. 2, p. 147, pi. 32, figs. 1, 7-10, pi.

33, figs. 7, 8, 1941.

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu, no. 7,

pi. 10, fig. 83, 1950. 

Watanabe, Aral, and Hayashi, Chichibu Mus. Hist. Bull.,

no. 1, pi. 4, fig. 11, 1950 [no discussion].

Mya (Arenomya) grewingki Hirayama, Sci. Rept. Tokyo 

Kyoiku Daigaku, sec. c, v. 4, no. 29, p. 109, pi. 3, figs. 21- 

24, 1955.
G28 CONTRIBUTIONS TO PALEONTOLOGY

Mya grewingki Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4,

v. 9, no. 4, p. 386, pi. 5, figs. 6, 7, pi. 6, figs. 2, 4a-b, 1957.

Oyama, Mizuno, and Sakamoto, Illustrated handbook of

Japanese Paleogene molluscs; Japan Geol. Survey, p. 210,

pi. 64, figs. 4a-c, 1960.

Mya (Arenomya) grewingki Kanno, Japan Soc. for the promotion of Science, Ueno, p. 317, pi. 45, figs. 4-7, 1960.

Mya cf. M. truncata MacNeil in Drewes and others, U.S. Geol. 

Survey Bull., 1028-S, p. 606,1961.

Mya grewinyki Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 

11, no. 3, p. 404, 1962.

Mya (Arenomya) grewingki Kamada, Palaeont. Soc. Japan, 

Special Papers, no. 8, p. 140, pi. 17, figs, la-b, 1962.

As shown by Fujie (1957, p. 391), Mya grewingki has 

an arenaria-liks spoon. Judging from his figures 

(Fujie, 1957, pi. 5), the spoon is more robust than that 

of M. arenaria, and it stands about midway, in this respect, between M. arenaria and M. elegans.

The pallial sinus of this species is very large. It is not 

clear from Fujie's heavy retouching whether the sinus 

is detached to the extent he shows, or whether it is 

partly confluent with the pallial line. I suspect that 

Fujie has traced the outer edge of the pallial line and 

the inner edge of the pallial sinus attachment, so that 

it appears to be narrowly detached throughout. Mya 

arenaria has the sinus wholly detached except for the 

posterior juncture, and M. elegans has the sinus narrowly detached either throughout or in part. In size 

the sinus of M. grewingki is most like that of M. elegans.

The shell of Mya grewingki is subtrigonal to suboval, 

and it is more inflated anteriorly. Its general proportions are more like those of M. priapus, M. truncata, 

and M. elegans than they are like M. arenaria or M. 

japonica.

I do not regard Mya grewingki as being conspecific 

with either M. salmonensis Clark (= M. grewingki 

elongata Nagao and Inoue; renamed M. grewingki 

nagaoi Oyama and Mizuno), or M. kusiroensis Nagao 

and Inoue (M. grewingki kusiroensis Nagao and Inoue). 

Mya is known from several localities in Alaska in beds 

of Oligocene or Miocene age, but only one specimen is 

doubtfully referred to M. grewingki; the others are referred to M. salmonensis and M. kusiroensis.

The similarity of M. grewingki to M. elegans (= M. 

crassa] was recognized by early Japanese authors.

Holotype: Kyoto Univ. No. JC-100010. Measures 64 mm in 

length, 47 mm in height.

Occurrence: This species occurs in Japan and Sakhalin in 

beds of late Oligocene to early Miocene age that locally are 

designated the Asagai, Poronai, and Maoka Stages. Its southernmost occurrence is in the Nenokami Sandstone in the Chichibu basin, Saitama Prefecture, Honshu. The holotype is from 

the Asagai Formation in the Joban coal field, Fukushima Prefecture, Honshu. It occurs also in the Poronai Formation of 

Hokkaido, in the Nishisakutan (= Nissakutan) Formation of

southern Sakhalin, and in the Marie Formation at Matchgar in 

northern Sakhalin.

Doubtful Alaskan occurrence: Poul Creek Formation, about 

1,900 ft below the top of the formation, north flank of Yakataga 

Ridge, Yakataga district, Alaska, USGS 15433. This specimen 

measures 95 mm in length, 56 mm in height; double convexity 

is 48 mm.

In 1954, I identified some poorly preserved specimens, found 

in association with teeth of Cornwallius sp. in a green volcanic 

graywacke on Unalaska Island in the Aleutians, USGS M-1679, 

as Mya cf. M. truncata (Drewes and others, 1961, p. 606). 

Further preparation of these specimens, and a better knowledge 

of the species than I had then, indicates that this form is not 

M. truncata. These specimens are distorted internal molds and 

no spoons are visible. At the present time I am inclined to believe they are mpre likely to be either M. grewingki or M. 

kusiroensis.

Mya (?Arenomya) grewingki haboroensis Fujie 

Mya grewingki var. haboroensis Fujie, Hokkaido Univ. Fac. Sci. 

Jour., ser. 4, v. 9, no. 4, p. 392, pi. 5, figs. 1-4,1957.

This form was described from the Chikubetsu Formation of Hokkaido. As pointed out by Fujie, it has 

no anterior subumbonal groove and its spoon is more 

like that of Mya grewmgki. The anterior ridge of the 

spoon is not as broadly shelved as in M. elegans, but, 

judging from the specimen shown in Fujie's plate 5, 

figure 2, neither is it as slender as shown in his diagram 

(Fujie, 1957, p. 391, fig. 2C). In my opinion, this subspecies is the prototype of the M. elegans group; it gave 

rise to typical M. dickersoni from which M. elegans is 

descended. No late Miocene representatives of this 

group are known from Japan.

Holotype: Univ. Hokkaido Reg. 11340. Measures 51 mm in 

length, 35 mm in height; convexity is 21.3 mm. A paratype 

bears the same register number.

Occurrence: Chikubetsu Formation (middle Miocene), Takinoue Stage, Kawabata Series, Hokkaido, Japan.

According to Uozumi (1962, p. 522), the Chikubetsu 

Formation is the cold-water equivalent of the warmwater Takinoue Formation.

Mya (?Arenomya) dickersoni Clark

Plate 2, figures 1, 2, 5,10,11 

Mya dickersoni Clark, California Univ. Pubs, in Geology, v. 8,

no. 22, p. 478, pi. 63, fig. 3 [not fig. 4], 1915. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9, p. 410,

1957.

The holotype of M. dickersoni comes from the Neroly 

Formation (late late Miocene) of the San Pablo Group, 

Contra Costa County, Calif. Clark figured another 

specimen (his fig. 4) that is believed to be from the 

Briones( ?) Sandstone (early late Miocene) of the San 

Pablo Group, Contra Costa County, Calif. The latter 

specimen was listed as a "paratype" by Keen and Bentson (1944, p. 70), and they gave its occurrence as "Upper
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G29

San Pablo." I have been unable to find any other 

published reference to the stratigraphic occurrence of 

the "paratype."

Mya dickersoni is very similar to M. truncata externally. Fujie suggested that it might be related 

to M. cuneiformis.

Several spoons of Mya dickersoni were prepared from 

topotype material. They were found to range from 

ventrally elongate and deeply concave, with a broad 

dorsal shelving of the anterior ridge, a broad posterior 

furrow, and no ligamental callus to more triangular 

and shallower, with a narrower anterior ridge, a narrow 

posterior furrow, and a small thin callus having about 

the same location and shape as the rib in the callus of 

M. arenaria. The former type is like the spoon of M. 

elegans. The spoon with the small callus represents 

the morphological intermediate between the spoon of 

M. arrosis that has a large spatulate callus and the 

uncallussed spoon of M. elegans. M. elegans is believed, therefore, to be derived from a form having a 

large spatulate callus.

The spoon of the holotype is not exposed, nor can it 

be prepared without destroying the figured valve. It is 

not known, therefore, which type of spoon it possesses. 

A specimen (pi. 2, figs. 10, 11) obtained from the same 

piece of matrix containing the holotype has a small 

narrow callus.

Holotype: Actually a lectotoype, UC 11554, selected by Keen 

and Bentson (1944, p. 70). Measures 57 mm in length, 37 mm 

in height. Figured topotypes, UC 15001,15002.

Occurrence: Neroly Formation (late late Miocene), San Pablo 

Group, Contra Costa County, Calif., UC 1617.

Doubtful identifications: A larger specimen from the Cierbo 

Sandstone (middle late Miocene), San Pablo Group, Contra 

Costa County, Calif., UC 1225, may be intermediate between 

typical Mya, dickersoni and M. grewingki haboroensis. It is 

very tumid centrally. The posterior part of the shell is much 

less inflated, narrower, and subtruncate. It measures 67 mm 

in length, 47 mm in height; double convexity is 26.5 mm at the 

center and only 7.5 mm at the posterior end. Its spoon is not 

known. This specimen is not figured.

Mya (?Arenomya) elegans (Eichwald) 

Plate 2, figures 3, 4, 6-8, 12; plate 3, figures 1, 4

Mya crassa Grewingk, Russisch-Kaiserliche Mineralogische Gesellschaft zu St. Petersburg, Verhandlungen 1848-49, p.

355, pi. 6, figs. 2a-d, 1850. 

Mya arenaria Grewingk, Russisch-Kaiserliche Mineralogische

Gesellschaft zu St. Petersburg, Verhandlungen 1848-49,

p. 356, pi. 6, figs. 3a-c, 1850. 

Anatina elegans Eichwald, Geognostiseh-palaeontologische Bemerkungen uber die Halbinsel Mangischalk und die

Aleutischen Inseln, p. 119,1871 (new name for M. arenaria

Grewingk).

Mya crassa Eichwald, Geognostiseh-palaeontologische Bemerkungen uber die Halbinsel Mangischalk und die Aleutischen Inseln, p. 124,1871.

Mya intermedia Dall, Wagner Free Inst. Sci. Trans., v. 3, pt. 4, 

p. 857,1898.

Mya crassa Dall, Wagner Free Inst. Sci. Trans., v. 3, pt. 4, p. 

858,1898.

Dall, Harriman Alaska Expedition, v. 4 (Geology), p. 117, 

1904.

Mya arenaria Dall, Harriman Alaska Expedition, v. 4 (Geology), p. 117, 1904 [reissued by Smithsonian Inst, 1910].

Mya intermedia Dall, Washington Acad. Sci. Jour., v. 9, no. 1, 

p. 2,1919.

Dall, U.S. Natl. Mus. Bull. 112, p. 52, pi. 4, 1921.

Mya (Mya) arenaria var. japonica Grand and Gale, San Diego

Soc. Nat. History Mem., v. 1, p. 412, 1931 [in part]. 

Mya (Mya) arenaria var. profundior Grant and Gale, San Diego

Soc. Nat. History Mem., v. 1, p. 414, 1931 [new name for

M. crassa Grewingk]. 

Mya crassa Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9,

no. 4, p. 411,1957. 

Mya arenaria var. profundior Fujie, Hokkaido Univ. Fac. Sci.

Jour., ser. 4, v. 9, no. 4, p. 411, 1957. 

Mya japonica MacGinitie, U.S. Natl. Mus. Proc., v. 109, no. 3412,

p. 187, pi. 19, fig. 6, 1959 [in part; reassignment of "lectotype" of M. intermedia Dall].

This is the largest species of Mya, a fact that is reflected in three of the names given it; crassa, profundior, 

and elegans. Newly collected fossils indicate that there 

is no apparent way to separate the late Miocene and (or) 

Pliocene form from the Recent species (M. intermedia 

Dall).

Mya elegans has a very heavy spoon. The broad dorsal shelving of the anterior ridge and the posterior furrow are subequal in size. The angle formed by the posterior ridge and the posterior dorsal margin varies in 

size; in specimens in which the angle is wider, the posterior furrow is broader and more deeply concave. The 

most concave part of the ligament area lies along the 

anterior part of the fibrum receptacle adjacent to the 

anterior ridge. The posterior part of the ligament 

area that part consisting of the posterior part of the 

fibrum receptacle and the laminum attachment is more 

flattened or weakly convex. The ventral margin of the 

spoon is strongly convex; the most projecting part of the 

spoon is just posterior of its center. There is no anterior subumbonal grove. I have not seen a specimen 

of this species that has a ligamental callus. This species has the deepest pallial sinus of any Mya. The sinus 

is relatively narrow, however, and it lies close to the 

pallial line. The entire pallial sinus is narrowly detached from the pallial line in some specimens; in others 

only about the anterior half is separated. Morphologically, M. elegans lies between M. arenaria and M. ja~
G30 CONTRIBUTIONS TO PALEONTOLOGY

ponica, species in which the pallial sinus is widely separated from the pallial line and M. truncata and M. priapus, species in which the sinus and pallial line are confluent throughout.

The posterior and anterior adductor muscle scars are 

subequal in size; the anterior scar may be slightly thinner and more elongate than the posterior scar. Both 

scars are located above the midline of the shell. This 

species has the smallest anterior muscle scar of any living Mya; it is less elongate than in other species, and 

it is the only species in which the anterior scar may be 

located in a more dorsal position than the posterior 

scar.

The shell ranges in shape from short oval to moderately elongate and has a narrower posterior end; in 

some specimens the posterior end is more squared than 

in others. The anterior part of the shell is the more 

inflated, and there may be a weak angulation extending 

from the beak to the anterior ventral margin; this may 

be greatly exaggerated in laterally compressed fossils. 

Dall (1921, pi. 4) showed the outline of 28 specimens 

from Chignik Bay.

This species is descended from Mya grewingki 

through M. grewingki lidboroensis and typical M. 

dickersoni. One doubtful occurrence of M. grewingki 

is here recorded from the Poul Creek Formation (late 

Oligocene and early Miocene) of the Yakataga district, 

Alaska. Fujie (1957, p. 411) did not believe any known 

Japanese species was related to M. elegans (as M. profimdior) . In my opinion, however, his M. cwieiformis 

forma a (1957, pi. 3, figs. 5a-b) belongs to M. elegans.

Holotype: Lost (Scarlato, Zoological Institute, Leningrad, 

written commun., Aug. 31, 1960). I am designating as neotype 

of Mya eleffOMS a specimen collected in 1960 from the Alaskan 

Penisula. The specimen, from a large suite, is closest to the 

one figured by Grewingk as M. arenaria Linne and for which 

the name M. eleyan<s was proposed. The locality from which 

this specimen was obtained may be close to the source of 

Grewingk's fossils; Pavlof, the locality given by Grewingk, 

probably was merely a base of operation. The neotype, an 

internal mold, USNM 644272 measures about 112 mm in length, 

68 mm in height; double convexity is 40.5 mm.

A specimen from the same lot is designated as the neotype of 

Mya, crassa Grewingk; the specimen, USNM 644271, measures 

89 mm in length, 63 mm in height; double convexity is 41 mm.

Occurrence: Unnamed Pliocene formation (see p. G18), about 

5.3 miles east of the lake north of Black Peak, northwest of 

Chignik Bay, Alaskan Peninsula, USGS M-807 (neotype locality) ; middle Pleistocene beds on St. Paul Island. Pribiloff 

Islands, Alaska, USGS M-1526; Recent, Pribiloff Islands, USGS 

M-1622, Kuskokwim Bay north of Cape Newenham, USGS 

M-363, Bristol Bay, Chignik Bay on the south side of the Alaskan 

Peninsula (lectotype locality of Mya intermedia Dall) and 

Kukak Bay on the west side of Shelikof Strait (Stanford 

University).

Other reported occurrences: Grewingk gives the southeast 

coast of Alaska near the settlement of Pavlof, Morzhovai Bay, 

Port Holler (?), Kodiak, Unga, and Atka; Eichwald added 

Unalaska. Some of these may represent other species.

Mya (Arenomya) fujiei MacNeil, n. sp. 

Plate 5, figure ?1

Utya dichersoni Clark, California Univ. Pubs, in Geology, v. 8,

no. 22, p. 478 [in part], pi. 63, fig. 4, 1915. 

Mya japonica oonogai Fujie, Hokkaido Univ. Fac. Sci. Jour.,

ser. 4, v. 9, no. 4, p. 403 [in part], pi. 2, figs. la,b, 2, 1957. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 11, no.. 3,

p. 404, 1962.

This species is based on the form occurring in the 

Takinotie Formation (middle Miocene) of Ishikari Prefecture, Hokkaido (Fujie, 1957, pi. 2, figs. la,b, 2). 

The paratype of Mya dickersoni from the Briones 

Sandstone (late Miocene) of California may be the 

same species.

The spoon, judging from Fujie's figure, is very similar to that of Mya, arenaria. The posterior ridge is 

longer than in M. arenaria, which makes the posterior 

margin of the spoon less concave. The pallial sinus is 

large and deep and has a well-rounded anterior 

extremity.

The shell is less inflated anteriorly than Mya 

japonica, and the beaks are less opisthogyrate. The 

posterior extremity of the shell is less pointed than in 

M. japonica.

At present this species is known from only a few 

rather poorly preserved specimens.

Some workers might prefer to regard this form as a 

subspecies of either Mya japonica or M. arenaria, or 

to regard all three as one species. The present arrangement shows what I believe to be the true phylogenetic 

relationships of the three forms. If M. fujiei were combined with either or both of the other species, it probably would be the oldest recorded occurrence for a living 

species. Otherwise, only M. truncata is believed to have 

been in existence since middle Miocene time.

Holotype: Univ. Hokkaido Reg. no. 11334a. Measures 87.5 

mm in length, 52 mm in height; convexity is 26 mm.

Occurrence: Takinoue Formation (early middle Miocene), 

Takinoue, Sorachi district, Ishikari Prefecture, Hokkaido. 

Uozumi (1962, p. 522) stated that the Takinoue Formation is 

the warm-water equivalent of the Chikubetsu Formation which 

carries a cold-water fauna. He mentioned Mya in the 

Chikubetsu but not in the Takinoue. The point raised in this 

apparent contradiction is not clear; according to Fujie's assignment M. fujiei would be a warm-water form.

Doubtful identifications: The paratype of Mya dickersoni from 

the Briones Sandstone (late Miocene) of California, UC 197, may 

be referable to M. fujiei, or it may be intermediate between it 

and M. arenaria.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G31

Mya (Arenomya) arrosis MacNeil, n. sp. 

Plate 2, figure 9; plate 3, figures 2,3, 5,6,9

Mya dickersoni Clark, California Univ. Pubs, in Geology, v. 8, 

no. 22, 478 [in part], table opposite p. 416, UC 1227, 1915.

This species is based on specimens in the collections 

of the University of California.

The shell is very thin. It ranges in shape from moderately elongate anteriorly and only moderately inflated such specimens more nearly resemble Mya japonica to shorter, higher, and more inflated anteriorly, 

tapering sharply posteriorly (the latter variant has 

more the shape of M. cimeiformis}.

The spoon is moderately large and inclined downwards anteriorly. The surface of the ligament area is 

flattened, the deepest part being immediately adjacent 

to the anterior ridge. The dorsal part of the anterior 

ridge is very broad, but it narrows ventrally. The 

posterior ridge is long, and the posterior furrow is 

moderately narrow with very little posterior alation.

The ligamental callus is large and spatulate, and its 

posterior edge stands up as a prominent ridge. There 

is no anterior subumbonal groove. A moderately large 

solution cavity lies immediately below the umbo.

The pallial sinus is not clearly defined on the internal 

mold, but it appears to be of much the same shape 

as in Mya japonica.

This form was included in Mya dickersoni in several 

early checklists, probably because it occurs in beds of 

the same general age as M. dickersoni, and because 

the spoon of M. dickersoni was not known at the time. 

