The North Pacific Miocene Record 

of Mytilus (Plicatomytilus), 

a New Subgenus of Bivalvia 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 962 

The North Pacific Miocene Record 

of Mytilus (Plicatomytilus), 

a New Subgenus of Bivalvia 

By RICHARD C. ALLISON and WARREN 0. ADDICOTT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 962 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Dir·ector 

Library of Congress Cataloging in Publication Data 

Allison, Richard C 1935-

The North Pacific Miocene record of Mytilus (Plicatomytilus), a new subgenus of Bivalvia. 

(Geological Survey professional paper; 962) 

Bibliography: p. 

Includes index. 

Supt. of Doc. no.: I 19.16:962 

1. Mytilus, Fossil. 2. Paleontology--Miocene. 3. Paleontology--North Pacific region. I. Addicott, Warren 0., joint 

author. II. Title. III. Series: United States. Geological Survey. Professional paper; 962. 

QE812.M94A38 564.11 76-608013 

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

\Vashington, D.C. 20402 

Stock Number 024-001-02764-0 
CONTENTS 

Page 

Albstract ------------------------------------------------------------------------------ 1 

Introduction -------------------------------------------------------------------------- 1 

Family Mytilidae _ _ _ _ ______ _ _ _ _ __ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ ____ _ _ _ _ _ _ __ _ _ _ _ _ _ ___ _ _ _ _ ___ __ _ _ _ _ __ 2 

Subfamily Mytilinae ____ _ _ _ _ ___ __ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ ___ _ _ _ _ _ __ _ _ _ _ ____ _ _ _ _ _ _ 2 

Genus Mytilus Linne', 1758 ---------------------------------------------------- 2 

Subgenus Plicatomytilus Alllison and 1\ddicott, n. subgen. ____________________ 2 

Mytilus (Plicatomytilus middendorffiGrewingk, 1850 -------------------- 3 

Mytilus (Plicatomytilus) gratacapi n. sp. -------------------------------- 9 

Mytilus (Plicatomytilus) n. sp. ------------------------------------------ 13 

Locality register ---------------------------------------------------------------------- 15 

References cited ---------------------------------------------------------------------- 19 

Index -------------------------------------------------------------------------------- 21 

ILLUSTRATIONS 

[Plates follow index] 

PLATE 1. Mytilus (Plicatomytilus) middendorffi. 

2. Mytilus (Plicatomytilus) gratacapi and Mytilus (Plicatomytilus) n. sp. 

3. Mytilus (Plicatomytilus) gratacapi, Mytilus (Plicatomytilus) middendorffi, Mytilus (subgenus?) n. sp., and Mytilus (Mytilus) 

condoni. 

Page 

FIGURE 1. Sketch showing comparison of muscle scars of Mytilus (Plicatomytilus) n. subgen. and Mytilus (Mytilus)__________________ 3 

2. Map showing middle Miocene distribution of Mytilus middendorffi Grewingk ------------------------------------------- 6 

3. Map showing geographic distribution of Mytilus gratacapi n. sp ------------------------------------ __________________ 11 

III 

THE NORTH PACIFIC MIOCENE RECORD OF MYTILUS 

(PLICATOMYTILUS), 

A NEW SUBGENUS OF BIVALVIA 

By RICHARD C. ALLISON 1 and WARREN 0. ADDICOTT2 

ABSTRACT 

A new subgenus of large plicate fossil mussels of the North 

Pacific, Mytilus (Plicatomytilus) n. subgen., includes three distinct 

species, Mytilus (P.) middendorffi Grewingk, 1850, Mytilus (P.) 

gratacapi n. sp., and Mytilus (P.) n. sp. This extinct subgenus ranged 

from central California to western Kamchatka during the Miocene. 

Plicatomytilus is distinguished by strong plications of the shell 

which deflect the plane of commissure and by the foot retractor muscle 

scar which is separated from the posterior byssal retractor and 

posterior adductor muscle scar. 

Mytilus middendorffi occurs in provincial middle Miocene deposits 

of (1) the Narrow Cape Formation, Kodiak Island, Alaska, (2) the 

upper part ofthe Astoria Formation, Tillamook County, Oreg., (3) an 

unnamed formation at Coos Bay, Oreg., ( 4) the lower (Miocene) part of 

Diller's (1903) Empire Formation near Cape Blanco, Oreg., (5) the 

Sobrante Sandstone near Castro Valley, Calif., (6) the Oursan 

Sandstone, Alameda County, Calif., (7) the Temblor Formation of 

Crittenden (1951), Santa Clara County, Calif., (8) the Sobrante 

Sandstone, Santa Clara County, Calif., (9) the Temblor Formation of 

Griswold Hills and the Vallecitos, San Benito County, Calif., and (10) 

the lower Temblor Formation, Patinopecten zone, Kings County, 

Calif. Mytilus gratacapi occurs on the Alaska Peninsula and at Unga 

Island, Alaska, in provincial middle(?) an'd late Miocene deposits of 

the upper part of the Unga Conglomerate Member of the Bear Lake 

Formation and upward into the overlying middle part of the Bear 

Lake Formation. 

These two species have been lumped under Mytilus middendorffi 

Grewingk, but they do not co-occur. Mytilus middendorffi ranges 

throughout the "Temblor" Stage and from the upper part of the 

Saucesian Stage to the Luisian Stage of the microfauna} sequence. 

Much, if not all, of the range zone ofMytilus gratacapi seems to be of 

late Miocene age. The standard correlation of the Narrow Cape 

Formation with the Unga Conglomerate Member ("Mytilus middendorffi zone" of MacNeil and others) therefore is probably incorrect. 

Mytilus (Plicatomytilus) n. sp. occurs in the middle and late Miocene 

Kakert and Etolon suites of the "Kavran Series" in western 

Kamchatka, U.S.S.R. Both Mytilus (P.) gratacapi and Mytilus (P.) 

n. sp. appear to have evolved from Mytilus middendorffi Grewingk. 

The heavy plicate shell of Plicatomytilus was probably well adapted 

to lite in high-energy environments in the shallow part of the inner 

sublittoral zone. Mytilus gratacapi may have been especially well 

adapted to heavy wave surge and surf conditions. 

Another distinctive mytilid, Mytilus (subgenus?) n. sp., bearing two 

folds of the shell along the posterodorsal margin, occurs in the early 

Miocene Pyramid Hill Sand Member of the Jewett Sand, Kern River 

area, Calif., as well as in the early Miocene Clallam Formation of 

1 Department of Geology and Geophysical Institute, University of Alaska, Fairbanks, 

Alaska 99701. 

2 U.S. Geological Survey, Menlo Park, Calif. 94025. 

Washington, and the early middle Miocene Kuluven suite ofwestern 

Kamchatka, U.S.S.R. This previously unrecognized taxon is not, 

however, referable to Plic.atomytilus. 

INTRODUCTION 

The existence of moderately large, heavy-shelled 

plicate mussels in the Tertiary beds ofKodiak and Unga 

Islands, Alaska, has been recognized since 1850 when 

Grewingk described Mytilus middendorffi. Following 

Grewingk (1850), many authors (Dall and Harris, 1892; 

Dall, 1896, 1904; Gratacap, 1912; Grant and Gale, 1931; 

Slodkevich [ =Slodkewitsch], 1938; Hall, 1958; Burk, 

1965; Addicott, 1967; and MacNeil, 1967) have repeated 

Grewingk's original records, or they themselves have 

assigned these plicate mytilids from Kodiak and many 

localities on the Alaska Peninsula and Unga to a single 

species, M. middendorffi. MacNeil, Wolfe, Miller, and 

Hopkins (1961) have indicated the correlation of 

Miocene strata on Kodiak Island, Unga Island, and the 

Alaska Peninsula that they assign to their "Mytilus 

middendorffi zone." 

Recently, both of us have realized independently that 

the plicate mytilids that occur on the Alaska Peninsula 

and U nga Island in the Bear Lake Formation are in fact 

a distinctly different new species, and that this new 

species and Mytilus middendorffi belong to a new 

subgenus of Mytilus Linne. This paper therefore: 

(1) describes the new subgenus Plicatomytilus, (2) describes the new species Mytilus (Plicatomytilus) 

gratacapi from the Bear Lake Formation, (3) reviews 

the stratigraphic and paleozoogeographic distributions 

of M. (P.) middendorffi Grewingk and M. (P.) gratacapi n. sp., and (4) reviews the reported occurrences of M. 

cf. middendorffi [ =Mytilus (Plicatomytilus) n. sp. of this 

paper] in Kamchatka. 

Addicott is primarily responsible for the sections on 

chronologie and zoogeographic significance, and Allison 

is primarily responsible for the systematic sections of 

the paper. All the fossils, those illustrated and the type 

specimens, have been placed on deposit in the U.S. 

National Museum. The fossils were photographed by 

Kenji Sakamoto. We wish to thank Ellen J. Moore and 

1 
2 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

J. Wyatt Durham for their critical reviews of the 

manuscript. 

Phylum Mollusca 

Class Bivalvia 

Subclass Pteriomorpha 

Order Mytiloida 

Super family Mytilacea 

Family Mytilidae 

Subfamily Mytilinae 

Genus Mytilus Linne, 1758 

Mytilus Linne, 1758, Systema Naturae, ed. 10, p. 704. 

Type.-By subsequent designation (Gray, 1847), Mytilus edulis 

Linne, 1758. 

Subgenus Plicatomytilus n. subgen. 

Type.-Mytilus middendorffi Grewingk, 1850. 

Description.-Shell moderate to large, heavy, 

mytiliform; beaks terminal; lunule grooved and sometimes incurved, forms two large teeth and several 

smaller ones; margins smooth; shell surface smooth, 

marked only by concentric growth lines and irregular 

undulations of growth; shell strongly plicate toward 

posterior and posterior ventral margin with two or three 

major plicae that strongly fold the plane of commissure; 

posterior dorsal area with or without irregular 

seminodulose divaricate branches of main posterior 

dorsal plica, little affecting plane of commissure; 

margin often alate at change in slope between anterior 

and posterior dorsal margins; resilial ridge compact; 

anterior adductor long, thin, and deeply sunken into 

shell, primarily on anterior ventral margin; posterior 

adductor and posterior byssal retractor continuous, may 

be poorly defined on shell; posterior byssal retractor 

usually narrow, continues to thin line near mid-dorsal 

break in margin slope where it occasionally is more 

deeply incised; foot retractor not continuous with 

posterior byssal retractor but placed inside pallial line 

and posterior byssal retractor at or near change in slope 

of dorsal margin; foot retractor large and elongate, but 

not usually deeply impressed into shell (fig. lA); 

anterior byssal retractor small, divided into two or 

possibly three well-separated circular points of attachment on dorsal slope of umbo well above resilial ridge. 

Discussion.-Plicatomytilus n. subgen. differs from 

all other mytilid genera and subgenera in possessing 

strong plications that clearly deflect the plane of 

commissure and in possessing a distinct foot retractor 

scar separated from the posterior byssal retractor and 

posterior adductor muscle scar (fig. lA). The anterior 

byssal retractor is divided into two small circular scars, 

and the anterior adductor scar is narrow and deep. The 

shell margins of Plicatomytilus are noncrenulate, and 

the resilial ridge lacks pits (compact condition). 

Grant a;d Gale (1931, p. 246) applied the subgeneric 

name Mytiloconcha Conrad, 1862, to several west coast 

species including Mytilus middendorffi because of their 

~~peculiar heavy terminal hinge." Soot-Ryen (1955, p. 

29) showed, however, that Mytiloconcha Conrad, 1862, 

is a junior subjective synonym of Perna Retzius, 1788. 

Perna Retzius differs from Plicatomytilus in possessing 

a pitted resilial ridge, in lacking an anterior adductor 

muscle, and in having a single elongate anterior byssal 

retractor scar. Perna does, however, have the foot 

retractor muscle placed anteriorly, separate from the 

posterior byssal retractor as in Plicatomytilus. 

Mytilus s.s. (fig. 1B) differs from Plicatomytilus in 

possessing a pitted resilial ridge, in having an elongate 

anterior byssal retractor muscle scar or scars, and in 

having the posterior retractor muscles coalescent. The 

anterior adductor of Plicatomytilus is generally similar 

to that of the type species of Mytilus, M. edulis Linne, 

1758, but may be longer and narrower. 

Crenomytilus Soot-Ryen, 1955, differs from 

Plicatomytilus in possessing crenulate shell margins, in 

having an obliquely striated shell surface, in having a 

larger, more circular anterior adductor muscle scar, in 

lacking the double anterior byssal retractor scars of 

Plicatomytilus, and in having the posterior retractor 

muscles coalescent without a separate foot retractor 

scar. 

Semimytilus Soot-Ryen, 1955, differs from 

Plicatomytilus in being edentate, in having a small, 

circular anterior adductor muscle scar, and in lacking 

the separated foot retractor muscle scar of 

Plicatomytilus. However, Semimytilus does possess a 

split anterior byssal retractor muscle scar, although, 

unlike Plicatomytilus, both halves of the scar are 

elongate. 

Choromytilus Soot-Ryen, 1952, differs from 

Plicatomytilus in having the posterior byssal and foot 

retractor muscle scars continuous, although sometimes 

only narrowly so, and in having the anterior byssal 

retractor entire and not split as in Plicatomytilus. The 

anterior byssal retractor of C horomytilus is stronger 

and more posteriorly placed than in Plicatomytilus. 

C horomytilus possesses only one central tooth formed 

from the lunule, has ~~punctae" on the inside ventral half 

of the shell, and lacks the anterior adductor in large 

adult specimens although It is present in the young. The 

resilial ridge is compact as in Plicatomytilus. 

Ischadium Jukes-Brown, 1905, possesses a radial 

surface sculpture with crenulated margins, lacks an 

anterior adductor, has the posterior foot and byssal 

retractors broadly united with the posterior adductor, 

and has a small, single muscle scar of the anterior 

byssal retractor. 
GENUS MYTILUS LINNE, 1758 3 

Mytilus (Plicatomytilus) r-----------------Beak 

Anterior byssal retractor Elongate anterior byssal retractor 

Anterior adductor 

Compact resilial ridge Anterior adductor 

Pitted resilial ridge 

Posterior byssal retractor 

Pallial line 

·Posterior adductor 

A FIGURE I.-Comparison of muscle scars of Mytilus (Plicatomytilus) n. 

subgen. andMytilus (My til us). A, Composite sketch of right valve of 

Mytilu (Plicatomytilus ). B, Sketch of right valve of Mytilus 

(Mytilus) edulis Linne, 1758. Four small paired scars, all beneath 

margin of shell and not directly visible in this view, mark earlier 

Aulacomya March, 1853, usually possesses radial 

surface sculpture, has only one tooth formed from the 

fold of the lunule, has the foot retractor coalescent with 

the posterior adductor, has an elongate single muscle 

scar of the anterior byssal retractor, and has the 

anterior adductor obsolete in larger individuals. 

Hormomya Morch, 1853, differs conspicuously from 

Plicatomytilus in having coarse radial sculpture dorsally and fine radial sculpture with unilaterally 

bifurcating ribs ventrally, in having crenulated margins, in having the foot retractor coalescent with the 

posterior byssal retractor and posterior adductor, and in 

having a single strong umbonal keel. Hormomya does, 

however, possess four or five teeth, of which the anterior 

are stronger, somewhat like Plicatomytilus. 

Three North Pacific Miocene species, M. middendorffi, M. gratacapi n. sp., and a new species from the 

Kakert and Etolon suites of the ((Kavran Series" of 

western Kamchatka are referable to Plicatomytilus. 

The subgenus apparently ranged from central California northward to the Alaska Peninsula, Kodiak Island, 

and westward to Kamchatka. 

Geologic range .-Middle to late Miocene. 

byssal retractor attachment and extend anteriorly to tip of beak. 

Specimen from Whale Island (Univ. Alaska loc. A-653), Katalla 

area, Alaska. Recent. University of Alaska figured specimen UA 

2433. Variation in details of these scars is readily apparent when 

several individuals are examined. 

Mytilus (Plicatomytilus) middendorffi Grewingk, 1850 

Plate 1, figures 1-10; plate 3, figures 2, 4, 6 

1850. Mytilus middendorffi Grewingk, Verhandlungen der Russischkaiserlichen Mineralogischen Gesselschaft zu St. 

Petersburg, Jahrgang 1848 and 1849, no. 6, p.167, 360-361, 

pl. 7, figs. 3a-c; reprinted 1850, p. 94, 287-288, pl. 7, figs. 

3a-c; notM. middendorffi, Unga, p. 171 and 361; reprinted 

1850, p. 98 and 288 [ =M. gratacapi n. sp.]. 

1871. Modiola (Mytilus) Dufrenoyi d'Orbigny. Eichwald, E., Geog.-

palaeon. bemerk. uber die Halbinsel Mangischlak und die 

Aleutischen Inseln, p. 128, St. Peterburg [incorrectly 

synonymizes M. middendorffi with a Cretaceous species 

from France]; Kodiak; not Unga [ =M. gratacapi n. sp.]; not 

M. dufrenoyi d'Orbigny, France. 

1892. Mytilus middendorffi Grewingk. Dall, W. H., and Harris, 

G. D., Correlation Papers, Neogene: U.S. Geol. Survey Bull. 

84, p. 253, Kodiak; not M. middendorffi, Unga [ =M. 

gratacapi n. sp.]. 

1896. Mytilus middendorffi Grewingk. Dall, W. H., U.S. Geol. 

Survey 17th Ann. Rept., Pt. I, p. 844, Kodiak; not M. 

middendorffi, Unga [=M. gratacapi n. sp.]. 

1904. Mytilus middendorffi Grewingk. Dall, W. H., Neozoic invertebrate fossils, a report on collections made by the 

expedition, in Harriman Alaska Expedition, v. 4 (Geology 

and Paleontology), p. 113, Kodiak; not M. middendorffi, 

Unga [=M. gratacapi n. sp.], New York, Doubleday, Page 

and Co. (Reprinted by Smithsonian Institution, 1910). 
4 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

1912. Mytilus middendorffi Grewingk. Gratacap, L. P., Am. Mus. 

Nat. History Bull., v. 31, art. VI, p. 69-70, pl. VII, figs. 4-6, 

Kodiak; not M. middendorffi, Unga, pl. VII, figs. 1-3 [ =M. 

gratacapi n. sp.]. 

