JOSEPH C. BR1TTON, Two New Species and

a New Subgenus of

Lucinidae {Mollusca:

Bivalvia), with Notes on *

Certain Aspects of .

Lucinid Phylogeny

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY NUMBER 129
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INTERNATIONAL BOOK YEAR • 1972
SMITHSONIAN CONTRIBUTIONS TO

ZOOLOGY

NUMBER 129

Joseph c. Button, jr. Tw o New Species and

a New Subgenus of

Lucinidae (Mollusca:

Bivalvia), with Notes on

Certain Aspects of

Lucinid Phylogeny

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1972
ABSTRACT

Britton, Joseph C. Two New Species and a New Subgenus of Lucinidae (Mollusca: Bivalvia), with Notes on Certain Aspects of Lucinid Phylogeny. Smithsonian Contributions to Zoology, number 129, 19 pages, 6 figures, 1972.—Two

new western Atlantic species of Lucinidae, Lucina (Pleurolucina) hendersoni,

new species, and Parvilucina (Bellucina) rehderi, new species, are described and

figured. A new subgenus, Radiolucina (type-species, Phacoides amiantus Dall,

1901), of the genus Parvilucina is proposed. Certain aspects of the shell morphology of several groups of Lucinidae with similar hinge structure are compared.

The nature of radial ornamentation in the subgenus Pleurolucina appears to

differ significantly from that of Pai~uilucina or Radiolucina, suggesting the former should be considered distinct from the latter groups. Certain aspects of the

shell morphology of Bellucina is demonstrated to be sufficiently distinct from

that of species such as Parvilucina amiantus (Dall, 1901) to justify the establishment of a new subgenus, Radiolucina, for the latter. Several additional aspects

of lucinid phylogeny are considered.

Official publication date for each title is hnndstamprd in a limited number of initial copies and

is recorded in the Institution's annual report, Smithsonian Year.

Library of Congress Cataloging in Publication Data

Britton, Joseph C.

Two new species and new subgenus of Lucinidae (Mollusca: Rivalvia)

(Smithsonian contributions to zoology, no. 129)

Bibliography: p.

1. Parvilucina rehderi. 2. Lucina hendersoni. 3. Lucinidae.

I. Title. II. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 129

QL1.S54 no. 129 [QL430.7.L8] 59!'.08s [594M1] 72-3864

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

Washington, 1). C. 20102 - Price S"> cents (paper cover)
Joseph C. Button, Jr. Two New Species and

a New Subgenus of

Lucinidae (Mollusca:

Bivalvia), with Notes on

Certain Aspects of

Lucinid Phylogeny

Introduction

Within the family Lucinidae (Mollusca: Bivalvia)

there is a large, complex assemblage of species

sharing several similar morphological characteristics, the most noticeable being the similarity of

hinge structure. Because previous authors have assigned these species to several different supraspecific categories, each of the supraspecific taxa

discussed herein must be defined. Table 1 contains

a list of the taxa and their type-species.

Except for minor modifications, all of the groups

listed in Table 1 possess a full complement of

lucinid dental elements. The following Bernard

dental formula (see Cox, et al., 1969:N56, for an

explanation of the Bernard formula) characterizes

the hinge of this assemblage:

AIII 3a 3b PHI

AM AIV 4b PII PIV

In some species of each of the groups except

Lticina, sensu stricto, and Bellucina, the right anterior cardinal tooth (3a) fails to develop or is

obscured by encroachment of the lunule; whereas

in some groups (particularly Bellucina) the left

dorsal lateral teeth (AIV and PIV) may be reduced.

Considering the total variation of dentition within

the entire family, these variations are slight and

Joseph C. Britlon, Department of Biology, Texas Christian

University, Fort Worth, Texas 76129.

suggest that these groups are more closely related

to each other than to any other group (s) of Lucinidae (e.g., Codakia has weak or obsolete posterior

laterals, Miltha lacks lateral dentition entirely, and

Anodontia is edentulate).

Previous authors (particularly Dall, 1901; Chavan, 1937, 1938, 1969; and Bretsky, 1969) have recognized the basic similarity of dentition among

the groups listed in Table 1, but their phylogenetic

and systematic interpretations vary according to

the degree of emphasis each author places upon

(1) subtile variations of hinge dentition, (2) other

aspects of shell morphology, or (3) a combination

of these two.

Although there were several earlier works which

purported to be revisionary, Dall (1901) should be

considered the "first reviser" of the Lucinidae. He

recognized the tremendous diversity of the lucinids

and attempted to demonstrate this knowledge nomenclatorially. Unfortunately, many of his nomenclatorial opinions were to confuse rather than to

clarify lucinid phylogeny. Dall recognized only six

genera of Lucinidae: Lucina Bruguiere, 1797 [typespecies considered by Dall to be Lucina edentuia

(Linnaeus, 1758), by subsequent monotypy, Lamarck, 1799]; Loripes Cuvier, 1799; Codakia Scopoli, 1777; Myrtea Turton, 1822; Phacoides

Blainville, 1825; and Divaricella von Martens,

1880. He subdivided each of these genera into several subgenera and sections. He considered all of

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE l.—Supraspecific taxa of Lucinidae receiving primary consideration in this publication

Taxon Synonym Type-species

Pleurolucina Dall, 1901

l.ucina Bruguiere, 1797

Dallucina Olsson and Harbison, 1953

Paslucina Olsson, 1964

lAnga deGregorio, 1885

Quasi lucina Stewart, 19S0

Here Gabb, 1866

Parvilucina Dall, 1901

Bellucina Dall, 1901

Radiolucina, new subgenui

Cavilinga Chavan, 19S7

Lucina leucocyma Dall, 1886, o.d.1

Lucina (Here) amabilis Dall, 1898, o.d.

Lucina (Paslucina) follis Olsson, 1964,

o.d.

Venus pensylvanica Linnaeus, 1758,

s.d.1, Schumacher, 1817

Lucina columbella Lamarck, 1819 s.d.,

Sacco, 1889 [fide Chavan, 1969]

Lucina carnifera Conrad, 193S, o.d.

Lucina (Here) richtofeni Gabb, 1866

(=Lucina excavata C a r p e n ter,

1857), s.d. Stoliczka, 1871

Lucina tenuisculpta Carpenter, 1864,

o.d.

Parvilucina eucosmia Dall, 1901 ( =

Lucina semperiana Issel, 1869), o.d.

Phacoides (Bellucina) amiantus Dall,

1901, designated herein

Lucina trisulcata Conrad, 1841, o.d.

1

 o.d. — original designation.

1

 s.d.=subsequent designation.

the species mentioned in Table 1 to be within his

largest and most inclusive genus, Phacoides (see

Table 2).