It almost certainly is the form that led Woodring and 

Stewart (in Woodring and others, 1940, p. 95) to identify the species in the Etchegoin and San Joaquin Formations as Mya cf. M. dickersoni. The spoon of typical 

M. dickersoni is more like the spoon of M. elegans.

Mya japonica probably descended from a form of M. 

arrosis rather than from M. arenaria. No Mya of this 

group is known to date from late Miocene beds of 

Japan, but I suspect one will be found, eventually. In 

all probability M. japonica originated in East Asia.

Holotype: UC 15006 measures 78 mm in length, (incomplete, 

probably about 85 mm), 57 mm in height; double convexity is 

about 28 mm.

Occurrence: The holotype is from the Cierbo Sandstone (middle late Miocene), San Pablo Group, at a locality north of 

Grizzley Creek, and about half a mile west of south from Tice 

Valley, Contra Costa County, Calif., UC 1227.

A similar spoon was found among specimens from 

the type locality of Mya dickersoni in the Neroly Formation (late late Miocene), San Pablo Group. The 

shell is a fragment, and its shape cannot be determined.

The spoon, however, is much more strongly callused 

than in specimens that are regarded as topotypes of 

M. dickersoni.

Mya (Arenomya) japonica Jay 

Plate 3, figures 7, 8, 10; plate 4, figures 1-11; plate 6, figure 16

Mya arenaria Middendorff, Malacozoologia Rossica; Acad. Sci.

St. Petersbourg Mem., ser. 6, v. 6, p. 586, pi. 20, figs. 1-3,

1849. 

IMya arenaria Middendorff, Reise in dem Aussersten Norden

und Osten Siberiens; K. Akad. Wiss., v. 2, pt. 1 (Mollusken), St. Petersbourg, p. 269, no. 3, 1851. 

Mya japonica Jay, in Narrative of the expedition of an American Squadron to the China Sea and Japan, 1852-54,

under the command of Commodore M. C. Perry, v. 2,

p. 292, pi. 1, figs. 7, 10, 1856. 

Mya arenaria Crosse and Debeaux, Jour, conchyliologie, v. 11, p.

253, 1863.

Lischke, Japanische Meeres-conchylien, v. 1, p. 138, 1869. 

Mya acuta Grabau and King, Shells of Peitaiho, p. 192, 1928. 

Mya arenaria japonica Makiyama, Kyoto Imp. Univ. Coll. Sci.

Mem., ser. B, v. 10, no. 2, art. 6, p. 159, 1934. 

Mya oonogai Makiyama, Warera-no-Kobutsu, v. 4, no. 3, p. 137,

text fig. 0,1935. 

arenaria Foster, Johnsonia, v. 2, no. 20, p. 32, 1946 [in

part].

japonica Cahn, Clam culture in Japan; Supreme Commander Allied Powers Nat. Res. Sec. Rept., no. 146, p. 85,

fig. 10 (unlettered), fig. 36, A-G, 1951. 

(Hirase) Taki, Handbook of illustrated shells, pi. 52, fig.

7, 1951. 

Mya (Arenomya) japonica Habe, Genera of Japanese Shells;

Pelecypoda, v. 3, p. 237, fig. 612, 1952. 

Mya (Arenomya) japonica oonogai Habe, Akkeshi Marine

Biol. Sta. Pub., no. 4, p. 22, pi. 6, fig. 3, 1955. 

Mya (Arenomya) japonica Kira, Coloured illustrations of the

shells of Japan, pi. 61, fig. 22, 1955. 

Mya japonica oonogai Fujie, Hokkaido Univ. Fac. Sci. Jour.,

ser. 4, v. 9, no. 4, p. 403, pi. 2, figs. 3-6, 1957. 

Mya (Arenomya) japonica oonogai Yamamoto and Habe,

Marine Biol. Sta. Asamushi Bull.; Tohoku Univ., v. 9,

no. 3, p. 113, pi. 12, fig. 18, 1959. 

Mya arenaria Wagner, Canada Geol. Survey Bull. 52, p. 8, pi. 1,

figs. 19 a, b, 1959. 

Mya japonica MacGinitie, U.S. Natl. Mus. Proc., v. 109, no.

3412, p. 187, pi. 19, fig. 8, 1959. 

Mya oonogai Hopkins, MacNeil, and Leopold, 21st Internat.

Geol. Gong. Rept., pt. 4, p. 52,1960. 

Mya (Arenomya) japonica Kira, Coloured illustrations of the

shells of Japan, pi. 61, fig. 22,1961 [revised and enlarged]. 

Mya japonica oonogai Fujie, Hokkaido Univ. Fac. Sci. Jour., ser.

4, v. 11, no. 3, p. 400, 1962. 

Mya (Arenomya) arenaria Kotaka, Tohoku Univ. Sci. Repts.,

ser. 2, spec, v., no. 5, p. 154, pi. 35, figs. 22-25, 1962.

The characters that distinguish this species from 

Mya arenaria are discussed under the latter species.

Kira (1955 and 1961) appears to be the only Japanese 

author since 1955 to continue to use the name Mya 

japonica for the southern Japanese species. He figured 

only the exterior of a shell, but its attenuated posterior
G32 CONTRIBUTIONS TO PALEONTOLOGY

end and his use of the Japanese vernacular name, 

Onogai, a name used for the southern species, leaves 

little doubt as to which species he meant. Yamamoto 

and Habe (1959, p. 113), several years after Habe had 

accepted the transfer of the name M. japonica to the 

northern species (M. priapus) , proposed a new vernacular name for the northern species, "Kitano-ono-gai."

Cahn (1951, p. 85), who must have had contact with 

Japanese workers at about the time the transfer of name 

became generally accepted, also used M. japonica for 

the southern species. Cahn gave a good account of the 

habits and distribution of the species in Japan, and he 

discussed the possibility of commercial culture. He 

gave some good illustrations of the veliger and successive juvenile stages. The successful culture of other 

edible clams has delayed any large scale culture of M. 

japonica, although experiments in harvesting the natural population have been carried out in Okayama 

Prefecture.

The transfer of the name Mya japonica to another 

species by Grant and Gale and the apparent acceptance 

of their interpretation by most modern Japanese 

authors was unfortunate. As reluctant as I am to 

reverse this action at this date, I can see no alternative 

to it. The pallial sinus on Jay's specimen indicates 

that it cannot be anything but the southern species that 

most modern Japanese authors call M. oonogai. Woodring and Stewart (in Woodring and others, 1940, p. 95) 

probably were also following Grant and Gale in their 

reference to M. japonica as a "living Alaskan and Japanese" species; the occurrence of M. japonica as here 

interpreted in Alaska has been known only since 1960. 

All other American and European authors, as well as 

the early Japanese authors, seem to have regarded M. 

japonica as being the southern Japanese species. Fixation of the name M. japonica on the northern species, in 

view of the pallial sinus shown in Jay's figure, could 

only be accomplished by the International Commission 

on Zoological Nomenclature, and I doubt if it could 

ever receive favorable action. Besides, the name M. 

priapus has priority for the northern species.

As further proof of my identification of Mya japonica, it might be pointed out that Jay's figure shows a 

large multiple solution cavity under the umbo of the 

left valve, and it appears to show a ligamental callus. 

As already discussed (p. G24), subumbonal solution is 

an almost universal condition in left valves of M. 

arenaria and M. japonica, but it has not been observed 

in left valves of M. priapus. Right valves of M. 

priapus occasionally have a single small solution pit

that indents the margin of the shell at the top of the 

chondrophore in the right valve.

Grabau and King (1929, p. 192) recorded Mya acuta 

Say from Peitaiho (near Tientsin in the Gulf of Chihli), 

China. Their statement that it is more pointed posteriorly than M. arenaria identifies it as M. japonica. 

Their use of the name M. acuta, however, makes one 

wonder what they had in mind. Mya acuta was described from the "southern coast of the United States," 

and it has long been placed in the synonymy of M. 

arenaria.

The most likely reason for their use of the name Mya 

acuta is that they followed Sowerby (1875-78, pi. 3, fig. 

12b). Sowerby used the name for M. japonica, and he 

also recognized both M. acuta and M. arenaria on the 

Atlantic coast. However, inasmuch as M. japonica is 

the most southern of the Asiatic species, Grabau and 

King might have suspected the migration of a southern 

Asiatic species to the Atlantic and a retreat of the species 

to a southern geographic position in the Atlantic, or vice 

versa. The recent discovery of M. japonica north of 

Bering Strait makes such a circumstance possible, but 

whether it is true, and whether Grabau and King 

thought so, is difficult to say.

It remains to be determined also whether Mya japonica still lives north of Bering Strait. Specimens 

picked up on the beach behind Sheshalik Spit in 1962 

are completely unworn, and they have pieces of all three 

ligament layers and the periostracum preserved. Another small specimen was found on the beach at Deering. In my opinion these are Recent shells, and in all 

probability a colony of the species lives in Kotzebue 

Sound.

Holotype: Location?; Dr. J. P. E. Morrison (written commun., 

Feb. 11, 1963) informed me that the type is not in the U.S. 

National Museum; he suspects it may have been added to the 

Jay collection, or remained in Perry's or other private hands. 

Until it is determined definitely whether or not Jay's specimen 

is in existence, nothing can be done about selecting a neotype. 

The rules are not specific regarding the necessity of designating a neotype if the original figure is recognizable, and in my 

opinion it is. If a neotype is required, it must be a specimen 

having a detached pallial sinus from Uchiura-wan, Hokkaido. 

The designation of a specimen having an attached pallial sinus, 

that is M. priapus, would be contested almost certainly.

Occurrence: I am dubious of the Miocene forms referred to 

this species. Fujie (1957, p. 412, table 3) gave some supposed 

Miocene occurrences (middle Miocene and older) but none from 

the late Miocene or Pliocene. The Miocene forms, in my opinion, 

are more like Mya arenaria. I have named this form H. fujiei.
EVOLUTION AND DISTRIBUTION OF THE GENUS MY A G33

Chinzei (1961, p. 126, pi. 3, fig. 13) figured an internal mold 

from the Togawa Formation of the Sannohe Group of northeastern Honshu as Mya japonica oonogai. The Togawa Formation is assigned to the late Pliocene.

Although I am inclined to believe My a japonica became differentiated during the Pliocene, the known occurrences of the 

species all seem to be in very young beds. The only unequivocal 

fossil specimen from Japan that I can find illustrated is from 

alluvial deposits around Lake Abashiri, northern Hokkaido 

(Fujie, 1957, pi. 2, figs. 6a-c). In 1962, Fujie (p. 419) gave the 

age of these deposits as Holocene (postglacial).

The species occurs at Nome, Alaska, USGS M-1440, M-1445, 

and at Cape Kruzenstern, Alaska, USGS M-1577, in beds that I 

regard as of possible middle-Wisconsin age. It also occurs in 

beds in the vicinity of Vancouver, British Columbia, that are 

dated (Wagner, 1959, p. 1) as "25,000 or more years" old and 

of Pleistocene age or younger. The oldest occurrences in the 

Vancouver area would also be, according to this date, of middleWisconsin age. The same form occurs in recently discovered 

beds, probably Pleistocene, along the north side of Willapa 

Bay, Wash., USGS M-1681, M-1682, the southernmost American 

occurrence for the species.

Mya japonica lives today from southern Hokkaido to Amakusa 

Island off west-central Kyushu, Japan, and it lives also in the 

Gulf of Chihli, China. It may also live in the Okhotsk Sea. 

Specimens collected from Sheshalik Spit, northern Kotzebue 

Sound, USGS M-1665 and at Deering, southern Kotzebue Sound. 

Alaska, USGS M-1425, appear to be Recent, although none 

of them were found alive. A Recent left valve and several 

live juveniles were found near Nome, Alaska, USGS M-364.

Foster (1946, p. 35) reported Mya arenaria, presumably Recent, from Akutan Island in the eastern Aleutians. This could 

be an otherwise unreported occurrence of M. japonica, or it could 

be some other species. It might also be based on Grewingk's "M. 

arenaria" (=M. elegans), which occurs in the area. I can 

find no other record of either M. japonica or M. arenaria from the 

Aleutians.

Mya (Arenomya) arenaria Linne

Plate 5, figures 2-12; plate 6, figures 1-15,17,18

Mya arenaria Linne, Systema naturae, ed. 10, p. 670, 1758. 

Mya communis Megerte von Miihlfeld, Mag. Gesellsch. Naturforscher Freunde Berlin, v. 5, p. 46, 1811 [based on

Chemnitz, Conchylien Cabinet, v. 6, pi. 1, figs. 3, 4, 1782]. 

Mya lata Sowerby, Mineral conchology Great Britain, v. 1, p.

185, pi. 81, 1815 [fossil from the Red Crag of England]. 

Smith, Strata identified by organized fossils, London, pi. 2,

fig. 9,1816. 

Mya acuta Say, Philadelphia Acad. Nat. Sci. Jour., v. 2, p. 313,

1822. 

Mya mercenaria Say, Philadelphia Acad. Nat. Sci. Jour., v. 2, p.

313,1822. 

Mya arenaria Conrad, American marine conchology, p. 42, pi.

9, fig. 1,1831-34. 

Mya subovata Woodward, Geology of Norfolk, p. 43, pi. 2, fig. 5,

1833. 

Mya subtruncata Woodward, Geology of Norfolk, p. 43, pi. 2,

fig. 6,1833.

Mya alba Agassiz, Soc. Sci. Nat. Neuchatel Mem., v. 2, p. 1, 1840. 

Mya corpulenta Conrad, Fossils of the medial Tertiary, p. 68,

pi. 39, fig. 1, 1845 [fossil from Petersburg, Va.].

Mya arenaria Wood, Palaeontographical Soc. London Mon., v.

9, p. 279, pi. 28, figs. 2a-f, 1857. 

Holmes, Post-Pleistocene fossils of South Carolina, p. 55,

pi. 8, fig. 15, 1860.

Verrill, Report upon the invertebrate animals of Vineyard 

Sound . . .; U.S. Commissioner Fish and Fisheries Rept., 

p. 672, pi. 26, fig. 179,1873. 

Wood, Palaeontographical Soc. London Mon., v. 27, p. 162,

1874.

Mya hemphilli Newcomb, Acad. Nat. Sci. Philadelphia Proc., v. 

5, p. 415, 1874 [based on transplants in San Francisco 

Bay]. 

Mya arenaria Sars, Mollusca Regionis Arcticae Norvegiae;

Universitets program, Christiania, p. 91, 1878. 

Mya elongata Locard, Prodrome de Malac. Francaise, p. 383,

586, 1886. 

Mya arenaria Dall, U.S. Natl. Mus. Bull. n. 37, p. 70, pi. 49, fig.

9, pi. 55, fig. 2; pi. 61, fig. 2,1889.

Dall, Wagner Free Inst. Sci. Trans., v. 3, pt. 4, p. 857, 1898. 

Br0gger, Norges geol, undersogelse Skrifter, no. 31, p. 605,

fig. 64, 1901. 

Clark, Pliocene and Pleistocene; Maryland Geol. Survey,

p. 194, pi. 53, figs. 5, 6; pi. 54, figs. 1-4, 1906. 

Mya (Arenomya) arenaria Winckworth, Malacological Soc.

London Proc., v. 19, p. 15,1930. 

Mya cf. M. dickersoni Woodring and Stewart, U.S. Geol. Survey

Prof. Paper 195, p. 95, pi. 9, figs. 4-9,1940. 

Mya arenaria Gardner, U.S. Geol. Survey Prof. Paper 199-A, p.

138, pi. 22, fig. 8,1943. 

Foster, Johnsonia, v. 2, no. 20, p. 32, pi. 20, figs. 1-4; pi.

21, fig. 1, 2,1946. 

Hessland, Arkiv for Zoologi, Stockholm, v. 37. pt. 2, no.

8, p. 1-51, pi. 1,1946. 

Dodge, Am. Mus. Nat. History Bull., v. 100, art. 1, p. 28,

1952.

Richards, Am. Philos. Soc. Trans., new ser., v. 52, pt. 3, 

p. 70, pi. 12, fig. 15,1962.

A complete synonymy for this species would run into 

many pages. The one given here probably includes all 

the synonyms and most of the works generally cited by 

authors.

Mya japwiica is excluded from this species, although 

this procedure may not have the approval of some authors. Several authors have regarded M. jap-onica as a 

synonym of M. ar&naria. Others might contend that 

if they are not identical, they are no more than local 

subspecies. In my opinion these species are members 

of parallel lineages. M. japonic® does not live in the 

same area as M. arenaria,, and I know of no accidental 

introductions of either species to an area inhabited by 

the other.

Mya arenaria has a heavier shell than M. japonica. 

The posterior end is less attenuated, the beaks are less 

twisted, which makes the anterior and posterior parts 

more evenly inflated, and the exterior of the shell is more 

irregular. The spoon of M. arenaria tends to be larger 

for a shell of the same size, and it is slightly more hori-

,732-763 O 64-
G34 CONTRIBUTIONS TO PALEONTOLOGY

zontal; in some specimens of M. japonica the spoon is 

inclined downwards rather steeply towards the anterior. 

The posterior ridge is relatively longer in M. japonica, 

making the posterior margin of the spoon less indented.

The spoon of Mya arenaria is elongate and the ventral margin is strongly rounded; the ventral edge of the 

spoon extends well below the ventral end of the anterior 

ridge; the posterior margin of the spoon extends nearly 

vertically to the end of the posterior ridge. The posterior furrow is moderately deep, and it merges with the 

dorsal margin of the shell at a point well back from the 

end of the posterior ridge. The anterior ridge is narrow 

and generally curves over the anterior part of the fibrum 

receptacle rather strongly. In large shells the ventral 

part of the anterior ridge may be swollen and strongly 

hooked, whereas the dorsal part appears to have been 

resorbed, apparently by the mantle during its invasion 

of the dorsal part of the fibrum receptacle to deposit the 

ligamental callus. The anterior ridge does not broaden 

dorsally, and it forms a moderately sharp angle with the 

dorsal margin; generally the angle is recessed or 

indented.

Mya arenarla has a thick ligamental callus, it has no 

anterior subumbonal groove, and there is always a large 

amount of subumbonal solution.

The pallial sinus of Mya arenarla is moderately long, 

and it is completely detached from the pallial line; the 

space between the sinus and the pallial line is nearly as 

wide as the sinus itself. The sinus joins the pallial line 

only at its posterior terminus. The lower limb of the 

pallial sinus is not parallel with the pallial line but, 

rather, it is directed upwards from it. The innermost 

end of the sinus may be pointed, blunt, or squared. The 

pallial sinus and pallial line range from weakly impressed to very strongly impressed; that is, they may be 

flush with the sliell or deeply indented.

The posterior muscle scar has about the shape of a 

three-quarter moon. The anterior scar is elongate tear 

shaped and moderately broad ventrally. It extends 

lower than the posterior scar; its ventral end is about 

opposite the inner end of the pallial sinus.

Myd arenarla and M. japonica are morphologically 

similar and probably closely related, but these two species are not very closely related to any other living Mya.

Holotype: According to Dodge (1952, p. 29), Linne's specimen, 

properly marked, is in the collection of the Linnean Society of 

London.

Occurrence: The occurrence of this species in Japan depends 

on how the delimitation of Mya arenaria and M. japonica is 

made. In my opinion, M. arenaria is the older species, and 

the form in the Takinoue Formation (middle Miocene) of 

Japan that Fujie (1957, pi. 2, figs. 1 a, b, 2) referred to M. 

japonica oonogai is ancestral to it. This species was reported

from the Kawabata Formation of Hokkaido as M. arenaria 

(Minato and others, 1950, p. 4). It is here named M. ftipiei. 