1913. Mytilus middendorffi Grewingk. Arnold, Ralph, and Hannibal, Harold, Am. Philos. Soc. Proc., v. 52, p. 590. 

1925. Mytilus middendorffi Gmelin. Hertlein, L. G., and Crickmay, 

C. H., Am. Philos. Soc. Proc., v. 66, no. 2, p. 266, 267. 

1931. Mytilus middendorffi Grewingk. Grant, U.S., IV, and Gale, 

H. R., San Diego Soc. Nat. History Mem., v. 1, p. 247, 

Kodiak; not M. middendorffi, Unga [ =M. gratacapi n. sp.]. 

1934. NotMytilus cf. middendorffi Grewingk. Slodkevich, V. S., On 

the stratigraphy of the Tertiary deposits of the western 

coast of Kamchatka: Academie des Sciences de L'Union des 

Republiques Sovietiques Socialistes (Akademiya N auk), 

C. R. (Dokl.), T. 3, no. 1, p. 60 and 62 [ =M. CPlicatomytilus) n. 

sp. of this report]. 

1936. NotMytilus cf. middendorffi Grewingk. Slodkevich, V. S., The 

stratigraphy and fauna of the Tertiary deposits of the 

western coast of Kamchatka: Trudy neftyanogo geologo 

razvedochnogo instituta, Seriya A, Vypusk 79, p. 125-126, 

pl. XV, figs. 5, 5a, Leningrad, Moscow [ =Mytilus 

(Plicatomytilus) n. sp. of this report]. 

1937. Mytilus middendorffi Grewingk. Woodring in Capps, S. R., 

U.S. Geol. Survey Bull. 880-C, p. 155. 

1938. Mytilus middendorffi Grewingk. Slodkevich, V. S., Paleontology of U.S.S.R., v. 10, pt. 3, fasc. 19, Tertiary Pelecypoda 

from the Far East, Pt. II, p. 231, pl. L, figs. 2, 2a, 

re-illustration ofGrewingk's figures ofM. middendorffi s.s.; 

Kodiak; not M. middendorffi, Unga, p. 231 [ =M. gratacapi 

n. sp. 

1938. Not Mytilus cf. middendorffi Grewingk. Slodkevich, V. S., 

Paleontology of U.S.S.R., v. 10, pt. 3, fasc. 18 and 19, 

Tertiary Pelecypoda from the Far East; fasc. 18, p. 237, 238; 

fasc. 19, p. 119, 231, pl. L, figs. 3, 3a [=Mytilus 

(Plicatomytilus) n. sp. of this report]. 

1943. Mytilus midendorfi Grewingk. Gilbert, C. M., Am. Assoc. 

Petroleum Geologists Bull., v. 27 (5), p. 645. 

1946. Mytilus middendorffi Grewingk. Stewart, Ralph, U.S. Geol. 

Survey Prof. Paper 205-C, p. 100, 102. 

1946. Mytilus cf. M. middendorffi Grewingk. Stewart, Ralph, U.S. 

Geol. Survey Prof. Paper 205-C, table 2, loc. 14393;? loc. 

14385. 

1953. Mytilus middendorffi Grewingk. Durham, J. W., Geol. Soc. 

America Bull., v. 64, no. 12, pt. 2, p. 1504-1505. 

1958. Mytilus middendorffi Grewingk. Hall, C. A., California Univ. 

Pubs. Geol. Sci., v. 34, no. 1, p. 49, 52, pl. 5, fig. 6, Kodiak and 

California; notM. middendorffi, Unga, p. 52 [ =M. gratacapi 

n. sp.]. 

1963. Mytilus cf. M. middendorffi Grewingk. Moore, E. J., U.S. Geol. 

Survey Prof. Paper 419, p. 62 [MacNeil's report from the 

"Oligocene of Alaska" seems invalid]. 

1963. Not Modiolus cf. middendorffi Grewingk. Il'ina, A. P., 

Mollusks of the Neogene of Kamchatka, pl. XXXVI, fig. 2 

(same individual illustrated by Slodkevich, 1936, pl. XV, 

figs. 5, 5a and 1938, pl. L, figs. 3, 3a) [ =M. CPlicatomytilus) n. 

sp. of this report]. 

?1965. Mytilus middendorffi Grewingk. Addicott, W. 0., U.S. Geol. 

Survey Prof. Paper 525-C, in part, p. C108 [field identification] not p. C104 [ =Mytilus (subgenus?) n. sp.]. 

1965. Mytilus middendorffi Grewingk. MacNeil, F. S., U.S. Geol. 

Survey Prof. Paper 483-G, p. G36. 

1965. Mytilus middendorffi Grewingk. Burk, C. A., Geol. Soc. 

America Mem. 99, p. 93 and 104 (Kodiak Island); not p. 91, 

92, 93, 116, 213, 214, 215, 228 (Alaska Peninsula) [=M. 

gratacapi n. sp.]. 

1967. Mytilus middendorffi Grewingk. Addicott, W. 0., U.S. Geol. 

Survey Prof. Paper 593-D, p. D7, in part, not Kern River 

area, California [ =Mytilus (subgenus?) n. sp.]; not Alaska 

Peninsula [ =M. gratacapi n. sp.]. 

1967. Not Mytilus middendorffi Grewingk. MacNeil, F. S., U.S. 

Geol. Survey Prof. Paper 553, p. 13 [ =M. gratacapi n. sp.]. 

?1969.Mytilus cf. middendorffi Grewingk. Pronina, I. G., Middle 

Miocene mollusks from deposits in the Kronotskiy region of 

the eastern shoreline of Kamchatka, p. 254, pl. III, fig. 3. 

1972. Mytilus middendorffi Grewingk. Addicott, W. 0., Am. Assoc. 

Petroleum Geologists, Pacific Sec., 1972 Guidebook, Geology and oilfields, west side central San Joaquin Valley 

[Calif.], p. 67. 

1972. Not Mytilus middendorffi Grewingk. Gladenkov, Y. B., 

Petrov, 0. M., and Sinel'nikova, V. N., Pliocene-Pleistocene 

boundary in the northwest Pacific in International Colloquium on the boundary between Neogene and Quaternary, coll. papers III, Moscow, p. 58. [Incorrect synonymy of 

Mytilus middendorffi Grewingk with Mytilus tichanovitchi 

Makiyama, 1934.] 

1973. Mytilus middendorffi Grewingk. Allison, R. C., and Addicott, 

W. 0., Geol. Soc. America, Abstracts with programs, v. 5, no. 

1, p. 2-3. 

1974. Mytilus middendorffi Grewingk. Addicott, W. 0., Veliger, v. 

16, no. 4, p. 354-358, figs. 1 and 2. 

Mytilus middendorffi is characterized by the broad 

plications of the shell that strongly deflect the plane of 

commissure. The sulcus of one valve meets the fold of 

the opposite valve producing two or three undulatory 

deflections of the plane of commissure posteriorly. The 

species may reach a fairly large size (largest specimen 

at hand is about 102 mm long) and may become strongly 

inflated (one articulated individua~ measuring about 95 

mm long has a height of about 51 mm). The shell is 

always elongate, usually with a gentle arch in the 

longitudinal profile in contrast to M. gratacapi n. sp. 

which is usually strongly contorted along the longitudinal axis. The dorsal margin is frequently alate at the 

break in slope between the anterior and posterior dorsal 

margins. The shell is typically mytiliform but readily 

distinguished by the several strong plications. With the 

exception of M. gratacapi n. sp. and the western 

Kamchatka Kakert and Etolon suite taxon, we know of 

no other North Pacific fossil mytilid with which M. 

middendorffi may be easily confused. 

As might be expected, various shells of the species 

display individual variation. Most of the shells are 

moderately inflated, as is typical in Mytilus, although a 

few are greatly inflated. A few specimens remain 

compressed even in the large adult stage. The amount of 

alation along the dorsal margin is variable, but it does 

not appear to be directly related to the size of the 

individual shell. A few individuals have very modest 

alar development, many have a moderate alation at the 

break in slope, and about an equal number have rather 

pronounced alation. The shape of the dorsal margin of 
MYTILUS <PLICATOMYTILUS) MIDDENDORFFI GREWINGK, 1850 5 

the shell above the alate flange varies considerably from 

vertical or even overhanging to gently merging with the 

dorsal alation. This variation seems to be governed both 

by the degree of inflation of the shell and the amount of 

alation. The apical angle of the shell varies to a 

moderate extent; it becomes larger with more pronounced alation and more pronounced arching of the 

anterior-posterior axis of the shell. In general, this 

anterior-posterior arch of the shell is fairly constant, as 

defined by the umbonal ridge along the dorsal edge of 

the shell; the latter culminates in the main posterior 

dorsal flexure of the shell, which usually terminates at 

the posteriormost point on the shell margin. Some 

individuals, however, display a sharper flexure in this 

umbonal ridge above the dorsal alation than do others. 

The ventral margin may be either perfectly straight or 

very gently concave but it is never prominently arched. 

Perhaps the greatest variation is in the rib or fold 

development. Two main ribs or folds appear when the 

shell has reached 35 to 45 mm in length; the 

anterior-ventral is the more prominent of the two. 

Several individuals, however, possess a weaker third 

fold placed still more anteroventrally. This anterior fold 

is faintly visible on many individuals; rarely it becomes 

strengthened to produce a three-ribbed variant (pl. 1, 

figs. 3 and 9) in which it weakly deflects the plane of 

commissure. Three-ribbed variants occur in the 

Miocene of California at USGS localities 5765 and 

M3614, but they are associated with other typical 

individuals and apparently are nothing more than 

individual variants of M. middendorffi. 

The strength of the main folds and sinuses is also 

variable and may affect the amount of deflection in the 

plane of commissure, but the plications never approach 

obsolescence. The main anteroventral fold is normally 

strongly flexed ventrally as it approaches the posterior 

end of the shell. The ventral curvature of this rib, which 

is variable, seems to be related to the degree of 

anterior-posterior arching of the shell. The main 

anterior-ventral rib never bends through more than 

about 60 degrees of rotation, whereas the same rib may 

be bent through a 90-degree turn in Mytilus gratacapi 

n. sp. 

In addition to the main folds, smaller irregular folds 

or ribs that branch off of the main dorsal fold may occur 

along the posterior dorsal area. This posterior dorsal 

area particularly displays marked variation. Most 

well-preserved individuals have two or three poorly 

defined irregular nodulose branches in this area. The 

posteriormost of these dorsal secondary ribs, usually the 

most clearly defined, branches off in a dorsal direction 

near the terminus of the main rib. These secondary 

dorsal ribs do not seriously deflect the plane of 

commissure, although they may cause mild undulations 

of it. A few individuals have only one secondary rib 

branching dorsally near the terminus of the main dorsal 

rib. On several individuals the main dorsal rib is 

crowded against the dorsal margin, and the secondary 

terminal rib is directed ventrally off of it into the sinus 

between the two main folds. A few individuals have 

little or no development of secondary ribs along the 

posterior dorsal margin. 

Figured specimens.-USNM 647057, 647058, 

647059, 647060, 647061, 647062, 647063, 647064, 

64 7065, 64 7076. 

Discussion.-Mytilus middendorffi was described by 

Grewingk in 1850 from collections of Wosnessensky, 

Fischer, and Kupreanof from the Alaska Peninsula, 

Kodiak Island, and the Aleutian Islands. Grewingk 

(1850, p. 167, 171, 361; reprinted 1850, p. 94, 98, 288) 

reported M. middendorffi from Kodiak Island (Igatskoj 

Bay= Ugak Bay, and Tonky Cape= Narrow Cape) and 

Unga Island at ((Sacharowschen" Bay ( = Zachary Bay). 

Unfortunately, Grewingk did not designate the type 

locality of the species, and his type specimens have not 

been found (see MacNeil, 1965, p. G12). Were it not for 

the fact that Grewingk's original description and 

illustrations of M. middendorffi are unmistakably 

clear, there might be some difficulty in recognition ofhis 

species, for we consider the UngaMytilus to be a distinct 

species, though closely related to the one found at 

Narrow Cape. Grewingk's illustrations (1850, pl. 7, figs. 

3a-c) leave no doubt that Kodiak Island, probably at 

Narrow Cape, is the type locality and that M. 

middendorffi properly applies to the abundant and 

characteristic Mytilus found there in the Miocene 

Narrow Cape Formation. The species from the Unga 

Conglomerate Member of the Bear Lake Formation, 

Mytilus gratacapi n. sp., we have named in honor ofL. P. 

Gratacap who first illustrated it in his 1912 paper ((An 

unusual specimen of Mytilus middendorffi Grewingk, 

from Alaska" (hills above Cape Seniavin). The morphologic differences between M. middendorffi and M. 

gratacapi are discussed under M. gratacapi. 

The first valid report of M. middendorffi outside the 

type region in Alaska was by Arnold and Hannibal 

(1913, p. 590) from localities in the basal ( = middle 

Miocene) sandstone of the Empire Formation near Cape 

Blanco, Oreg. Since 1913 a number of reports have been 

published that extend the known geographic range of 

M. middendorffi from central California to Alaska and 

doubtfully to Kamchatka (fig. 2). However, the species 

remains little known, perhaps owing to the paucity of 

illustrations of it in easily accessible literature. 

Grewingk's original figures were redrawn by Gratacap 

(1912); he also included three illustrations of the 

long -confused species here named M. gratacapi from the 

Unga Conglomerate Member. Slodkevich (1938) repro-
6 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

30° 

PACIFIC 

EXPLANATION 

• Occurrence 

(Material examined by authors) 

Q Mytilus cf. M. middendorffi 

• 

0 

Doubtful occurrence 

(Field idelltification) 

400 800 

..... ·· ·•,'IQ 'o•o' 

;.p 

OCEAN 

1200 1600 MILES 

0 400 800 1200 1600 2000 2400 KILOMETRES 

FIGURE 2.-Middle Miocene distribution of Mytilus middendorffi 

Grewingk. 1, Kodiak Island, Alaska. 2, Svenson quadrangle, 

Clatsop County, Oreg. 3, Cannon Beach quadrangle, Tillamook 

County, Oreg. 4, Coos Bay, Oreg. 5, Cape Blanco, Oreg. 6, Eden 

Canyon, near Castro Valley, Calif. 7, Sunol Valley Regional Park, 

Alameda County, Calif. 8, Milpitas-Calaveras Road, Santa Clara 

County, Calif. 9, Henry W. Coe State Park, Santa Clara County, 

duced Grewingk's original figures and illustrated 

another taxon now referable to Plicatomytilus that we 

consider to be a new species from the ~~Kavran Suite" of 

the west coast of Kamchatka (Slodkevich, 1936, 1938). 

More recently, Hall (1958) illustrated individuals ofM. 

middendorffi from California, and ll'ina (1963) reproduced Slodkevich's 1936 and 1938 illustration of the 

new species from western Kamchatka. Pronina (1969) 

illustrated a poorly preserved internal mold from the 

~~Ratitin suite, middle Miocene" of eastern Kamchatka 

that may be referable to Plicatomytilus but that cannot 

be adequately compared to M. middendorffi. 

Occurrence.-Narrow Cape Formation, Kodiak Island, Alaska (USGS Cenozoic loc. 13372, D227, M1735; 

University of Alaska loc. A-180, A-181, A-183, A-204, 

A-255, A-256, A-257, A-258, A-260, A-264, A-266, 

A-268, A-269, A-271, A-273, A-275, A-276, A-278; 

Calif. 10, Griswold Hills and the Vallecitos, San Benito County, 

Calif. 11, Reef Ridge, Kings County, Calif. 12, Tejon Hills, Kern 

County, Calif. 13, Kronotskiy area, eastern Kamchatka, U.S.S.R. 

(Pronina, 1969). Records of a new Plicatomytilus species from 

probable Miocene rocks on west coast of Kamchatka (Slodkevich, 

1934, 1936, 1938; Il'ina, 1963) are not shown. 

Stanford University loc. 43952, 43953); Astoria Formation of middle Miocene age, Clatsop County, Oreg. 

(USGS Cenozoic loc. M6382); Astoria Formation of 

middle Miocene age, Tillamook County, Oreg. (USGS 

Cenozoic loc. M5807); unnamed formation of middle 

Miocene age, Coos Bay, Oreg. (USGS Cenozoic loc. 

18284); lower part of Diller's (1903) Empire Formation 

near Cape Blanco, Oreg. (USGS Cenozoic loc. 3334, 

7901, M2142, M3637, M4126, M4129, M4130, M4132, 

M4135, M4136, M4687, M4690, M5737; University of 

Oregon loc. F-2011; University of California, Berkeley 

loc. A8711; Stanford University loc. NP23, NP26; 

California Academy of Sciences loc. CAS 17, CAS 19, 

CAS 22); Sobrante Sandstone, near Castro Valley, 

Calif. (University of California, Berkeley loc. B4162); 

Oursan Sandstone, Sunol Valley Regional Park, 

Alameda County, Calif. (Stanford University loc. 3248); 

Temblor Formation of Crittenden (1951), Milpitas-
MYTILUS (PLICATOMYTILUSl MIDDENDORFFI GREWINGK, 1850 7 

Calaveras Road, Santa Clara County, Calif. (Stanford 

University loc. 2982); Sobrante Sandstone, Henry W. 

Coe State Park, Santa Clara County, Calif. (USGS 

Cenozoic loc. M4756, M5162); Temblor Formation, 

Griswold Hills, San Benito County, Calif. (USGS 

Cenozoic loc. 5765, 5766, M3614; Stanford University 

loc. 49046); Temblor Formation, Vallecitos, San Benito 

County, Calif. (Stanford University uncatalogued collection); lower part of the Temblor Formation, Reef 

Ridge, Kings County, Calif. (USGS Cenozoic loc. 14385, 

14393). 

Range.-Middle Miocene. 

Doubtful occurrences.-A record of Mytilus middendorffi from middle Miocene strata exposed in the Tejon 

Hills area along the southeast margin of the San 

Joaquin basin, Calif. (Addicott, 1965, p. C108), was 

based upon a field identification that is considered 

doubtful. If this record is verified, this occurrence of M. 

middendorffi will be the most southerly along the 

Pacific coast. 