The most important aspect of this first revision

of the Lucinidae is the phylogenetic relationships

which can be inferred from it. Assuming Dall's

"subgenera" to roughly correspond to Bretsky's

(1971) higher "phenon groups," Dall recognized

two basic lineages: the Here lineage (corresponding to the Lucina lineage of this paper) including

the species Phacoides richtofeni, P. pensylvanica,

P. leucocyma, and P. trisulcata; and the Paivilucina

lineage (the Parvilucina, sensu lato, lineage or the

Parvilucina-Radiolucina-Bellucina complex of this

paper) including the species Phacoides tenuisculpta,

P. semperiana, and P. amiantus. As will be shown,

there is considerable merit to an arrangement of

this type.

Chavan (1937, 1938) obviously drew heavily

from Dall's classification of the Lucinidae, but his

interpretation of the family was influenced by two

new opinions: that Phacoides was a term introduced in the vernacular and was not a name available for zoological nomenclature, and that Lucina

jamaicensis (Spengler, 1784)* (=Tellina pectinata

Gmelin, 1791) was the type-species of Lucina according to subsequent designation. The problem

of the type-species of Lucina is a complex nomenclatorial matter. Except as indicated here it is beyond the scope of the present paper. (For additional information, see Chavan, 1937, 1938, 1952;

'Chavan (1937) and several other authors have cited Spengler, 1784, as the author of L. jamaicensis. Chemnitz (1784)

described Venus jamaicensis from the cabinet of Spengler.

The specimens Chemnitz described were apparently labeled

"jamaicensis" in Spenglcr's hand for purposes of identification within the collection ("Diese muschel wird im Spenglerischen Cabincttc Venus Jamaicensis genannt, wclche Benennung ich sehr gerne behbehalte," Chemnitz, 1784). Spengler

<lid not publish the name jamaicensis prior to publication of

Tellina pectinala Gmelin, 1791. Thus, Chemnitz (1784), not

Spengler, should be credited with the first use of jamaicensis

in a published work. Note that Chemnitz (1784) is on the

list of officially rejected works of the International Commission on Zoological Nomenclature.
NUMBER 129

TABLE 2.—Comparison of supraspecific assignments by previous authors of certain species of Lucinidae

(Type-species are indicated by an asterisk (*) in each column according to the interpretation of the author whose name appears

at the top of each classification. Only those species which were explicitly specified by a particular author as belonging to a

particular taxon arc included in that author's classification.)

Dall, 1901 Chavan, 1937, 1938 Bretsky, 1969, 1971 Chavan, 1969

Genus Phacoides

Subgenus Here

Section Here s.s.1

*richtojeni

pensylvaniea

Section Pleurolucina

*leucocyma

Section Cavilucina Fischer, 1887

trisulcata

Subgenus Parvilucina

Section Parvilucina s.s.

•tenuisculpta

Section Bellucina

*semperiana

amiantus

Genus Linga

Subgenus Linga s.s.

*columbella

pensylvaniea

Subgenus Here

*richtofeni

Subgenus Pleurolucina

*leucocyma

amiantus

Subgenus Cavilinga

•trisulcata

Subgenus Parvilucina

•tenuisculpta

Subgenus Bellucina

*semperiana

Genus Lucina

Subgenus Lucina s.s.

*pensylvanica

Subgenus Here

*richtofeni

Subgenus Pleurolucina

*leucocyma

Subgenus Cavilinga

• trisulcata

Subgenus Parvilucina

* tenuisculpta

Subgenus Bellucina

*semperiana

amiantus

Genus Linga

Subgenus Linga ts.

*columbella

Subgenus Pleurolucina

*leucocyma

Subgenus Bellucina

*semperiana

Genus Here

Subgenus Here s.s.

*richtofeni

Genus Parvilucina

Subgenus Parvilucina s.s.

• tenuisculpta

Subgenus Cavilinga

*trisulcata

•s.s.=sensu stricto.

Bretsky, 1969; Britton, 1970.) Thus, instead of the

groups of Table 1 being considered of the genus

Phacoides, Chavan placed them in the genus Linga.

He affirmed that phylogenetic relationships between and among these taxa were very difficult

to understand, and proposed a taxonomic solution

whereby each of the major lineages within his

genus Linga were subgenera with more-or-less equal

status. Like Dall, Chavan recognized all of the

groups of Table 1 to be more closely related to

each other than to other Lucinidae, a fact which

becomes less obvious in his more recent classification (Chavan, 1969). The details of both Chavan

classifications are given in Table 2. Note that

Chavan (1937, 1938) considered Phacoides amiantus Dall, 1901, to be a member of the subgenus

Pleurolucina rather than Bellucina to which it

was originally referred by Dall. Much more will

be said of this matter shortly.

In the more recent Chavan classification (1969),

several groups previously considered subgenera are

elevated to genera, including Here and Parvilucina

(Table 2). Pleurolucina and Bellucina are considered subgenera of the genus Linga; whereas

Cavilinga is a subgenus of the genus Parvilucina.

Hence, Chavan (1969) does not consider Bellucina

to be as closely related to Parvilucina as it was

originally considered by Dall (1901).

A few months before publication of Chavan's

more recent classification, Bretsky (1969) completed

a doctoral dissertation on phenetic and phylogenetic classifications of the Lucinidae. Bretsky's systematic treatment of the Lucina, sensu lato, complex

is quite similar to that of Chavan (1937, 1939), as

she considers each of the groups subgenera of a

single taxon (Table 2). Yet her classification differs

in several details from both of Chavan's classifications. For example, Bretsky gives a very convincing

argument (accepted in this paper) favoring Schumacher's (1817) subsequent designation of Venus

pensylvaniea Linnaeus, 1758, as the first valid typespecies designation of Lucina. She also rejects

Chavan's contention that Phacoides amiantus Dall,

1901, is a Pleurolucina, placing it in the subgenus

Bellucina. Bretsky indicates, however, that specimens ol the type-species of Bellucina (i.e., speci-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

mens of Lucina semperiana Issel, 1869) were not

available for her examination. Hence, Bretsky's

concept of Bellucina is based on P. amiantus and

its close relatives rather than upon the type-species.

Some of these data have subsequently been published (Bretsky, 1971).

While preparing a monograph of the Western

Atlantic Lucinidae, I discovered two new species

which help to clarify relationships among the taxa

of Table 1. One of the new species also has been

influential in the decision to designate a new subgenus, although it is not of the new subgenus

itself. The new species and new subgenus are described below, followed by a discussion of their

significance and relationship to the taxa of Table 1.

Acknowledgments

This paper is based on data obtained in part during preparation of a doctoral dissertation for The

George Washington University, under the direction

of Dr. Harald A. Rehder, National Museum of

Natural History, Smithsonian Institution. I would

like to express my gratitude to Dr. Rehder for

many valuable hours of consultation which helped

make this work possible, and for numerous helpful

suggestions during preparation of the manuscript.

I am also indebted to Dr. Joseph Rosewater, also

of the National Museum of Natural History, for

additional guidance and criticism.

Lucina (Pleurolucina) hendersoni, new species

FIGURES I, 2, and 6c

TYPE.-Holotype, USNM 503399; type-locality,

off English Harbor, Antigua in 120 fms.