The species in the Toshima Sand (Pleistocene) that Hayasaka 

(1961, p. 64, pi. 8. figs. lOa, b) identified as M. (Arenomya) 

japoriica, oonogai, I identify as M. arenaria, but, if this identification is correct, it is the last form from Japan that I would refer 

to this species. Kotaka (1962, p. 154, pi. 35, figs. 22-25) identified two young Recent specimens from Okhotsk Sea as If. 

arenaria. It is not clear from his figures what they are, but 

they may be juveniles of If. japonica.

In western North America, Mya arenaria is known in the 

following: the Cierbo Sandstone (middle late Miocene) of the 

Mount Diablo region, Alameda County, central California, U.C. 

1224; the upper part of the Etchegoin Formation (Pliocene), 

Kettleman Hills district, western San Joaquin Valley, Fresno 

and Kings Counties, Calif. U.C. A-1686; San Joaquin Formation (late Pliocene), Kettleman Hills district, U.C. A-3167 (for 

further records see Woodring and others, 1940), Merced Formation (late Pliocene and early Pleistocene?), San Mateo 

County, Calif., U.C. B-4807; Recent from Monterey, Calif., to 

Southeastern Alaska. The Recent representatives all come, 

probably, from an introduction of the species in San Francisco 

Bay about 1865.

A species occurring in Pleistocene beds around Vancouver 

in southwestern British Columbia has been identified as Mya 

arenaria. Judging from Wagner's (1959, pi. 1, figs. 19a-b) 

figures, it has a thin shell and the spoon is tilted. It thus resembles more closely the late Pleistocene fossils from Nome 

and Kotzebue Sound, Alaska, here referred to M. japonica.

In eastern North America, Mya arenaria is known in the 

following: Yorktown Formation (late Miocene), Virginia, Yorktown, USGS 2247b, Petersburg, USGS 3122; Waccamaw Formation (Pliocene), North Carolina, Lake Waccamaw, Columbus 

County (fide Gardner, 1943, p. 139), Neill's Eddy Landing, 

Columbus County (fide Gardner, 1943, p. 139), Wilmington, 

USGS 2295; Richards (1962, p. 70) records the species from 45 

Pleistocene localities (probably ranging in age from Sangamon 

to postglacial), Labrador (1), Hudson Bay (1), Newfoundland (6), Quebec (4), New Brunswick (4), Maine (10), Massachusetts (2), Vermont (3), New York (2), New Jersey (5), 

Delaware (1), Maryland (3), North Carolina (1), South Carolina (2) ; the species is known from the Recent of Labrador 

to North Carolina, but it is common only between the Gulf of 

St. Lawrence and Long Island Sound. The species from Greenland so identified probably is M. pseudoarenaria, USGS D-385.

In Europe, Mya arenaria was abundant in the Newbournian 

and Butleyan Stages of the Red Crag and in the Norwich Stage 

of the Icenian Crag (all early Pleistocene) of England. It 

does not occur, however, in the Waltonian (the earliest stage 

of the Red Crag), or in the underlying Coralline Crag (late 

Pliocene). Wood (1856, p. 279) gave "Bridlington" as a locality 

for this species, which may refer to the Bridlington Crag 

(early glacial Pleistocene) and thus place the species in postCromer Forest beds. In Belgium it occurs in the Sables du 

Kruisschans (the lower part of the Merxemien or Poederlien 

Stage; early Pleistocene), the probable correlative of the Newbournian Stage.

Most European workers seem to be of the opinion that Mya 

arenaria became extinct in Europe during the early part of 

the glacial Pleistocene. Some authors have thought that M. 

arenaria reinvaded Europe during the iron age, but according 

to Hessland (1946), it was first noticed as a prominent species
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G35

in the littoral fauna during the 17th century. The last emergent 

peripheral sediments of the Baltic Sea, the so-called Mya Sea, 

date from about this time. Hessland believed the species was 

brought to the coast of Europe during the 16th century by 

sailing vessels. At present the species is established from 

northern Norway to the southern part of the Bay of Biscay, 

southern France.

Subgenus MYA Linne 1758

Mya (Mya) salmonensis Clark 

Plate 7, figures 1, 4

Mya salmonensis Clark, Geol. Soc. America Bull., v. 43, p. 822,

pi. 17, figs. 3, 4, 8, 1932. 

Mya grewingki var. elongata Nagao and Inoue, Hokkaido Imp.

Univ. Fac. Sci. Jour., ser. 4, v. 6, no. 2, p. 150, pi. 33,

figs. 1-4,1941. 

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu (Studies

of the Cenozoic), no. 7, p. 2, pi. 10, fig. 89, 1950. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9, no. 4, p.

389, pi. 7, figs. 1, 2, ?6, ?7, ?10, ?11, ?12, 1957 [in part]. 

Mya grewingki nagaoi Oyama and Mizuno, Japan Geol. Survey

Bull., v. 9, no. 9, p. 603, 1958. 

Oyama, Mizuno, and Sakamoto, Illustrated handbook of

Japanese Paleogene molluscs; Japan Geol. Survey, p. 211,

pi. 64, figs. 3a-d, 1960. 

Mya (Arenomya) grewingki var. elongata Kanno, Japan Soc.

for the Promotion of Science, Ueno, p. 318, pi. 45, figs. 2, 3,

1960.

The spoon of Mya salmonensis has not been figured 

previously. Their similar shape, and the fact that this 

species and M. grewingki elongata from Japan are of 

the same approximate age, leaves little doubt in my 

mind that they are the same species. Fujie's illustrations of the spoon of the latter show it to be like that 

of M. salmonensis. The spoon is rounded anteriorly as 

in M. arenaria, but the anterior ridge is very broad 

dorsally as in M. truncata. The spoon has a simple but 

moderately large callus. M. salmonensis also has a welldefined anterior subumbonal groove. M. salmonensis 

appears in all respects to be the prototype of the M. 

truncata group.

Curiously, Fujie placed Mya grewingki eltmgata and 

M. salmonensis in different groups. The former he 

regarded as related to M. japonica (as M. japonica, 

oonogai], whereas he suggested (1957, p. 411) that M. 

salmonensis resembled M. cwneiformis.

Unfortunately, the holotype of Mya salmo-nensis is a 

float specimen. According to the late D. J. Miller, who 

attempted to locate Taliaf erro's localities, Salmon Creek 

must be a field name and its whereabouts is unknown; 

he thought from the lithology of the specimen, however, 

that it could only have come from the Poul Creek 

Formation.

Holotype of Mya salmonensis, UC 30397, measures about 56 

mm in length, 32 mm in height; double convexity is 32 mm.

Lectotype of M. grewingki elongata, Univ. of Hokkaido Reg. 

8987 and selected by Fujie, 1957, measures 63 mm in length, 

35 mm in height; convexity is 18 mm.

Occurrence: This species occurs in the Poronai Stage of 

southern Sakhalin (type locality) and Hokkaido. In Alaska 

it is found in the Poul Creek Formation, UC 3851 (?loc.) and 

at two localities near Priest River, USGS 17783 (2,400 ft below 

the top of the formation), and USGS 17787 (1,100 ft below top 

of the formation).

Mya (Mya) cuneiformis (Bohm)

Plate 7, figures 2, 3, 5-8,12,15

Pleuromi/a cuneiformis Bohm, Preuss. geol. Landesanstalt

Jahrb., v. 26, p. 557, pi. 29, figs, la-c, text figs. 1, 2, 1915. 

Mya crassa Yokoyama, Tokyo Imp. Univ. Fac. Sci. Jour., sec.

2, v. 1, p. 232, pi. 29, figs. 6-8,1926. 

Mya atrenaria Yokoyama, Tokyo Imp. Univ. Fac. Sci. Jour.,

sec. 2, v. 1, p. 241, pi. 30, fig. I, 1926. 

IMya japonica Matsumoto, Tohoku Imp. Univ. Sci. Repts., ser. 2,

v. 13, p. 98, pi. 39, fig. 11,1930. 

Mya peternalis Matsumoto, Tohoku Imp. Univ. Sci. Repts., ser.

2, v. 13, p. 98, pi. 39, figs. 5-10,1930.

IMya japonica Kuroda [in Homma], Fossil Mollusca [in Geology of Central Shinano], p. 64, pi. 8, fig. 55, pi. 9, figs.

57, 58, 1931. 

Mya donaciformis Kuroda [in Homma], Fossil Mollusca [in

Geology of Central Shinano], p. 63, text fig. 7, 1931. 

Mya urusikuboana Nomura, Saito Ho-on Kai Mus. Res. Bull.,

no. 5, p. 119, pi. 5, figs. 6, 7,1934. 

Mya cuneiformis Makiyama, Kyoto Imp. Univ. Coll. Sci. Mem.,

ser. B, v. 10, no. 2, art. 6, p. 157,1934. 

Makiyama, Kyoto Imp. Univ. Coll. Sci. Mem., ser. B, v. 11,

no. 4, art. 8, p. 216,1936. 

Nagao and Inoue, Hokkaido Imp. Univ. Fac. Sci. Jour. ser.

4, v. 6, no. 273, p. 151, pi. 34, figs. 1-6,1941. 

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu [Cenozoic Research], no. 7, p. 3, pi. 10, figs. 90, 91, 1950. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9, no. 4, p.

395, pi. 3, fig. 5, pi. 4, figs. 1-6,1957. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 11, no. 3,

p. 406,1962 [?inpart]. 

Kamada, Palaeontological Soc. Japan, Special Papers, no.

8, p. 141, pi. 16, figs. 14-16,1962.

Fujie (1962, p. 406) said this species occurs in Alaska. 

This may be based on his former (1957, p. 411) statement that Mya salmonensis Clark resembles M. cwneiformis. M. cuneiformis probably is descended directly 

from M. salmonensis and the boundary between them 

is not sharp. M. salmomensis, however, appears to have 

come from the Poul Creek Formation (late Oligocene 

and early Miocene), whereas the specimen I refer to 

M. cmnelformis are from the lower part of the Ya,kataga 

Formation and probably they are of middle Miocene 

age. As far as I am aware, the Yakataga occurrences 

of M. ctmeif'Ormis are recorded here for the first time.

The spoon of Mya cuneiformis is definitely triangular. The ventral margin is weakly concave, the concavity centering at about the boundary between the
G36 CONTRIBUTIONS TO PALEONTOLOGY

laminum attachment and the fibrum receptacle. There 

is a well-defined subumbonal groove. The area bounded by the subumbonal groove and the anterior leg is 

triangular; the leg is nearly vertical and forms a right 

angle with the anterior margin of the shell. The configuration of the margin so formed is more like that of 

Arenomya, but Arenomya has no subumbonal groove. 

There is no indication of any subumbonal solution in M. 

cuneiformis. (See p. G24.)

The anterior ridge is of moderate width and has no 

marked dorsal broadening; the growth lines of the 

fibrum receptacle rise up the side of the anterior ridge 

and partly cover its crest. The ventral part of the 

anterior ridge is more projecting and weakly hooked 

over the fibrum receptacle, another character recalling 

Arenomya.

The fibrum receptacle is concave, the deepest part 

being immediately adjacent to the anterior ridge. The 

posterior part of the fibrum receptacle and the laminum 

attachment together form a moderately strong convexity. The posterior part of the laminum attachment, 

however, forms another narrow concave area. The 

posterior ridge is moderately strong. The most projecting part of the posterior part of the spoon is opposite the posterior ridge and the narrow concavity 

immediately anterior to it. The posterior furrow is 

moderately narrow to narrow; its dorsal posterior extremity forms a long narrow wing.

The pallial sinus is moderately broad and moderately 

deep; its ventral leg is confluent with the pallial line 

throughout. The posterior muscle scar is subrounded; 

the anterior scar is elongate and narrow.

The shell of Mya cuneiformis, as its name implies, is 

wedge shaped. The anterior is broad and rounded, but 

the shell narrows to a sharply rounded posterior extremity. The dorsal margin between the beak and the 

posterior end is nearly straight. The anterior part of 

the shell is more inflated than the posterior part, and the 

beak is set rather high. There is a weak angulation 

extending from the beak to the anteroventral margin, 

which, in laterally compressed specimens, may be quite 

sharp.

Some features of the spoon of this species, such as the 

backward curving of the anterior ridge over the fibrum 

receptacle and the nearly vertical strike of the anterior 

leg, are more resemblant of Mya arenaria. As one of 

the more primitive species of Mya (Mya) it is not 

strange that it has some features close to Mya 

(Arenomya). Its spoon, however, is heavier and more 

triangular than in any Mya (Arenomya) of comparable 

size, and it has a well-defined anterior subumbonal 

groove, a character typical of Mya (Mya). There is no

evidence of subumbonal solution in the left valves of 

M. cuneiformis, a circumstance that seems always to be 

linked with a subumbonal groove. (See p. G24).

It is not clear at the present time whether Mya 

cuneiformis gave rise directly to M. pseudoarenaria, or 

whether both species are coderivatives from M. salmonensis. M. cuneiformis takigawensis Fujie (1957, 

p. 397, pi. 4, figs, la-c) from the Takigawa Formation 

(early Pliocene) of Hokkaido may connect these two 

species; judging from the figures it is closer morphologically to M. pseudoarenaria. At present, M. cuneiformis is extinct, and M. pseudoarenaria lives only in 

the Arctic Ocean and in the northern boreal Atlantic 

Ocean. M. cuneiformis probably gave rise directly 

to M. priapus, probably in late Miocene time.

Like Eichwald, who thought Mya crassa and M. 

elegans were of Turonian age, Bohm thought M. cuneiformis was of Cretaceous age.

Holotype: The holotype, if preserved, is in the Naturhistorischen Museum (Geologisches Staatsinstitut), Hamburg, 

Germany.

Occurrence: Bohm's specimens, including the type, are stated 

to be from Kap Jonquiere (Due), west-central Sakhalin; they 

probably are from beds of middle Miocene age. Fujie (1957, 

p. 396) recorded this species from several formations in Hokkaido ranging in age from middle Miocene to early Pliocene: 

the Chikubetsu and Kawabata Formations (middle Miocene), 

the Togeshita and Wakkanai Formations (late Miocene), and 

the Honbetsu and Takigawa Formations (early Pliocene).

Kamada (1962, p. 142) recorded the species from three formations of middle Miocene age in the Joban coal field of Fukushima and Ibaraki Prefectures, Honshu. These are the Nakayama Formation of the Shirado Group and the Numanouchi and 

Kokozura Formations of the Taga Group.

The species is known for certain only in the lower 4,000 

feet of the Yakataga Formation of Alaska. This part of the 

formation is assigned to the middle Miocene. The species is 

represented in the Geological Survey collections from: an unnamed creek north of and parallel to Yakataga Ridge, USGS 

15437 (near base of formation), Oil Creek, USGS 17850 (in 

lower 100 ft of formation), the north end of Duktoth Mountain, 

USGS 17782 (in lower 200 ft of formation), Sunshine Point near 

mouth of Kulthieth River, USGS 17827 (about 1,000 ft above 

base of formation), the south flank of Kulthieth Mountain, 

USGS 17835 (about 3,000 ft above base of formation), and 

the west end of Yakataga Ridge, USGS 15431 (about 3,200 ft 

above base of formation).

The species is known from beds on Kodiak Island where it 

is associated with Mytilus middendorffi Grewingk, USGS 13372 ; 

these beds are also referred to the middle Miocene. Specimens 

from the lower part of an unnamed formation (370 ft above 

the base) on Cenotaph Island, Lituya Bay, USGS D169 (T) 

also appear to be this species; their spoon is unknown. The 

lower part of the unnamed formation is referred to the middle 

Miocene.

The identity of specimens in the late Miocene and Pliocene 

beds of Alaska is more problematical. No spoons have been seen 

on any specimens within this stratigraphic and biologic sequence,
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G37

but judging from the exterior of the known specimens, most of 

which are crushed or distorted, there seems to be an even 

gradation between Mya cuneiformis and M. priapus. These 

are assigned tentatively to M. priapus.

Mya (Mya) pseudoarenaria Schlesch 

Plate 7, figures 9-11, 13, 14; plate 9, figure ?4

IMya arenaria Moller, Naturhist. Tidsskrift, ser. 1, v. 4, no. 1,

p. 21,1842.

Middendorff, Malacozoologia Rossica; Acad. Sci. St. Petersbourg Mem., ser. 6, v. 6, p. 586, 1849 [in part].

IMya truncata Loven [in Heer], Kongl. Svenska Vetenskapsakad. Handl., v. 8, no. 7, p. 92, 1870.

Mya arenaria Leche, Kongl. Svenska Vetenskapsakad. Handl., 

,v. 16, no. 2, p. 4, 1878.

fMya intermedia Dall, Wagner Free Inst. Sci. Trans., v. 3, pt. 4, 

p. 857, 1898 [in part].

Mya truncata forma ovata Jensen, Videnskabelige Meddeleser 

naturhist. Forening, Copenhagen, p. 139, figs. 3, 4, p. 140, 

fig. 4, p. 141, fig. 6, p. 142, 1900 [not Donovan, 1802].

Mya truncata ovata Schlesch. Archiv f. Molluskenkunde Abhl., 

v. 1, no. 3, p. 323, pi. 6, fig. 1, 1924.

Mya intermedia Dall [in O'Neill], Rept. Canadian Arctic Expedition 1913-18, v. 11, pt. A, p. 31, 32, 1924.

Mya pseudoarenaria Schlesch, Archiv f. Molluskenkunde, v. 63, 

p. 136, pi. 13, figs. 10-12,1931.

Mya truncata forma ovata Laursen, Meddelelser om Gr0nland, 

v. 135, no. 8, p. 62, 1944.

Mya pseudoarenaria Foster, Johnsonia, v. 2, no. 20, p. 34, 1946.

Mya truncata forma ovata Madsen, Marine bivalvia; Zool. Iceland, v. 4, pt. 63, p. 76, 1949.

Mya pseudoarenaria Feyling-Hanssen and Jorstad, Norsk Polarinstitutt Skrifter, no. 94, p. 74, 1950. 

Soot-Ryen, Astarte; Tr0mso Mus., no. 1, p. 3, 1951.

Mya cf. M. arenaria MacNeil, U.S. Geol. Survey Prof. Paper 

294-C, p. 118, pi. 17, fig. 6, 1957.

Mya pseudoarenaria MacGinitie, U.S. Natl. Mus. Proc., v. 109, 

no. 3412, p. 186, pi. 19, fig. 7, pi. 25, fig. 4, 1959.

Mya japonica Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 11, 

no. 3, p. 401, 1962 [in part].

Mya truncata ovata Merklin, Petrov, and Amitrov, Atlas-Guide 

of mollusks of Quaternary deposits of the Chukotsk Peninsula ; Commission for Study of the Quaternary Period, 

Acad. of Sci., U.S.S.R., p. 48, pi. 10, figs. 5-8, 1962.

Unless Dall had some suspicion of it in 1898, Jensen 

seems to have been the first to realize the existence of an 

Arctic species distinct from both Mya truncata and M. 

arenaria. Jensen's delimitation of the species was accurate by modern standards, and except for the addition 

of new records no revision is necessary.

The spoon of this species is subtrigonal. The ventral 

margin of the spoon between the anterior and posterior 

ridges is weakly convex anteriorly and weakly concave 

posteriorly. In this respect it is more like Mya cuneiformis and M. truncata; the ventral margin of the 

spoon in M. priapus is more convex. The deepest part 

of the ligament area is along the anterior part of the 

fibrum receptacle adjacent to the anterior ridge. The

laminum attachment is convex. The anterior ridge is 

moderately thick ventrally and may be turned back 

rather strongly over the fibrum receptacle as in M. 

arenaria. The dorsal part of the anterior ridge is broad. 