Incorrect records of Mytilus middendorffi.-Records 

of Mytilus middendorffi from the Alaska Peninsula and 

Unga Island, Alaska (Grewingk, 1850; Dall, 1896, 1904; 

Gratacap, 1912; Grant and Gale, 1931; Slodkevich, 

1938; Hall, 1958; MacNeil and others, 1961; Moore, 

1963, p. 62; Burk, 1965; Addicott, 1967; MacNeil, 1967) 

are of the strongly arched, plicate species herein named 

Mytilus gratacapi n. sp. Many of these are secondary 

citations of Grewingk (1850) and Dall (1896, 1904). 

Dall (1904, p. 113) commented that Mytilus middendorffi ((is represented in the Pliocene of Oregon 

[southwestern Washington] by Mytilus condoni Dall 

which is somewhat similarly sculptured." The late 

Tertiary species from Washington was described by W. 

H. Dall in a letter to the editor of ((Nautilus" printed 

under the title ((Concho logical Notes from Oregon" 

(Dall, 1890). The type locality of M. condoni was given 

as ('marine Pliocene*** at [Shoalwater] Willapa Bay, 

Wash.," but the species was neither adequately described nor illustrated. Addicott (197 4) collected a 

Mytilus from the north shore of Willapa Bay (USGS 

Cenozoic loc. M5219) that fits Dall's original description, and it is presumed to be topotypic material (pl. 3, 

fig. 10). We consider this Mytilus to be conspecific with 

the later named species M. highoohiae Mandra 1949, 

from the Pliocene of Humboldt County, Calif. It is not 

clear whether Dall (1904) intended to include M. 

condoni as a synonym of M. middendorffi or merely to 

indicate supraspecific relationship. Dall's meaning is 

not critical, however, because M. condoni is a slender 

species characterized by fine divaricate ribbing (pl. 3, 

fig. 10), and it is both specifically and subgenerically 

distinct from M. middendorffi. 

Mytilus ficus Dall (1909, p. 113, pl. 9, figs. 1, 4), from 

the Empire Formation at Coos Bay, Oreg., has been 

treated as a possible synonym ofM. condoni Dall (Grant 

and Gale, 1931). The Empire species, however, does not 

possess radial or bifurcating sculpture and is therefore 

clearly separable from both M. condoni and M. 

middendorffi. 

A rather small (length 68 mm), plicate Mytilus (pl. 3, 

fig. 9) from the early Miocene Jewett Sand of the Kern 

River area, Calif., has been incorrectly identified as M. 

middendorffi (Addicott, 1965, p. C104; 1967, p. D7). This 

species has a pronounced dorsal alation and strongly 

inflated valves; its strong umbonal ridge extends from 

the beak to the posterior extremity, and a distinctive 

parallel ridge of secondary strength is located at the 

base of the dorsal alation. This Jewett Sand taxon 

differs from M. middendorffi in that the folds are not 

staggered on opposing valves. Consequently, the plane 

of commissure remains perfectly flat without any gape 

although the marginal outline of the shell protrudes 

slightly where the folds of the two valves meet (pl. 3, 

fig. 9). 

We found that well-preserved specimens of this 

Jewett Sand species also occur in the lower Miocene 

Clallam Formation (Addicott, 1975) of the northern 

Olympic Peninsula, Wash. (USGS Cenozoic loc. M4051, 

M4679; Stanford University loc. NP87, 89, 160; 

Portland State University loc. PSU-A0008). The same 

species has also been illustrated by Il'ina (1963, pl. 10, 

figs. 1 and 6), under the name ((Mytilus ochotensis 

Slodkewitsch." Il'ina's (1963) specimen came from beds 

of the Kuluven suite Czone of Thyasira disjuncta var. 

ochotica") exposed along the seashore 4.35 km south of 

the mouth ofthe Polovinka River, western Kamchatka. 

Through the courtesy of Academician V. V. Menner and 

Dr. V. N. Sinel'nikova, both of the Geological Institute 

·in Moscow, we have recently received a well-preserved 

specimen of this same taxon from the Kuluven suite of 

the Shainaga River area, western Kamchatka. We 

consider the Kamchatkan specimens to be conspecific 

with the specimens from the Clallam Formation and the 

Jewett Sand. This distinctive mytilid, Mytilus (subgenus?) n. sp., cannot, however, be assigned to Mytilus 

ochotensis Slodkevich, 1936, because the latter species 

lacks the characteristic pair of ribs or plications of the 

dorsal part of the shell. G ladenkov ( 197 4) considered the 

Kuluven suite to be of early middle Miocene age. 

Dr. Saburo Kanno of Tokyo University of Education 

has recently sent us specimens of Mytilus tichanovitchi, 

Makiyama, 1934 (Makiyama, 1934, p. 134-135, pl. IV, 

figs. 11 and 12; Uozumi, 1966, p. 129--130, pl. 9, figs. 2-4, 

8), a similar species from the lower part of the Ashai 

Formation of Hokkaido Island, Japan, and Neogene 

strata in Sakhalin. This Japanese species, however, also 

lacks the paired ribs or plications of the dorsal area of 
8 NORTH PACIFIC MIOCENE RECORD OF MYTILUS CPLICATOMYTILUS), A NEW SUBGENUS 

the shell that characterize the species from the Jewett 

Sand-Clallam Formation-Kuluven suite. 

We conclude that this distinctive taxon from the 

Jewett Sand-Clallam Formation-Kuluven suite is as 

yet undescribed and that it is not referable to 

Plicatomytilus. 

Reports of Mytilus middendorffi in Kamchatka.-

Although Plicatomytilus is clearly recognizable in the 

deposits of the Kakert and Etolon suites of the ~~Kavran 

Series" ofwestern Kamchatka, we are not aware of any 

Asian material that can be confidently assigned to 

Mytilus middendorffi sensu stricto. Slodkevich (1934, 

1936, 1938) and Il'ina (1963) discussed and (or) 

illustrated this ~~Kavran Series" taxon that we consider 

to be specifically distinct from M. middendorffi. Further 

discussion of this taxon is included under Mytilus 

(Plicatomytilus) n. sp. of this paper. 

Pronina (1969) reported rrMytilus cf. middendorffi" 

from the ~~Ratitin suite, middle Miocene" of the 

Kronotskiy area, eastern Kamchatka. She also summarized the distribution of Mytilus middendorffi as: 

Alaska (Miocene), Oregon (Pliocene) [presumably the 

middle Miocene occurrence in the lower part of the 

Empire Formation near Cape Blanco], western coast of 

Kamchatka, lower part of the Kavran Series (upper 

Miocene) [our Mytilus (Plicatomytilus) n. sp.]. Unfortunately, Pronina's (1969) illustration is of a poorly 

preserved internal mold that is inadequate for species 

determination. 

Gladenkov, Petrov, and Sinel'nikova (1972) considered Mytilus tichanovitchi Makiyama, 1934, from the 

lower part of the Ashai Formation of Japan and the 

Neogene of Sakhalin and Kamchatka, to be synonymous with Mytilus middendorffi Grewingk. We believe 

M. tichanovitchi to be distinct, however, because this 

Japanese species lacks any convolution of the plane of 

commissure in association with folds of the shell (see 

Uozumi, 1966). 

Mytilus (Plicatomyt'ilus) therefore does occur in 

Kamchatka in rocks of probable middle to late Miocene 

age [see discussion of age of the ~~Kavran Series" taxon 

under Mytilus (Plicatomytilus) n. sp. of this report], but 

the presence of Mytilus middendorffi Grewingk there is 

yet to be demonstrated. 

Age and correlation.-The biozone of Mytilus middendorffi is an important index to the provincial middle 

Miocene of the eastern North Pacific. Many of the 

occurrences of this species have been recognized only 

during the past 10-15 years, and a few are recorded here 

for the first time. Occurrences of this species in the 

California Coast Ranges and southwestern Oregon can 

be confidently assigned to the middle Miocene 

~~Temblor" Stage of Weaver and others (1944) and, in 

some places, can be correlated with the provincial 

benthonic foraminiferal chronology. The high-latitude 

occurrence in the Narrow Cape Formation on the 

northeast coast of Kodiak Island, Alaska, is also of 

provincial middle Miocene age although correlation of 

the associated fauna with sequences in the conterminous United States is difficult. 

Occurrences of Mytilus middendorffi in the Diablo 

Range of central California indicate that it ranges 

throughout the ~~Temblor" Stage and that its range 

includes the upper part of the Saucesian Stage as well as 

the Relizian and Luisian Stages of the microfauna!, 

sequence ofKleinpell (1938). The earliest occurrence of 

M. middendorffi is in the lower part of the ~~Temblor" 

Stage at Reef Ridge (lat 35.9° N.) in Stewart's (1946) 

Vertipecten [Patinopecten] zone of the Temblor Formation. This part of the ~~Temblor" Stage can be defined, in 

central California, by the concurrent range zone of 

Lyropecten miguelensis and Patinopecten propatulus; 

and it is coeval with the upper part of the Saucesian 

foraminiferal stage (Addicott, 1972). The latest occurrences of M. middendorffi are farther north in the Diablo 

Range near San Jose, Calif. (lat 37.3° N.). In this area it 

occurs in the Sobrante and Oursan Sandstones which 

are assigned, respectively, to the middle Miocene 

Relizian and Luisian Stages of the foraminiferal 

chronology (Kleinpell, 1938). 

Occurrences in southwestern Oregon near Cape 

Blanco and at Coos Bay are within the concurrent range 

zone of Bruclarkia and Patinopecten and, therefore, are 

referable to the ~~Temblor" Stage. There are also several 

stratigraphically restricted ml;emblor".~species such as 

Crepidula rostralis (Conrad), Molopophorus matthewi 

Etherington, Nassarius arnoldi (Anderson), and Acila 

conradi (Meek) associated with M. middendorffi in 

southwestern Oregon. 

On Kodiak Island, Alaska, Mytilus middendorffi is 

associated with a large but poorly known fauna in the 

Narrow Cape Formation that is currently being studied 

by the authors. Preliminary analysis of this fauna 

suggests that it is coeval with the fauna of the Astoria 

Formation of Oregon and Washington, on the basis of 

specimens of Anadara, Dosinia, Ficus, and 

Molopophorus that appear to be conspecific with species 

whose range zones are restricted to the Astoria 

Formation. 

Zoogeographically, Mytilus middendorffi has an 

unusually broad distributional pattern for a shallowwater Miocene mollusk (fig. 2) although many modern 

mytilids have an equally extensive, or even greater, 

latitudinal distribution (Soot-Ryen, 1955). Its known 

range during the middle Miocene was from the San 

Joaquin basin of central California (lat 36° N.) to the 

Gulf of Alaska (lat 58° N .); this range makes it an 

extremely useful species for stratigraphic correlation. If 
MYTILUS (PLICATOMYTILUS) GRATACAPI N. SP. 9 

verified, the doubtful occurrence in the middle Miocene 

of eastern Kamchatka (Pronina, 1969) would significantly extend its range westward across the North 

Pacific rim. 

The Plicatomytilus species of western Kamchatka 

(Slodkevich, 1934, 1936, 1938; Il'ina, 1963) seems to be 

of middle to late Miocene age (Sinel'nikova and 

Drushchits, 1971; Gladenkov and others, 1972; Gladenkov, 197 4) but it does not appear to be Mytilus 

middendorffi. These records confirm the presence 

Plicatomytilus in Kamchatka without confirming the 

occurrence ofM. middendorffi there. The absence ofthis 

species in most faunal assemblages of the middle 

Miocene Astoria Formation of the central and northern 

Oregon coast (Moore, 1963) can be explained by the fact 

that these assemblages represent relatively deep 

sublittoral environments from which the shallow-water 

genus Mytilus was excluded. Assemblages from the 

early Miocene Clallam Formation (Addicott, 1975) of 

northwestern Washington contain Mytilus (subgenus?) 

n. sp. (a taxon from the Jewett Sand-Clallam 

Formation-Kuluven suite); its presence suggests a 

generally shallower sublittoral environment, but to 

date, Mytilus middendorffi has not been recorded from 

the Clallam Formation. The absence ofM. middendorffi 

from probable middle Miocene beds of the lower 

Yakataga Formation of the Gulf of Alaska (Kanno, 

1971; Miller, 1971) may be due to the deeper water 

environment represented by many lower Yakataga 

faunules (Kanno, 1971, p. 21-24). Kanno (1971, p. 22) 

reported fragments oC(Mytilus sp." from shallow-water 

faunules in the eastern part of the Yakataga Formation 

exposure belt, but to date M. middendorffi has not been 

recorded there. 

Ecology.-Nothing is known directly of the ecological 

tolerances of Plicatomytilus inasmuch as the subgenus 

is extinct. Many specimens at hand seem to show some 

wear or abrasion of the juvenile part of the shell on the 

umbos, but the shell as a whole is often very well 

preserved even retaining parts of the heavy periostracum. It does not seem probable that Plicatomytilus 

lived in the intertidal zone where sand abrasion caused 

by wave surge and surf severely corrodes the umbonal 

area of living Mytilus californianus Conrad. Mytilus 

characteristically lives in extremely shallow water 

although it may live at depths down to 40 or 50 fathoms 

and has been dredged from as deep as 120 fathoms 

(Soot-Ryen, 1955, p. 105-110). Berry (1954) reported a 

maximum known depth of 48 fathoms for M. californianus, taken alive off the coast of Humboldt County, 

Calif. This individual was very large (228 mm by 89.5 

mm by 69.2 mm) but quite thin shelled. These data 

suggest that a thin shell may be correlated with a 

deeper water habitat or conversely that M. middendorffi, with its heavy plicate shell, was well adapted to 

life in high-energy environments in the shallow part of 

the inner sublittoral zone. 

Mytilus middendorffi has been found associated with 

a number of other shallow-water molluscan genera 

including Acila, Anadara, Diplodonta, Glycymeris, 

Macoma, Siliqua, Solen, Spisula, Securella, Cancellaria, Crepidula, Olivella, Dosinia, Mya (Mya), and 

Pseudocardium (see Arnold and Hannibal, 1913, p. 

590--591; University of Alaska Kodiak Island Miocene 

collection). With the exception of Acila, Macoma, 

Cancellaria, and Glycymeris, which range downward 

into the upper bathyal zone, these genera range from 

intertidal or shallow subtidal depths to various depths 

between about 33 and .120 fathoms. The extinct genus 

Pseudocardium also possesses a very heavy shell that 

probably was adapted to the high-energy environments 

of the inner sublittoral zone. 

Mytilus (Plicatomytilus) gratacapi n. sp. 

Plate 2, figures 1, 3, 4, 6-10; plate 3, figures 1, 3, 5, 7, 8 

1850. Mytilus middendorffi Grewingk. Verhandlungen der Russichkaiserlichen Mineralogischen Gesellschaft zu St. 

Petersburg, Jahrgang 1848 and 1849, No.6, p. 171 and 361, 

Unga; reprinted 1850, p. 98 and 288; not M. middendorffi, 

Kodiak, p. 167, 360--361, pl. 7, figs. 3a-3c; reprinted 1850, p. 

94 and 287-288, pl. 7, figs. 3a-3c. 

1871. Modiola (Mytilus) Dufrenoyi d'Orbigny. Eichwald, E., Geog.-

palaeon. bemerk. iiber die Halbinsel Mangischlak und die 

Aleutischen Inseln, p. 128, St. Petersburg [incorrectly 

synonymizes M. middendorffi with a Cretaceous species from 

France], Unga; not Kodiak [ =M. middendorffi Grewingk]; 

not M. dufrenoyi d'Orbigny, France. 

1892. Mytilus middendorffi Grewingk. Dall W. H., and Harris, G. D., 

Correlation Papers, Neogene: U.S. Geol. Survey Bull. 84, p. 

253, Unga; not M. middendorffi, Kodiak. 

1896. Mytilus middendorffi Grewingk. Dall, W. H., U.S. Geol. Survey 

17th Ann. Rept., pt. I, p. 844, Unga; not M. middendorffi, 

Kodiak. 

1904. Mytilus middendorffi Grewingk. Dall, W. H., Neozoic invertebrate fossils, a report on collections made by the expedition, in 

Harriman Alaska Expedition, v. 4 (Geology and Paleontology), p. 113, Unga; not M. middendorffi, Kodiak; New 

York, Doubleday, Page & Co. (reprinted by Smithsonian 

Institution, 1910). 

1912. Mytilus middendorffi Grewingk. Gratacap, L. P., Am. Mus. 

Nat. History Bull. 31, art. VI, p. 69-70, pl. VII, figs. 1-3, 

Unga; not M. middendorffi, pl. VII, figs. 4-6, Kodiak. 

1931. Mytilus middendorffi Grewingk. Grant, U.S., IV, and Gale, H. 

R., San Diego Soc. Nat. History Mem., v. 1, p. 247, Unga; not 

M. middendorffi, Kodiak. 

1938. Mytilus middendorffi Grewingk. Slodk~vich, V. S., Paleontology ofU.S.S.R., v. 10, pt. 3, fasc. 19, Tertiary Pelecypoda from 

the Far East, Pt. II, p. 231, Unga; not M. middendorffi, p. 231, 

pl. L, figs. 2, 2a, Kodiak. 

1938. Not Mytilus cf. middendorffi Grewingk. Slodkevich, V. S., 

Paleontology ofU.S.S.R, v. 10, pt. 3, fasc. 18 and 19, Tertiary 

Pelecypoda from the Far East; fasc. 18, p. 237, 238; fasc. 19, p. 

119, 231, pl. L, figs. 3, 3a [ =Mytilus (Plicatomytilus) n. sp. of 

this report]. 
10 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

1958. Mytilus middendorffi Grewingk. Hall, C. A., California Univ. 

Pubs. Geol. Sci., v. 34, no. 1, p. 52, Unga; not M. middendorffi, 

California and Kodiak, p. 49, 52, pl. 5, fig. 6. 

1965. Mytilus middendorffi Grewingk. Burk, C. A., Geol. Soc. 

America Mem. 99, p. 91, 92, 93, 116, 213, 214, 215, 228, 

Alaska Peninsula; not M. middendorffi, Kodiak, p. 93, 104. 

1967. Mytilus middendorffi Grewingk. Addicott, W. 0., U.S. Geol. 

Survey Prof. Paper 593-D, p. D-7, Alaska Peninsula; not M. 

middendorffi, central California, Oregon, Pleasanton area, 

Santa Clara County, Griswold Hills, Reef Ridge and Kern 

River areas. 

1967. Mytilus middendorffi Grewingk. MacNeil, F. S., U.S. Geol. 

Survey Prof. Paper 553, p. 13. 