DESCRIPTION.—General Form: Shell attaining

12.5 mm in length and 12.3 mm in height, more

or less trigonal, equivalve, inequilateral with beaks

posterior to midlength, valves moderately inflated;

posterodorsal margin gently curving from beak to

beyond posterior termination of hinge plate; posterior margin gently curving to marginal termination of posterior sulcus, there becoming indented;

posteroventral, ventral, and anteroventral margins

smoothly curving (see p. 6); anterior margin

slightly projecting, indented at marginal termination of dorsalmost anterior sulcus; anterodorsal

margin slightly arching above hinge plate.

Beaks, Umbos: Beaks coiled under umbos, posterior to midlength of shell. Umbos coiled, prosogyrate, distinctly projecting above body of shell.

Sulci, Folds, Ridges: Posterior sulcus strong, extending from beak to ventral margin; posterior

a

FIGURE \.-Lucina (Pleurolucina) hendersoni, new species, holotype, USNM 503399: a, external

aspect of left valve; b, internal aspect of left valve. Length, 12.3 mm.
NUMBER 129

FIGURE 2.—Paratype specimens of Lucina (Pleurolucina) hendersoni, new species, USNM 712452. Note how ventral marginal outline becomes less irregular with increase in size.

Length of (e), 10.2 mm; others to scale.

dorsal area bearing sculpture as on body of shell.

Three or four anterior sulci variably expressed;

dorsalmost anterior sulcus strongly impressed, extending from beak to anterior margin, forming distinct anterior dorsal area or pseudolunule; second

or next posteriormost sulcus relatively strong on

dorsal half of valve, but becoming weak or obscure

toward margin; third sulcus restricted to umbo,

centrally located, crossing few strongly elevated

concentric lamellae; fourth sulcus extremely obscure, occuring only on dorsal portion of umbo between third sulcus and posterior sulcus.

Lunitlc, Escutcheon, External Ligament Area:

Lunule very small, slightly depressed, located immediately ventral of and extending slightly posterior

to beaks, essentially symmetrical, not projecting.

Escutcheon absent. Insufficient material to describe

ligament suture or nature of external ligament

area.

Ornamentation: Except for sulci noted above,

radial ornamentation absent; concentric sculpture

consisting of several widely spaced, distinctly erect,

concentric lamellae, fewer than one lamella per

millimeter at a point between 4 and 5 millimeters

ventral to umbo, dorsal edge of each lamella

sharply formed; secondary concentrics present on

interspaces between primary lamellae, low, feeble,

numerous in each interspace; primary lamellae interrupted by posterior and first anterior sulcus,

interrupted on dorsal half of shell by second anterior sulcus, and interrupted on umbo by third

anterior sulcus.

Internal Shell Morphology: Hinge plate moderately thickened; ligament opisthodetic, moderately inset, relatively short; dorsal lamellar layer

very thin, extending from beak to half-way to anterior termination of posterior laterals, in contact

with ventral fibrous layer along entire length of

latter; fibrous layer separated from posterior laterals by undifferentiated portion of hinge plate

almost equal to length of posterior laterals, moderately thickened centrally, separated from ventral margin of hinge plate by undifferentiated

region narrower than width of ligament area.

Dentition of right valve including anterior lateral tooth (A HI), opisthocline, narrow, sharply

pointed, distinctly protruding, separated from anterodorsal margin by shallow groove, ventral portion of tooth on distinct ridge of hinge plate and

with cusp to receive left ventral anterior lateral;

hinge plate narrowing toward cardinal area; anterior lateral separated from anterior termination

of lunule; lunule not jutting, majority of lunule

under and posterior to beaks; anterior cardinal

tooth (3a) small, feeble, slightly elevated, essentially orthocline, positioned on ventral portion of

hinge plate and slightly posterior to anterior termination of lunule, separated from posterior cardinal by small narrow socket to receive left anterior

cardinal; posterior cardinal tooth (3b) moderately

enlarged, prosocline, bifid, situated on ventral margin of hinge plate, anterior portion projecting

slightly ventrad, separated from ligament area by

broad shallow socket to receive left posterior cardinal; posterior lateral tooth (p in) prosocline, moderately elongate, distinctly elevated but less so
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

than right anterior lateral, separated from posterodorsal margin by narrow groove, ventral surface

with distinct cusp to receive left ventral posterior

lateral.

Dentition of left valve including two orthocline

anterior lateral teeth with ventral member somewhat anterior to dorsal member; dorsal anterior

lateral tooth (A IV) not strongly elevated, separated

from dorsal margin by broad shallow groove, separated from ventral anterior lateral by broad, deep

socket to receive right anterior lateral; left ventral

anterior lateral tooth (A II) bluntly pointed, distinctly projecting, located on ventral portion of

hinge plate posterior and immediately dorsal to

dorsal termination of anterior adductor muscle impression; anterior laterals separated from cardinal

area by undifferentiated portion of hinge plate

extending approximately three times length of left

dorsal anterior lateral; lunule as in right valve;

anterior cardinal tooth (2) essentially orthocline,

distinctly projecting, located on ventral projection

of hinge plate, not elongate in dorsoventral axis,

dorsal termination of tooth separated from ventral

rim of lunule by narrow depression, apex of tooth

lying almost ventral and slightly anterior to anterior termination of posterior cardinal, separated

from latter by relatively deep, broad socket to receive right posterior cardinal, less remote from

beak than corresponding tooth in P. leucocyma;

posterior cardinal tooth (4b) prosocline, lamelliform, distinctly elevated, separated from ligament

area by narrow undifferentiated portion of hinge

plate; posterior lateral teeth prosocline; dorsal posterior lateral tooth (p iv) very weak, slightly elevated, separated from ventral posterior lateral by

elongate socket to receive right posterior lateral;

left ventral posterior lateral tooth (P II) strongly

elevated, elongate, apex bluntly rounded and almost appearing flattened, posterior termination of

tooth immediately dorsal to dorsal termination of

posterior adductor muscle impression.

Anterior adductor muscle impression elongate,

more or less typically lucinoid, somewhat L-shaped,

pallial line junction slightly dorsal to midlength

of adductor impression, dorsal and ventral portions

of impression undifferentiated, anterior pedal retractor impression small, separated from anterior

adductor impression, located immediately above

dorsal termination of latter and immediately below

anterior termination of anterior laterals; pallial

line typical, relatively narrow; posterior adductor

muscle impression relatively small, ovate, bluntly

pointed dorsally, rounded ventrally, pallial line

junction slightly above distalmost portion of impression. Line of gill attachment and pallial blood

vessel impression faintly indicated. Internal ventral margin finely crenulate.

Soft Parts: Neither living specimens nor specimens with preserved soft parts were available for

study.

Color of Shell: All fresh specimens examined

possessed uniformly chalky white shells.