The posterior ridge forms the most projecting part of 

the ventral margin of the spoon. The posterior furrow 

is moderately broad and it is extended posteriorly as a 

long wing. The wing may be nearly twice as long as the 

remainder of the spoon; in such shells it projects from 

the dorsal margin like a long lateral tooth.

The shell has a well-defined anterior subumbonal 

groove. None of the specimens I have examined show 

any evidence of subumbonal solution. Some specimens 

appear also to have a small very thin ligamental callus 

at the dorsal end of the ligament pit. The anterior leg 

parallels the subumbonal groove.

The pallial sinus is moderately large. Its anterior 

end is rounded and curves backwards slightly to the 

point where it joins the pallial line; the lower limb of 

the sinus and the pallial line are confluent. The pallial 

line is thicker where it adjoins the sinus. The anterior 

extension of the pallial line is often very wavy.

The anterior muscle scar is moderately narrow and 

elongate, its ventral end lying about opposite the midpoint of the sinus. The anterior part of the shell is 

high and inflated, and it narrows posteriorly; the posterior end is moderately acuminate. The exterior of the 

shell at the posterior extremity is often very wrinkled. 

The beaks are strongly opisthogyrate.

Mya pseudoarenaria is closely related to M. cuneiformis from which it probably is descended directly. 

Its spoon resembles the spoon of M. truncata. In my 

opinion, M. cuneiformis and M. truncata are coderivatives from M. salmonensis.

The most conspicuous difference in the spoon of Mya 

cuneiformis and M. pseudoarenaria is in the strike of 

the anterior leg and subumbonal groove. In M. cuneiformis the area bounded by the leg and the groove is 

triangular, and the leg is vertical; the posterior edge 

of the leg actually overhangs the dorsal extremity of 

the fibrum receptacle. In M. pseudoarenaria the leg 

and groove are more nearly parallel, and they are more 

inclined towards the anterior.

Holotype: Inasmuch as Mya pseudoarenaria is a substitute 

name for M. truncata var. ovata Jensen, one of Jensen's specimens must be recognized as the lectotype of the species. The 

specimen figured by Jensen (1899, p. 139, fig. 3) appears, from its 

dimensions, to be one of the Pleistocene fossils listed from western Greenland on his page 142. Presumably all of Jensen's specimens are in the Universitetets Zoologiske Museum, Copenhagen, 

Denmark. Of these, specimen d is closest in size to his figure, 

which he says is not enlarged. It measures 66 mm in length, 45
G38 CONTRIBUTIONS TO PALEONTOLOGY

mm in height; convexity is 27 mm. His largest specimen has 

a length of 78 mm.

Occurrence: I know of no unequivocal record of this species 

in late Tertiary beds of the Pacific Ocean area, although I have 

no doubt of its descent from My a cuneiformis of the middle 

Miocene. The earliest specimen known to me that could possibly belong to this species is one from the Coralline Crag (late 

Pliocene) of England; this specimen is on exhibit in the Ipswich 

Museum.

I believe also that a specimen I collected from the Chillesford 

Beds of the Icenian Crag (early Pleistocene) of England, USGS 

M-1671, belongs to this species. Mya pullus Sowerby from the 

Butleyan Stage of the Red Crag may also prove to be a diminutive form of M. pseudoarenaria, but, on the basis of two specimens I collected, I am inclined to doubt it. The species is known 

in Iceland in beds that may be of early Pleistocene age. It is 

known in beds of probable late Pleistocene age in the Chukotsk 

Peninsula, eastern Siberia, Point Barrow, Alaska, USGS 15937, 

and at Gostinoj on the Yenisey River in northern Russia. It 

also occurs in Pleistocene beds in Spitzbergen and western 

Greenland.

The species is known from the Recent of Point Barrow, 

Alaska, GAS 35052, the Arctic Coast of Canada as far east as 

Dolphin and Union Strait, western Greenland (but not eastern 

Greenland), USGS D-385, Iceland, Spitzbergen, northern Norway as far south as 67°8' N. and probably along the Arctic 

Coast as far east as the Taymir Peninsula. I can find no record 

of this species in present Bering Sea or elsewhere in the Pacific 

Ocean area; reports to the contrary are incorrect as nearly as 

I can determine.

Mya (Mya) truneata Linne 

Plate 8, figures 1-12; plate 9, figures 1-3, 5-20

Mya truneata Linne", Systema naturae, ed. 10, p. 670, 1758.

Lamarck, SystSme des animaux sans vertebres, p. 127,

1801. 

Mya ovalis Turton, Sheila of the British Islands, p. 33, pi. 3,

figs. 1, 2,1822. 

Sphenia swainsoni Turton, Shells of the British Islands, p. 37,

pi. 19, fig. 2,1822. 

Mya truneata Lyell, Geol. Soc. London Trans., ser. 2, v. 6,

art. 8, p. 137, pi. 17, figs. 5, 6,1842 [Pleistocene of 9uebec]. 

Mya truneata var. uddevalensis Forbes, Geol. Survey Great

Britain Mem., v. 1, p. 407,1846. 

Mya truneata Middendorff, Malacozoologia Rossica; Acad. Sci.

St. Petersbourg Mem., ser. 6, v. 6, p. 585, pi. 19, figs.

13-15,1849. 

Mya praecisa Gould, Boston Soc. Nat. History Proc., v. 3, p.

215,1850. 

Mya truneata Middendorff, Reise in dem Aussersten Norden

und Osten Siberiens; K. Akad. Wiss., v. 2, pt. 1 (Mollusken), St. Petersbourg, p. 266, pi. 25, figs. 11-14, 1851. 

Wood, Palaeontographical Soc. London Mon., v. 9, p. 277,

pi. 28, figs, la-c, 1857. 

Mya truneata var. abbreviata Jeffreys, British Conchology, v.

3, p. 67, 1865. 

Mya truneata Wood, Palaeontographical Soc. London Mon., v.

27, p. 163,1874. 

Sars, Mollusca Regionis Arcticae Norvegiae; Universitets 

program, Christiania, p. 92,1878. 

Dall, Wagner Free Inst Sci. Trans., v. 3, pt. 4, p. 857, 1898.

Jensen, Videnskabelige Meddelesser naturhist. Forening,

Copenhagen, p. 147, 1900 [with extended synonymy]. 

Br0gger, Norges geol. Undersokelse Skrifter, no. 31, pi. 7,

figs. 9a-b, 10,12,1901. 

Arnold, U.S. Natl. Mus. Proc., v. 32, no. 1545, pi. 50, fig. 1,

1907.

Dall, U.S. Geol. Survey Prof. Paper 59, p. 132, 1909. 

Oldroyd, Stanford Univ. Pubs. Geol. Sci., v. 1, no. 1, p. 197,

pi. 10, fig. 4,1924. 

Grant and Gale, San Diego Soc. Nat. History Mem., v. 1, p.

414,1931 [with extended synonymy]. 

Nagao and Inoue, Hokkaido Imp. Univ. Fac. Sci. Jour., v.

6, no. 273, p. 155, pi. 33, figs. 5, 9, 10, 1941. 

sp. indet, Ma.cNeil, Jour. Paleontology, v. 17, no. 1, p. 93,

pi. 16, fig. 3,1943. 

Mya truneata Foster, Johnsonia, v. 2, no. 20, p. 30, pis. 17-19,

1946. 

Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9, no. 4,

p. 399, pi. 3, figs. 1-4,1957. 

MacGinitie, U.S. Natl. Mus. Proc., v. 109, no. 3412, p. 184, pi.

25, figs. 1-3,1959. 

Fujie, Hokkaido Univ. Fac. Sci Jour., ser. 4, v. 11, no. 3, p.

410,1962.

Mya truneata truneata Merklin, Petrov, and Amitrov, AtlasGuide of mollusks of Quaternary deposits of the Chutotsk 

Peninsula; Commission for Study of the Quaternary Period, Acad. of Sci., U.S.S.R., p. 47, pi. 10, fig. 3, 1962. 

Mya truneata uddevalensis Merklin, Petrov, and Amitrov, ibid,

fig. 4.

Mya truneata is the most widespread living species 

of Mya. It is also the most variable species. It ranges 

in shape from specimens that have a moderately elongate tapering but truncated posterior end (pi. 8, fig. 

11), to elongate and subrectangular, to very short and 

high with the posterior end less than a quarter the total 

length of the shell and the posterior margin long and 

nearly vertical, often concave. The latter variant was 

named M. truneata var. uddevalensis by Forbes. None 

of the variant types can be considered a geographical 

subspecies. Both the elongate varieties and the uddevalensis variety occur together in all areas where the 

species now lives, from the North Sea to the Gulf of 

Alaska. The same apparent varieties are found in the 

Yakataga Formation (Miocene and Pliocene) of 

Alaska, in very late Pleistocene (probably postglacial) 

beds near Juneau, Alaska, along the Gulf of St. Lawrence, eastern Canada, and at Uddevalla, Sweden, the 

locality from which the variety takes its name.

The shell of Mya truneata is rugose and very often it 

is malformed, apparently by objects in the substratum. 

Even the spoon takes on forms that might better be 

described as abnormalities rather than variations.

The spoon is more symmetrical than in Mya pseudoarenaria; the dorsal part of the anterior ridge is broader 

and the posterior furrow is not as alate. The ventral 

margin of the spoon is not as rounded as in M. priapus. 

The anterior subumbonal groove and the anterior leg
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G39

form a lower angle with the dorsal margin than in M. 

pseudoarenaria; that is, they are more nearly parallel 

with the dorsal margin. M. pseudoarenaria stands 

about midway between M. cuneiformis and M. truncata 

in this respect; in M. cuneiformis the anterior leg is 

nearly perpendicular to the dorsal margin. The boundary between the laminum attachment and the fibrum 

receptacle often stands up as a thin ridge in M. truncata, 

whereas in M. pseudoarenaria there is a broader convex 

area that includes the laminum attachment and the posterior part of the fibrum receptacle.

Mya truncata has the shortest pallial sinus of any 

Mya. It extends from the posterior muscle scar to the 

pallial line. The inner margin is nonlobate, the point 

of maximum depth being the juncture with the pallial 

line. In the more elongate variants the dorsal leg is 

moderately curved, but in the short uddevalensis 

variety it may be a much straighter line, inclined only 

a few degrees from vertical.

The anterior subumbonal groove in Mya salmonensis 

has a strike intermediate between that of the other two 

species; in M. cuneiformis it is more vertical, in M. 

truncata it is more horizontal.

M. truncata appears for the first time in Alaska in 

beds only a few hundred feet above the earliest occurrence of M. cuneiformis and yet is clearly distinct from 

the latter. It seems probable, therefore, that these two 

species are coderivatives from M. salmonensis. Its 

abrupt appearance in Alaska suggests that it originated 

in East Asia, probably from the representative there 

of M. salmonensis that has been known as M. grewingki 

var. elongata Nagao and Inoue (=M. grewingki nagaoi 

Oyama and Mizuno).

Holotype: According to Dodge (1952, p. 28), there is a specimen in a properly marked box in the collection of the Linnaean 

Society of London.

Occurrence: The earliest recorded occurrences of this species 

are in beds of early middle Miocene age in the Pacific Ocean 

area. Inasmuch as its probable ancestor is the Oligocene to 

Miocene species Mya salmonensis, it is not likely that this range 

will be extended downwards. It occurs in the Takinoue 

(Chikubetsu?) Formation of the Kawabata Series of Hokkaido 

and in the lower part of the Yakataga Formation (about 700 

ft above the base), Alaska.

Mya truncata is known from so many localities and stratigraphic levels in the northern Pacific that it would be pointless 

to list them ; it is sufficient to say that it has existed continuously 

in the far northern Pacific from early middle Miocene to Recent 

time.

Its southernmost records are of interest, however, inasmuch 

as it is a cold-water species. (See p. G4.) It occurs in the 

Coos Conglomerate (early Pliocene) at Coos Bay, Oreg., and in 

the Towsley Formation (late Miocene and early Pliocene) at 

Elsmere Canyon in the Ventura Basin, Los Angeles County, Calif. 

It occurs also in the Timms Point Silt Member of the San Pedro

Formation (early Pleistocene) of the Palos Verde Hills, Los 

Angeles, and in the upper part of the Pico Formation, Ventura 

County, Calif. The upper part of the Pico Formation may be 

of early Pleistocene age.

The species now ranges southward to southern Hokkaido and 

Puget Sound. Known recorded occurrences in Japan indicate 

that it did not extend its range southward nearly as much on 

the Asiatic side of the Pacific as it did on the American side. 

Fujie gave one Miocene and two Pliocene occurrences in northern 

Honshu. There are no known Pleistocene occurrences south of 

Hokkaido.

Mya truncata is known as a fossil in eastern North America 

from Hudson Bay and Labrador south to Nantucket Island, 

Mass. According to Richards (1962, p. 12), all recorded occurrences north of Nantucket are in beds deposited by the sea that 

invaded areas vacated by melting Wisconsin ice, preceding postglacial emergence. They are, thus, of post-Wisconsin age. The 

beds at Sankaty Head, Nantucket, he regarded as being of Sangamon age. Hyyppa (1955) concluded, on the other hand, that 

the Sankaty beds are of middle-Wisconsin age. At any rate, 

M. truncata is known on the Atlantic Coast only in very young 

beds.

The species is known as a fossil in both Greenland and Iceland 

in beds that may also be very young. Probably the species in 

beds of early Pleistocene age in Iceland is Mya pseudoarenaria. 

M. truncata certainly was in Europe prior to its first appearance 

in North America and probably it reached America from the 

region of extreme northern Europe or Spitzbergen. Shells of 

the species are strewn over the floor of the North Atlantic Ocean 

between Greenland, Iceland, and Jan Mayen (Soot-Ryen, 1932, 

p. 29) at a depth of 1,300 fathoms, far deeper than its living 

depth. Possibly there was an isostatic rise in the North Atlantic 

Ocean in response to the depression of continental areas by Wisconsin ice, which, together with eustatic lowering of sea level, 

made the North Atlantic sufficiently shallow to allow M. truncata to migrate westward in Wisconsin time.

I have been unable to verify the occurrence of this species 

in the Coralline Crag (late Pliocene) of England. A specimen 

figured by Wood (1856, pi. 29, fig. 1) from supposed Coralline 

Crag beds at Ramsholt was refigured by Chatwin (1961, fig. 24, 

no. 13) as a Norwich Stage (late early Pleistocene) fossil. The 

Ispwich Museum has a specimen on display that I thought, when 

I examined it in 1960, was more probably Mya pseudoarenaria. 

Wood (1856, p. 278) stated that specimens from the Coralline 

Crag "are all of the longer variety." No very recent lists of 

fossils from the Coralline Crag have included M. truncata. Probably this point can be clarified by British workers.

If Mya pullus Sowerby from the Butleyan Stage of the Red 

Crag (early Pleistocene) is a diminutive form of this species, 

it may be its earliest occurrence in Europe. M. pullus may be 

conspecific, however, with M. pseudoarenaria, or it may be closer 

to M. priapus. I am equally uncertain of the identity of a 

juvenile specimen I collected at Chillesford; M. truncata has 

been reported from there as well.

Mya truncata is found unquestionably in the Norwich Stage 

of the Icenian Crag, and this may be its earliest European occurrence. (The Norwich Stage is believed currently to be of late 

Calabrian age, corresponding approximately to the only known 

occurrence of M. truncata in the Mediterranean region; it is 

found in the upper part of the Calabrian Stage in Sicily, Calabria, 

and Tuscany.
G40 CONTRIBUTIONS TO PALEONTOLOGY

Mya trunocuta probably lived in northern European waters 

throughout Pleistocene time. It has been reported from beds 

of middle Pleistocene age in the Taymir Peninsula, although I 

am not certain that the distinction between M. truncata and 

M. pseudoarenaria was clear at the time the identification was 

made.

The species is nearly circumarctic at the present time. SootByen (1932, p. 21) did not believe that it occurs in the East 

Siberian Sea. This would suggest, if true, that the species has 

not made a full counterclockwise migration of the Arctic Ocean. 

It ranges southward to Hokkaido and Puget Sound in the 

Pacific and to Cape Cod and the Bay of Biscay in the Atlantic.

Mya (Mya) priapus Tilesius 

Plate 10, figures 1-7 ; plate 11, figures 1-8,10,13-15

Mya priapus (Steller MSS) Tilesius, Acad. Sci. St. Petersburg 

Mem., v. 8, p. 295, pi. 9, fig. 1, 1822.

Mya arenaria Middendorff, Reise in dem Aussersten Norden 

und Osten Siberiens; K. Akad. Wiss., v. 2, pt. 1 (Mollusken), St. Petersbourg, p. 269, no. 2, pi. 24, fig. 12, 1851.

IMya near arenaria Dall in Mertie, U.S. Geol. Survey Bull. 335, 

p. 46,1908.

Mya (Mya) arenaria variety japonica Jay, Grant and Gale, San 

Diego Soc. Nat. History Mem., v. 1, p. 412, 1931 [in part].

Mya japonica Makiyama, Kyoto Imp. Univ. Coll. Sci. Mem., ser. 

B, v. 10, no. 2, art. 6, p. 159,1934.

Mya arenaria japonica Kinoshita and Isahaya, Report of Aquatic Products; Hokkaido Fish Exp. Sta., no. 33, rept. 1, 

pi. 14, fig. 103,1934.

Mya japonica Makiyama, Warera-no-Kobutsu, v. 4, no. 3, p. 37, 

text fig. j, 1935.

Mya truncata Stejneger, Georg Wilhelm Steller; Harvard 

Univ. Press, p. 397, pi. 24, fig. 1, 1936 [reproduction of 

Tilesius' plate labelled "Mya priapus"].

Mya uzenensis Nomura and Zinbo, Saito Ho-on Kai Mus. Res. 

Bull., v. 13, p. 167, pi. 22, fig. 17,1937.

Mya arenaria var. truncata Slodkewitsch, Pal. U.S.S.R. (Tertiary Pelecypoda from the Far East), Acad. of Sci., 

U.S.S.R., v. 10, pt. 3, fasc. 19, pi. 103, fig. 4, 1938.

Mya arenaria Nagao and Inoue, Hokkaido Imp. Univ. Fac. Sci. 

Jour., v. 6, no. 273, p. 145, pi. 32, figs. 14, 14a, 1941. (On 

p. 147 name changes recommended by Makiyama are discussed.)

Minato, Matsui, and Uozumi, Shinseidai-no-Kenkyu, no. 7, 

p. 3, pi. 10, fig. 82,1950.

Mya (Arenomya) japonica, Habe, Akkeshi Marine Biol. Sta. 

Publ., no. 4, p. 22, pi. 7, fig. 12,1955.

Mya japonica Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 9, 

no. 4, p. 406, pi. 1, figs. 1-5, 1957.

Mya (Arenomya) japonica Yamamoto and Habe, Marine Biol. 

Sta. Asamushi Bull.; Tohoku Univ., v. 9, no. 3, p. 113, pi. 

12, fig. 24, 1959.

Mya japonica Fujie, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 

11, no. 3, p. 401,1962.

Mya arenaria Merklin, Petrov, and Amitrov, Atlas-Guide of 

mollusks of Quaternary deposits of the Chukotsk Peninsula ; Commission for Study of the Quaternary Period, 

Acad. Sci., U.S.S.R., p. 46, pi. 9, figs. 1-9, 1962.

In 1743, after Steller had returned to Kamchatka 

with the survivors of Bering's second and fateful voyage, he visited the northern Kuril Islands, and on the 

trip he spent some time at Bolsheretsk in southwestern 

Kamchatka. There he found a giant and wholly unfamiliar clam washed up on the beach at the mouth 

of the Bolshaya Kiver. Among the things that Steller 

managed to have forwarded to St. Petersbourg were 

some notes and a sketch of the animal and the shell 

made by an artist named Berkhan who accompanied 

him. The way in which this species eventually became 

published and named is given by Stejneger (1936, p. 