1973. Mytilus n. sp. Allison, R. C., and Addicott, W. 0., Geol. Soc. 

America, Abstracts with programs, v. 5, no. 1, p. 2-3. 

Description.-The shell is moderate sized, variable, 

heavy and ventricose for genus, often is strongly curved 

along anterior-posterior axis, and occasionally approaches the shape of Crepidula. The heavy shell is 

much thickened from within during growth; the breaks 

are terminal, pointed, and situated well above the plane 

of commissure above a large prominent lunule. A deep 

groove extends postero-dorsally from the beak on each 

valve becoming the broadly concave surface of the 

heavy thickened nymphae. A sharply incised groove 

that arches from the beak ventrally to the shell margin 

below the beak strongly marks the edge of the lunule; 

the lunule is semispade shaped (two valves together), 

the posterior dorsal point is attenuated, and the other 

two points beneath the beaks are strongly uncinate. The 

surface of the lunule has one or occasionally two strong 

ribs immediately dorsal to the incised ventral margin, 

and occasionally it has several additional very weak 

ribs dorsally; the lunule is not turned under such that 

ribs become hinge teeth; the hinge is normally edentate 

although some less inflated individuals may have valve 

margins slightly overlapped beneath beaks so that the 

ridges and grooves of the lunule barely interlock; the 

overall aspect of the shell is strongly governed by the 

variable degree of curvature of the anterior-posterior 

axis; the juvenile shell is mytiliform; large adults are 

usually bent posteriorly, inflated, and have one or two 

prominent bends in the dorsal margin. The dorsal 

margin is usually bent sharply between 20-30 mm in 

length marking the end of the juvenile mytiliform 

shape; occasionally there is another rather sharp bend 

toward the ventral between 50-60 mm in length; this 

posterior bend may be more evident on the dorsal 

umbonal ridge than on the dorsal shell margin which 

may become somewhat alate posteriorly. The bend 

between 20 and 30 mm in length may give the 

appearance of a modioliform shape. The ligament is 

long, heavy anteriorly, thin posteriorly; it reaches to the 

angulation between the dorsal and posterior slopes. 

Rapid growth on the posterior and ventral margins of 

the shell may cause marked bending of the shell along 

the posterior-anterior axis such that the plane of 

commissure diverges continually from the juvenile 

plane through a twisting rotation. The angle between 

the adult plane of commissure and the juvenile 

mytiliform plane (angle measured in elevation view) 

·may reach about 95° in large old individuals; the angle 

between the ventral shell margin of the adult and 

juvenile shell (measured as seen from above with shell 

resting on plane of commissure = plan view) may reach 

up to 110°. The ventral shell margin is usually slightly 

concave but may be nearly straight or strongly concave. 

The shape of the posterior end of the shell is extremely 

variable; it ranges between broadly rounded or 

subquadrate-angulate to slightly pointed or rarely very 

pointed; the posterodorsal margin is either alate or 

nonalate. The valves are sharply tumid or relatively 

thin posteriorly, and either broader or narrower than 

the medial part of the shell. The shell varies from very 

weakly plicate, hardly deflecting the plane of commissure, to very strongly plicate; however, the intermediate condition is the most common. The shell is 

usually modestly sulcate anterior to the main anteroventral fold. The shells have either two or three folds 

separated by sinuses; the posterior dorsal fold usually is 

less distinct in those with three folds. The folds cross the 

shell from the beak to the posteroventral and posterior 

margin; the folds often are sharply bent ventrally 

toward the posterior end of the shell; this bend is 

sometimes associated with a posteroventral production 

of the shell margin. The posterior dorsal area shows no 

evidence of branching secondary folds. The surface of 

the shell has prominent growth lines and constrictions 

(rugose) that may break up the continuity of the folds by 

forming a line of ill-defined ovate nodes. The juvenile 

mytiliform shell is often set off by a prominent growth 

constriction. The shell is covered with a heavy 

periostracum, which is often preserved as a tough black 

carbonaceous layer. The weathered specimens frequently display numerous parallel wavy lines internally between the umbonal ridge and the dorsal margin; 

R, right valve; L, left valve; :f, specimen incomplete; M, internal mold without shell; C, 

crushed specimen. 

Specimen Length (mm) 

USNM 647066 (R) 1 __ _ 

(Ll -------------- USNM 647067 (bothl ________ _ 

USNM 647068 \bothl _ USNM 647069 <Ll _____________ _ 

USNM 647070 (bothl ___________ _ 

USNM 647071 (bothl ___________ _ USNM 647072 (bothl ___________ _ USNM 647073 (Rl _____________ _ 

USNM 647074 (bothl ___________ _ 

USNM 647075 (bothl ___________ _ USNM 647079 <bothl ___________ _ USNM 647080 (R) _____________ _ 

USNM 647081 <bothl ___________ _ USNM 64 7082 <bothl ___________ _ 

USNM 647083 (bothl _ 

lHolotype. 

70 

71 

72 

82 

53 56L; 57R 

72 

70 

70 

63 

52 

82 

~71+ 

67 65R; 65L 

76 

Measurements 

Height (mm) 

47 

46 

47 

42 

+ 

35R; 39L 

46 

47 

40 

34 

37 

51 

46 

49 

47 

39 

Thickness (mm) 

one valve 

31 

29 

16R; 15L ~19R; 21L 

23 

25L; 27R 20R; 19L 23L; 20R (Ml 

-20:1: 

19R; ~17U 

19L; 19R 18L; 22R 20 

~16L; -19R:f ~17R; -14L (Cl 

23R; ~19U 
MYTILUS (PLICATOMYTILUS) GRATACAPI N. SP. 11 

these lines mark the successive posterior migration of 

the posterior adductor and retractor muscles and their 

scars. The musculature is as described for 

Plicatomytilus. 

Holotype.-USNM 647066. 

Type locality.-U.S. Geol. Survey M5182. 

Discussion.-Mytilus gratacapi n. sp. has long been 

confused with M. middendoiffi Grewingk, probably 

owing in part to Grewingk's (1850) report of M. 

middendoiffi from both Kodiak and Unga Islands, 

Alaska, as well as to subsequent repetitions of 

Grewingk's locality records by Dall and Harris (1892) 

and Dall (1896, 1904). In 1904 Dall (p. 113) includedM. 

middendoiffi in a listing of Miocene fossils from the 

Shumagin Islands collected by himself in 1865, 1872, 

187 4, and 1880, and by Mr. Trevor Kincaid in 1899; he 

gave the distribution as ~~u nga Island, and on Kadiak 

Island near Cape Tonki, Igatskoi Bay (Grewingk)". It 

seems likely, however, that this citation is merely a 

repetition of Grewingk's original record rather than a 

new confirmation of the Unga Island occurrence by 

recollection ofmytilid fossils there. The paucity of easily 

accessible published illustrations of M. middendoiffi, 

the much repeated early locality record of Grewingk's, 

the uniquely folded or plicate shells of both the Kodiak 

and the Alaska Peninsula Miocene mytilids, and finally 

Gratacap's (1912) concurrence that the same species 

occurs at Kodiak Island and on the Alaska Peninsula 

have prevented recognition of the Alaska Peninsula 

fossil mytilids as a distinct species. 

In 1912, Gratacap described and illustrated aMytilus 

from the divide of the Alaska Peninsula near Cape 

Seniavin, presumably in the vicinity of Bear Lake (fig. 

3). The specimen came to Gratacap from a Mr. Dunham 

of Nome, Alaska, who had obtained it from a Spanish 

sea captain named de Soto. Both valves of the single 

specimen are embedded in a conglomerate matrix, 

presumably the Unga Conglomerate Member of the 

Bear Lake Formation. Dall (in Gratacap, 1912, p. 69) 

identified this specimen as M. middendoiffi Grewingk 

and commented on it being a much distorted specimen 

with exaggerated resting stages, an exaggerated dental 

ridge, and an arcuate shape. Although Dall regarded 

this individual as gerontic and distorted by a ~~hard life," 

Gratacap's illustrations (1912, pl. 7, figs. 1-3) show the 

strong arching of the anterior-posterior axis, the 

prominent umbonal rib beneath the beak, and the 

strong growth constrictions. These characteristics, 

together with our examination of several mytilid 

collections from the Miocene of the Alaska Peninsula, 

make it clear that Gratacap's (1912, p. 69) individual is 

not ~~an unusual specimen of Mytilus middendorffi," 

but a representative of a very distinctive undescribed 

species herein named M. gratacapi. M. gratacapi is 

56° 

I 

EXPLANATION 

• Material examined by authors 

0 Incorrect previous record of the 

My titus middendorffi group 

0 

Cape Seniavin 

... 

\ 

illJ ~ 

Q:> 

Popof 

Island 

~~ 

~~f Sh~magin ~ Islands tf 

Unga Island 

50 MILES 

I I I I I I I I I I I Ol (b 0 70 KILOMETRES 

I 

162° 160° 

FIGURE 3.-Geographic distribution of Mytilus gratacapi n. sp. 

abundant in the upper part of the Unga Conglomerate 

Member of the Bear Lake Formation (Burk, 1965, p. 91 

and 116) and ranges upward into the middle part of the 

formation; we have seen no specimen of M. middendorffi 

from the Miocene beds on the Alaska Peninsula. As far 

as we know now, the two mytilids do not co-occur, for we 

do not know of any record of M. gratacapi aside from 

those on the Alaska Peninsula and Unga Island (fig. 3) 

in the Bear Lake Formation. Although M. gratacapi and 

M. middendorffi are doubtless related, the standard 

correlation of the Narrow Cape Formation of Kodiak 

Island with the Unga Conglomerate Member of the 

Bear Lake Formation CMytilus middendorffi zone" of 

MacNeil and others, 1961, and Burk, 1965, p. 90) merits 

careful review, because the probability is that much, if 

not all, of the range zone of M. gratacapi is of late 

Miocene age. 

Mytilus gratacapi n. sp. is characterized by its 

prominently ribbed lunule, edentate hinge, lack of 

secondary folds on the posterodorsal surface, strong 

arching of the anteroposterior axis of the shell, strong 

ventral bending of the main folds of the shell toward the 

posterior margin, and by the usual presence of 

numerous semiregular constrictions of the shell along 

growth lines. Although the species exhibits great 

individual variation, it may be readily distinguished 

from M. middendorffi: (1) the adult M. gratacapi 

possesses a large ribbed lunule with beaks situated well 

above the plane of commissure and has a sharp groove 

running posterodorsally from beneath the beaks, 

whereas the lunule of M. middendoiffi is small, 

externally indistinct, and turned under to form the 
12 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

hinge teeth; (2) M. middendorffi usually possesses 

secondary folds on the posterodorsal surface that branch 

off of the main dorsal fold; M. gratacapi does not possess 

secondary branch folds; (3) M. middendorffi has a 

regular elongate mytiliform shell, whereas adult M. 

gratacapi typically has a strongly arched and twisted 

shell that has a trapezoidal or subquadrate shape; (4) 

the main shell folds of M. gratacapi are usually more 

sharply bent ventrally toward the posteroventral 

margin than those of M. middendorffi; this bend may 

accompany a posteroventral production of the shell 

margin by giving it a broader blunter aspect than that of 

M. middendorffi; (5) the main fold and sinuses of M. 

gratacapi are weaker and, accordingly, deflect the plane 

of commissure less severely than those of M. middendorffi; (6) M. gratacapi usually bears well-marked 

semiregular constrictions along growth lines (rugae) 

that tend to give the main folds of the shell an indistinct 

nodose appearance; such constrictions are not as 

common or well marked on shells of M. middendorffi, 

and as a result the main folds do not appear nodose, and; 

(7) M. gratacapi usually has three primary folds; if 

present, the third fold develops posterodorsally of the 

main folds, whereas inM. middendorffi, the third fold, if 

present, apparently develops anteroventrally of the 

main folds. 

The large number of specimens at hand show much 

individual variation even among specimens collected 

from a single locality. Accordingly, we have chosen a 

number of paratypes in order to depict the range of 

variation of this species. Were it not for many 

intermediate forms in the collections, one might easily 

regard some of the more extreme variants as distinct 

taxa. This variation affects a number of characteristics 

of the shell. The lunule, although external and large in 

most specimens, may occasionally be slightly turned 

under, producing a very weak dentition. The wide 

variation in the arching and twisting of the shell, along 

the anteroposterior axis, greatly affects the overall 

aspect of the shell as well as its component parts such as 

the dorsal, ventral, and posterior margins. The shape of 

the posterior end of the shell is in fact perhaps the most 

singly variable characteristic. The dorsal margin may 

be strongly alate or almost nonalate as it is in M. 

middendorffi. The strength of the plicae or shell folds 

too may vary from strong to nearly absent on rare 

individuals. The development of the posterior dorsal 

fold is especially variable, and some shells may wholly 

lack this fold. 

Occurrence.-Unga Conglomerate Member of the 

Bear Lake Formation, Unga Island (Grewingk, 1850; 

Dall, 1896, 1904), Alaska Peninsula (USGS Cenozoic 

loc.5046,M805,M806,M1192,M1904,M1905,M3586, 

M5180, M5738); middle part of the Bear Lake Formation stratigraphically above the Unga Conglomerate 

Member, Alaska Peninsula, Alaska (USGS Cenozoic 

loc. M1022, M5182, M5185); unnamed marine rocks of 

nPliocene" age of Burk (1965) [Bear Lake? Formation] 

(USGS Cenozoic loc. M517 4). 

Range.-Middle(?) to late Miocene. 

Incorrect record of Mytilus gratacapi.-Mytilus 

gratacapi is present in a collection that was supposedly 

acquired from beds exposed on the north shore of Popof 

Island (USGS Cenozoic loc. 7905). The collection 

appears, however, to have been derived from several 

collecting stations, and it is very doubtful if the M. 

gratacapi specimens actually came from Popof Island. 

Subsequent mapping of Popof Island indicates that the 

marine Tertiary strata exposed along the shore eastward from East Head are referable to the Stepovak 

Formation of Burk (1965). All the other records of M. 

gratacapi are from the stratigraphically higher Bear 

Lake Formation. None of the several modern collections 

of mollusks from exposures of the Stepovak on Popof 

Island (USGS Cenozoic loc. M1160, M1162, M1164, 

M1167, M1654, M1655, M1656) contains M. gratacapi; 

rather they contain a shallow-water fauna characterized by Ostrea tigiliana Slodkevich that is considered 

(MacNeil in Burk, 1965) to have western North Pacific 

affinities and is roughly coeval with the fauna of the 

Oligocene ((Lincoln" Stage of the eastern North Pacific. 

Burk (1965, p. 226) noted that this collection (USGS 

Cenozoic loc. 7905) contains species from both an 

Oligocene and a ((middle" Miocene fauna, and that the 

faunal elements are associated with two different 

lithologies. Accordingly, the specimens of M. gratacapi 

and large Crepidula labeled USGS Cenozoic loc. 7905 

are believed to have been collected from exposures of the 

Unga Conglomerate Member of the Bear Lake Formation either on neighboring Unga Island or on the Alaska 

Peninsula to the north of Popof Island. The mixing of 

fossils from two formations in the collection labeled 

7905 was indirectly noted by MacNeil, Wolfe, Miller, 

and Hopkins (1961, p. 1804, annotation 2c). 

Age and correlation.-Occurrences of Mytilus 

gratacapi are limited to a relatively small area on the 

Alaska Peninsula near Port Moller and in the adjacent 

Shumagin Islands (fig. 3). The age and correlation of the 

lowest strata bearing M. gratacapi (in terms of Gulf of 

Alaska and conterminous United States sequences) are 

problematic owing to the fact that associated mollusks 

are rare and poorly preserved. The highest occurrences, 

however, can be confidently assigned to the provincial 

late Miocene. 

The lowest stratigraphic occurrence of Mytilus 

gratacapi is in the Unga Conglomerate Member of the 

Bear Lake Formation where it is associated with a 

commonly occurring Crepidula that is characterized by 
MYTILUS (PLICATOMYTILUS) N. SP. 13 

a large internal septum with nearly parallel insertions. 

This species is considered distinct from Crepidula 

ungana Dall from the underlying Stepovak Formation 

of Burk (1965) (MacNeil in Burk, 1965, p. 92, 226). 

Other mollusks from the Unga include poorly preserved 

tellinid and venerid bivalves (USGS Cenozoic loc. 5046, 

M3587) that cannot be identified specifically. Plant 

fossils collected by W. H. Dall from ~just beneath [the] 

Crepidula bed" on Zachary Bay, Unga Island, were 

considered by Wolfe (in Burk, 1965, p. 234) to be of no 

younger than middle Miocene age. Wolfe (1972, p. 203) 

assigned this Unga Island flora to the late Seldovian 

paleobotanical stage. 

Although the floral evidence suggests that the lowest 

occurrence ofMytilus gratacapi could be as old as middle 

Miocene, a collection from the middle part of the Bear 

Lake Formation on the Alaska Peninsula about 50 

miles to the northeast is clearly of late Miocene age 

(USGS Cenozoic loc. M5182). This locality, about 2¥2 

miles southeast of Bear Lake (fig. 3 ), is stratigraphically 

above a collection of well-preserved mollusks that has 

been correlated with the late Miocene fauna of the 

Montesano Formation of western Washington (MacNeil 

in Burk, 1965, p. 228). A chronologically significant 

species in this collection is Clinocardium pristinum 

Keen. So far as is known, this occurrence and possibly 

an occurrence near Milky River (USGS Cenozoic loc. 

M1022) a few miles to the northeast are the highest 

stratigraphic occurrences of M. gratacapi. This species 

had not previously been recorded from above the Unga 

Conglomerate Member of the Bear Lake Formation. 

Another important record of Mytilus gratacapi is from 

beds exposed inland from the west shore of Herendeen 

Bay (USGS Cenozoic loc. M5174) in strata mapped as 

unnamed marine rocks of Pliocene age by Burk (1965, 

geologic map; p. 94). Associated with M. gratacapi at 

this locality are a species ofClinocardium with crested 

ribs similar to Clinocardium yakatagense (Clark) 

Clinocardium ciliatum (Fabricius) and specimens of a 

large Mya of the Mya elegans group. The occurrence of 

Mytilus gratacapi in this unit suggests that it may be in 

part coeval with the middle(?) and upper part of the 

Miocene Bear Lake Formation, rather than with the 

unnamed Pliocene beds as earlier supposed (Burk, 1965, 

p. 94). Pliocene strata do crop out on the west shore of 

Herendeen Bay north of Village Spit, but the coastal 

exposures of ~~marine Pliocene" beds south of Village 

Spit (Burk, 1965, geologic map) probably belong to 

Burk's (1965) Upper Cretaceous Coal Valley Member of 

the Chignik Formation. The nearest known exposures 

of the Bear Lake Formation are located about 8 miles to 

the northwest near the mouth of Port Moller. 