Measurements: There are no paired valves of

this species available for study. Measurements below are in millimeters.

length

12.3

9.4

6.5

4.4

12.5

9.9

9.8

9.2

9.1

8.5

6.5

5.2

height

12.3

9.1

6.5

4.0

12.0

10.9

9.9

9.5

8.9

8.5

6.1

4.9

inflation

4.4

3.0

2.0

1.6

4.0

3.6

3.1

2.9

2.7

2.7

1.9

1.7

holotype

paratypc

paratype

paratype

Off Payne's Bay Church, Barbados

Off Payne's Bay Church, Barbados

Off Telegraph Station, Barbados

Off La Habana, Cuba

Off Payne's Bay Church, Barbados

Off Payne's Bay Church, Barbados

Off Telegraph Station, Barbados

Off Pelican Id., Barbados

VARIATION.—With very few specimens available

for examination, only a few remarks on variation

are possible here. Marginal outline changes noticeably with the growth of the shell (Figure 2). In

younger shells (6 mm or less in length) there are

two distinct marginal indentations: one on the

posteroventral margin at the termination of the

posterior sulcus, and the other on the anteroventral

margin at the termination of the second anterior

sulcus. As the shell increases in size, the second

anterior sulcus becomes progressively weaker until

it is no longer impressed in the ventral portion of

the shell. Concurrently the anteroventral indention

of the shell margin becomes less noticeable. In the

adult (8 mm or more) this area is smoothly curving without a trace of indentation.

The spacing of primary concentric lamellae on

the shell exterior of the holotype is representative

of the condition observed in most specimens available for study. In one valve (a single specimen

from off La Habana, Cuba) these lamellae are more

numerous than on the holotype and considerably

more closely spaced (about two per millimeter).
NUMBER 129

The lamellae of this specimen does not approach

even closely the high density condition of the

lamellae of L. leucocyma, but it certainly demonstrates that a potential for more numerous, more

closely spaced primary concentrics exists within the

lineage.

REMARKS.—This species is named in honor of

J. B. Henderson, Jr., a collector extraordinaire during the early years of this century.

L. hendersoni is a species linking Lucina, sensu

stricto, with Pleurolucina. The nature of the external sculpture is very similar to that of Lucina

pensylvanica, and L. hendersoni also possesses a

distinct pseudolunule or anterior dorsal area quite

similar to that of the Lucina, sensu stricto, assemblage. The secondary sulcations, however, are

decidedly as in Pleurolucina, even if they are incompletely indicated in the adult. These sulcations

are discussed in considerable detail below. The

nature of the shell interior further establishes the

affinities of L. hendersoni with Pleurolucina. This

species and L. leucocyma are almost identical in all

characters of internal shell morphology except in

the left valve the anterior cardinal of L. hendersoni is less ventrally jutting on the hinge plate,

less remote from the beak, and the socket between

this tooth and the posterior lateral is shallower

and narrower than in L. leucocyma. L. hendersoni

shares many common characteristics with the fossil

Lucina (Paslucina) follis Olsson, 1964, from the

early Miocene of Ecuador.

RANGE.—Based on the present records for this

species, L. hendersoni is assumed to occur in moderate depths from Cuba to the Lesser Antilles. It

appears to be quite uncommonly collected.

MATERIAL EXAMINED.—CUBA: off La Habana in

127 fms (USNM). LESSER ANTILLES: off English

Harbor in 120 fms, off Paynes Bay Church in 50

fms, off Telegraph Station in 50 to 60 fms, and off

Pelican Is. in 100 fms, Barbados (all USNM).

Parvilucina (Bellucina) rehderi, new species

FIGURE 3

TYPE.-Holotype, USNM 208255; type-locality,

Brazil.

DESCRIPTION.—General Form: Shell attaining 4.2

mm in length and 4.2 mm in height, subtrigonal,

equivalve, slightly inequilateral with beaks posI K.I'RK 3.—Parvilucina (Bellucina) rehderi, new species, holotype, USNM 208255: a, external aspect of the left valve; b,

external aspect of right valve; c, internal aspect of left

valve; d, internal aspect of right valve; e, dorsal aspect of

paired valves. Length, 4.2 mm.

terior to midlength, valves moderately inflated.

Posterodorsal margin slightly curving from beak

to point near posterior termination of hinge plate,

thereafter passing rather abruptly ventrad; posterior margin straight; posteroventral margin

rather sharply angular; posterior margin gently

curving to about midlength of shell, thereafter arc

of curve becomes sharper; anteroventral margin

somewhat produced but smoothly curving; anterior

margin dorsoventrally straight for short distance;

anterodorsal margin arching above anterior laterals.

Beaks, Umbos: Beaks small, depressed, adjacent

but not touching. Umbos moderately projecting

above body of shell.

Sulci, Folds, Ridges: Posterior sulcus broad and

widening ventrally, sufficiently depressed to indi-
8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

cate posterior dorsal area; posterior dorsal area

distinct, tending to be elevated marginally. Anterior sulcus poorly impressed; anterior dorsal area

poorly differentiated.

Lunule, Escutcheon, External Ligament Area:

Lunule distinct, approximately as long as wide,

inserted slightly beneath beak, extending from

there to point immediately posterior to posterior

termination of anterior laterals, depressed, slightly

unsymmetrical with portion on right valve projecting and portion on left valve recessed. Escutcheon absent. External ligament area quite short,

about one-half width of lunule.

Ornamentation: Dominant sculpture concentric,

lamellae elevated, thickened, moderately spaced,

interspaces between lamellae at least width of lamellae and usually broader, lamellae on ventral portion

of valve usually more elevated than those on upper

third of valve, lamellae often appear scalloped by

forming nodules in positions adjacent to elevated

regions of radial sculpture; radial ribs present but

poorly distinguished, best developed in interspaces

between concentric lamellae particularly on dorsal

third of valve, appearing as poorly elevated columnar elements between concentrics, rarely sufficiently

distinct so as to appear to cross concentrics although

ventral nodes on some concentric lamellae may be

fused with some ribs; ribs broad, separated by very

shallow, narrow interspaces; ribs tend to become

progressively less distinct toward ventral margin

or to lie primarily upon dorsal surface of the

broadest concentric lamellae instead of being located only in interspaces between lamellae. Very

low scales formed by local elevations of concentric

lamellae tend to occur on posterior dorsal area.

Internal Shell Morphology: Hinge plate noticeably thickened; ligament opisthodetic, slightly

inset, quite short, extending from beak to approximately midlength between beak and apex of

I>osterior laterals, extending only slightly beyond

posterior termination of cardinal plateau; material

insufficient to determine nature of ligament layers.