396):

There was little interest in St. Petersbourg at the time in the 

fauna of the sea. The new school of zoologists headed by Pallas 

were primarily interested in the land vertebrates. Pallas, however, intended his Zoographica Rosso-Asiatica to include the 

invertebrates, and when he left Russia in 1810 for Berlin he 

took with him Steller's notes and the illustrations which Berkhan had made of the specimens described. One of these was 

rescued and published by Tilesius under the name Mya priapus. 

The accompanying illustration is the only one attributed 

directly to Berkhan by name (whom Tilesius calls a "dexterrimus pictor") and as it is so little known that it has been 

missed even by the authoritative Sherborn in his Index Animalium, it is here reproduced. Steller, who picked it up on the 

beach at the mouth of the Bolshaya, was so impressed by the 

startling appearance of this giant soft clam, of which the 

shell alone measured 4 inches, that he at once wrote a detailed 

description of it in latin which covers two and one-half quarto 

printed pages. Middendorff has since identified it with Linnaeus' Mya truncata, a name given to the European clam 

fifteen years after Steller found the species in the Okhotsk Sea.

Middendorff cited the species as "Mya priapus vel 

Mentula marina Stelleri" a nonbinomial expression, 

and possibly this treatment discouraged an investigation of the name by subsequent authors. However, 

Tilesius' plate is labeled simply "Mya priapus" which, 

for that date, constitutes a valid proposal.

The shell as depicted by Steller's artist, Berkhan, 

appears to be so crudely drawn that it could not possibly 

be identified. In my opinion, however, this is the common Mya of northern and western Bering Sea. Many 

individuals of the species are equally crude and misshapen. A large suite from St. Lawrence Island in 

northern Bering Sea in the collections of the Geological 

Survey contains several specimens that could well be 

the one drawn by Berkhan. Even granting that Berkhan's drawing of the shell cannot be identified with 

certainty, the large fleshy animal should be recognizable. 

I have little doubt that future attempts to identify it 

will show M. priapus to be the species here determined. 

The tough wrinkled siphonal tube is more like that of 

M. truncata, but it is shorter and thicker than in that 

species. The shell characters also indicate a close 

relationship to M. truncata.
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G41

Middendorff did not associate the name My a priapus 

with this species. In 1849 (p. 585) he placed the species 

by name in the synonymy of M. truncata, but subsequently (1851, pi. 24, fig. 12) he figured a shell of the 

species as M. arenaria. Grant and Gale, and recent 

Japanese authors who follow them, interpreted this 

northern species as the M. japonica of Jay; the species 

ranges southward to Hokkaido.

Most Russian authors combine Mya priapus, M. pseudoarenaria, and probably M. japonica under UM. 

arenaria" apparently in the sense that Middendorff 

used the latter. Merklin, Petrov, and Amitrov (1962, 

pi. 9, figs. 1-9) illustrated several specimens from 

Pleistocene beds of the Chukotsk Peninsula as M. 

arenaria. The three spoons they figured are triangular, 

there is a well-defined anterior subumbonal groove, 

and there is no indication of subumbonal solution. 

None of these spoons could belong to a specimen of M. 

arenaria. Without illustrations of the spoon and pallial 

sinus of the rest of their specimens, it would be difficult to reidentify them with confidence. However, the 

specimens figured probably are all M. priapus. Their 

figure 7 is the youngest specimen figured. The specimen shown in their figure 1 is from beds they regard as 

pre-Riss, and it is the oldest specimen figured. The 

specimen shown in their figure 8 is very similar to a 

specimen from the Matsuzawa Formation (Miocene or 

Pliocene) of Honshu described by Nomura and Zinbo 

(1937, p. 167, pi. 22, fig. 17) as M. ezenensis. In my 

opinion both of these belong to M. priapus. The spoon 

of M. ezenensis is unknown.

The spoon of Mya priapus from different geographical areas shows some variation in shape. Northern 

Japanese specimens (Fujie, 1957, pi. 1, fig. 5b) have a 

spoon with a much straighter ventral margin than 

specimens from Bering Sea or Alaska. If the spoon of 

M. ezenensis is found to be similarly truncated, this 

name might be available as a subspecific name for the 

modern Japanese form.

Specimens from Bering Sea have a spoon with a 

well-rounded ventral margin. The entire ligamental 

area is deeply concave, although in some specimens 

there is a slight shallowing along the laminum attachment. The anterior ridge is thick, and it is very broad 

dorsally. The posterior furrow is broad, shallow, and 

produced posteriorly to form a winglike shelf. There 

is a well-defined anterior subumbonal groove set at a 

very low angle with respect to the dorsal margin.

My a priapus has a moderately large ligamental callus. 

The callus is restricted to about the dorsal third of the 

fibrum receptacle, and generally it occupies only the 

anterior dorsal part. In some specimens the ventral

margin of the callus is toothed or comblike. The callus 

layer continues across the dorsal part of the anterior 

ridge and merges with the last deposited layer of the 

interior of the shell. The ligamental callus is almost 

always present in this species, and it is generally larger 

and thicker than the callus of M. truncata. The callus 

is not present in all specimens of M. truncata. A few 

specimens of M. pseudoarenaria have a very small callus 

at the dorsal end of the ligament pit. The callus of 

M. priapus is of moderate length, and it ranges from 

thin and smooth to thick and rough; the callus of M. 

arenaria is long and spatulate, often reaching nearly to 

the ventral margin of the spoon, and it generally has a 

pronounced radial ridge or swelling near its posterior 

margin.

The pallial sinus of M. priapus is of moderate depth. 

The dorsal leg descends to the pallial line in a gradually steepening curve; at the juncture the two are 

nearly perpendicular. The ventral leg is confluent with 

the pallial line. The anterior part of the pallial line 

may be wavy.

The anterior adductor scar is elongate and wider 

ventrally; it is less elongate and wider than in M. 

truncata.

The shell of M. priapus is quite variable in shape. 

It ranges from suboval to more attenuated posteriorly, 

and the part of the shell posterior to the beaks may be 

either longer or shorter than the anterior part. The 

exterior surface is often deeply pitted and irregular, 

probably indicating that it can live in an unsorted 

gravelly substratum.

Without any question, Mya truncata is the closest 

living relative of M. priapus. M. truncata, however, 

is known from older beds, and I am inclined to believe 

that M. priapus actually is descended from M. cuneiformis. The spoon of M. cuneiformis has a very 

pronounced shallowing or convexity of the posterior 

part of the ligament area, and in this respect it is more 

like M. pseudoarenaria,; the ligament area of the spoon 

of M. priapus is more uniformly deep and concave. If 

M. cuneiformis and M. priapus are in linear succession, 

the modification in the spoon must have taken place 

during late Miocene time, and in forms whose spoon is 

unknown.

Mya, priapus is unique in having a single sometimes 

moderately large solution pit at the top of the chondrophore of the right valve. There is no solution of the 

left valve as is common in the M. arena.ria group. This 

species has its anterior subumbonal groove set at a lower 

angle than in other members of the M. truncata group, 

a condition that may weaken the strong intervalve 

periostracum-elasticum connection found ordinarily in
G42 CONTRIBUTIONS TO PALEONTOLOGY

this group. The species also has a very deep ligament 

pit. Probably the fibrum element of the ligament is 

more apt to be torn away from a deep receptacle and in 

turn to be reinforced from behind by a deposit of ligamental callus. At any rate, a combination of greater 

fibrum severance and a weaker periostracum-elasticum 

connection probably contribute to a periostracumelasticum rupture. This exposes a small area of the 

shell along the hinge to solution by sea water. Although the structural weaknesses responsible for a 

periostracum-elasticum rupture are similar in this 

species and in M. arenaria, the morphological differences provide for a slightly different vector of strain, 

causing the periostracum-elasticum rupture to take 

place along the margin of the right valve rather than 

the left valve.

Holotype: The historical evidence as given by Stejneger indicates that the specimen Steller found was not sent to St. Petersbourg. Tilesius based the species on Steller's notes and on a 

drawing made under his direction. Although Tilesius' plate 

is the original indication of the species, it is not an identifiable 

illustration of the shell. The species, however, should be 

identifiable from the soft parts without difficulty. Until recently the only good illustration of the shell of this species was 

one given by Middendorff (1851, pi. 24, fig. 12) as M. arenaria.

Occurrence: Fujie (1962, p. 404) reported this species (as 

M. japonica) from the Togeshita Formation (late Miocene) of 

Hokkaido, the Kamiiso and Ikeda Formations (Pliocene) of 

Hokkaido, and the Matsuzawa and Tatsunokuchi Formations 

(Pliocene) of northern Honshu. He gave only one Pleistocene 

occurrence; an unnamed formation in southern Sakhalin.

The species probably occurs in late Miocene beds of eastern 

Russia, but available figures are difficult to determine. It certainly occurs in the Kavran Series (Pliocene?) of western 

Kamchatka (Slodkewitsch, 1938, pi. 108, fig. 2) where it has 

been identified as Mya arenaria var. japonica.

Merklin, Petrov, and Amitrov (1962, pi. 9, figs. 1-9) figured 

the species from middle and late Pleistocene beds of the 

Chokotsk Peninsula. The species was collected in 1963 from 

beds of the same approximate age span between the Kukpowruk and Kuk Rivers, Alaska.

The upper part of an unnamed formation in the Lituya district, Alaska, contains a form that appears to be intermediate 

between Mya cuneiformis and typical M. priapus. The part 

of the formation containing them is believed to be of very late 

Miocene or early Pliocene age. Specimens from the following localities are referred tentatively to M. priapus: cliff at 

east margin of Fairweather Glacier, USGS D-264, D-389, 

southwest shore of Cenotaph Island, USGS D-174, seacliff about 

0.55 mile north of mouth of Topsy Creek, USGS D-180. The 

last locality is the southeasternmost record of any age for the 

species known to me.

The species occurs in a marine clay till of probable Pleistocene age at the southeast point of Wingham Island, Controller 

Bay, Alaska, USGS 4309 (Dall, in Martin, 1908, p. 46; as Mya 

near arenaria).

Mya priapus is living from southern Hokkaido to northern 

Bering Sea; it is one of the most abundant species in a large

collection of Recent shells from St. Lawrence Island, USGS 

M-1661, M-1663. It occurs in Alaska from near Port Clearance, USGS M-1430, southward to Unalaska, USGS D-S3, and 

eastward to Kachemak Bay, USGS M-1625, an arm of Cook 

Inlet; I have not seen the species east of Homer Spit. The 

species occurs in postglacial beds, possibly a midden, at the 

mouth of Cottonwood Greek on the north side of Kachemak 

Bay, Alaska, USGS 5871.

Mya (Mya) pullus Sowerby 

Plate 11, figures 9, 11, 12

Mya pullus Sowerby, Mineral Conchology Great Britain, v. 6,

p. 58, pi. 531, figs. 6-8 (2), 1826. 

Mya arenaria Forbes and Hanley, History of British Mollusca,

v. 1, p. 172,1848 [in part]. 

Mya truncata Wood, Palaeontographical Soc. London Mon.,

v. 9, p. 278, pi. 28, figs. Id, e, ?tf, 1857 [in part]. 

Wood, Palaeontographical Soc. London Mon., v. 27, p. 163,

1874 [in part]. 

IMya, arenaria Schlesch, Archiv f. Molluskenkunde, v. 63, p. 139,

1931 [in part]. 

Mya truncata Foster, Johnsonia, v. 2, no. 20, p. 30, 1946 [in

part].

This small Mya is abundant in the Butleyan Stage 

of the Red Crag. It has been known to collectors for 

years, but most authors have regarded it either as the 

young of another species or an abnormality.

It has been suggested by some workers that Mya 

pullus is a cold-water dwarf and by others that it is a 

brackish-water dwarf. As such it has been placed in 

the synonymy of both M. arenaria and M. truncata. 

Its spoon and pallial sinus show that it definitely is not 

M. arenaria. If it is a dwarf, it is a dwarf of some 

member of the M. truncata group. It is difficult, however, to see how it could be a cold-water dwarf of a 

species that lives normally in very cold water.

I collected two valves of this form in 1960 when I 

visited East Anglia. I am not convinced that it is a 

diminutive form of M. truncata, but for the time being 

I would prefer to leave the question open. It is entirely possible that this is a diminutive form of M. priapus. It resembles juveniles of that species very closely, 

particularly the variant found in northern Japan. 

(See Fujie, 1957, pi. 1, fig. 2.) The right valve I collected has a tiny solution pit at the top of the chondrophore, a very common condition in M. priapus and 

one that, as far as I know, is peculiar to it. The form 

from the Butleyan Stage also has some resemblance to 

juveniles of M. pseudoarenaria.

Whatever the synonymy of Mya pullus, it is of significance in one way or another. If it is M. truncata, 

it is the earliest European recorded occurrence for the 

species, unless, of course, the species really occurs in 

the Coralline Crag. If it is M. priapus, it is the only
EVOLUTION AND DISTRIBUTION OF THE GENUS MTA G43

known occurrence of the species outside the Pacific 

Ocean-Chukchi Sea area. If it is M. pseudoarenaria, 

it takes priority in name. Pending a thorough study 

of this form, it would be unwise, therefore, to make any 

decision concerning it.

Holotype: In the British Museum?

Occurrence: Butleyan Stage of the Red Crag (early Pleistocene), England.

LOCALITIES

U.S. National Museum catalog numbers:

USNM 210970. Recent Kodiak Island, Alaska.

USNM 221269. Recent, Chignik Bay, south side of Alaskan

Peninsula. 

California Academy of Sciences locality:

CAS 35052. Recent marine shells from Deadman Island,

Point Barrow, Alaska. G. D. Hanna, collector. 

University of California (Berkeley) localities:

UC 197. On same horizon and about one-quarter of a mile 

to the northwest of loc. 189 (UC 189 very close to base of 

Miocene [locally] on south side of Muir Station .syncline, 

about 1% miles and 70° to southwest of town of Pacheco), 

Contra Costa County, Calif. Briones Sandstone (early late 

Miocene). J. C. Merriam, collector.

UC 1224. Near south edge of NE^4NE% sec. 2, T. 2 S., R. 2 W., 

about half a mile south of bend in Alameda-Contra Costa 

County line, Alameda County, Calif. Cierbo Sandstone 

(middle late Miocene). B. L. Clark, collector.

UC 1227. On top of knob about one-quarter of a mile southeast of Burton's (?ranch) above loc. 1221 in altitude and 

stratigraphically (UC 1221 about 1% miles north of Los 

Trampos Creek and about % mile a little to the west of south 

from Tice Valley on the side of Grizzley Creek), Contra 

Costa County, Calif. Cierbo Sandstone (middle late Miocene) . B. L. Clark, collector.

UC 1617. About one-quarter of a mile east of town of Rodeo 

(as seen on Napa topographic sheet, 1902 edition, it is due 

west of the top of the letter R of Rodeo), about 150 ft below 

base of Pinole Tuff, Contra Costa County, Calif. Neroly 

Formation (late late Miocene). B. L. Clark, collector.

UC 1687. To north of road leading to Tice Valley, just west 

of Franklin fault and about 1.7 miles west of south from 

Walnut Creek (as seen on Concord quadrangle (areal geology), U.S. Geol. Survey Geol. Atlas Folio 193). Briones 

Sandstone (early late Miocene). R. E. Dickerson, collector.

UC 3851. Float, probably Poul Greek Formation. Not plotted 

on field map; location of Salmon Creek not known (fide 

D. J. Miller). Yakataga district, Alaska. N. L. Taliaferro, 

collector.

UC A-1686. 50-60 ft stratigraphically below A-1685 (UC 

A-1685 I mile south of P. G. and E. compressor plant), 

Kettleman hills, Kings County, Calif. Etchegoin Formation 

(Pliocene). A. R. Hall, collector.

UC A-3167. "Mya japonica" zone, about 200 ft below base of 

Tulare Formation, NE*4 sec. 35, T. 21 S., R. 17 E., Kings 

County, Calif. San Joaquin Formation (late Pliocene). 

B. L! Clark field class, collectors.

UC B^t807. On beach, 7,000 ft north of Merced-Franciscan 

Formation contact at Mussel Rock; 850 ft due west of 

triangulation point just west of Edgemar Road; in cliff 

face at beach level, in massive grayish-blue medium- to 

fine-grained sandstone. William Glen, collector.

U.S. Geological Survey Tertiary localities (Washington catalog) :

USGS 2247b. "Fragmentary series," extending from onequarter of a mile above Temple Place to half a mile above 

Yorktown, right bank of York River, York County, Va. 

Yorktown Formation (late Miocene). G. D. Harris, collector.

USGS 2295. Sewer excavation at corner of Nut and Mulberry 

Streets, Wilmington, New Hanover County N. C. Duplin ( ?) 

Formation (late Miocene). T. W. Stanton, 1891, collector.

USGS 2451. Jones Wharf at Drum Cliff, Patuxent River, St. 

Marys County, Md. Choptank Formation (middle Miocene). 

Frank Burns, collector.

USGS 3122. On the headwaters of a little creek about 2% or 

3 miles southwest of Petersburg, above the city waterworks 

reservoir, Dinwiddie County, Va. Yorktown Formation 

(late Miocene). Frank Burns, collector.

USGS 4309. Wingham Island, 5.58 miles W. 100° S. from 

northwestern point of Kayak Island, Controller Bay, 

Alaska. Pleistocene. A. G. Maddren, collector.

USGS 5871. Mouth of Cotton wood Creek, north side of Kachemak Bay, an arm of Cook Inlet, Alaska. Postglacial or 

Recent; this deposit may be a midden. G. C. Martin, collector.

USGS 6694. Mouth of large gulch on south slope of White 

River valley at foot of glacier; from talus but nearly in 

place (Bering Glacier A-4 quadrangle, 2.4 miles N. 14° E. 

of mouth of Fulton Creek), Yakataga district, Alaska. 

Yakataga Formation, about 1,500 ft above base (middle 

Miocene). A. G. Maddren, collector.

USGS 6697. Talus material (recent slide) from south face of 

Island Mountain, north side of main lobe of White River 

Glacier (Bering Glacier A-3 quadrangle, between 1 mile 

and 2.5 miles above the foot of the White River Glacier). 

Yakataga Formation, 3,000-5,000 ft above base (middle or 

late Miocene). A. G. Maddren, collector.

USGS 12480. North Dome, Kettleman Hills, sec. 35, T. 21 S., 

R. 17 E., 630 ft south of north section line, 1,630 ft west 

of east section line, Kings County, Calif. San Joaquin 

Formation (Pliocene). W. P. Woodring, collector.

USGS 13372. South side of Narrow Cape, at north side of 

entrance to Ugak Bay, eastern Kodiak Island, Alaska. 

Mytilus middendorfft-bearing beds (middle Miocene). S. R. 

Capps, collector.

USGS 15431. West end of Yakataga Ridge, 2.3 miles S. 88° 

W. of peak 2430 near west end of Yakataga Ridge (shown 

on Bering Glacier A-4 quad), Yakataga district, Alaska. 

Yakataga Formation, about 3,200 ft above base (middle 

Miocene). E. M. Spieker, collector.

USGS 15433. North fiank of Yakataga Ridge at margin of 

Yakataga Glacier, 0.68 mile N. 34° W. of peak 2430 near 

west end of Yakataga Ridge (shown on Bering Glacier A-4 

quad). Poul Creek Formation, about 1,900 ft below top 

(late Oligocene or early Miocene). E. M. Spieker, collector.