It seems probable thatMytilus gratacapi evolved from 

Mytilus middendorffi during or near the end of the 

middle Miocene and that it represents the last 

occurrence of rugose, coarsely plicate species of 

Plicatomytilus in western North America. Mytilus 

(Plicatomytilus) n. sp. from western Kamchatka is 

clearly distinct from M. gratacapi. 

Ecology.-Mytilus gratacapi usually occurs in shell 

beds by itself without the preserved remains of other 

mollusks. It is known, however, to co-occur with 

Crepidula sp., Clinocardium sp., and Mya (?Arenomya) 

cf. M. (?A.) elegans (Eichwald), 1871 (USGS Cenozoic 

loc. M5174). AlthoughCrepidula andClinocardium are 

known to range in depth from the intertidal zone to 90 

fathoms and 125 fathoms respectively, we have not been 

able to find any record of members of the Arenomya 

stock ranging below the shallow subtidal zone. This 

association seems to indicate a habitat in the intertidal 

to very shallow subtidal range. The very heavy shell 

and considerable variation in shape also suggest thatM. 

gratacapi may have lived on exposed coastlines where it 

was especially well adapted to heavy wave surge and 

surf conditions. 

Mytil us (Plicatomytil us) n. sp. 

Plate 2, figures 2, 5 

1934. Mytilus cf. middendorffi Grewingk. Slodkevich, V. S., On the 

stratigraphy of the Tertiary deposits of the western coast of 

Kamchatka: Academie des Sciences de L'Union des Republiques Sovietiques Socialistes (Akademiya Nauk), C. R. 

(Dokl.), T. 3, no. 1, p. 60 and 62 (Russian and English). 

1936. Mytilus cf. middendorffi Grewingk. Slodkevich, V. S., The 

stratigraphy and fauna of the Tertiary deposits of the 

western coast of Kamchatka: Trudy neftyanogo geologo 

razvedochnogo instituta, Seriya A, Vypusk 79, p. 125-126, pl. 

XV, figs. 5, 5a, Leningrad, Moscow. 

1938. Mytilus cf. middendorffi Grewingk. Slodkevich, V. S., Paleontology of U.S.S.R., v. 10, pt. 3, fasc. 18 and 19, Tertiary 

Pelecypoda from the Far East; fasc. 18, p. 227, 238; fasc. 19, 

p.119, 231, pl. L, figs. 3, 3a [not figs. 2, 2a=Mytilus 

middendorffi Grewingk, Kodiak]. 

1963. Modiolus cf. middendorffi Grewingk. Il'ina, A. P., Mollusks of 

the Neogene of Kamchatka, pl. XXXVI, fig. 2 (same 

individual illustrated by Slodkevich, V. S., 1936 and 1938). 

Discussion.-Slodkevich (1934) seems to have first 

recognized the similarity of a plicate shelled mytilid 

from the ~~Kavran Series" of western Kamchatka to 

Mytilus middendorffi Grewingk. Later, in 1936, and 

again in 1938, he described this east Asiatic taxon and 

illustrated a single specimen from the ~~River Reel'nyevayam" area. Il'ina (1963) re-illustrated Slodkevich's 

(1936, 1938) specimen and reported it as ~~Modiolus cf. 

middendorffi Grewingk." 

Slodkevich's (1936, 1938) descriptions of ~~Mytilus cf. 

middendorffi" indicate that he had only a single 

steinkern of one valve from the River Reel'nye-vayam 

area available for study. He clearly discussed the 

characteristic folding of the shell, reflected by the 

steinkern, and noted (1938) that the holotype of M. 
14 NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

middendorffi is lost. In order to describe the external 

features of the shell, he offered a short quotation from 

Grewingk (1850) dealing with the folding of the shell. 

These descriptions are somewhat confusing until one 

realizes that Slodkevich has incorrectly considered the 

beak of the shell to be posterior and the opposite folded 

end of the shell to be anterior. In the discussion, 

Slodkevich follows Dall's (1904) and Grant and Gale's 

(1931) views on the relationships of M. middendorffi to 

M. condoni Dall and M. ficus Dall. The tentative 

identification was offered because of the poor preservation of the single specimen. Although this much 

illustrated specimen is poorly preserved, Slodkevich's 

descriptions and the illustrations clearly indicate the 

characteristic folding of the shell and the plane of 

commissure that typifies Plicatomytilus. 

Through the kindness of the Academician V. V. 

Menner and Dr. V. N. Sinel'nikova, both of the 

Geological Institute of Moscow, we have recently 

received a specimen of Plicatomytilus from the Kakert 

suite of the ~~Kavran Series" at the mouth of the Kavran 

River (Geological Institute, Moscow, loc. 69), western 

Kamchatka (pl. 2, figs. 2, 5). We consider this specimen 

to be synonymous with Mytilus cf. M. middendorffi of 

Slodkevich (1934, 1936, 1938) and Modiolus cf. middendorffi of Il'ina (1963), but not with Mytilus middendorffi Grewingk, 1850. 

This specimen from the Ka vran River area is a left 

valve that measures 77 mm in length (incomplete), 

about 43 mm in maximum height, and about 17 mm 

thick (one valve). A moderate umbonal ridge extends 

from the umbo to the posterior end of the shell, gently 

diverging from the posterodorsal margin. A wellmarked sulcus, immediately anteroventrally of the 

umbonal ridge, extends from the umbo to the posteroventral corner of the shell where it clearly deflects the 

plane of commissure. Immediately anterior of this 

sulcus, a moderate fold extends from near the center of 

the shell to the ventral margin where it weakly deflects 

the plane of commissure. The characteristics of the 

beak, hinge, and lunule are not known because the shell 

is broken. The umbonal ridge is prominently undercut 

near the center of the dorsal margin where a moderately 

marked alation occurs between the anterodorsal and 

the posterodorsal edges of the shell. The convexity of the 

shell, which is moderate but not great, is greatest along 

the dorsal margin. Well-marked growth lines occur on 

the surface of the shell. 

Although Mytilus (Plicatomytilus) n. sp. is quite 

similar in outline to Mytilus middendorffi Grewingk 

and is clearly related to it, we believe that the ~~Kavran 

Series" taxon should be recognized as a distinct species. 

Mytilus (P.) n. sp. appears to differ from M. middendorffi: 

(1) by being slightly smaller in fully adult size, (2) by 

having the major folds of the shell and plane of 

commissure much less pronounced and therefore 

weaker than in M. middendorffi, (3) by totally lacking 

the secondary bifurcated folds of the posterodorsal 

surface area that are characteristic of M. middendorffi, 

and ( 4) by being slightly less inflated and tumid than 

typical adult individuals of M. middendorffi. 

Mytilus (P.) n. sp. also differs markedly from Mytilus 

gratacapi n. sp.: (1) by lacking the strong arching and 

twisting of the anteroposterior axis of the shell of M. 

gratacapi, (2) by lacking the strong ventral bending of 

the main folds of the shell toward the posterior margin 

as seen in the Alaska Peninsula species, (3) by lacking 

the prominent growth constrictions and nodose surface 

tendency of M. gratacapi, and ( 4) by probably lacking 

the prominently ribbed lunule of M. gratacapi. 

Figured specimen.-VSNM 647084. 

Occurrence.-Etolon suite of the ~~Kavran Series," 

River Reel'nye-vayam area, and Kakert suite of the 

~~Kavran Series," at the mouth of the Kavran River, 

western Kamchatka, U.S.S.R. The Etolon suite overlies 

the Kakert suite. 

Range.-Middle to late Miocene. 

Stratigraphic distribution and age.-The specimen of 

Mytilus (P.) n. sp. that was considered to be Mytilus cf. 

middendorffi by Slodkevich (1934, 1936, 1938) and to be 

Modiolus cf. middendorffi by Il'ina (1963) has been 

referred to the ~~Kavran Series" (Slodkevich, 1934), the 

~~Kavran suite" (Slodkevich, 1936, 1938), and to the 

~~Etolon Suite, zone of Swiftopecten swiftii var. etchegoini" (Il'ina, 1963). The label with the specimen 

donated to us by V. V. Menner and V. N. Sinel'nikova 

(pl. 2, figs. 2, 5) indicates it to be from the ~~Kakert 

Suite." The Kakert and Etolon suites are considered to 

be parts of the ~~Kavran Series" (see Gladenkov, 1974). 

The former specimen comes from the ~~River Reel'nyevayam" area, and the latter specimen is from the 

~~mouth of Kavran River" area, western Kamchatka. 

Slodkevich (1934 and 1936) considered the ~~Kavran 

Series" or ~~Kavran Suite" to be middle and late Pliocene 

in age. In 1938, Slodkevich revised his view by referring 

the ~~Kavran Suite" to the ~~Miocene-Pliocene." Il'ina 

(1963) considered ~~the zone of Swiftopecten swiftii var. 

etchegoini" (Etolon suite) to be of middle Pliocene age. 

More recently, Sinel'nikova and Drushchits (1971) 

and Gladenkov, Petrov, and Sinel'nikova (1972) considered the ~~Kavran Series" and the Etolon suite of 

western Kamchatka to be of middle to late Miocene age. 

Gladenkov (1972, 1974) considered the Kakert suite to 

be of middle Miocene age and the Etolon suite to be of 

middle and late Miocene age. Gladenkov's (1972, 197 4) 

age interpretations seem to agree well with what may 

be inferred from the presence ofMytilus (Plicatomytilus) 

n. sp.; its nearest relative, Mytilus middendorffi, is 
LOCALITY REGISTER 15 

restricted to deposits of middle Miocene age in western 

North America. 

LOCALITY REGISTER 

[Localities from which Mytilus middendorffi and M. gratacapi have been collected. Age and 

formational assignments in brackets are those of the present authors ] 

Locality 

3334 

5046 

5765 

5766 

7901 

7905 

13372 

14385 

14393 

18284 

D227 

Description 

USGS localities (Washington, D. C., register) 

Base of beach bluff half a mile north of Blacklock Point 

[Curry County], Oreg. Same description as loc. 7901. 

[Lower part of Diller's (1903) Empire Formation.] 

North side of Port Moller, Alaska Peninsula, Alaska 

[same as loc. M805 according to notation on locality 

label written by F. S. MacNeil]. Collected by W. W. 

Atwood and H. M. Eakin, July, 1912. [Bear Lake 

Formation.] 

East end of Vallecitos, 500ft southeast of New Bedford 

well, in bed of Silver Creek just below where branch 

road to well crosses creek, San Benito County, Calif. 

From basal sand oflower Miocene [Temblor Formation, 

middle Miocene]. Collected by R. W. Pack, 1909. 

East end ofVallecitos, 1.1 miles almost due north ofNew 

Bedford well, on north side of first large gully draining 

into Silver Creek north of well. Near center ofW¥2 sec. 

32, T. 16 S., R. 12 E., San Benito County, Calif. From 

sandstone underlying shale of loc. 5789 and directly 

above Oligocene(?) diatomaceous shale. Basal Miocene 

[Temblor Formation, middle Miocene]; same horizon as 

loc. 5765. Collected by R. W. Pack, 1909. 

Base of beach bluff half a mile north of Blacklock Point 

[Curry County], Oreg. Same description as loc. 3334. 

[Lower part of Diller's (1903) Empire Formation.] 

North side of Popof Island, Shumagin Islands, Alaska. 

Collected by W. H. Dall [Collection mixed, specimens of 

Mytilus gratacapi probably from Unga Island or Alaska 

Peninsula (p. 12) ]. 

South west corner ofN arrow Point, en trance to U gak Bay, 

Kodiak Island, Alaska. [Narrow Cape Formation, 

middle Miocene.] Collected by S. R. Capps, 1934. 

On east side of ridge between Garza and Baby King 

Canyons about 300ft south of road, 1,150 ft S., 250ft W. 

of NE cor. sec. 10, T. 23 S., R. 17 E., Reef Ridge 

15-minute quad., Kings County, Calif. Lower part of 

Temblor Formation [middle Miocene]. Collected by 

Ralph Stewart. 

Southeast and southwest sides ofRoundtop, in sec. 12, T. 

23 S., R. 16 E., Reef Ridge 15-minute quadrangle, 

Kings County, Calif. Pebble beds near top oflower part 

of Temblor Formation [middle Miocene]. Collected by 

Ralph Stewart. 

Dredging from between mile 3.5 and mile 4 in Coos Bay 

opposite pulp mill, Empire 15-minute quadrangle, 

Coos County, Oreg. Unnamed formation of middle 

Miocene age. Collected by E. J. Moore, 1949, 1951, 

1952. 

USGS localities (Denver, Colorado, register) 

Sea cliff at east margin of beach south of Twin Lakes 

about 0.2 mile N. 5° W. ofsouthwesternmost projection 

at Narrow Cape, Kodiak Island, Alaska (coordinates on 

Kodiak 1:250,000 quadrangle: 15.60, 7.48). [Narrow 

Cape Formation.] Collected by C. E. Kirschner and J. E. 

Reppert, 1953. 

Locality Description 

USGS localities (Menlo Park, California, register) 

M805 Northeast shore of Left Head, 5.4 miles N. 31° E. of Jerk 

triangulation station, Port Moller quadrangle, Alaska 

Peninsula, Alaska. Collected by M. C. Lachenbruch, 

1959. 

M806 Northeast shore of Right Head, 4 miles N. 84° E. of Jerk 

triangulation station, Port Moller quadrangle, Alaska 

Peninsula, Alaska. Collected by M. C. Lachenbruch, 

1959. 

M1022 17.3 in. N., 19.8 in. E. of SW cor. Port Moller 1:250,000 

quadrangle, Alaska Peninsula, Alaska. Unga Conglomerate Member of Bear Lake Formation. Collected 

by M. C. Lachenbruch. 

M1192 East shore of Port Moller between Left Head and Right 

Head, lat 55°49' N., long 160°18.5'W., Port Moller 

1:250,000 quadrangle, Alaska Peninsula, Alaska. 

Unga Conglomerate Member of Bear Lake Formation. 

Collected by C. A. Burk, 1959-61. 

M1735 From 1,250 ft above base of section at Narrow Cape, lat 

57°26' N., long 152°19' W., Kodiak 1:250,000 quadrangle, Alaska. Narrow Cape Formation. Collected by 

G. W. Moore, 1963. 

M1904 Six miles N. 85° E. of southernmost tip ofBear Lake and 1 

mile S., 0.9 mile W. of NE cor. Port Moller 1:250,000 

quadrangle, Alaska Peninsula, Alaska. Collected by 

Mobil Oil Co., 1963. 

M1905 On north coast of Left Head, Port Moller Bay, 9.5 miles S. 

72o E. of Harbor Point and 8.8 miles S., 13.4 miles W. of 

NE cor. Port Moller 1:250,000 quadrangle, Alaska 

Peninsula, Alaska. Collected by Mobil Oil Co., 1963. 

M2142 Seacliffexposure southeast of Cape Blanco in E% sec. 2, 

T. 32 S., R. 16 W., Cape Blanco 15-minute quadrangle, 

Curry County, Oreg. Unnamed sandstone and conglomerate of middle Miocene age exposed below 

unconformity within Diller's (1903) Empire Formation. Collected by W. 0. Addicott, 1964. 

M3586 Northeast shore of Right Head, approximately 600ft E., 

2,300 ft S. of NW cor. sec. 32, T. 50S., R. 71 W., Port 

Moller (D-1) 15-minute quadrangle, Alaska Peninsula, Alaska. Collected by Standard Oil Co., 1965. 

M3614 Concretionary sandstone in cliff on west side of Silver 

Creek, 1,700 ft N., 900ft E. ofSW cor. sec. 5, T. 17 S., R. 

12 E., New Idria 15-minute quadrangle, San Benito 

County, Calif. About 50 ft above base of Vaqueros 

Formation of Anderson and Pack (1915), [Temblor 

Formation]. Collected by W. 0. Addicott, 1967. 

M3637 Seacliffexposure about halfway between Blacklock Point 

and Floras Lake, 1,000 ft N., 2,400 ft W. ofSE cor. sec. 

18, T. 31 S., R. 15 W., Cape Blanco 15-minute 

quadrangle, Curry County, Oreg. Empire Formation of 

Diller (1903). Collected by W. 0. Addicott, R. J. Janda, 

and H. E. Clifton, 1967. 

M4126 Seacliff exposure of Mytilus middendorffi-bearing conglomerate lenses stratigraphically below prominent 

tuffbed southeast of Cape Blanco, in E% sec. 2, T. 32 S., 

R. 16 W., Cape Blanco 15-minute quadrangle, Curry 

County, Oreg. Lower part of Diller's (1903) Empire 

Formation. Same as USGS loc. M2142. Collected by W. 

0. Addicott and R. J. Janda, 1969. 

M4129 Seacliff exposure east of waterfall on north side of 

Blacklock Point, 2,500 ft N., 200ft W. ofSE cor. sec. 24, 

T. 31 S., R. 16 W., Cape Blanco 15-minute quadrangle, 

Curry County, Oreg. Lower part of Diller's (1903) 
16 

Locality 

M4130 

M4132 

M4135 

M4136 

M4687 

M4690 

M4756 

M5162 

M5174 

M5180 

M5182 

NORTH PACIFIC MIOCENE RECORD OF MYTILUS (PLICATOMYTILUS), A NEW SUBGENUS 

Description Locality 

Empire Formation. Collected by W. 0. Addicott and R. M5185 

J. Janda, 1969. 

Seacliff exposures about 1 mile northeast of Blacklock 

Point, inS% sec. 18, T. 31 S., R. 15 W., Cape Blanco 

15-minute quadrangle, Curry County, Oreg. Mytilusbearing concretions from 50-ft-thick unit in lower part 

ofDiller's (1903) Empire Formation. Collected by W. 0. M5737 

Addicott and R. J. Janda, 1969. 