Dentition of right valve including anterior

lateral tooth (A HI), large, bulbous, prominently

elevated, located immediately in front of and ventral to anterior termination of lunule, resting on

ventrally projecting ridge of hinge plate, separated

from anterodorsal margin by broad groove, possessing cusp on ventral surface to receive left ventral anterior lateral; right anterior cardinal tooth

(3a) present, opisthocline, small, slightly crowded

by encroachment of lunule, more or less lamelliform, extending from point ventral and anterior

to posterior termination of lunule and passing anteroventrally, not in contact with ventral margin

of hinge plate, separated from ventral surface of

lunule by shallow groove, contacting dorsal termination of right posterior cardinal but separated

from remainder of latter by triangular socket receiving left anterior cardinal; right posterior cardinal tooth (3b) prosocline, large, well elevated,

separated from ligament area by elongate socket

receiving left posterior cardinal; right posterior

lateral tooth (P HI) elongate, anteriorly broad,

posterior portion centrally excavated to receive left

posterior lateral, separated from posterodorsal

margin by broad groove, separated from cardinal

area by undifferentiated portion of hinge plate

less than length of posterior lateral.

Dentition of left valve including two anterior

lateral teeth; dorsal anterior lateral tooth (A IV)

extremely feeble, essentially obsolete; ventral anterior lateral tooth (A II) bluntly pointed, moderately elevated, occupying ventrally projecting ridge

of hinge plate, located noticeably in front of and

ventral to dorsal anterior lateral, separated from

latter by deep socket receiving right anterior

lateral; left cardinal teeth lamelliform; anterior

cardinal tooth (2) orthocline, noticeably elevated,

extending from posterior termination of lunule

toward but not reaching ventral termination of

hinge plate, separated from greater portion of

lunule by narrow socket receiving right anterior

cardinal, separated from left posterior cardinal by

broad triangular socket receiving right posterior

cardinal; left posterior cardinal tooth (4b) prosocline, extending from near posterior termination

of lunule toward ventral margin of hinge plate,

essentially adjacent and in contact with ligament

area; two posterior lateral teeth; dorsal posterior

lateral tooth (p iv) extremely feeble, essentially

obsolete; ventral posterior lateral tooth (P II) bulbous, elevated, positioned on ventrally projecting

ridge of hinge plate, located behind and below

dorsal posterior lateral, separated from latter by

broad, elongate socket receiving right posterior

lateral.

Anterior adductor muscle impression longer

than wide but very short, pallial line joining anterior adductor impression near ventral termina-
NUMBER 129 9

tion of latter; anterior pedal retractor muscle

impression small, separate from anterior adductor

muscle impression, ovate, located on lower surface

of anterior lateral tooth of each valve; posterior

pedal retractor impression obscure. Line of gill

attachment and pallial blood vessel impression

not indicated on specimens available for study.

Ventral margin dentate, almost appearing fluted.

Soft Parts: Neither living specimens nor specimens with preserved soft parts were available for

study.

Color of Shell: All specimens examined possessed

uniformly chalky white shells.

MEASUREMENTS.—Including the holotype, there

were 26 left valves and 30 right valves of the new

species P. rehderi available for study. Measurements (in mm) given below are of a representative

series selected from this material.

width inflation

(paired (unpaired

length height values) values)

42 42 4.1 _ holotype

5.7 S.7 - 1.9 paratype

S.5 S.6 - 1.8 paratype

92 32 - 1.4 paratype

S.I 3.0 - 1.4 paratype

3.0 3.0 - 1.4 paratype

2.8 2.9 - 1.3 paratype

2.7 2.7 - 1.3 paratype

2.4 2.4 - 1.1 paratype

2.3 2.4 - \2 paratype

VARIATION.—The most noticeable variation observed among the specimens available for study

concerns the thickness and spacing of concentric

lamellae and the degree to which radial elements

of sculpture are developed and expressed on the

shell exterior. Radial sculpture never approaches

the degree of expression demonstrated by that of

Parvilucina (Bellucina) semperiana.

In Parvilucina rehderi, the posterior sulcus tends

to be more deeply impressed in some specimens

than in others. In those specimens with a more

deeply impressed posterior sulcus the angles

formed along the posterior margins of the shell

tend to be more acute.

The degree to which the shell is produced anteroventrally is variable. Some specimens possess

an anteroventral margin only slightly produced,

whereas others demonstrate a markedly extended

anteroventral margin.

Among those characters which demonstrate very

little variation are the nature of the hinge and

dentition, the nature of the lunule, and the nature

of the anterior adductor impression and its junction with the pallial line.

REMARKS.—The species name honors Harold A.

Rehder of the National Museum of Natural History, Smithsonian Institution.

Although the hinge plate of P. rehderi is not

quite as broad as that of P. semperiana (Figures

3 and 4a), these two species demonstrate virtually

identical hinge structure and dentition. Most other

species of shell morphology correspond closely

between the two species. P. semperiana differs from

P. rehderi, however, in being larger, with a slightly

shorter and more noticeably unsymmetrical lunule.

The anterior dorsal area of P. semperiana tends

to be slightly more distinct than that of P. rehderi.

Similarly, the radial sculpture of the former species

is more apparent but by no means dominant. Most

aspects of the internal shell morphology of the two

species are identical, including the nature of the

anterior adductor impression and its junction with

the pallial line.

Some criticism may be leveled at the description

of a new species based on one lot from such a

generalized locality as Brazil. Were it not for the

fact that significant sculptural and other differences

tend to separate P. rehderi and P. semperiana, I

would be hesitant to describe the new form. However, there is definite morphological differentiation

between the two. It is with some reluctance, therefore, that the new species is proposed; perhaps

workers in the western South Atlantic region will

be advised to search for additional records of this

small species.

Parvilucina rehderi is certainly closely related to

Parvilucina (Bellucina) semperiana (Issel, 1869).

The latter is of the type of the subgenus Bellucina,

hence P. rehderi is a member of the subgenus

Bellucina. Thus, P. rehderi is the first species of

Bellucina described from the Western Atlantic.

RANGE AND MATERIAL EXAMINED.—The species is

known only by a single lot of material. The only

locality record given is "Brasil."

Genus Parvilucina

Subgenus Radiolucina, new subgenus

TYPE-SFECIES.— Phacoides amiantus Dall, 1901

DIAGNOSIS.—Shell suborbicular to slightly elongate, equivalve, moderately to well inflated, usually
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

less than 20 mm. Anterior and posterior dorsal

areas moderately to weakly indicated; lunule moderately elongate, narrow, unsymmetrical with portion in right valve slightly wider, not inserted

beneath beaks, slightly to moderately depressed;

escutcheon absent or very narrow. Dominant

sculpture radial, consisting of less than 20 broad,

prominently elevated ribs; concentric sculpture

consisting of numerous fine lamellae, moderately

spaced, elevated on and between ribs, definitely

secondary in prominence to radials. Periostracum

thin, obscure; ligament external, poorly depressed,

extremely short. Hinge plate usually dorsoventrally broad; anterior and posterior lateral teeth

well developed, single in right, paired in left valve;

two cardinal teeth in left valve, right anterior

cardinal tooth (3a) usually present but weak, right

posterior cardinal tooth (3b) strong. Anterior adductor muscle impression relatively short, junction

with pallial line usually ventral to midlength of

muscle impression; anterior pedal retractor muscle

impression separate from anterior adductor impression. Ventral margin crenulate.