USGS 15437. Unnamed creek on north fiank and parallel to 

Yakataga Ridge, 0.30 mile N. 16° E. of peak 2430 near west 

end of Yakataga Ridge (shown on Bering Glacier A-4 

quad). Yakataga Formation near base (early middle 

Miocene). E. M. Spieker, collector.

USGS 15937. From a gravel terrace at Point Barrow, Alaska. 

Late Pleistocene. L. C. Barksdale, collector.

USGS 16864. West flank of Donald Ridge, 1.4 miles S. 61° 

E. of north end of Hanna Lake, Bering Glacier quad.,
G44 CONTRIBUTIONS TO PALEONTOLOGY

Yakataga district, Alaska. Poul Creek Formation, about 

300 ft above base (the lower part of the Poul Creek Formation falls within the Acila shumardi zone; late middle Oligocene). D. J. Miller, collector.

USGS 16891. West shore of Hanna Lake, 0.3 mile S. 50° W. 

of north end ot lake, Bering Glacier quad, Yakataga district, Alaska. Float, from near base of Poul Creek Formation (the lower part of the Poul Creek Formation falls 

within the Acila shumardi zone; late middle Oligocene). 

D. J. Miller, collector.

USGS 16899. East side of spur extending north into Bering 

Glacier, 14.6 miles N. 64° E. of north end of Hanna Lake, 

Bering Glacier quad, Yakataga district, Alaska. Poul Creek 

Formation, about 1,800 ft above base (probably late Oligocene) . D. J. Miller, collector.

USGS 17782. Cliff at north end of Duktoth Mountain, 2.2 

miles N. 06° W. of peak 4014 on Duktoth Mountain (shown 

on Bering Glacier A-4 quad), Yakataga district, Alaska. 

Yakataga Formation, lower 200 ft (early middle Miocene). 

D. J. Miller, collector.

USGS 17788. Crystal Creek, 1.58 miles N. 18° E. of junction 

with Priest River, Icy Bay D-2 and D-3 quad, Yakataga 

district, Alaska. Poul Creek Formation, about 2,400 ft 

below top (probably late Oligocene). D. J. Miller, collector.

USGS 17787. Priest River, at mouth of bedrock canyon, 3.63 

miles N. 85° W. of mouth of Carson Creek, Icy Bay D~2 

and D-3 quad, Yakataga district, Alaska (late Oligocene 

or early Miocene). D. J. Miller, collector.

USGS 17827. Gulch on south face of ridge at Sunshine Point, 

1.9 miles S., 56° E. of mouth of Kulthieth River, Bering 

Glacier quad., Yakataga district, Alaska. Yakataga Formation, lower part (middle Miocene). R. B. Johnson, 

collector.

USGS 17835. Gulch on south flank of Kulthieth Mountain, 

0.94 mile S., 02° E. of peak 3447 (shown on Bering Glacier 

quad.), Yakataga district, Alaska. Yakataga Formation, 

about 3,000 ft above base (middle Miocene). D. J. Miller, 

collector.

USGS 17850. Oil Creek, 3.1 miles S., 82° E. of Watson Peak, 

Bering Glacier A-4 quad., Yakataga district, Alaska. Yakataga Formation, lower 100 ft (early middle Miocene). D. J. 

Miller, collector.

U.S. Geological Survey Tertiary localities (Denver catalog; 

specimens transferred to Menlo Park) :

USGS D-53. Recent, tidal flat of Usof Bay, Unalaska Island, 

Aleutian Islands, Alaska. E. H. Meitzner and R. P. Platt, 

collectors.

USGS D-169. Calcareous siltstone in sandstone unit, about 

380 ft below top. Measured section, southeast shore of 

Cenotaph Island, 2,600 ft S. 29° W. of easternmost cape of 

island, Lituya Bay, Alaska. Unnamed formation, lower 

part (middle Miocene). D. J. Miller, collector.

USGS D-174. Southwest shore of Cenotaph Island, 0.67 mile 

S. 70° W. of easternmost cape of island, Mount Fairweather 

quad., Lituya Bay, Alaska. Unnamed formation, about 

1,170 ft above base; upper mudstone unit (probably Pliocene). D. J. Miller, collector.

USGS D-180. Ocean beach reef, 0.55 mile N. 50° W. of mouth 

of Topsy Creek, Mount Fairweather quad., Lituya district, 

Alaska. Unnamed formation, about 3,100-3,200 ft above 

base; upper mudstone unit (probably Pliocene). D. J. 

Miller, collector.

USGS D-264. Cliff at east margin of Fairweather Glacier, 

about 3.8 miles N. 80° W. of Mount Escures, Mount Fairweather quad., Lituya district, Alaska. Unnamed formation, probably in lower sandstone-siltstone unit (late Miocene or early Pliocene). D. J. Miller, collector.

USGS D-385. Recent, strandline at Narssarssuk, 12 miles 

southwest of Thule, northwestern Greenland. W. E. Davies 

and G. Gold, collectors.

USGS D-386. Raised beach, 10-35 ft above sea level, at Narssurssuk, 12 miles southwest of Thule, northwestern Greenland. Probably postglacial. W. E. Davies, collector.

USGS D-389. Probably same locality as D-264. J. B. Fernstrom, collector.

U.S. Geological Survey Tertiary localities (Menlo Park 

catalog) :

USGS M-214. Recent marine glacial deposits. Road north of 

bridge, south of Fish Creek, Douglas Island, Juneau area, 

Alaska. D. J. Miller, collector.

USGS M-225. Recent, dead shells dredged from depth of 75 

ft, east arm of Excursion Inlet, north side of Icy Strait, 

southeastern Alaska. D. J. Miller, collector.

USGS M-237. Dead beach shells from several localities on 

Beardslee Island and shore of Glacier Bay, southeastern 

Alaska. D. J. Miller, collector.

USGS M-363. Recent, on beach at mouth of Salmon River, 

about 25 miles north of Cape Newenham, southern Kuskokwim Bay, Alaska. D. M. Hopkins, collector.

USGS M-364. Recent, lagoon behind Safety Spit, Nome, 

Alaska. D. M. Hopkins, collector.

USGS M-807. East of Yellow Bluff Creek, about 5.3 miles east 

of lake north of Black Peak and 16.4 miles N. 55° W. of 

west end of Anguvik Island in Chignik Bay, altitude about 

1,600 ft Unnamed formation (Yellow Bluff Zone of Western Gulf Oil Co. usage) (probably Pliocene). M. C. Lachenbruch, Western Gulf Oil Co., collector.

USGS M-807a. Same locality as M-807, later collection.

USGS M-1164. North shore of Popof Island, Shumagin Islands, Alaska ; lat 55°20.6' N., long 160°26' W. Upper part 

of Acila shumardi zone (late middle Oligocene). C. A. 

Burk, Richfield Oil Co., collector.

USGS M-1256. Dredge tailings near oil tanks in FAA Warehouse area on west side of Snake River, lat 64°30' N., long 

165°25'30" W., Nome, Alaska. Submarine Beach (early 

Pleistocene). D. M. Hopkins, collector.

USGS M-1425. Recent, beach at Deering, southern Kotzebue 

Sound, Alaska. D. M. Hopkins and D. S. McCulloch, 

collectors.

USGS M-430. Recent, Lost River, lat 65°23'10" N., long 

167°09'05" W., west of Port Clearance, Alaska. D. M. 

Hopkins, collector.

USGS M-1440. Estuarine deposits at Nome, Alaska. "Second 

Beach" or younger. Pleistocene. D. M. Hopkins, collector.

USGS M-1445. Estuarine deposits at Nome, Alaska, north 

wall of dredge pit no. 6. "Second Beach" or younger. 

Pleistocene. D. M. Hopkins, collector.

USGS M-1493. 140 ft above base of glacial-marine sequence 

approximately 3,500 ft thick, at about midpoint of south 

end of Tugidak Island, Trinity Islands, Alaska. Late(?) 

Pliocene. G. W. Moore, collector.

USGS M-1526. Upper fossiliferous bed at Tolstoi Point, east 

side of English Bay, St. Paul Island, Pribiloff Islands,
EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G45

Alaska. Pleistocene, probably middle. D. M. Hopkins, 

collector.

USGS M-1577. Northeast end of lagoon behind Cape Kruzenstern, lat 67°11.75' N., long 163°32' W., Alaska. Late 

Pleistocene. D. S. McCulloch, collector.

USGS M-1622. Recent, beach along Lukanin Bay near Tonki 

Point, St. Paul Island, Pribiloff Islands, Alaska. D. M. 

Hopkins, collector.

USGS M-1625. Recent, Homer Spit at entrance to Kachemak 

Bay, an arm of Cook Inlet, Alaska. J. Wolfe, collector.

USGS M-1634. Beach at Ferry Landing, Nanaimo, Vancouver 

Island, British Columbia. Recent. F. S. MacNeil, collector.

USGS M-1655. North side of Popof Island, Shumagin Islands, 

Alaska; lat 50°20.35' N., long 160°25.6' W. Upper part of 

Acila shumardi zone (late middle Oligocene). A. Grantz, 

collector.

USGS M-1662. Recent, about 9 miles east of southwest cape, 

St. Lawrence Island, northern Bering Sea. H. B. Alien, 

collector.

USGS M-1663. Recent, beach about 3 miles west of Invute 

Mountain, St. Lawrence Island, northern Bering Sea. H. B. 

Alien, collector.

USGS M-1664. Fur Sund at Branden Ferry, Jutland, Denmark. Postglacial or Recent. F. S. MacNeil, collector.

USGS M-1665. Recent, east side of tip of Sheshalik Spit, 

northern Kotzebue Sound, Alaska. D. S. McCulloch, 

collector.

USGS M-1668. Stratton Hall on River Orwell, Suffolk, England. Newbournian Stage, Red Crag (early Pleistocene). 

D. F. W. Baden-Powell, F. S. MacNeil, and D. M. Hopkins, 

collectors.

USGS M-1669. Neutral farm, near Butley, Suffolk, England. 

Butleyan Stage, Red Crag (early Pleistocene). D. F. W. 

Baden-Powell, F. S. MacNeil, and D. M. Hopkins, collectors.

USGS M-1670. Virtue farm, north of Alderton, Suffolk, England. Butleyan Stage, Red Crag (early Pleistocene). D. F. 

W. Baden-Powell, F. S. MacNeil, and D. M. Hopkins, 

collectors.

USGS M-1671. Six feet below top of section, highest shelly 

layer below clay, Stackyard pit, Chillesford, Suffolk, England. Chillesford Beds, Icenian Crag (early Pleistocene). 

D. F. W. Baden-Powell, F. S. MacNeil, and D. M. Hopkins, 

collectors.

USGS M-1672. Aldeburg, Suffolk, England. Norwich Stage, 

Icenian Crag (early Pleistocene). D. F. W. Baden-Powell, 

D. M. Hopkins, and H. E. P. Spencer, collectors.

USGS M-1679. Road and building cuts on northeast side of 

Unalaska Lake near head of Illiuliuk Bay, Unalaska Island, 

Aleutian Islands, Alaska. From greenish volcanic graywacke containing Cornwallius teeth. H. F. Barnett, Jr., 

collector.

USGS M-1681. Roadcut on Tokeland Road along north shore 

of Willapa Bay, approximately 45 ft above high-water mark, 

1,700 ft south of NB. cor. sec. 6, T. 14 N., R. 10 W., Pacific 

County, Wash. Unnamed formation, probably Pleistocene. 

W. O. Addicott, collector.

USGS M-1682. Roadcut on Tokeland Road along north shore 

of Willapa Bay, approximately 37 ft above high-water mark, 

3,400 ft south and 2,200 ft east of NW. cor. sec. 5, T. 14 N., 

R. 10 E., Pacific County, Wash. Unnamed formation, probably Pleistocene. W. O. Addicott, collector.

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EVOLUTION AND DISTRIBUTION OF THE GENUS MYA G47

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INDEX

[Italic numbers indicate descriptions]

abbreviata, Mya truncata.......... ._...__ G38

Actta.. .................................... 8

gettysburgensis........ __________ 10

shumardi . . 10,14,27

acuta, Mya................................ 31,32,33

adamsi, Protothaca __________..__.. 16 

alaskana, Spisula.......__.....___....... 8

alaskensis, Astarte......__------____.. 8

alba, Mya..... ....... . -.. ......... 33

aleuticus, Glycymeris......................... . 18

Anatina degans... ..--____..___.___ 12,29

Ancestry of Mya...,......................... IS

Arctic climate and its effect on organisms_.. 7 

Arctica....................................... 6,7,9

islandica..... .......................... 9

arctica, Hiatella ........................... 8,9,10

arenaria japonica, Mya..................... 18,31,42

japonica, Mya (Mya)..................... 29,40

Mya... 3,8,12,13,14,15,16,17,18,19, 20,21,22, 23, 

24, 25,26, 28,29,30,31,32, 33,34,35,36, 

37,40,41,42. 

(Arenomya).................. 31,33; pis. 5,6

profundior, Mya.......................... 29

Mya (Mya)........................... 29

truncata, Mya............................ 40

Arenomya................................. 25,26,36

(Arenomya) arenaria, Mya... ____ 31, S3; pis. 5,6 

arrosis, Mya........................ Si; pis. 2,3

dickersoni, Mya........................ 28; pi. 2

elegans, Mya........................ 29; pis. 2,3

ezoensis, Mya............................. 26

fujiei, Mya............................. SO; pi. 5

grewingki elongata, Mya................... 35

haboroensis, Mya...................... 28

Mya............................... 27; pi. 1

japonica, Mya................. 31,40; pis. 3,4,6

oonogai, Mya......................... 31,34

kusiroensis, Mya....................... 27; pi. 1

Mya......................... 14,24,25,26,27,36

producta, Mya.............______ 26; pi. 1

arrosis, Mya........ ............-___ 15,29,31

Mya (Arenomya)....________ S/; pis. 2,3

Astarte alaskensis............................. 8

ettiptica................................... 8,10

Batissa....................................... 6

Bicorbula......................_-------_.. 13

Biological and temporal aspects of migration.. 2 

bisecta, Thyasira.............................. 7,9

Blakely Formation of Washington... _____ 14,18 

Boreal regions..________-__.-.- 3,4,9

Boreal species..._________________ 9,18 

Boreoscala....-............................... 8

Brachiopods, distribution____._ ___ __ 9 

Briones Sandstone......- ...- 14,15,16,28,30,43

calcarea, Macoma............................. 8

California Current________________ 4

Caloosahatchee Formation.......______ 8,17

Page

Cannonball Member of Fort Union Formation.. ---------.-------..--_ 6

Cardium edule................................ 9

groenlandicum zone of the Icelandic Crag. 20 

Chikubetsu Formation...--. ......._. 14,17,28

Choptank Formation..-.-----.---.--- . 13,26.43

Cierbo Sandstone...._.. 14,15,16,17,29,31,34,43

Cipangopaludina sp_. __ __ __ _ __ 6

clintonius, Placopecten........................ 8

communis, Mya.............................. 33

Coos Conglomerate... ___...__ 18,39 

Coralline Crag...... ._. 8,19,20,34,38,39

CornwaUius sp__-.-.--___-.-.._. 28 

corpulenta, Mya.............................. 33

Correlation and migration of mollusks. ... 5 

crassa, Mya................. 12,13,17,27,28,29,35,36

crispatus, Photos.............................. 9

Croatan Sand....____________.__. 17

cuneiformis, Mya...................... 14,15,17,18,

19, 20, 29, 30, 31, 35,36,37,38,39,41,42 

Mya (Mya)............................ SB; pi. 7

Pleuromya................................ 35

takigawensis, Mya.................... . 36

Cyrtodaria.. ................................ 7

D

dickersoni, Mya................................. 13,

14,15,16,17,22,25,28,29,30,31,33. 

Mya (Arenomya)......... .......... 28; pi. 2

Distribution and phylogeny of species 10 

donaciformis, Mya............................ 35

E 

Echinophoria apta zone....__ _- 9

Ecology and migration of mollusks-.. 2 

edule, Cardium....................--......... 9

Elasticum. _ . 21,22, 24

elegans, Anatina.............. .... ...... 12,29

Mya............................ 12,13,14,15,16,

17,18,21,24,25,28,29,30,31,33,36. 

(Arenomya).... .. 29; pis. 2, 3

elliptica, Astarte.... ....................... 8,10

elongata, Mya................................. 33

Mya (Arenomya) grewingki............... 35

grewingki..... ......... 14,18,27,28,35,39

Eocene deposits... _..__ __ 6 

Equus..-.. ....... ..... ...... 8

Etchegoin Formation. . . 16,31,34,43 

E volution and migration of mollusks.. _.-.. 5 

ExflabeUaria groenlandica..................... 7

ezenensis, Mya................................ 41

ezoensis, Mya........................... 13,14,26,27

Mya (Arenomya)-..-..................... 26

sagittaria, Mya........................... 26

Faunas in Norwegian fiords.________.. 4 

Flbrum. 21,22,24

Page 

fujiei, Mya........................ 14,15,16,30,32,34

Mya (Arenomya)...................... SO; pi. 5

Fusitriton............................ ....... 10

G 

gettysburgensis, Acila.......................... 10

Glycymeris aleuticus.......................... 18

grewingki elongata, Mya........... 14,18,27,28,35,39

elongata, Mya (Arenomya)................ 35

haboroensis, Mya.............. 14,15,17,28, 29, 30

Mya (Arenomya)..................... 28

kusiroensis, Mya.......................... 27,28

Mya....................... 14,17,24,25,27,28,30

(Arenomya)................... .. 27; pi. 1

nagaoi, Mya.........__________ 28,35,39

groenlandica, ExflabeUaria.................... 7

H

haboroensis, Mya (Arenomya) grewingki------- 28

Mya grewingki................ 14,15,17,28,29,30

hemphilli, Mya............................... 33

Hiatella arctica.............................. 8,9,10

pholadis.........._..__.___...___ 9

sakltalinensis..--.......................... 9

Hiatula .................................... 25

Honbetsu Formation________.__.. 17 

Horoshin Formation.....___________ 14

Icenian Crag. - --. 8,19,34,39 

Imperial Formation..____._____...... 8

Indigenous Atlantic species Mya producta... IS 

intermedia, Mya.................. 12,13,18, 29,30,37

Introduction....-_.___ __ . ..... 1

Ishikari Group,-.....__. __-. 14

islandica, Arctica__.__ .-... . 9

Jacob Sand.____________.______ 17 

Japan Current_-...-__...__ ... 4

japonica, Mya....3, 10, 12, 13, 14, 15, 16, 17, 19, 20, 22,

24, 26, 28, 29, 30, 31, 32, 33, 34, 35, 37, 

40, 41,42. 

Mya arenaria.--.......----..-.----...- 18,31,42

(Arenomya)........... SI, 40; pis. 3, 4, 6

(Mya) arenaria...__..__.___.. 29,40 

oonogai, Mya ........ 12,14,15,16,30,31,33,34,35

Mya (Arenomya)............__.__ 31,34

K 

Kirkwood Formation. _____ ....... 13,26

kusiroensis, Mya..................... 14,18,25,27,28

Mya (Arenomya)...................... 27; pi. 1

grewingki....... ................... 27,28

Labrador Current. __ 

Laminum. ___._ -_... 

Lanceolaria pisciformis. 

lota, Mya..............

G49
G50 INDEX

Ligament of Mya. 

Ligamental callus . 

Localities..-_-_-_-.

Page

Hi 

22 

4S

M

Macoma..... __ 

calcarea.... 

nasuta.....

Maoka Group.