North bank of small draw near Floras Lake, in SE% NE% 

sec. 18, T. 31 S., R. 15 W., Cape Blanco 15-minute 

quadrangle, Curry County, Oreg. 1,650 ft S., 1,000 ft 

W. ofNE cor. sec. 18. Concretions in massive sandstone 

of lower part of Diller's (1903) Empire Formation. M5738 

Collected by W. 0. Addicott and R. J. Janda, 1969. 

Seacliff exposure of massive gray, micaceous silty 

sandstone containing large (2- to 5-ft-thick) concretions with minute Spisula, 3,650 ft S., 100ft E. of NW M5807 

cor. sec. 1, T. 32 S., R. 16 W., Cape Blanco 15-minute 

quadrangle, Curry County, Oreg. Near top of lower 

part of Diller's (1903) Empire Formation and stratigraphically above tuff. Collected by W. 0. Addicott, M6381 

1969. 

Seacliff exposure of Mytilus middendorffi-bearing beds, 

40 to 50 ft stratigraphically above tuff bed, in E% SE% 

sec. 2, T. 32 S., R. 16 W., Cape Blanco 15-minute 

quadrangle, Curry County, Oreg. Lower part of Diller's 

(1903) Empire Formation. Collected by W. 0. Addicott, M6382 

1969. 

Seacliff exposure southeast of Cape Blanco in E% sec. 2, 

T. 32 S., R. 16 W., Cape Blanco 15-minute quadrangle, 

Curry County, Oreg. Lower part of Diller's (1903) 

Empire Formation. Same as USGS loc. M2142. 

Collected by W. 0. Addicott, 1971. 

Seacliff exposure stratigraphically above M 4689, 2, 7 00 ft 

S., 950 ft W. of NE cor. sec. 2, T. 32 S., R. 16 W., Cape A-180 

Blanco 15-minute quadrangle, Curry County, Oreg. 

Collected by W. 0. Addicott and R. J. Janda, 1971. 

Bench mark north of head of Samson Ridge, 850ft S., 

2,700 ft W. ofNE cor. sec. 5, T. 9 S., R. 4 E., Mt. Sizer 

7%-minute quadrangle, Santa Clara County, Calif. 

Sobrante Sandstone. Collected by Susan Bartsch, 1971. 

Cut along Steeley Road near north line of sec. 5, T. 9 S., R. 

4 E., Mt. Sizer 7%-minute quadrangle, Santa Clara 

County, Calif. Sobrante Sandstone. Collected by K. J. 

Murata, 1972. 

North of Village Spit on west side ofHerendeen Bay, from 

measured section along shoreline between 2,700 ft N., 

1,800 ft W. ofSW cor. sec. 31 and 1,200 ft N., 2, 700ft E. 

ofSW cor. sec. 25, T. 50S., R. 75 and 76 W., Port Moller 

(D-3) 15-minute quadrangle, Alaska. Collected by 

Union Oil Co., 1971 [probably coeval with upper Bear 

Lake Formatio~]. 

South of Sundean triangulation station on northeast 

shore ofRight Head, Port Moller, 200ft N., 2,500 ft W. A-181 

of SE cor. sec. 30, T. 50 S., R. 71 W., Port Moller (D-1) 

15-minute quadrangle, Alaska. Collected by Union Oil 

Co., 1971. 

From measured section about 2% miles southeast of Bear 

Lake, section extends from 1,500 ft N., 1,800 ft W. ofSE 

cor. sec. 9 to 600ft N., 1,000 ft W. ofSE cor. sec. 4, T. 49 

S., R. 69 W., Port Moller (D-1) 15-minute quadrangle, 

Alaska Peninsula, Alaska. Collected by Union Oil Co., 

1971. 

Description 

Measured section on northeast side of Milky River, 

section extends from 1,500 ft N., 2,000 ft E. of SW cor. 

sec. 16, to 1,900 ft S., 800ft W. ofNE cor. sec. 16, T. 48 

S., R. 68 W., Chignik (A-6) 15-minute quadrangle, 

Alaska Peninsula, Alaska. Collected by Union Oil Co., 

1971. 

Seacliff exposure 130 ft stratigraphically above lowest 

exposure of Diller's ( 1903) Empire Formation southeast of Cape Blanco in NE% sec. 2, T. 32 S., R. 16 W., 

Cape Blanco 15-minute quadrangle, Curry County, 

Oreg. Collected by W. 0. Addicott and R. J. Janda, 

1971. 

Seacliff exposure at westernmost point of peninsula 

between Right Head and Left Head, Port Moller, 

Alaska Peninsula, Alaska. Collected by A. W. 

Schlottman, 1961. 

Roadcut on west side of logging road spur in SE%NE% 

sec. 4, T. 3 N., R. 10 W., Cannon Beach 15-minute 

quadrangle, Tillamook County, Oreg. [Astoria Formation.] 

Cut on south side of logging road in NE%NE%SW% sec. 

23, T. 6 N., R. 9 W., Cannon Beach 15-minute 

quadrangle, Tillamook County, Oreg. Approximately 

380ft above base of Astoria Formation. Collected by A. 

Niem, D. M. Cooper, J. W. Miller, and W. 0. Addicott, 

1974. 

Bank on east side of Big Creek, 150ft S., 1,100 ft W. ofNE 

cor. sec. 10, T. 7 N., R. 7 W., Svenson 15-minute 

quadrangle, Clatsop County, Oreg. Astoria Formation. 

Collected by A. Niem, D. M. Cooper, J. W. Miller, and 

W. 0. Addicott, 1974. 

University of Alaska Museum localities 

Massive blue-gray fine- to medium-grained sandstone 

unit about 85 ft thick includi:qg several concretionary 

beds. A large landslide from this unit has produced a 

rubble cone at head ofbeach and toe of sea cliff. Includes 

concretionary lenses rich in Mytilus middendorffi, 

Clinocardium, Pseudocardium, Kewia kannoi, 

Dosinia, Mya, and Acila. Below this bed is a massive 

black chert and white quartz pebble to granule 

conglomerate. Top of unit marked by a 2-ft-thick 

concretionary bed rich in Pseudocardium and Mytilus 

middendorffi. Locality A-180 includes fossils from 

lower half of this 85-ft-thick unit. Locality approximately 700-800 ft southeast of southwest end of south 

Twin Lake in seacliff at Narrow Cape, Kodiak Island, 

Alaska. Narrow Cape Formation, middle Miocene. U.S. 

Geol. Survey Kodiak B-1 and B-2 quadrangles, 

Alaska, 1:63,360, edition of 1949. Coli. R. C. Allison, 

1969 and 1970, C. W. Allison, 1969, and J. W. Durham, 

1970. 

Locality in seacliff about 125 ft southeast of start of 

seacliff exposure at northeast end of south Twin Lake, 

Narrow Cape, Kodiak Island, Alaska. Locality in a 

2-ft-thick concretionary bed rich in Mytilus middendorffi, Pseudocardium, and Kewia kannoi. Fossil bed 

overlain by massive medium-grained gray buffweathering sandstone and underlain by fine-grained 

massive gray sandstone. Locality exposed on rock 

promontory projecting out from seacliff on southeast 

side of small doubly reentrant cove on beach. Narrow 
Localit_v 

A-183 

A-204 

A-255 

LOCALITY REGISTER 

Description Locality 

Cape Formation, middle Miocene, U.S. Geol. Survey 

Kodiak B-1 and B-2 quadrangles, Alaska, 1:63,360, 

edition of 1949. Coll. J. W. Durham, 1970. 

Fossil locality in 25-ft-thick light-gray massive fine- to 

medium-grained sandstone, 14 ft. below prominent A-256 

2-ft-thick concretionary bed rich in Pseudocardium 

which bounds top of unit. Another 1-ft-thick concretionary unit occurs 5 ft above base of unit and has a 

6-in.-thick discontinuous concretionary bed directly A-257 

above it. Bedding shown by laminae of shell detritus. 

Base of unit bounded by a 1-ft to 6-in.-thick hard 

concretionary bed that is rich in Mytilus middend01ffi 

(loc. A-273). Locality A-183 is 125ft east ofloc. A-181. 

Locality includes mollusks and echinoids. Site located 

in sea cliff on northwest side of small slotlike cave about 

800ft southeast of start of seacliff exposures (southeast 

of Twin Lakes Valley) on northeast side of Narrow 

Cape, Kodiak Island, Alaska. Narrow Cape Formation, 

middle Miocene. U.S. Geol. Survey Kodiak B-1 and 

B-2 quadrangles, Alaska, 1:63,360, edition of 1949. 

Coll. J. W. Durham, 1970. 

Outcrop of very fine to fine-grained gray soft buff- A-258 

weathering blocky fossiliferous sandstone with Mya, 

Mytilus middendorffi, and fossil bone debris. Mya 

upright in life position. Outcrop consists of the 

stratigraphically highest bed that is exposed immediately southeast of east Twin Lake on southwest 

shore of Narrow Cape (northeast entrance to U gak 

Bay), Kodiak Island, Alaska. Outcrop exposed in bluffs 

at head of beach and a short distance to northeast along 

southeast valley slope of east Twin Lake. This bed, 

about 50 ft thick, immediately overlies a thin calcareous concretionary bed of fine-grained gray unfossiliferous sandstone. Stratigraphic interval immediately 

above this bed is coyered beneath surficial deposits of 

east Twin Lake. Narrow Cape Formation, middle 

Miocene. U.S. Geol. Survey Kodiak B-1 and B-2 

quadrangles, Alaska, 1:63,360, edition of1949. Coll. R. A-260 

C. Allison, 1969 and 1970, C. W. Allison, 1969, and J. 

W. Durham, 1970. 

Bulk collection of fossils from about 290 ft of strata 

exposed in seacliff immediately southeast of south 

Twin Lake, on southwest shore of Narrow Cape, 

Kodiak Island, Alaska. Top oflocality includes highest 

stratigraphic unit exposed southeast of Twin Lakes, a 

very fine to fine-grained gray soft buff-weathering A-264 

blocky fossiliferous sandstone with Mya, Mytilus 

middendorffi, and some fossil bone debris ( = loc. 

A-204). Bottom of locality just northwest of large 

landslide debris cone on beach, stratigraphically in the 

middle of a massive blue-gray fine- to medium-grained 

sandstone unit about 85ft thick ( = unit ofloc. A-180). 

Fossil locality in interval primarily of sandstone, with 

some mudstone and marked by several conspicuous 

concretionary beds and discontinuous concretionary A-266 

horizons. A conspicuous unfossiliferous concretionary 

bed occurs about 50 ft below top of locality; another 

conspicuous 2-ft-thick concretionary bed rich in 

Pseudocardium andMytilus middendorffi occurs about 

40ft above base oflocality. This second bed is a fine- to 

medium-grained calcareous pebbly shell fragment 

sandstone. Locality continues along beach for about 

600ft. Narrow Cape Formation, middle Miocene. U.S. 

17 

Description 

Geol. Survey Kodiak B-1 and B-2 quadrangles, 

Alaska, 1:63,360, edition of 1949. Coll. R. C. Allison, 

1969 and 1970, C. W. Allison, 1969, and J. W. Durham, 

1970. 

Collection from float boulders on beach below loc. A-255. 

Narrow Cape Formation, middle Miocene, Kodiak 

Island, Alaska. Coll. R. C. Allison and C. W. Allison, 

1969. 

Fossils from buff-weathering massive gray fine- to very 

fine-grained sandstone that includes occasional concretions 4-5ft in diameter. Unit exposed in high seacliff 

and about a quarter of a mile northwest along beach on 

southwest side ofNarrow Cape from small point which 

is last of proximal beach visible to northwest from end 

of road on hill between two Twin Lakes. Locality near 

base of this mailsive sandstone which forms cliff and 

near axis of a syncline and highest strata in section 

exposed at beach level. Narrow Cape Formation, 

middle Miocene, Kodiak Island, Alaska. U.S. Geol. 

Survey Kodiak B-1 and B-2 quadrangles, Alaska, 

1:63,360, edition of 1949. Coll. R. C. Allison, 1969. 

Collection from 100-ft-thick unit of massive gray 

brownish-weathering medium-grained sandstone with 

minor concretions and a few lenses of Mytilus middendorffi. Irregular lenses of conglomerate scattered 

throughout unit. Mytilus lenses at base of unit in 

3-ft-thick pea gravel to pebble conglomerate. Mytilus 

bed at top ofunitjust below massive white quartz and 

black chert granule to pebble conglomerate. Base of 

unit about 25 ft stratigraphically above base of this 

seacliff, almost to southwest tip of cape. Base of unit 

about 1,500 ft southeast along beach from southwest 

end of south Twin Lake, Narrow Cape, Kodiak Island, 

Alaska. Exposures in high seacliff. Narrow Cape 

Formation, middle Miocene. U.S. Geol. Survey Kodiak 

B-1 and B-2 quadrangles, Alaska, 1:63,360, edition of 

1949. Coll. R. C. Allison and J. W. Durham, 1970. 

Collection from beach boulder float at top of landslide of 

locality A-180, on beach approximately 800ft southeast of southwest end of south Twin Lake, Narrow 

Cape, Kodiak Island, Alaska. Mytilus middendorffi, 

Dosinia, Mya, and Acila. Narrow Cape Formation, 

middle Miocene. U.S. Geol. Survey Kodiak B-1 and 

B-2 quadrangles, Alaska, 1:63,360, edition of 1949. 

Coll. J. W. Durham, 1970. 

Bulk collection of fossils from uppermost 180 ft of strata 

exposed in seacliff immediately southeast of northeast 

end of south Twin Lake, Narrow Cape, Kodiak Island, 

Alaska. Base of collection 25 ft below conspicuous 

2-ft-thick concretionary bed, rich in Pseudocardium. 

Narrow Cape Formation, middle Miocene. U.S. Geol. 

Survey Kodiak B-1 and B-2 quadrangles, Alaska, 

1:63,360, edition of 1949. Coll. R. C. Allison, J. W. 

Durham, and W. 0. Addicott, 1970. 

Fossils from 40-ft-thick unit of massive hard gray 

medium-grained sandstone with concretions up to 5 ft 

in diameter. Locality in seacliffs immediately southeast of small stream that crosses beach on northeast 

side of Narrow Cape, Kodiak Island, Alaska. Fossils 

located in concretions or concretionary lenses. Unit 

without pebbles. Top of unit is a 1-ft-thick unfossiliferous concretionary bed. Priscofusus, Dentalium, 

Macoma, Mytilus middendorffi, Tellina, and Lucino-
18 

Locality 

A-268 

A-269 

A-271 

A-273 

NORTH PACIFIC MIOCENE RECORD OF MYTILUS (JJLICATOMYTILUS), A NEW SUBGENUS 

Description Locality 

ma. Base of unit about 35 ft stratigraphically above a 

4-ft-thick sandy granule to pebble conglomerate bed. 

Narrow Cape Formation, middle Miocene. U.S. Geol. 

Survey Kodiak B-1 and B-2 quadrangles, Alaska, 

1:63,360, edition of 1949. Coll. W. 0. Addicott, 1970. 

Concretionary bed forming rock rib on beach platform at 

northeast corner of Narrow Cape, Kodiak Island, A-275 

Alaska. Bed located about 25ft stratigraphically above 

basal unconformity of Narrow Cape Formation. Three 

concretionary zones below this bed and above base of 

formation are unfossiliferous. Concretionary beds in 

fine-grained light-gray buff-weathering massive 

sandstone. Narrow Cape Formation, middle Miocene. 

U.S. Geol. Survey Kodiak B-1 and B-2 quadrangles, 

Kodiak Island, Alaska, 1:63,360, edition of 1949. Coli. 

J. W. Durham, 1970. 

Fossils from a 45-ft-thick unit of fine- to very fine-grained 

massive red-brown-weathering fossiliferous 

sandstone. Twenty feet above base of unit 1- to 

2-ft-thick hard concretionary bed bears gastropods and A-276 

bivalves. Top of unit is 1-ft-thick conglomerate lens and 

concretionary bed with Mytilus middendorffi and 

?Fulgoraria. Bottom of unit marked by concretionary 

bed which is loc. A-268. Locality A-276 is about 20 ft 

stratigraphically higher than top of this unit. Locality 

A-269 in seacliff and beach platform that runs for 

about 100 ft along coast immediately northwest of 

northeast tip or point of Narrow Cape, Kodiak Island, 

Alaska. Narrow Cape Formation, middle Miocene. U.S. 

Geol. Survey Kodiak B-1 and B-2 quadrangles, 

Alaska, 1:63,360, edition of 1949. Coli. J. W. Durham, 

1970. [No Mytilus middendorffi collected = field 

identification.] 

Collection from basal 2 ft of a 40-ft-thick massive 

buff-weathering gray fine- to medium-grained 

sandstone with scattered rare pebbles, several pebble A-278 

lenses, and a concretion up to 5 ft in diameter at tip of 

small point. Fossil bed immediately underlain by 

4-ft-thick pebble to cobble conglomerate bed. Locality 

A-271 about 80 ft stratigraphically below loc. A-266. 

Locality A-271 in seacliff exposures on northeast shore 

of Narrow Cape, Kodiak Island, Alaska, between 

promontories or points in small cove southeast of 

stream which crosses beach. Small point immediately 

to southeast impassible on foot at high tide. Narrow 

Cape Formation, middle Miocene. U.S. Geol. Survey 

Kodiak B-1 and B-2 quadrangles, Alaska, 1:63,360, 

edition of 1949. Coll. J. W. Durham, 1970. F-2011 

Fossil collection from 2 ft stratigraphically below top of 

25-ft-thick unit of sandstone. Lower 5 ft of unit 

composed of pebbly medium-grained sandstone; remainder of unit of fine- to medium-grained massive A8711 

gray sandstone. Bottom of unit a 1-ft-thick unfossiliferous concretionary bed; top of unit a 1-ft- to 

6-in.-thick hard concretionary bed bearing Mytilus 

middendorffi. Mytilus middendorffi also occurs in 

lenses 2, 10, and 15ft above base of unit. Kewia occurs 

with Mytilus middendorffi at locality A-273. Locality 

A-273 about 25 ft stratigraphically below conspicuous 

2-ft-thick concretionary bed rich in Pseudocardium. B4162 

Base of unit about 25 ft stratigraphically above 10- to 

25-ft-thick granule to fine pebble conglomerate. Locaiity A-273 in seacliff approximately 900 ft southeast of 

Description 

start of seacliff exposures (southeast of Twin Lakes 

valley) on northeast side of Narrow Cape, Kodiak 

Island, Alaska. Narrow Cape Formation, middle 

Miocene. U.S. Geol. Survey Kodiak B-1 and B-2 

quadrangles, Alaska, 1:63,360, edition of1949. Coll. J. 