REMARKS.—Since the original description of

Phacoides amiantvs Dall, 1901, the systematic position of this species has been subjected to several

interpretations (Table 2). Most recently, Bretsky

(1969) suggested the possibility that P. amiantus

might represent a lineage distinct from any previously designated group. She rejected Chavan's

(1937, 1938) assignment of P. amiantus to PleuroIttcina on grounds never adequately explained but

presumably according to some of the points developed in the discussion below. Because she

lacked specimens of the type-species of Belhicina

(Lucina semperiana Issel, 1869) with which she

could compare P. amiantus, Bretsky accepted Dall's

assignment of the latter to Belhicina, noting that

P. amiantus and L. semperiana could be of distinct

lineages.

I have had an opportunity to compare Phacoides

amiantus with specimens of Lucina semperiana and

several other species (Figure 4, Table 3). I believe

P. amiantus represents a distinct lineage within the

Lucinidae, for reasons given in the discussion.

Thus, I propose the new subgenus, Radiohicina,

for those species similar to Phacoides amiantus

Dall, 1901. This includes the Recent Eastern Pacific species Lucina cancellaris Philippi, 1846, and

several Tertiary fossils, including Phacoides waccamawensis Dall, 1903, Phacoides tuomeyi Dall,

1903, Lucina katherinepalmerae Weisbord, 1964,

Phacoides nereidcdita Maury, 1910, and Phacoides

euphaea Gardner, 1926.

DISCUSSION.—The discussion is primarily concerned with two considerations previously noted

by Bretsky (1969): (1) the possibility that Parvihtcina, Bellucina (fide Bretsky; that is, those species

of Radiolucina herein), and Plcurolucina form "a

phyletic progression with sequential decrease in

number and increase in size of radial ribs" (Bretsky,

1969:72); and (2) the possibility that "the type of

Bellucina is actually a Parvilucina [or otherwise

not related to Lucina amiantus, JCB] in which

case a new subgeneric name would have to be proposed for the distinctive group of species to which

L. amiantus belongs" (Bretsky, 1969:278).

RADIAL ORNAMENTATION AND THE CONDITION IN

PI.EUROLUCINA.—Both of the above considerations

involve, to a greater or lesser degree, the nature of

radial ornamentation on Plcurolucina. It is generally agreed among the major revisers of the

Lucinidae that Pleurolucina possesses radial "ribs."

An undefined assumption seems to hold that these

ribs are primary elevations upon the shell exterior

and arise in a manner analogous with the ribs of

certain species of Parvilucina and Radiolucina. By

comparing the radial ornamentation of several species of each of these groups, certain trends or

central tendencies within and between the groups

become apparent. Phylogenetic interpretations

may vary according to the direction one assigns

to these tendencies. For example, Bretsky (1969)

presents evidence which favors recognition of a

Pa)~vilucina-Radiolucina lineage (Figure 5). I concur with Bretsky's hypothesis, considering the lineage as possessing "true" radial ribs (i.e., ribs formed

as primary localized elevations above an external

shell base) which demonstrate the tendency to

become more prominently elevated and fewer in

number. Bretsky also suggests that Pleurolucina,

with a few broad radial "ribs," could form a terminal element of the Parvilucina-Radiolucina lineage.

I disagree.

The radial ribs of Pleurolucina do not seem to

be analogous to those of the Parvilucina-Radiolucina complex. The ribs of the former apparently

are not primary elevations above the shell base;

rather they are secondary "elevations" formed subsequent to and mostly as a result of the formation
NUMBER 129

11

FIGURE 4.—Comparison of the type-species of the subgenera Bellucina, Radiolucina, and Pleurolucina: a, Parvilucina (Bellucina) semperiana (Issel, 1869), USNM 598440, right valve exterior,

length 3.2 mm; b, Parvilucina (Radiolucina) amiantus (Dall, 1901), USNM 64276, right valve

exterior, length 8.6 mm; c, Lucina (Pleurolucina) leucocyma Dall, 1886, USNM 83140, right

valve exterior, length 6.8 mm.

of radial sulci (i.e., localized depressions below

the shell base).

Consider the condition of L. (Pleurolucina)

hendersoni, new species. The crest or high point

of each of the "ribs" of L. hendersoni is equivalent

to the base level of elevation on the shell exterior.

Concentric lamellae are elevated above this base

level, while several shell sulci or grooves are incised below it. [According to a figure (Keen, 1958:

97), L. leucocymoides (Lowe, 1935) of the eastern

Pacific has radial elements of sculpture almost

identical to that of L. hendersoni. I have not seen

specimens of L. leucocymoides.] When sulci fail

to be impressed on the ventral third of the valve,

the base level is essentially at the same relative

elevation as the "rib" crests on the more dorsal

portion of the valve. The condition of L. hendersoni is in contrast to that of certain Radiolucina
12

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 5.—Possible sequence of a Parvilucina—Radiolucina lineage with Recent species as examples. All specimens right valves with external view: a, Parvilucina (Parvilucina) tenuisculpta

(Carpenter, 1864), USNM 108826, length 13.6 mm; b, P. (P.) multilineata (Tuomey and Holmes,

1856), USNM 60981, length 5.1 mm; c, P. (P.) peclinella (C. B. Adams, 1852), MCZ 155597,

length 6.8 mm; d, P. (P.) costata (d'Orbigny, 1842), USNM 68S297, length 9.4 mm; e, P.

(Radiolucina) amiantus (Dall, 1901), USNM 64276, length 8.6 mm.
NUMBER 129 13

which also demonstrate a slight tendency toward

ventral obsolescence of radial sculpture [e.g.,

Pai-uilucina (Radiolucina) waccamaxoensis (Dall,

1903) of the South Carolina Pliocene, or P. (R.)

tuomeyi (Dall, 1903), a Miocene species from the

same geographic region]. In these species the base

level on the central valve exterior corresponds not

with the crests of the ribs, but with the floor of the

grooves between the ribs as they exist on the more

dorsal portions of the valve exterior.

An alternative to Bretsky's (1969) Parvihicina,

sensu lato, Plcurolucina progression hypothesis

takes into consideration the nature of radial ornamentation in L. hendersoni. According to the new

hypothesis Pleurolucina is visualized acquiring

radial "ribs" secondarily after sulci formation

rather than as primary formations elevated above

a shell base. The radial ornamentation of L. leucocyma could have arisen just as easily by this secondary, sulci-related process.

The first stage of the progression might be similar to the condition in L. sombrerensis (Dall, 1901),

a Recent western Atlantic species. The shell of

this species almost lacks radial ornamentation. On

the anterior slope of each valve, however, are two

radial sulci. The anteriormost sulcus is slightly

weaker than the other but extends entirely to the

anterior margin. The second or more posteriorly

located sulcus fails to extend entirely to the anteroventral margin. Figure 6a illustrates the external ornamentation on the shell of L. sombrerensis.