 12

_______________ 8 

._...-_-..._.___._.___-__ 27

 9

Merced Formation.....______.____. 16,17

mercenaria, Mya.............................. 33

Meshik Formation...______________ 18

middendorffi, Mytilus.. 18,36

Migration and correlation of mollusks ___ . B 

Migration and dispersal of mollusks..___ _ __ %

Migration and ecology of mollusks _______ __ Z

Migration and evolution of mollusks__ .. B 

Migration and specific variability of mollusks. 4 

Migrations of Pacific and Atlantic Ocean

mollusks--.--________.__ H

Migration, biological and temporal aspects.. i

periods and routes_ _.___ ___ . 8

minor, Sphenia.................... ._____ 13

Mollusks, migrations... ______._____ % 

Monterey Group.____...___....... 15

Morphologic characters of Mya. ________- HO

Muscle scars of Mya.. _ _. _ Si 

Mya................................... 1,2,10,25,35

acuta.................................. 31,32,33

alba...................................... 33

arenaria.................................. 3,

8, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 

22, 23, 24, 25, 26, 28, 29, 30, 31, 32, 33, 

34, 35, 36, 37, 40, 41, 42. 

japonica........................... 18,31,42

profundior.--------................... 29

truncata......................_.__ 40

arrosis................................. 15,29,31

communis.......-.... _____________ 33

corpulenta................___.__ 33

crassa................... 12,13,17,27,28,29,35,36

cwneiformis.-.-........................... 14,

15, 17, 18, 19, 20, 29, 30, 31, 35, 36, 37, 

38, 39, 41, 42. 

takigawensis............ _______-_-__ 36

dickersoni... 13,14,15,16,17,22,25,28,29,30,31,33 

donaciformis...............-.-.-.......... 35

degans..___ _.. 12, 

13, 14, 15, 16, 17, 18, 21, 24, 25, 28, 29, 

30, 31, 33, 36. 

dongata................................... 33

ezenensis......................... 41

ezoensis............................. 13,14,26,27

sagittaria.............................. 26

fujiei......................... 14,15,16,30,32,34

grewingki.... ... . 14,17,24,25,27,28,30

elongata................... 14,18,27,28,35,39

haboroensis................ 14,15,17,28,29,30

kusiroensis............. ........... 27,28

nagaoi............................. 28,35,39

hemphilli.................................. 33

intermedia.................... 12,13,18,29,30,37

japonica... ................... 3,10,12,13,

14, 15, 16, 17, 19, 20, 22, 24, 26, 28, 29,

30, 31, 32, 33, 34, 35, 37, 40, 41, 42

oonogai.......... 12,14,15,16, 30,31, 33, 34, 35

kusiroensis....................... 14,18,25,27,28

lota....................................... 33

mercenaria............ .__-_-_-__-- 33

nagaoi.................................... 14

oonogai............................. 12,22,31,32

ovalis..................................... 38

peternalis................................. 35

praecisa..........____.__._____. 38

priapus.................. 12, 13,16, 18, 19, 20, 21,

22, 24, 25, 28, 30, 32, 36, 37, 38, 40, 41, 42

Mya Continued Page 

producta................... 13, 20, 21, 24, 25, 26, 27

profundior..................._____ 12,13,30

pseudoarenaria.................. 8, 13, 16, 18, 19,

20, 25, 26, 34, 36, 37, 38, 39, 40, 41, 42, 43 

pullus.............................. 18,38,39,42

salmonensis ....... 14,18,19, 20, 25, 27, 28, 35, 39

subovata................______...__ 33

subtruncata............................... 33

truncata........ 3, 4, 8, 10,12, 14, 18,19, 20, 21, 22,

24, 25, 28, 29, 30, 35, 37, 38, 39, 40, 41, 42 

abbreviata.............. ___________ 38

forma ovata........................... 20,37

ovata.... ________________ 19,37

truncata.............................. 38

uddevalensis........____.___ 21,38

urusikuboana............................. 35

uzenensis................................. 40

(Arenomya).................. 14,24,25,26,27,36

arenana.................... 31,33; pis. 5, 6

arrosis.........____._.__ 51; pis. 2, 3

dickersoni................. _____ &8; pi. 2

elegans......................... %9; pis. 2, 3

ezoensis............................... %6

fujiei.............................. SO; pi. 5

grewingki.......................... #7; pi. 1

elongata........................... 35

haboroensis........................ Z8

japonica................... 31, 40; pis. 3, 4, 6

oonogai........................... 31,34

kusiroensis........... ..-._._.-_---. £7; pi. 1

producta........... ..-.-__.__-_---. %6; pi. 1

(Mya)........................ 14, 24, 25, 26, 27, 36

arenaria japonica...................... 29,40

profundior.-...................... 29

cuneiformis......... _____--.-_. 35; pi. 7

priapus...................... 40; pis. 10, 11

pseudoarenaria.......... ________ 57; pis. 7, 9

pullus-........................... 48; pi. 11

salmonensis........................ 35; pi. 7

truncata......................... S8; pis.8,9

sp. _______________________________________ 38

(Mya) arenaria japonica, Mya................ 29,40

arenaria profundior, Mya................. 29

cuneiformis, Mya.................... SB; pi. 7

Mya.......................... 14,24,25,26,27,36

priapus, Mya.................... 40; pis. 10, 11

pseudoarenaria, Mya.............. 57,- pis. 7, 9

pullus, Mya........................ 4%; pi. 11

salmonensis, Mya.................... S6; pi. 7

truncata, Mya...................... S8; pis. 8, 9

Mya arenaria group......_______ 14, 17,18,26,41

Mya elegans group_..._________.. .77,28

Mya producta indigenous Atlantic species... 13

Mya truncata group.____ 17, 18, 24,25,26,35,41,42

Mya, ancestry..______...______. IS

sculpture of shell...______-_____ HO

shell shape...__._____________ 90

shell thickness.._______________ SO

variability of form..._______.___ 90

Myarius...................................... 25

Mytilus middendorffi............... ._____ 18,36

N 

nagaoi, Mya.................................. 14

Mya grewingki......................... 28,35,39

nasuta, Macoma.............................. 27

Neptunea............................... 2,3,4,5,8,9

beringiana................................ 9

decemcostata.............................. 9

ventricosa................................. 9

Neroly Formation,... _._._- 14,15,17,28,29,31,43 

Norwegian Current....-__.________- 4

Nuwok Formation of Dall___________ 6,7

O 

Oligocene deposits.,_______-____ 6

oonogai, Mya........................... 12,22,31,32

Mya (Arenomya) japonica...........__ 31,34

japonica......... 12,14,15,16,30,31,33,34,35

ovalis, Mya..................... _____________. 38

ovata, Mya truncata........................... 19,37

Pacific species, early__..._________ IS 

Paleocene deposits____._____... _. 6,7 

Pallialline and pallial sinus...._______ il 

Palliolum.................................... 6,9

groenlandicum............................ 10

Pamlico Formation.._________ ____ 17 

Panomya..................._________ 8

Panope....................................... 13,26

Paphia restorationensis........................ 16

Pelagic larvae.._________________ 3,5 

Periods and routes of migration. __ __.. 8 

Periostracum.__________________ 21,23 

Periploma.................................... 21

peternalis, Mya............................... 35

pholadis, Hiatella............................. 9

Pholas crispatus.............................. 9

Phylogeny and distribution of species..------ 10

Phylogeny of myarian species. _____ 23 

pisciformis, Lanceolaria....................... 6

Placopecten clintonius......................... 8

Pleuromya cuneiformis........................ 35

polynyma, Spisula............................ 8

Poronai Series-------.---.-.._._-_._...___..- 14,18

Poul Creek Formation...... 9,14,18, 28,30,35,43,44

praecisa, Mya................................ 38

priapus, Mya................. 12,13,16,18,19, 20,21,

22,24,25,28, 30,32,3P, 37,38,40,41,42

Mya (Mya)...................... 40; pis. 10, 11

Pribilof Islands..---------------.--------- 18,30

producta, Mya................. 13,20,21,24,25,26,27

Mya (Arenomya)...................... &6; pi. 1

profundior, Mya........................... 12,13,30

Mya arenaria............................. 29

(Mya) arenaria....................... 29

Protothaca adamsi...................._____ 16

pseudoarenaria, Mya................. 8,13,16,18,19,

20, 25,26,34,36,37,38,39,40, 41,42,43

Mya (Mya)........................ 57; pis. 7, 9

Puget Group._______________._-__ 6 

puttus, Mya............................ 18,38,39,42

Mya (Mya)........................... 4«,-pl. 11

Quillayute Formation.

Q

18

R

Raetomya..................................... 13

Recent marine invertebrates___._..._ 3 

Red Crag of England.. 8,17,20,22,23,34,38,39,42,43 

restorationensis, Paphia....................... 16

sagittaria, Mya ezoensis....................... 26

sakhalinensis, Hiatella........................ 9

salmonensis, Mya........ 14,18,19,20, 25,27,28,35,39

Mya (Mya)............................ 56; pi. 7

San Joaquin Formation -.-..--.-. 16,17,22,31,34,43 

SanPablo Group........---.---._.... 14,15,28,31

San Pedro Formation..___________... 18 

Sculpture of Mya........................ ... 80

Setana Formation..____________. 19

Shitakara Formation. ______________ 14,27 

shumardi, Actta............................ 10,14, 27

Sttigua....................................... 8

Sobrante Sandstone.-.-..__..._._.--__ 15 

Solemya...................................... 21

Spawning temperatures.. _________.. 3
INDEX G51

Specific variability and migration _ 

Sphenia minor-------- ___ _.__.--

swainsoni _ - _ _-_ __ _ __-

Spisula alaskana. ... ___ _ ____ _

polynyma. --------------------

voyi. ------------ ..............

Page

_____ 4

._ _ - 13

-_'- 38

_ __ 8

----- 8

..... 8

Spoonof Mya..---- _____ _._-___._ __ ... 21, 25

Subarctic Current_.-.__ _ _.__.._ _ ____ _ .. 4

Subemarginula _ --_-__-_-_____--_------_.__._- 6

subovata, Mya,--- _ - _ _____._--_ __ ---_-_-_ 33

subtruncata, Mya---------. ____._-_-_-_-_-.._ 33

Subumbonal solution _ _________ _ _._____.- 24

swainsoni, Sphenia-- _ _-__-_-.---_--_---_.-- 38

Systematic paleontology __ ___ _ ______ . 25

takigawensis, Mya cuneiformis_..-_.______. 36

Takinoue Formation__________ 14,15,16,18,28,30,34

Tamiami Formation____________________-_-__ 8

Page

Temperature as a factor in global distribution. 3 

Temperature, spawning.._________ ________ 3

Temporal and biological aspects of migration. 2 

Tertiary paleogeography of the Arctic and the

boreal regions,.--_.-_______ 6

Thais-.-----.---------.---.---------..--.-..- 8

Thickness of Mffo shell.----.__________ 20

Thrada....................................... 21

Thyasira bisecta...____..._________ 7,9 

Timms Point Silt Member.-------------.--- 18,39

Togeshita Formation___________________ 19

Toshima Sand__ _._...__________.. 16,17 

Towsley Formation.____-_.____.___. 18,39

truncata abbreviata, Mya______--_-_-_-._.____ 38

Mya- 3, 4, 8, 10, 12, 14, 18, 19, 20, 21, 22, 24,

25, 28, 29, 30, 35, 37, 38, 39, 40, 41, 42

arenaria.-.-- _._._-------_.__. 40

(Mya)...............-......... 58; pis. 8, 9

truncata-------.- _________.----_._ 38

ovata, Mya-- _--......_..._._____ 19,37

tnmcata abbreviata, Mya Continued Page 

truncata, Mya---.... __...._-._________. 38

uddevalensis, Mya.-------------__.... 21,38

U

uddevalensis, Mya truncata--- _---------_.- 21,38

Urohoro Group___...._.----..-.__.. 14

urusikuboana, Mya------ _.______---_..- 35

uzenensis, Mya-.-...-________.___.- 40

Variability of form-,.. __...____. 

Venerupis (Protothaca) restorationensisvoyi, Spisula.--------------_-... ..

W

Wakkanabe Formation.....____.._________-.- 13,27

Yakataga Formation....___....____ 8,18,44 

Yorktown Formation............. 8,13,17,19,34,43

PLATES 1-11
PLATE 1

FIGURES 1, 3, 4. Mya producta Conrad (p. G26).

Figured specimen (XI), after Glenn, 1904, pi. 68, figs, la, Ib, 2. Choptank Formation, Jones Wharf,

Patuxent River, Md. 

1. Left valve, exterior.

3. Spoon.

4. Interior showing pallial line and pallial sinus. 

2, 7. Mya producta Conrad (p. G26).

Figured specimen, topotype (X 1), USNM 146004. Choptank Formation, Jones Wharf, Patuxent River,

Md., USGS 2451. 

2. Spoon.

7. Left valve, exterior. Length 113 mm, height (incomplete) 39 mm, convexity (not including spoon) 12 mm. 

5, 6, 8. Mya kusiroensis Nagao and Inoue (p. G27).

Figured specimen (XI), USNM 644267. Base of Poul Creek Formation, west shore of Hanna Lake, Yakataga District, Alaska, USGS 16891.

5. Spoon, rubber cast.

6. Left valve, exterior, rubber cast. Length 60 mm, height 38 mm.

8. Right valve, internal mold, showing pallial line and pallial sinus. Double convexity 20 mm. 

9, 10. Mya kusiroensis Nagao and Inoue (p. G27).

Figured specimens (X 1). Upper part of Acila shumardi zone, north shore of Popof Island, Shumagin Islands, Alaska, USGS M-1164.

9. Left valve, internal mold, USNM 644268.

Length 52 mm, height 38.5 mm, double convexity 21.3 mm.

10. Left valve, internal mold, USNM 644269.

Length 38.7 mm, height 29 mm, double convexity 16 mm. 

11. Mya cf. M. grewingki Makiyama (p. G27).

Figured specimen (X 1), "USNM 644270. Poul Creek Formation, about 1,900 ft below top, Yakataga 

District, Alaska, USGS 15433. Length 93 mm, height 56 mm, double convexity 47 mm.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 1

ft^^j&Vr'i- *s?L- "^

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FROM THE CHOPTANK FORMATION (MARYLAND), THE POUL CREEK FORMATION (ALASKA), 

AND THE ACILA SHUMARDI ZONE, POPOF ISLAND (ALASKA)
PLATE 2

FIGURE 1. Mya dickersoni Clark (p. G28).

Holotype (X 1), UC 11554. Neroly Formation, San Pablo Group, Contra Costa County, Calif., UC 1617.

Right valve, exterior. Length 57 mm, height 37 mm. 

2, 5. Mya dickersoni Clark (p. G28).

Figured specimen, topotype, UC 15001. Neroly Formation, San Pablo Group, Contra Costa County, Calif.,

UC 1617.

2. Spoon (XI). Length 35 mm, height 26.5 mm. 

5. Same (X 2), different illumination. 

3. Mya elegans (Eichwald) (p. G30).

Figured specimen (X 1), USNM 644271. This specimen is here designated the neotype of Mya crassa 

Grewingk. Beds of Pliocene age, east side of Yellow Bluff Creek near headwaters, northwest of Chignik 

Bay, Alaskan Peninsula, USGS M-807a. Right valve, exterior, partly testaceous. Length 89 mm, height 

63 mm, double convexity 41 mm. 

4, 12. Mya elegans (Eichwald) (p. G29).

Figured specimen (X 1), USNM 221269. Recent, Chignik Bay, Alaskan Peninsula. 

4. Spoon.

12. Left valve, interior, showing pallial line and pallial sinus. Length 113 mm, height 72 mm, convexity (not 

including spoon) 23 mm.

6. Mya elegans (Eichwald) (p. G29).

Figured specimen (XI), USNM 635283. Recent, southern part of Kuskokwim Bay, between Goodnews Bay 

and Cape Newenham, Alaska, USGS M-363. Spoon. Same specimen as pi. 3, figs. 1, 4.

7. Mya elegans (Eichwald) (p. G30).

Neotype (XI), USNM 644272. This specimen is here designated the neotype of Mya arenaria Linne1 Grewingk 

for which the name Anatina elegans Eichwald was proposed. Beds of Pliocene age, east side of Yellow Bluff 

Creek near headwaters, northeast of Chignik Bay, Alaskan Peninsula, USGS M-807. Left valve, internal 

mold. Length (incomplete) 108 mm, height 68 mm, double convexity 40.5 mm.

8. Mya elegans (Eichwald) (p. G29).

Figured specimen (X 1), USNM 644273. Middle Pleistocene, upper bed at Tolstoi Point, St. Paul Island, 

Pribiloff Islands, USGS M-1526. Spoon.

9. Mya arrosis MacNeil, n. sp. (p. G31).

Figured specimen (X 1), UC 15003. Briones Sandstone, San Pablo Group, Contra Costa County, Calif.,

UC 1687. Spoon. Same specimen as pi. 3, fig. 3. 

10, 11. Mya dickersoni Clark (p. G28).

Figured specimen, topotype (X 1), UC 15002. Specimen obtained from matrix enclosing holotype. Neroly 

Formation, San Pablo Group, Contra Costa County, Calif., UC 1617.

10. Spoon, showing small ligamental callus.

11. Left valve, exterior, decorticated. Length 59 mm, height 35 mm, convexity (not including spoon) 12 mm.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 2

MY A FROM THE BRIONES AND NEROLY FORMATIONS (CALIFORNIA), PLIOCENE BEDS, CHIGNIK BAY 

(ALASKA), PLEISTOCENE BEDS, ST. PAUL ISLAND (ALASKA), AND RECENT (ALASKA)
PLATE 3

FIGURES 1, 4. Mya elegans (Eichwald) (p. G29).

Figured specimen (X 1), TJSNM 635283. Recent, southern part of Kuskokwim Bay, between Goodnews Bay

and Cape Newenham, Alaska, USGS M-363.

1. Left valve, exterior. Length 115 mm, height 75 mm, convexity (not including spoon) 31 mm. 

4. Same, interior, showing palliall line and pallial sinus. Spoon on pi. 2, fig. 6.

2. Mya arrosis MacNeil, n. sp. (p. G31).

Figured specimen (X 1J4), UC 15004). Neroly Formation, San Pablo Group, Contra Costa County, Calif., 

UC 1617. Spoon.

3. Mya arrosis MacNeil, n. sp. (p. G31).

Figured specimen (X 1), UC 15003. Briones Sandstone, San Pablo Group, Contra Costa Country, Calif., UC

1687. Left valve, exterior, partly testaceous. Height 61 mm. Spoon on pi. 2, fig. 9. 

5. Mya arrosis MacNeil, n. sp. (p. G31).

Figured specimen, topotype (X 1), UC 15005. Cierbo Sandstone, San Pablo Group, Contra Costa County,

Calif., UC 1227. Left valve, exterior, partly testaceous. Height 38.5 mm. 

6, 9. Mya arrosis MacNeil, n. sp. (p. G31).

Holotype (X 1), UC 15006. Cierbo Sandstone, San Pablo Group, Contra Costa County, Calif., UC 1227. 

6. Spoon. 

9. Left valve, exterior, partly testaceous. Length (incomplete) 78 mm, height 57. mm, convexity (not including

spoon) 15 mm. 

7. Mya japonica Jay (p. G31).

Figured specimen (X 2), USNM 644274. Late Pleistocene terrace deposit at Cape Kruzenstern, Alaska, USGS

M-1577. Spoon. 

8, 10. Mya japonica Jay (p. G31).

Figured specimen (X 1), USNM 635284. Recent, Sheshalik Spit, northern Kotzebue Sound, Alaska, USGS

M-1665. 