W. Durham, 1970. 

Fossils from massive blue-gray fine- to medium-grained 

sandstone unit about 85 ft thick including several 

concretionary beds ( = unit of A-180). Fossils collected 

from 10-15 ft stratigraphically below conspicuous 

2-ft-thick fine- to medium-grained calcareous pebbly 

shell fragment sandstone bed rich in Pseudocardium, 

Mytilus middendorffi, andDosinia. Locality in seacliff 

approximately 600-700 ft southeast of southwest end of 

south Twin Lake, at Narrow Cape, Kodiak Island, 

Alaska. Narrow Cape Formation, middle Miocene. U.S. 

Geol. Survey Kodiak B-1 and B-2 quadrangles, 

Alaska, 1:63,360,edition of 1949. Coll. W. 0. Addicott, 

1970. 

Concretionary lens with Mytilus middendorffi within 

40-ft-thick fine-grained gray sandstone unit. Top of 

unit marked by 2-ft-thick concretionary bed of finegrained gray unfossiliferous sandstone. Base of unit 

(top of loc. A-269) marked by 1-ft-thick fossiliferous 

conglomerate lens and concretionary bed with Mytilus 

middendorffi and ?Fulgoraria. Locality A-276 is 100ft 

northwest of loc. A-269 in the seacliff on northeast 

coast of Narrow Cape, Kodiak Island, Alaska. Next 

100-ft distance along beach to northwest with red 

staining on rock in small cove where small fault strikes 

N. 33° W., dips 53° N. Narrow Cape Formation, middle 

Miocene. U.S. Geol. Survey Kodiak B-1 and B-2 

quadrangles, Alaska, 1:63,360, edition of 1949. Coli. J. 

W. Durham, 1970. [No Mytilus middendorffi collected=field identification.] 

"Fossil cliffs, Pasagshak Pt., Pasagshak Bay, off U gak 

Bay, Kodiak Island, Alaska. Found in sandstone cliffs 

about 20-25 ft above sea level in 6-in-thick bed. Total 

cliff height above sea level about 100 ft. Collected by 

Everett W. Stone, Jr. of Kodiak, 1973." [This may come 

from Narrow Cape rather than Pasagshak Point; 

precise locality considered unknown-R. C. Allison.] 

Narrow Cape Formation, middle Miocene. U.S. Geol. 

Survey Kodiak B-1 and B-2 quadrangles, Alaska, 

1:63,360, edition of 1949. 

University of Oregon locality 

Cape Blanco and south for about 1 Y2 miles. Lower part of 

Empire Formation. Collected by Ellen James. 

University of California, Berkeley, localities 

Fossils from limy lens in sandstone that is about 100ft 

lower than A8710 below unconformity at base of 

Empire Formation and below pumiceous tuff beds. 

A8711 about 400 yards nearer the Cape Blanco light 

than loc. A8710. Astoria Formation, Curry County, 

Oreg. SW%NE% sec. 2, T. 32 S., R. 16 W., Cape Blanco 

15-minute quadrangle. [Lower part of Diller's (1903) 

Empire Formation.] 

Cut on east side of Canyon Road 0.2 mile above Dublin 

Highway at Eden Creek, in NW% sec. 6, T. 3 S., R. 1 W., 

Hayward 7%-minute quadrangle, Alameda County, 

Calif. Sobrante Sandstone. Collected in 1956. 
REFERENCES CITED 19 

Locality 

2982 

3248 

43952 

Description 

Stanford University localities 

Summit of Milpitas-Calaveras Road Gust south ofnorth 

line of sec. 2, T. 6 S., R. 1 E., Calaveras Reservoir 

7112-minute quadrangle), Santa Clara County, Calif. 

Temblor Formation of Crittenden (1951). Collected by 

Harold Hannibal. 

Along road in NElf.!NElf.!NElf.l sec. 14, T. 5 S., R. 1 E., 554 

mm [21.8 in.] S., 181 mm [7.1 in.] E. ofNW cor. La Costa 

Valley 7%-minute quadrangle, Alameda County, Calif. 

Oursan Sandstone of Hall (1958) [locality is incorrectly 

plotted near base ofTice Shale in SWlf.!SElf.l sec. 25, T. 4 

S., R. 1 W., on Hall's (1958) geologic map]. Collected by 

Stanford Geological Survey and W. G. Cooper. 

On coast 5,500 ft north-northwest of northeast tip of 

Narrow Cape, Kodiak Island, Alaska. Narrow Cape 

Formation. Collected by Union Oil Company. 

43953 Along coast 3,800 ft north-northwest of northeast tip of 

Narrow Cape, Kodiak Island, Alaska. Narrow Cape 

Formation. Collected by J. C. Hazzard. 

49046 

NP23 

NP26 

Uncataloged 

collection 

CAS 17 

CAS 19 

CAS 22 

In SElf.!SWlf.l sec. 18, T. 17 S., R. 12 E., Priest Valley 

15-minute quadrangle, San Benito County, Calif. 

Temblor Formation. Collected by R. H. Vaughn, 1957. 

Seacliffbetween Blacklock Point and Floras Lake, north 

of Cape Blanco, Curry County, Oreg. Basal sandstone 

of Empire Formation. Collected by Harold Hannibal, 

1911 or 1912. [Lower part of Diller's (1903) Empire 

Formation.] 

Seacliffs southeast of [Cape Blanco] lighthouse for mile 

along shore, Curry County, Oreg. Basal sandstone of 

Empire Formation. Collected by Harold Hannibal, 

1911 or 1912. [Lower part of Diller's (1903) Empire 

Formation.] 

Near well in SWlf.l sec. 14, T. 17 S., R. 11 E., New Idria 

15-minute quadrangle, San Benito County, Calif., from 

unit in Temblor Formation striking east-west through 

S% sec. 14 and SWlf.l sec. 13, and near Slf.l corner. South 

side of Vallecitos. 

California Academy of Sciences localities 

In sea cliff about llf.l to 1% miles southeast of Cape 

Blanco, Oreg. Empire Formation. [Lower part of 

Diller's (1903) Empire Formation] 

In sea cliff about llf.l to 1 V2 miles southeast of Cape 

Blanco, Oreg. Empire Formation. [Lower part of 

Diller's (1903) Empire Formation.] 

In sea cliff about 3 miles northeast of Cape Blanco, Oreg., 

or about half a mile northeast of Blacklock Point, 

Empire Formation. [Lower part of Diller's (1903) 

Empire Formation.] 

REFERENCES CITED 

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the San Andreas fault, California: U.S. Geol. Survey Prof. Paper 

593-D, p. Dl-Dl2, 4 text figs. 

---1972, Provincial middle and late Tertiary molluscan stages, 

Temblor Range, California, in Symposium on Miocene biostratigraphy of California: Soc. Econ. Paleontologists and 

Mineralogists, Pacific Section, Bakersfield, Calif., March 1972, p. 

1-26, pls. 1-4. 

---197 4, Recognition and distribution of Mytilus condoni Dall, a 

unique Pliocene and Pleistocene bivalve from the Pacific Coast: 

Veliger, v. 16, no. 4, p. 354-358, figs. 1-9. 

---1975, Provincial age and correlation of the Clallam Formation, 

northwestern Washington [abs.]: Geol. Soc. America, Abs. with 

Programs, v. 7, no. 3, p. 289. 

Allison, R. C., and Addicott, W. 0., 1973, The Mytilus middendorffi 

group (Bivalvia) of the North Pacific Miocene [abs.]: Geol. Soc. 

America, Abs. with Programs, v. 5, no. 1, p. 2-3. 

Anderson, Robert, and Pack, R. W., 1915, Geology and oil resources of 

the west border of the San Joaquin Valley north of Coalinga, 

California: U.S. Geol. Survey Bull. 603, 220 p., 14 pls., 5 figs. 

Arnold, R., and Hannibal, H., 1913, The marine Tertiary stratigraphy 

of the North Pacific coast of America: Am. Philos. Soc. Proc., v. 52, 

no. 212, p. 559-605, pls. 37-48, tables. 

Berry, S. S., 1954, On the supposed stenobathic habitat of the 

California sea mussel: California Fish and Game Bull., v. 40, no. 

1, p. 69-73, 1 fig. 

Burk, C. A. 1965, Geology of the Alaska Peninsula-island arc and 

continental margin: Geol. Soc. America Mem. 99, pt. 1, 250 p., pls. 

1-8, figs. 1-28, 1 table. 

Capps, S. R., 1937, Kodiak and adjacent islands: U.S. Geol. Survey 

Bull. 880-C, p. 111-184, pls. 2-10. 

Crittenden, M.D., Jr., 1951, Geologyofthe San Jose-Mount Hamilton 

area, California: California Div. Mines Bull. 157, 74 p., 11 pls., 14 

figs. 

Dall, W. H., 1890, Conchological notes from Oregon: N au til us, v. 4, no. 

8, p. 87-89. 

--1896, Report on coal and lignite of Alaska: U.S. Geol. Survey 

17th Ann. Rept., pt. 1, p. 763-908, pls. 48-58. 

---1904, Neozoic invertebrate fossils, a report on collections made 

by the expedition, in Harriman Alaska expedition, v. 4 (Geology 

and Paleontology), p. 99-122, pls. 9-10: New York, Doubleday, 

Page and Co. (Reprinted by the Smithsonian Institution, 1910). 

---1909, Contributions to the Tertiary paleontology of the Pacific 

Coast, pt. 1, The Miocene of Astoria and Coos Bay, Oregon: U.S. 

Geol. Survey Prof. Paper 59, p. 1-278, pls. 1-23, figs. 1-14. 

Dall, W. H., and Harris, G. D., 1892, Correlation papers Neocene: U.S. 

Geol. Survey Bull. 84, p. 1-349, pls. 1-3, figs. 1-43. 

Diller, J. S., 1903, Description of the Port Orford quadrangle, Oregon: 

U.S. Geol. Survey Geol. Atlas Folio 89, 6 p. 

Durham, J. W., 1953, Miocene at Cape Blanco, Oregon [abs.]: Geol. 

Soc. America Bull., v. 64, no. 12, pt. 2, p. 1504-1505. 

Eichwald, E., 1871, Geognostische-palaeontologische bemerkingen 

iiber die Halbinsel Mangischlak und die Aleutischen lnseln: 

Kaiserlichen Akademie der Wissenschaften, St. Petersburg, p. 

1-200, pls. 1-20. 

Gilbert, C. M., 1943, Tertiary sediments northeast of Morgan Hill, 

California: Am. Assoc. Petroleum Geologists Bull., v. 27, no. 5, p. 

640-646, figs. 1-3. 

Gladenkov, Y. B., 1972, Neogene of Kamchatka (problems of 

biostratigraphy and paleontology): Moscow, Publishing Office 

"Nauka", Trans., v. 214, 251 p., 8 pls., 48 figs., 37 tables. . 

---1974, The Neogene Period in the subarctic sector ofthe Pacific, 

in Herman, Yvonne, ed., Marine geology and oceanography of the 

Arctic Seas: Springer-Verlag, p. 271-281, 3 figs., 2 tables. 

Gladenkov, Y. B., Petrov, 0. M., and Sinel'nikova, V. N., 1972, 

Pliocene-Pleistocene boundary in the north-west Pacific: in 

International Colloquium on the problem "The boundary 

between Neogene and Quaternary", collection of papers, v. 3, p. 

67-73, Moscow. [In Russian and English.] 

Grant, U.S., IV, and Gale, H. R., 1931, Catalogue of the marine 

Pliocene and Pleistocene Mollusca of California and adjacent 

regions .... :San Diego Soc. Nat. History Mem., v. 1, p. 1-1036, 

diagrams A-D, Tables 1-3, figs. 1-15, pls. 1-32. 
20 NORTH PACIFIC MIOCENE RECORD OF MYTILUS CPLICATOMYTILUS), A NEW SUBGENUS 

Gratacap, L. P., 1912, An unusual specimen of Mytilus middendorffi 

Grewingk, from Alaska: Am. Mus. Nat. History Bull., v. 31, art. 6, 

p. 69-70, pl. 7. 

Grewingk, C., 1850, Beitrage zur Kenntniss der orographischen und 

geognostischen Beschaffenheit der Nord-West Kuste Amerikas 

mit den anliegenden Inseln: V erhandlungen der Russischkaiserlichen Mineralogischen Gessellschaft zu St. Petersburg, 

1848-1849, p. 76-424, maps 1-3, pls. 4-7, 2 maps in text. 

Reprinted, 1850, p. 3-351, maps 1-111, pls. 4-7, 2 maps in text, 

Karl Kray, St. Petersburg. 

Hall, C. A., Jr., 1958, Geology and paleontology of the Pleasanton 

area, Alameda and Contra Costa Counties, California: California 

Univ. Pubs. Geol. Sci., v. 34, no. 1, p. 1-90, pls. 1-12, 2 figs., 5 

maps. 

Hertlein, L. G., and Crickmay, C. H., 1925, A summary of the 

nomenclature and stratigraphy of the marine Tertiary of Oregon 

and Washington: Am. Philos. Soc. Proc., v. 64, no. 2, p. 223-282, 

tables. 

Il'ina, A.P., 1963, Mollyuski Neogena Kamchatki [Neogene mollusks 

of Kamchatka]: Vses. Neft. Nauchno-Issled. Geol.-Razved. Inst. 

Trudy (VNIGRI), v. 202, p. 1-242, tables 1-3, pls. 1-54. 

Kanno, Saburo, 1971, Tertiary molluscan fauna from the Yakataga 

District and adjacent areas of southern Alaska: Palaeont. Soc. 

Japan Spec. Paper 16, 154 p., 18 pls. 

Kleinpell, R. M., 1938, Miocene stratigraphy of California: Tulsa, 

Okla., Am. Assoc. Petroleum Geologists, 450 p. 

MacNeil, F. S., 1965, Evolution and distribution of the genusMya, and 

Tertiary migrations of Mollusca: U.S. Geol. Survey Prof. Paper 

483-G, p. G1-G51, 3 figs., pls. 1-11. 

---1967, Cenozoic pectinids of Alaska, Iceland, and other northern 

regions: U.S. Geol. Survey Prof. Paper 553, p. 1-57, pls. 1-25. 

MacNeil, F. S., Wolfe, J. A., Miller, D. J., and Hopkins, D. M., 1961, 

Correlation of Tertiary Formations of Alaska: Am. Assoc. 

Petroleum Geologists Bull., v. 45, no. 11, p. 1801-1809, figs. 1-2. 

Makiyama, J., 1934, The Asagaian molluscs of Yotukura and 

Matchgar: Kyoto Univ. Coll. Sci. Mem., Ser. B, v. 10, no. 2, art. 6, 

p. 121-167, figs. 1 and 2, pls. 3-7. 

Mandra, Y. T., 1949, A new species of Mytilus from the Pliocene of 

Humboldt County, California: Jour. Paleontology, v. 23, no. 1, p. 

104-105, fig. 1. 

Miller, D. J., 1971, Geologic map of the Yakataga district, Gulf of 

Alaska Tertiary Province, Alaska: U.S. Geol. Survey Misc. Geol. 

Inv. Map 1-610 (scale 1:125,000). 

Moore, E. J., 1963, Miocene marine mollusks from the Astoria 

Formation in Oregon: U.S. Geol. Survey Prof. Paper 419, 109 p., 9 

figs., 3 tables, 32 pls., map [1964]. 

Pronina, I. G., 1969, Mollyuski srednemiotsenovyikh otlozhenii 

Kronotskogo raiona vostochogo poberezh'ya Kamchatka [Middle 

Miocene mollusks from deposits in the Kronotskiy region of the 

eastern shoreline of Kamchatka]: Vses. Neft. Nauchno-Issled. 

Geol.-Razved. Inst. (VNIGRI) Trudy, Paleont. Sbornik, 4, Vyp. 

268, p. 244-261, pls. 1-4. 

Sinel'nikova, V. N., and Drushchits, Yu. G., 1971, The biostratigraphy of the Kavran and Enemten deposits of western Kamchatka (Miocene-Pliocene): Akad. Nauk SSSR lzv. Ser. Geol., no. 

5, p. 101-109, text figs. 1-3. 

Slodkevich, V. S. [ =Slodkewitsch], 1934, On the stratigraphy of the 

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USSR Doklady, Earth Sci. Sec. (Akademiya Nauk), C. R. (Dokl.), 

T. 3, no. 1, p. 58-62. 

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Geol.-Razved. Inst. (VNIGRI) Trudy, Seriya A, Vyp. 79, 202 p., 1 

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1, p. 1-17 4, figs. 1-78, pls. 1-10. 