The next stage of the series is represented by a

form like L. hendersoni, or the fossil L. follis Olsson, 1964, and has been described (Figure 6r). The

dominance of sulci over "ribs" is obvious in this

stage.

L. lencocyma (Figure 6rf) is an example of the

final stage where the radial "ribs" take the form

of definite elevations. This seems to have been

achieved by two simultaneous developments: (1)

the sulci deepen and widen, while (2) the shell

undergoes a moderate anteroposterior compression

(i.e., a dorsoventral elongation). These two processes acting together cause slight folding of the

radial ornamentation, additional deepening of the

sulci, and elevation of the "ribs."

If Plcurolucina originated in a manner such as

has just been postulated, perhaps additional evidence could be presented suggesting a closer relationship between it and some other lucinid group

lacking primary radial elevations of the shell exterior (i.e., lacking ribs). Such is the case between

Pleurolucina and Lucina, sensu stricto.

THE RELATIONSHIP BETWEEN LUCINA, SENSU STRICTO, AND PLEUROLUCINA.—A cursory examination of

the type-species of Lucina, sensu stricto, and

Pleurolucina gives one cause to doubt that these

species are closely related. Not only is L. leucocyma

considerably smaller than L. pensylvanica and, unlike the latter, possesses "radial" ornamentation,

but the concentric ornamentation of the valve

exterior appears to be different. L. leucocyma

possesses relatively broad concentric lamellae separated by narrow interspaces, whereas L. pensylvanica has fewer narrow primary concentrics separated by wider interspaces. Closer examination

of the shell morphology of the two groups reveals,

however, several important similarities between

them.

The similarity of hinge structures has already

been mentioned. This similarity is an inconclusive correspondence shared by a number of lucinid

groups. Other common features of Lucina, sensu

stricto, Pleurolucina, and Here (a group very

closely related to Lucina, sensu stricto, but differing from it primarily by the nature of the lunule)

can be listed and compared with corresponding

features of the Parvilucina-Radiolucina complex.

1. The lunule of Pleurolucina is either very

small and inserted below and posterior to the beaks

as in Lucina, sensu stricto, or deeply incised in a

manner similar to the condition in Here; whereas

the lunule of Parvilucina, sensu lato, tends to be

more elongate.

2. Most species of Pleurolucina possess a relatively broad anterior dorsal area or pseudolunule

as in Lucina, sensu stricto, and Here; whereas the

anterior dorsal area in Parvilucina, sensu lato,

usually is considerably narrower and less noticeable.

3. The junction of the pallial line with the anterior adductor muscle impression in Pleurolucina

is located dorsal to midlength of the muscle scar

as in the genus Lucina; whereas this condition is

observed rarely among species of Parvilucina, sensu

lato.

4. The posterior sulcus of Pleurolucina is usually well impressed and the posteroventral margin
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 6.—Possible derivation of radial ornamentation in Pleurolucina: a, Lucina (Pleurolucina)

sombrerensis (Dall, 1901), USNM 329253, length 5.9 mm, left valve exterior; b, line drawing of

preceding, indicating position of radial ornamentation; c, L. (P.) hendersoni, new species,

USNM 503399, length 12.3 mm, left valve exterior; d, L. (P.) leucocyma Dall, 1886, USNM

83140, length 6.8 mm, right valve exterior photographically reversed to facilitate comparison

with other specimens.

is noticeably incised at the termination of this

sulcus; this condition occurs in Lucina, sensu

stricto, and Here, but is expressed weakly or not

at all in Parvilucina, sensu lato.

The major weakness in the case for a close

phylogenetic relationship between Pleurolucina

and Lucina, sensu stricto, has been the nature of

external ornamentation of the two groups. Simi-
NUMBER 129 15

larly, this has seemed to be one of the major arguments for a relationship between Pleurolucina and

Parvilucina, sensu lato. If differences of shell ornamentation between the former pair could be satisfactorily accounted for, the case for a closer

relationship between these groups would be considerably strengthened. By resolving the matter

of radial ornamentation in Pleurolucina in the

preceding section, there remains only to demonstrate some degree of relationship between the two

groups with regard to concentric lamellae. L. hendersoni, new species, can be employed again to

represent an intermediate stage between the two

types.

There should be little doubt that L. hendersoni

is a Pleurolucina, considering the typical five sulci

of the shell exterior and the close correspondence

of its internal shell morphology with that of L.

leucocyma. Its concentric lamellae are quite unlike

those of L. leucocyma, being very narrow, well elevated, and broadly spaced in a manner similar to

that expressed by L. pensylvanica. Thus, species

such as L. hendersoni seem to suggest a transitional

stage betwene Lucina, sensu stricto, and Pleurolucina with respect to concentric ornamentation

and the other morphological shell characters mentioned above.

A good case can be made, then, for a close phylogenetic relationship between Pleurolucina and

Lucina, sensu stricto. Now consider the relationships of Pleurolucina and Parvilucina, sensu lato.

RELATIONSHIPS OF RADIOLUCINA, BELLUCINA, AND

PLEUROLUCINA.—Radiolucina, Bellucina, and Pleurolucina are compared primarily to demonstrate the

need for the new subgeneric designation, and also

to establish a basis for additional phylogenetic considerations (Figure 4). Table 3 summarizes certain

morphological shell characteristics of each of the

type-species. Most species of Parvilucina, sensu

stricto, produce weak or relatively feeble elements

of radial ornamentation; hence, this subgenus is

omitted from the present discussion. Bretsky (1969)

has pointed out the tendency of some Parvilucina,

sensu stricto, species to produce relatively stronger

radial elements which approach the condition of

Radiolucina.

Radiolucina and Bellucina share a number of

very similar morphological shell characters including several not included in Table 3. Hence, both

are considered of the Parvilucina, sensu lato, lineage (see Bretsky, 1969). The justification for designating the former group as a new subgenus, however, is based primarily on differences with respect

to (1) the nature of the ventral margin, (2) certain

aspects of cardinal and lateral dentition, and especially (3) the nature of external ornamentation.

The latter difference is particularly pronounced.

Radial ribs of Radiolucina are unquestionably

dominant over concentric lamellae, usually tending to obscure the latter. In Bellucina the condition is reversed with the concentric lamellae being

dominant. Radial sculpture in Bellucina is restricted to interspaces between concentrics giving

the appearance of numerous separate, short columnar elements.

The basic difference between Pleurolucina and

Radiolucina with respect to radial ornamentation

has already been discussed. In addition, there are

a number of other dissimilarities between analgous

characters of the two groups. These include (1)

the nature of the lunule, (2) the position of the

junction of the pallial line with the anterior adductor impression, (3) the nature of the anterior

dorsal area, and to a lesser degree (4) the nature

of the ventral margin and (5) certain aspects of

hinge dentition (Table 3). Similar differences exist between Pleurolucina and Bellucina. Thus,

Pleurolucina appears to be more remotely related

to Radiolucina and Bellucina than the latter two

are related to one another. This is an additional

justification, then, for considering Pleurolucina

outside the Parvilucina, sensu lato, lineage.