8. Spoon.

10. Left valve, exterior. Length 82.5 mm, height 47.5 mm, convexity (not including spoon) 15 mm. Same 

specimen as pi. 4, fig. 11.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 3

'.«!' -j^*0ftfew':^r««J

* : *&'',. - » >* ' £ *£' X'.'^V .^j sj;. :.<*.. .-. *-.'~f:t

MY A FROM THE BRIONES, CIERBO, AND NEROLY FORMATIONS (CALIFORNIA), PLEISTOCENE BEDS,

CAPE KRUZENSTERN (ALASKA), AND RECENT (ALASKA)
PLATE 4

[All figures natural size]

FIGUEES 1, 5, 8. Mya japonica Jay (p. G31).

Figured specimen, GAS 12534. Recent, Tokyo Bay, GAS 34859.

1. Left valve, exterior. Length (incomplete) 105 mm, height 66 mm, convexity (not including spoon) 22 mm. 

5. Same, interior, showing pallial line and pallial sinus. 

8. Same, spoon. 

2. Mya japonica Jay (p. G31).

Figured specimen, USNM 644275. Late Pleistocene lagoon deposit, Nome, Alaska, USGS M-1445. "Second 

Beach" or younger. Spoon of a distorted specimen; for comparison with Middendorff, 1849, pi. 20, figs. 1-3. 

3, 4. Mya japonica Jay (p. G31).

Figured specimen, USNM 644276. Late Pleistocene lagoon deposit, Nome, Alaska, USGS M-1440. 

"Second Beach" or younger.

3. Spoon.

4. Left valve, interior, showing pallial line and pallial sinus. Length 69 mm, height 41 mm, convexity (not

including spoon) 13 mm. 

6. Mya japonica Jay (p. G31).

Figured specimen, USNM 635285. Recent, Safety Spit, near Nome, Alaska, USGS M-364. 

7, 9, 10. Mya japonica Jay (p. G31).

Figured specimen, USNM 644277. Late Pleistocene lagoon deposit, Nome, Alaska, USGS M-1440.

"Second Beach" or younger. 

7. Spoon.

9. Left valve, exterior. Length 70 mm, height 43 mm, convexity (not including spoon) 14 mm.

10. Left valve, interior, showing pallial line and pallial sinus. 

11. Mya japonica Jay (p. G31).

Figured specimen, USNM 635284. Recent, Sheshalik Spit, northern Kotzebue Sound, Alaska, USGS M1665. Left valve, interior, showing pallial line and pallial sinus. Same specimen as pi. 3, figs. 8, 10.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 4

\

MYA FROM PLEISTOCENE BEDS, NOME (ALASKA), AND RECENT (JAPAN AND ALASKA)
PLATE 5

FIGUBE 1. My a cf. M. fujiei MacNeil, n. sp. (p. G30).

"Paratype" of Mya dickersoni (Clark (X 1), UC 11533. Briones Sandstone, San Pablo Group, Contra Costa

County, Calif., UC. 197. Left valve, exterior partly decorticated. 

2, 3. Mya arenaria Linn6 (p. G33).

Figured specimen (X 1), USNM 644278. Yorktown Formation, Yorktown, York County, Va., USGS 

2247b.

2. Left valve, exterior. Height 40.5 mm.

3. Spoon.

4. Mya arenaria Linn6 (p. G33).

Figured specimen (X 2), USNM 644279. Yorktown Formation, 2J4-3 miles southwest of Petersburg, Dinwiddie County, Va., USGS 3122. Spoon.

5. Mya arenaria Linn6 (p. G33).

Figured specimen (X 1), UC 15007. Cierbo Sandstone, San Pablo Group, Alameda County, Calif., UC 1224. 

Left valve, exterior. Length 63 mm, height 36.8 mm, double convexity 22 mm.

6. Mya arenaria Linn6 (p. G33)~.

Figured specimen (XI), USNM 495304, after Woodring and others, 1940, pi. 9, fig. 7. San Joaquin Formation, North Dome, Kettleman Hills, Kings County, Calif., USGS 12480. Left valve, interior, showing 

pallial line and pallial sinus. 

7, 8, 11. Mya arenaria Linn6 (p. G33).

Figured specimen (X 1), UC 34840. Etchegoin Formation, Kettleman Hills, Kings County, Calif., UC 

A-1686.

7. Left valve, exterior. Length 92 mm, height 62 mm.

8. Spoon.

11. Left valve, interior, showing pallial line and pallial sinus. 

.9, 10. Mya arenaria Linne" (p. G33).

Figured specimen (X 1), UC 30802. San Joaquin Formation, Kettleman Hills, Kings County, Calif., 

UC A-3167.

9. Spoon.

10. Left valve, exterior. Height 39 mm. 

12. Mya arenaria Linn6 (p. G33).

Figured specimen (X 1), UC 30801. San Joaquin Formation, Kettleman Hills, Kings County, Calif., UC 

A-3167. Left valve, exterior.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 6

2 

tiMYA FROM THE BRIONES, CIERBO, ETCHEGOIN, AND SAN JOAQUIN FORMATIONS (CALIFORNIA), AND

THE YORKTOWN FORMATION (VIRGINIA)
PLATE 6

FIGURES 1, 6, 9. Mya arenaria Linne1 (p. G33).

Figured specimen (X 1), TJSNM 635286. Recent, Nanaimo, Vancouver Island, British Columbia,

USGS M-1634.

1. Left valve, exterior. Length 82 mm, height 49 mm, convexity (not including spoon) 11 mm. 

6. Left valve, interior, showing pallial line and pallial sinus. 

9. Spoon. 

2, 3, 4. Mya arenaria Linne1 (p. G33).

Figured specimens (X 1). Newbournian Stage, Red Crag, Stratton Hall, Suffolk, England, 

USGS M-1668.

2. Spoon, USNM 644280.

3. Spoon, USNM 644281.

4. Spoon, USNM 644282. 

5. Mya arenaria Linne1 (p. G33).

Figured specimen (X 1), USNM 644283. Butleyan Stage, Red Crag, Neutral farm, Suffolk,

England, USGS M-1669. Spoon. 

7, 8, 10, 11, 12, 15. Mya arenaria Linns' (p. G33).

Figured specimens (X 1). Butleyan Stage, Red Crag, Virtue farm, Suffolk, England, USGS 

M-1760.

7. Spoon, USNM 644284.

8. Spoon, USNM 644285.

10. Spoon, USNM 644286.

11. Spoon, USNM 644287.

12. Spoon, USNM 644288. 

15. Spoon, USNM 644289.

13. Mya arenaria Linne1 (p. G33).

Figured specimen (X 1), USNM 644290. Norwich Stage, Icenian Crag, Aldeburg, Suffolk, England, 

USGS M-1672. Spoon.

14. Mya arenaria Linne1 (p. G33).

Figured specimen (X 1), USNM 644291. Sub-Recent deposits, Brandon Ferry Landing, Fur Sund,

Jutland, Denmark, USGS M-1664. Dorsal view showing spoon. 

16. Myajaponica Jay (p. G24).

Figured specimen (X 2), USNM 644292. Late Pleistocene lagoon deposit, Nome, Alaska, USGS 

M-1440. "Second Beach" or younger. Right-valve chondrophore showing pointed marginal 

projection at dorsal anterior edge; compare with broad spur at this position in M. truncata, pi. 8, 

figs. 2, 3. 

17, 18. Mya arenaria Linne1 (p. G33).

Figured specimen (X 1), after Wood, 1957, pi. 28, figs. 2a, b. Newbournian Stage, Red Crag, 

Sutton, Suffolk, England.

17. Left valve, exterior.

18. Left valve, interior, showing pallial line and pallial sinus.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 6

10

12

MY A FROM THE RED CRAG AND ICEN1AN CRAG (ENGLAND), PLEISTOCENE BEDS, NOME (ALASKA),

AND RECENT (DENMARK AND BRITISH COLUMBIA)
PLATE 7

FIGURES 1, 4. Mya salmonensis Clark (p. G35).

Figured specimen, USNM 644293. Poul Creek Formation, 2,400 ft below top, Yakataga District,

Alaska, USGS 17783.

1. Left valve, exterior, partly testaceous (X 1). 

4. Spoon (X 1H)

2. Mya cuneiformis (Bohm) (p. G35) .

Figured specimen (XI), USNM 644294. Basal part of Yakataga Formation, Yakataga District, Alaska, 

USGS 15437. Spoon.

3. Mya cueniformis (Bohm) (p. G35).

Figured specimen (XI), USNM 644295. Basal part of Yakataga Formation, Yakataga District, 

Alaska, USGS 15437. Left valve, exterior, partly decorticated. Length 65 mm, height 42 mm, 

double convexity 29 mm. 

5. Mya cuneiformis (Bohm) (p. G35).

Figured specimen (X 1), USNM 644296. Basal part of the Yakataga Formation, Yakataga District,

Alaska, USGS 15437. Spoon. 

6, 8. Mya cuneiformis (Bohm) (p. G35).

Figured specimen (XI), USNM 644297. Mylilus middendorffi-bearmg beds, mouth of Ugak Bay,

Kodiak Island, Alaska, USGS 13372. 

6. Left valve, exterior, incomplete. 

8. Spoon. 

7, 12, 15. Pleuromya cuneiformis Bohm (p. G35).

Figured specimens, topotypes (XI), after Bohm, 1915, pi. 29, figs, la, b, 2. The specimen shown in 

Bohm's text figure (right), p. 557, is here designated the lectotype. Middle Miocene beds at Kap 

Jonquiere (?Cape Due), northern Sakhalin. 

9. Mya pseudoarenaria Schlesch (p. G37).

Figured specimen (X 1) (Riksmuseet, Stockholm). Middle Pleistocene beds at Gostinoj, Yenisey River,

Russia, Nordensiold Yenisey Expedition, 1876, no. 1876b. Spoon. 

10, 11, 13, 14. Mya pseudoarenaria Schlesch (p. G37).

Figured specimen (XI), CAS 12535. Recent, Point Barrow, Alaska, GAS 35052.

10. Left valve, exterior. Length 68 mm, height 45.5 mm, convexity (not including spoon) 14 mm.

11. 13. Spoon, different views and illumination.

14. Left valve, interior, showing pallial line and pallial sinus.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 7

MYA FROM THE POUL CREEK AND YAKATAGA FORMATIONS (ALASKA), MIDDLE MIOCENE BEDS 

(SAKHALIN AND KODIAK ISLAND), PLEISTOCENE BEDS, YENISEY RIVER (RUSSIA), AND RECENT 

(ALASKA)
PLATE 8

FIGURES 1, 5, 6. My a truncate Linng (p. G38).

Figured specimens (X 1), after Wood, 1857, pi. 28, figs, la, Ib, If (assigned to Coralline Crag). Norwich(?)

Stage, Icenian Crag, Ramsholt, Suffolk, England.

1. Right valve, exterior. This figure reproduced by Chatwin, 1961, fig. 24, no. 13 and reassigned to Norwich Stage of the Icenian Crag.

5. Right valve, interior, showing pallial line and pallial sinus.

6. Left valve, spoon. 

2, 3. Mya truncata Linng (p. G24).

Figured specimen (X 2) USNM 644298. Early Pleistocene, "Submarine Beach," Nome, Alaska, USGS 

M-1256.

2. Broad spur bordering right valve chondrophore, view from anterior side. Edge of spur inserts along 

posterior edge of anterior ridge of left valve.

3. Same, viewed from posterior side. 

4. Mya truncata var. uddevalensis Forbes (p. G38).

Figured specimen (XI), after Wood, 1857, pi. 28, fig. Ic. Late(?) Pleistocene, Clyde Beds, Scotland. Right

valve, interior, showing pallial line and pallial sinus. 

7. Mya truncata var. uddevalensis Forbes (p. G38).

Figured specimen (X 1), USNM 635287. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1663. 

Left valve, exterior. Length 54 mm, height 48 mm, convexity (not including spoon) 16 mm. Same 

specimen as pi. 9, figs. 19, 20. 

8,11, 12. Mya truncata Linng (p. G38).

Figured specimen (XI), USNM 635288. Recent, Excursion Inlet, north side of Icy Strait, Southeastern

Alaska, USGS M-225. 

8. Spoon.

11. Left valve, exterior. Length 74 mm, height 50 mm, convexity (not including spoon) 17 mm.

12. Left valve, interior. 

9. Mya truncata Linne (p. G38).

Figured specimen (X 1), USNM 644299. Yakataga Formation, 1,500 ft. above base, Yakataga district,

Alaska, USGS 6694. Left valve, exterior. Length 53 mm, height 43 mm, double convexity 26 mm. 

10. Mya truncata var. uddevalensis Forbes (p. G38).

Figured specimen (XI), USNM 644300. Yakataga Formation, float from 3,000 to 5,000 ft above base, 

Yakataga district, Alaska, USGS 6697. Right valve, exterior. Length 56 mm, height 65 mm, double 

convexity 27 mm.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE

MYA FROM THE YAKATAGA FORMATION (ALASKA), THE ICENIAN CRAG (ENGLAND), THE CLYDE 

BEDS (SCOTLAND), PLEISTOCENE BEDS, NOME (ALASKA), AND RECENT (ALASKA)
PLATE 9

FIGURES 1, 6, 9. Mya truncata Linne (p. G38).

Figured specimen (X 1), (USNM 210970). Recent, Kodiak Island, Alaska.

1. Left valve, exterior. Length 61 mm, height 41.8 mm, convexity (not including spoon) 15 mm. 

6. Left valve, interior, showing pallial line and pallial sinus. 

9. Spoon. 

2. Mya truncata Linne (p. G38).

Figured specimen (X lK)f USNM 644301. Norwich Stage, Icenian Crag, Aldeburg, Suffolk, England,

USGS M-1672. Spoon. 

3, 5, 8, 12, 15. Mya truncata Linne (p. G38).

Figured specimens. Recent(?), 12 miles southwest of Thule, northwestern Greenland, USGS D-386. 

3. Spoon (X IK) USNM 635289. 

5. Spoon (X IK), USNM 635289. 

8. Spoon (XI), USNM 635289. 

12. Spoon (X IK), USNM 635289. 

15. Spoon (X IK), USNM 635289. 

4. Mya cf. M. pseudoarenaria Schlesch (p. G37).

Figured specimen (X IK), USNM 644302. Chillesford Beds, Icenian Crag, Chillesford, Suffolk, England,

USGS M-1671. Spoon. 

7, 10, 11. Mya truncata Linne (p. G38).

Figured specimens (X IK)- Late(?) Pliocene, near base of section, Tugidak Island, south of Kodiak

Island, Alaska, USGS M-1493. 

7. Spoon, USNM 644303.

10. Spoon, USNM 644304.

11. Spoon, USNM 644305. 

13, 16, 17, 18. Mya truncata Linne (p. G38).

Figured specimens (XI). Postglacial beds near Juneau, Alaska, USGS M-214. 

13. Spoon, USNM 644306.

16. Spoon, USNM 644307.

17. Spoon, USNM 644308.

18. Spoon, USNM 644309. 

14. Mya truncata Linne (p. G38).

Figured specimen (X 1), USNM 635290. Recent, Beardslee Island, Glacier Bay, southeastern Alaska,

USGS M-237. Spoon. 

19, 20. Mya truncata var. uddevalensis Forbes (p. G38).

Figured specimen (X 1), USNM 635287. Recent, St. Lawrence Island, northern Bering Sea, USGS 

M-1663. Same specimen as pi. 8, fig. 7.

19. Spoon.

20. Left valve, interior, showing pallial line and pallial sinus.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 9

11

13 14 15

16

MY A FROM THE ICENIAN CRAG (ENGLAND), PLIOCENE BEDS, TUGIDAK ISLAND (ALASKA), POSTGLACIAL BEDS, JUNEAU (ALASKA), AND RECENT (GREENLAND AND ALASKA)
PLATE 10

FIGURE 1. Mya priapus Tilesius (p. G40).

Engraving by Maslovsky from the original drawing by Berkhan, prepared under the direction of Georg Wilhelm 

Steller, Acad. Sci. St. Petersbourg Mem., v. 8, pi. 9, 1822. Recent, mouth of Bolshaya River, southwestern 

Kamchatka. 

2, 5, 6. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 635291. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

2. Left valve, exterior. Length 70 mm, height 48 mm, convexity (not including spoon) 17 mm.

5. Spoon.

6. Left valve, interior, showing pallial line and pallial sinus.

3. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 635292. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

Left valve, exterior, a specimen similar to the one in Berkhan's drawing, fig. 1.

4. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 635293. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662.

Spoon. 

7. Mya priapus Tilesius (p. G40).

Figured specimen (XI), USNM 635294. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

Left valve, exterior. Same specimen as pi. 11, figs. 5, 6.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 10

MYA FROM RECENT (KAMCHATKA AND ALASKA)
PLATE 11

FIGUBES 1, 2, 3. Mya priapus Tilesius (p. G12).

Figured specimen (X 1), USNM 644310. Postglacial (?) beds, mouth of Cottonwood Creek, north shore of 

Kachemak Bay, Cook Inlet, Alaska, USGS 5871. (Mya japonica, Dall, in Martin and others, 1915, p. 92; 

probably the source of Grant and Gale's, 1931, concept of M. japonica, followed by most modern Japanese 

authors).

1. Left valve, exterior. Length 69 mm, height 50 mm, convexity (not including spoon) 16 mm.

2. Spoon.

3. Left valve, interior, showing pallial line and pallial sinus. 

4. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 635295. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

5, 6. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 635294. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

Same specimen as pi. 10, fig. 7.

5. Spoon; note comb-shaped ventral edge of ligamental callus.

6. Left valve, interior, showing pallial line and pallial sinus.

7. Mya piiapus Tilesius (p. G40).

Figured specimen (X 1), USNM 644311. Postglacial (?) beds, mouth of Cottonwood Creek, north shore of 

Kachemak Bay, Cook Inlet, Alaska, USGS 5871. Spoon.

8. Mya cf. M. priapus Tilesius (p. G42).

Figured specimen (X 1), USNM 644312. Pleistocene, Wingham Island, Controller Bay, Alaska, USGS 4309.

(Mya near arenaria, Dall, in Martin, 1908, p. 46). Spoon. 

9,11. Mya pullus Sowerby (p. G42).

Figured specimen (X 2j/2), USNM 644313. Butleyan Stage, Red Crag, Neutral farm, Suffolk, England,

USGS M-1669.

9. Left valve, exterior. Length 24 mm, height 14 mm, convexity (not including spoon) 4 mm. 

11. Spoon. 

12. Mya pullus Sowerby (p. G42).

Figured specimen (X 2>0, USNM 644314. Butleyan Stage, Red Crag, Neutral farm, Suffolk, England, USGS

M-1669. Right valve, interior, incomplete, showing pallial line and pallial sinus. 

10. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 644315. Postglacial (?) beds, mouth of Cottonwood Creek, north shore of 

Kachemak Bay, Cook Inlet, Alaska, USGS 5871. Spoon, showing comblike ventral margin of ligamental 

callus. 

13, 14. Mya priapus Tilesius (p. G40).

Figured specimen (X 1), USNM 644316. Postglacial (?) beds, mouth of Cottonwood Creek, north shore of 

Kachemak Bay, Cook Inlet, Alaska, USGS 5871.

13. Left valve, exterior. Length 65.5 mm, height 41 mm, convexity (not including spoon) 12 mm.

14. Spoon. 

15. Mya priapus Tilesius (p. G24).

Figured specimen (X 2), USNM 635296. Recent, St. Lawrence Island, northern Bering Sea, USGS M-1662. 

Right-valve chondrophore, showing round solution pit at dorsal end of chondrophore.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G PLATE 11

MY A FROM THE RED CRAG (ENGLAND), PLEISTOCENE BEDS, WINGHAM ISLAND (ALASKA), POSTGLACIAL BEDS, KACHEMAK BAY (ALASKA), AND RECENT (ALASKA)