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North America: Elsevier Publ. Co., p. 201-233,2 figs., 3 tables, 14 

pls. 
Page 

A 

Acila ________________ -- -------------- 9, 16, 17 

conradi _________ _ -------------------- 8 

Alameda County, Calif __________________________ 6 

Alaska Peninsula __________________ 1, 5, 7, 11, 12, 13 

Aleutian Islands ________________________________ 5 

Anadara ------------------------------------- 8, 9 

Arenomya ______ ------------------------------ _ 13 

(Arenoyma) elegans, Mya ________________________ 13 

arnoldi, Nassarius ------------------------------ 8 

Ashai Formation ------------------------------ 7, 8 

Astoria Formation ______________________________ 6 

fauna ___ ---------------------------------- 9 

Aulacomya -------------------------------------- 3 

B 

Bear Lake, Alaska __ _ ----------------- 11, 13 

Bear Lake Formation ________________ 1, 5, 11, 12, 13 

Bruclarkia, range zone _________________________ 8 

Burk's unnamed marine rocks, 

Pliocene ________________________ 12, 13 

c 

californianus, Mytilus __ _________________________ 9 

Cancellaria-------------------------------------- 9 

Cape Blanco, Oreg __________________________ 5, 6, 8 

Cape Seniavin ---------------------------------- 11 

Cape Tonki_ _____________________________________ 11 

Castro Valley, Calif______________________________ 6 

Chignik Formation ------------------------------ 13 

Choromytilus ------------------------------------ 2 

ciliatum, Clinocardium __________________________ 13 

Clallam Formation -------------------------- 7, 8, 9 

fauna -------------------------------------- 9 

Clatsop County, Oreg ____________________________ 6 

Clinocardium -------------------------------- 13, 16 

ciliatum ------------------------------------ 13 

pristinum ---------------------------------- 13 

yakatagense -------------------------------- 13 

sp __ __ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ __ __ _ _ __ __ _ _ __ ___ _ __ 13 

Coal Valley Member ____________________________ 13 

Coast Ranges, Calif------------------------------ 8 

condoni, Mytilus ------------------------------ 7, 14 

Mytilus !Mytilus) __________________________ pl. 3 

conradi, Acila ---------------------------------- 8 

Coos Bay, Oreg ------------------------------ 6, 7, 8 

Crenomytilus ________ __ ________________________ __ 2 

Crepidula ------------------------------ 9, 10, 12, 13 

bed ---------------------------------------- 13 rostral is ___________________________________ _ 

ungana ____________ _ ---------------- 13 

sp ----------------------------------------- 13 

D 

Dall, W. H., quoted ___________ _ 

Dentalium _____________________________________ 17 

Diablo Range, Calif______________________________ 8 

Diplodonta _ ____ ____ ______ _____ __________ _ 9 

Dosinia ------------------------------ 8, 9, 16, 17, 18 

Dufrenoyi, Modiola <Mytilus) ____________________ 3, 9 

dufrenoyi, Mytilus _______________________ 9 

INDEX 

[Italic page numbers indicate major references] 

Page 

E 

East Head ___________ _ ------------------ 12 

edulis, Mytilus ________________________________ _ 

elegans, Mya ----------------------------- 13 

Mya !Arenoyma J ___________________________ 13 

Empire Formation ________________________ 5, 6, 7, 8 

Etolon suite, Kavran Series ______________ 3, 4, 8, 14 

F 

Fauna, Astoria Formation_________ ______________ 9 

Clallam Formation ____ __________ ___________ 9 

Narrow Cape Formation ____________________ 8 

Yakataga Formation ________________________ 9 

Ficus __________________ _______________________ 8 

ficus, Mytilus __________________________________ 7, 14 

Foraminiferal chronology, provincial 

benthonic __________________________ 8 

Fossils, bone debris_____________________ 17 

plant _____________________________________ 13 

Fulgoraria ___________ _ _________________ 18 

G 

Glycymeris _ ------------------------------------ 9 

Gratacap, L. P., cited ___________________________ _ 

gratacapi, Mytilus __________________ 4, 5, 7, 11, 12, 15 

My til us (Plicatomytilus) _______ 1, 9, 14; pis. 2, 3 

Grewingk, C., cited ____________________________ 5, 6 

Griswold Hills, Calif ____________________________ 7 

Gulf of Alaska ______________________________ 8, 9, 12 

H 

Henry W. Coe State Park _________ _ 

Herendeen Bay---------------------------------- 13 

highoohiae, Mytilus __________ ___________________ 7 

Hokkaido Island, Japan ________________________ _ 

Hormomya _____________________________________ _ 

Humboldt County, Calif _ ___________ 7, 9 

I, J 

Igatskoi Bay _________ _ 11 

lgatskoj Bay ________ _ 

Introduction __________________ _ 

Ischadium _________ _____________________ 2 

Jewett Sand _______________________________ 7, 8, 9 

K 

Kadiak Island ____ _ --------- 11 

Kakert suite, Kavran Series ______________ 3, 4, 8, 14 

Kamchatka __________________________________ 1, 5, 8 

eastern---------------------------------- 6, 8, 9 

western ____________________ 3, 4, 6, 7, 8, 9, 13, 14 

kannoi, Kewia _______________________ 16 

Kavran River ---------------------------------- 14 

Kavran Series __________________________ 3, 8, 13, 14 

Kavran Suite____________________________________ 6 

Kern River, Calif-------------------------------- Kewia __________________________________________ 18 

kannoi -------------------------------------- 16 

Kings County, Calif_ ____________________________ _ 

Kodiak Island, Alaska __________________ 1, 5, 6, 8, 11 

Kronotskiy area, Kamchatka ____________________ 8 

Kuluven suite ------------------------------ 7, 8, 9 

Page 

L 

Lincoln Stage _________________________________ 12 

Localities, California Academy of Sciences ________ 19 

Stanford University __________________________ 19 

University of Alaska Museum ________________ 16 

USGS, Denver, Colo., register ________________ 15 

Menlo Park, Calif., register ______________ 15 

Washington, D.C., register ______________ 15 

Locality register -------------------------------- 15 

Loca!ity, University of Oregon-------------------- 18 

Lucinoma -------------------------------------- 17 

Luisian Stage ---------------------------------- 8 

Lyropecten miguelensis, range zone________________ 8 

M 

Macoma ______________ _ ____________ 9, 17 

matthewi, Molopophorus__________________________ 8 

middendorffi, Modiolus -------------------- 4, 13, 14 

Mytilus ________________ 1, 2, 3, 4, 5, 7, 9, 10, 11, 

12, 13, 14, 15, 16, 17, 18 

<Plicatomytilus) ________________ 1, 3; pis. 1, 3 

midendorfi, Mytilus ----------------------------- 4 

Milky River ------------------------------------ 13 

Modiola (Mytilus) Dufrenoyi -------------------- 3, 9 

Modiolus middendorffi ____________________ 4, 13, 14 

Molopophorus ------------------------ 8 

matthewi ______________________ ______________ 8 

Montesano Formation---------------------------- 13 

Mya ------------------------------------ 13, 16, 17 

elegans _ ___________________________________ 13 

!Arenomyal elegans __________________________ 13 

(Mya I _____ -------------------------------- 9 

\Mya I, Mya ______ ------------------------------- 9 

Mytilidae _______________ ---------------------

Mytilinae _____________________________________ _ 

Mytiloconcha _______________________ --- ____ ------

Mytilus ____________________ 1, 2, 4, 5, 7, 9, 11, 15, 17 

californianus -------------------------------- 9 

condoni ---------------------------------- 7, 14 

dufrenoyi__ __ _ ___ __ _ _ __ _ ___ ___ ___ ___ ___ __ _ _ __ 9 

edulis _ _ __ _ _ _ _ _ _ ___ ___ _ _ _ _ ___ ___ __ _ _ __ ___ _ __ 2 

ficus ______ ------------------------------- 7, 14 

gratacapi ______________________ 4, 5, 7, 11, 12, 15 

highoohiae ---------------------------------- 7 

middendorffi ________ 1, 2, 3, 4, 5, 7, 9, 10, 11, 12, 

13, 14, 15, 16, 17, 18 

doubtful occurrences ____________________ 7 

incorrect records ___________ -----------· 

Kamchatka reports______________________ 8 

zone _________________________________ 1, 11 

midendorfi ---------------------------------- 4 

ochotensis ---------------------------------- 7 

tichanovitchi ____________________________ 4, 7, 8 

sp ---------------------------------------- 9, 10 

!Mytilus) condoni -------------------------- pl. 3 

(Plicatomytilus )______________________________ 8 

gratacapi __________________ 1, 9, 14; pis. 2, 3 

age -------------------------------- _ 12 

correlation ____________________________ 12 

description ____________________________ 10 

discussion ---------------------------- 11 

distribution pattern____________________ 8 

ecology ________________________________ 13 

holotype ------------------------------ 11 

incorrect record ________________________ 12 

occurrence ---------------------------- 12 

21 
22 

Page 

Mytilus-Continued 

range _________ _ --- 12 

range zone ___________________________ 11 

synonymy ____ ____________________ 9 

type locality ________________________ 11 

IPlicatomytilus) middendorffi ______ 1, 3; pis. 1, 3 

middendorffi, age________________________ 8 

biozone 

correlation _____________________ _ 

8 

8 

discussion _______________ ____________ 5 

ecology___ _ ___________________ 9 

figured specimens______________________ 5 

occurrence ________________ _ 6 

range _______________________________ _ 

synonymy _________________ 3 

iPlica.tomytilus l sp ____________ 1, 4, 8, 9, 13; pl. 2 

sp, age---------------------------------- 14 discussion ____________________________ 13 

figured specimen _____________________ 14 

occurrence ____________________________ 14 

range ___________________ _ 14 

stratigraphic distribution ______________ 14 

synonymy ____________________________ 13 

Mytilus (subgenus?) sp ____________________ 7, 9; pl. 3 

IMytilus) condoni, Mytilus ______________________ pl. 3 

Dufrenoyi, Modiola ________________________ 3. 9 

N 

Narrow Cape_______________ ___________ ________ 5 

Narrow Cape Formation __________________ 5, 6, 8, 11 

fauna _________ ---------------------------- 8 

Nassarius arnoldi____ ___________________________ 8 

0 

ochotensis, Mytilus __ 

Olivella ___________ _ 9 

Olympic Peninsula, Wash__ 7 

Oregon, southwestern___________________________ 8 

Ostrea tigiliana ___________________ 12 

Oursan Sandstone ____________________________ 6, 8 

INDEX 

Page 

p 

Patinopecten, range zone 

propatulus, range zone _ 

Perna _________________________________________ _ 

Plicatomytilus __________________ 1, 2, 8, 9, 11, 13, 14 

description _________________________________ 2 

discussion_ _ _____________________ 2 

geologic range ________________________________ 3 

(Plicatomytilus ), Mytilus __________________________ 8 

gratacapi, Mytilus ______________ 1, 9, 14; pis. 2, 3 

middendorffi, Mytilus ______________ 1, 3; pis. 1, 3 

sp., Mytilus · __________________ 1, 4, 8, 9, 13; pl. 2 

Polovinka River, Kamchatka ____________________ 7 

Popof Island ------------------------------------ 12 

Port Moller---------------------------------- 12, 13 

Priscofusus ____ ___________ ____________________ 17 

pristinum, Clinocardium ________________________ 13 

Pseudocardium ____ 9, 16, 17, 18 

R 

Ratitin suite ---------------------------------- 6, 8 

Reef Ridge, Calif ______________________________ 7, 8 

References cited -------------------------------- 19 

Relizian Stage ---------------------------------- 8 

River Reel'nye-vayam area ___________________ 13, 14 

rostra.lis, Crepidula __ ____________________ 8 

s 

Sacharowschen Bay___ ___________________ 5 

Sakhalin _____________________________________ 7, 8 

San Benito County, Calif ________________________ 7 

San Joaquin basin, Calif ________________________ 7, 8 

San Jose, Calif---------------------------------- 8 

Santa Clara County, Calif_ ____________________ _ 

Saucesian Stage ______________________________ _ 

Securella 9 

Seldovian paleobotanical stage ____________________ 13 

Semimytilus ________________ ___________________ 2 

Shainaga River, Kamchatka______________________ 7 

Shumagin Islands ____________________________ 11, 12 

Siliqua__ __ _ _ __ __ _ _ _ _ __ _ ___ ___ ___ __ __ _ ____ _ _ _ __ __ 9 

Page 

Slodkevich, V. S., cited __________________ ------- 5, 6 

Sobrante Sandstone __________________________ 6, 7, 8 

Solen _ _ __ __ _ _ __ __ _ _ __ __ __ _ ___ __ __ __ ___ __ _ ___ ___ 9 

Spisula -------------------------------------- 9, 16 

Stepovak Formation-------------------------- 12, 13 

(subgenus?) sp., Mytilus ------------------ 7, 9; pl. 3 

Sunol Valley Regional Park______________________ 6 

Swiftopecten swiftii etchegoini zone _______________ 14 

T 

Tejon Hills, Calif ______________________ _ 

Tel/ina--------------------------------------____ 17 

Tellinid bivalves -------------------------------- 13 

Temblor Formation -------------------------- 6, 7, 8 

Temblor Stage ---------------------------------- 8 

Thyasira disjuncta ochotica zone__________________ 7 

tichanovitchi, Mytilus ________________________ 4, 7, 8 

tigiliana, Ostrea __________________________ 12 

Tillamook County, Oreg__________________________ 6 

Tonky Cape ___ -------------------------------- 5 

u 

Ugak Bay _______ _ ---- 5 

Unga Conglomerate Member ____________ 5, 11, 12, 13 

Unga Island, Alaska ______________ 1, 5, 7, 11, 12, 13 

flora __ __ ____ ___ ___ __ _ _ __ __ ___ __ _ ___ ___ ___ _ _ _ 13 

ungana, Crepidula ___ _ ___________________ 13 

V,W 

Vallecitos, Calif ___ __ ______ ------ 7 

Venerid bivalves -------------------------------- 13 

Vertipecten IPatinopecten) zone____________________ 8 

Village Spit ____________________________________ 13 

Willapa Bay, Wash________________ _____________ 7 

Y,Z 

Y aka tag a Formation _ 9 

fauna -------------------------------------- 9 

yakatagense, Clinocardium ______________________ 13 

Zachary Bay---------------------------------- 5, 13 

*U.S. GOVERNMENT PRINTING OFFICE: 1976 0-211-3 17/66 
PLATES 1-3 

[Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal 

Center. Denver, Colo. 80225] 
PLATE 1 

[All figures x 1] 

FIGURES 1-10. Mytilus (Plicatomytilus) middendorffi Grewingk, 1850 (p. 3). 

1. USNM 647057. Length 100 mm. Narrow Cape Formation, Kodiak Island, Alaska. UA loc. 

A-268. 

2. USNM 647058. Length 70 mm. Temblor Formation, Griswold Hills, California. USGS Cenozoic 

loc. M3614. 

3. USNM 64 7059. Length 70 mm. Temblor Formation, Griswold Hills, California. USGS Cenozoic 

loc. M3614. 

4, 6. USNM 647060. Length 102 mm. Lower part of the Empire Formation of Diller (1903), near 

Cape Blanco, Oregon. USGS Cenozoic loc. M5737. 

5. USNM 647061. Length 47 mm, a rubber cast. Lower part of the Empire Formation of Diller 

(1903), near Cape Blanco, Oregon. USGS Cenozoic loc. M4130. 

7. USNM 64 7062. Length 86 mm, a rubber cast. Lower part of the Empire Formation of Diller 

(1903), near Cape Blanco, Oregon. USGS Cenozoic loc. M4130. 

8. USNM 64 7063. Length 90 mm. Narrow Cape Formation, Kodiak Island, Alaska. U A loc. A-183. 

9. USNM 64 7064. Length 87 mm. Temblor Formation, Griswold Hills, California. USGS Cenozoic 

loc. M3614. 

10. USNM 64 7065. Length 92 mm. Narrow Cape Formation, Kodiak Island, Alaska. UA loc. A-256. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 962 PLATE 1 

9 10 

MYTILUS (PLICATOMYTILUS) MIDDENDORFFI 
PLATE 2 

[All figures x 1] 

FIGURES 1, 3, 4, 6-10. Mytilus (Plicatomytilus) gratacapi, n. sp. (p. 9). 

1, 3, 9, 10. Holotype USNM 647066. Length: right valve 70 mm, left 

valve 71 mm. Bear Lake Formation, Alaska Peninsula, Alaska. 

USGS Cenozoic loc. M5182. 

4. USNM 647067. Length 72 mm. Unga Conglomerate Member of the 

Bear Lake Formation, Alaska Peninsula, Alaska. USGS Cenozoic 

loc. M1022. 

6. USNM 647069. Length 53 mm. Bear Lake Formation, Alaska 

Peninsula, Alaska. USGS Cenozoic loc. M5182. 

7, 8. USNM 647070. Length: right valve 57 mm, left valve 56 mm. Bear 

Lake Formation, Alaska Peninsula, Alaska. USGS Cenozoic loc. 

M5 182. 

2, 5. Mytilus (Plicatomytilus) n. sp. (p. 13). 

USNM 647084. Length 77 mm. Kakert suite of the "Kavran Series", 

mouth of the Kavran River, western Kamchatka, U.S.S.R. 

Geological Institute, Moscow, loc. 69. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 962 PLATE 2 

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MYTIL US (PLICA TOMYTIL US) GRATA CAP! AND 

MYTILUS (PLICATOMYTILUS) N. SP. 

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PLATE 3 

]All figures x 1] 

FIGURES 1, 3, 5, 7, 8. Mytilus (plicatomytilus) gratacapi n. sp. (p. 9). 

1. USNM 647071. Length 72 mm. Bear Lake(?) Formation, Herendeen 

Bay, Alaska. USGS Cenozoic loc. M5174. 

3. USNM 647072. Length 70 mm. Bear Lake Formation, Port Moller, 

Alaska. USGS Cenozoic loc. M805. 

5. USNM 647073. Length 70 mm. Bear Lake Formation, Port Moller, 

Alaska. USGS Cenozoic Joe. M805. 

7. USNM 64 7074. Length 63 mm. [Bear Lake Formation.] North side of 

Port Moller, Alaska. USGS Cenozoic loc. 5046. 

8. USNM 647075. Length 52 mm. Bear Lake Formation, Port Moller, 

Alaska. USGS Cenozoic Joe. M805. 

2, 4, 6. Mytilus (plicatomytilus) middendorffi Grewingk, 1850 (p. 3). 

2. USNM 647065. Length 92 mm. Narrow Cape Formation, Kodiak 

Island, Alaska. UA loc. A-256. 

4. USNM 64 7076. Length 95 mm. Lower part ofthe Empire Formation 

of Diller (1903), near Cape Blanco, Oregon. USGS Cenozoic loc. 

M4130. 

6. USNM 647060. Length 102 mm. Lower part of the Empire 

Formation of Diller (1903), near Cape Blanco, Oregon. USGS 

Cenozoic loc. M5737. 

9. Mytilus (subgenus?) n. sp. (p. 7). 

USNM 647077. Length 68 mm. Pyramid Hill Sand Member of the 

Jewett Sand, Kern River area, California. USGS Cenozoic loc. 

M1591. Although this undescribed species is not referable to 

Plicatomytilus, it is found in the Jewett Sand of California, the 

Clallam Formation of Washington, and the Kuluven suite of 

western Kamchatka. 

10. Mytilus (Mytilus) condoni Dall, 1890 (p. 7). 

USNM 647078. Length 55 mm. Unnamed strata of late Pliocene age, 

Willapa Bay, Washington. USGS Cenozoic loc. M5219. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 962 PLATE 3 

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MY TIL US (PLICA TOM YTIL US) GRATA CAP!, MYTIL US (PLICA TOMYTIL US) MIDDENDORFFI, 

MYTILUS (SUBGENUS?) N. SP., AND MYTILUS (MYTILUS) CONDON!