CONCLUSIONS.—A systematic revision of those

groups listed in Table 1 is proposed. A summary

of the revision follows, including names of only

those species given primary consideration herein.

Genus Lucina

Subgenus Lucina, sensu stricto, including L. pensylvanica.

Subgenus Here, including L. richtofeni.

Subgenus Pleurolucina, including L. leucocyma,

L. hendersoni, and L. sombrerensis.

Genus Parvilucina

Subgenus Parvilucina, sensu stricto, including P.

tenuisculpta.

Subgenus Radiolucina, including P. amiantus.

Subgenus Bellucina, including P. semperiana and

P. rehderi.
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE $.—Comparison

Characters

ORNAMENTATION

Radial elements

Concentric elements

DORSAL AREAS

Anterior dorsal area

Posterior dorsal area .

LUNULE

LOCATION OF JUNCTION OF ANTERIOR

ADDUCTOR IMPRESSION AND

PALLIAL LINE

HINGE STRUCTURE

Appearance of hinge plate

Length of ligament area .

Left dorsal lateral teeth

(AIV and PIV)

Right anterior cardinal (3a)

VENTRAL MARGIN

of certain morphological

Radiolucina

Strongly elevated ribs, crossing or superimposed over

concentrics

Lamellae

Poorly differentiated

Distinct with portion of area

consisting exclusively of

concentric sculpture

Usually as long as wide,

never deeply excavated,

slightly unsymmetrical

Pallial line joining anterior

adductor impression near

ventral termination of latter; pallial line appears

fused to outer surface of

anterior adductor impression along most of length

of latter

Strongly thickened

Very short

Present but weaker than

typical

Faintly indicated or obsolete

Coarsely crenulate

shell characters for three

Bellucina

Poorly elevated ribs, not

crossing or superimposed

over concentrics

Lamellae

Poorly differentiated

Moderately expressed with

portion of area consisting

exclusively of concentric

sculpture

Usually as long as wide,

never deeply excavated,

slightly unsymmetrical

As in Radiolucina

Moderately thickened

Very short

Essentially obsolete

Present

Very coarsely crenulate,

almost fluted

lucinid sub genera

Plcurolucina

Sulci and sometimes

secondarily-formed ribs

Lamellae

Moderately distinct

Distinct

Either obscure and deeply

inserted beneath beaks or

noticeably excavated,

symmetrical

Pallial line joining anterior

adductor impression dorsal

to midlength of latter;

pallial line appears to be

free of anterior adductor

impression for about 2/3

length of latter

Moderately thickened

Short

Well developed

Obsolete

Finely crenulate

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Index

(Names of new subgenus, species, and page numbers of principal accounts in italics).

amabilis, Lucina, 2

amiantus, Bellucina, 3

Linga, 3

Lucina, 3, 10

Parvilucina, 11 (fig.), 12 (fig.), 15

Phacoidcs, 2, 3, 4, 9, 10

Plcurolucina, 3

Anodontia, 1

Bellucina, 1, 2, 3, 4, 9, 10, 11, 15, 16

amiantus, 3

srmperiana, 3

cancellaris, Lucina, 10

rarnifera, Lucina, 2

C.avilinga, 2, 3

trisulcata, 3

C.avilucina, 3

trisulcata, 3

Codakia. 1

columbclla, Linga, 3

Lucina, 2

costata, Parvilucina, 12 (fig.)

Dallucina, 2

Divaricella, 1

cndcntula, Parvilucina, 2

cuphaca, Phacoides, 10

cxcavata, Lucina, 2

follis, Lucina, 2, 7, 13

Here. 2. 3, 13, 14, 15

richtofeni, 3

hendersoni, Lucina (Plcurolucina) 4

(fig.), 5 (fig.), 11, 13, 14 (fig.), 15

katherinepalmcrae, Lucina, 10

lcucocyma, Linga, 3

Lucina, 2, 3. 7. 11 (fig.), 13, 14 (fig.),

15

Phacoides, 2, 3

Plcurolucina, 3

lcucocyinoidcs, Lucina, 11

Linga, 2, 3

amiantus, 3

columbclla, 3

pcnsylvanica, 3

richtofeni, 3

semperiana, 3

trisulcata, 3

Loripes, 1

Lucina, 1,2, 3, 4, 7. 13, 14, 15

amabilis, 2

amiantus, 3, 10

cancellaris, 10

carnifera, 2

columbella, 2

cxcavata, 2

follis, 2, 7, 13

(Plcurolucina) hendersoni, 4 (fig.), 5

(fig.), 11, 13, 14 (fig.), 15

kathcrinepalmerae, 10

leucocyma, 2, 3, 7, 11 (fig.), 13, 14

(fig.), 15

leucocymoides, 11

pcnsylvanica, 3, 7, 13, 15

richtofeni, 2, 3, 15

sombrcrensis, 13, 14, 15

tcnuisculpta, 2, 3

trisulcata, 2, 3

Miltha, 1

multilineata, Parvilucina, 12 (fig.)

Myrtea, 1

ncrcidedita, Phacoides, 10

Parvilucina, 2, 3, 10, 13, 14, 15

amiantus, 11 (fig.) 12 (fig.), 15

costata, 12 (fig.)

cdcntula, 2

miltilineata, 12 (fig.)

pectinclla, 12 (fig.)

(Bellucina) rehderi, 7 (fig.), 8, 9, 15

semperiana, 11 (fig-), 15

tcnuisculpta, 3, 12 (fig.), 15

trisulcata, 3

tuomeyi, IS

wacamawensis, 13

Paslucina, 2

pectinata, Tcllina, 2

pcctinella, Parvilucina, 12 (fig.)

pcnsylvanica, Linga, 3

Lucina, 3, 7, 13. 15

Phacoides. 2, S

Venus, 2

I'hacoides, 1, 2, 3

amiantus, 2, 3, 4, 9, 10

euphaea, 10

leucocyma, 2, 3

nereidedita, 10

pcnsylvanica, 2, 3

richtofeni, 2, 3

semperiana, 2, 3

tcnuisculpta, 2, S

trisulcata, 2, 3

tuomeyi, 10

wacamawensis, 10

Pleurolucina, 2, 3, 7, 10, 11, 13, 14 (fig.),

15, 16

amiantus, 3

leucocyma, 3

Quasilucina, 2

(Radiolucina), 2, 9, 10. 11, 15, 16

rehderi, Parvilucina (Bellucina), 7

(fig.), 15

lichtofeni, Here, 3

Linga, 3

Lucina, 2, 3, 15

Phacoides, 2, 3

semperiana, Bellucina, 3

Linga, 3

Parvilucina, 11 (fig.). 15

Phacoides, 2. 3

sombrcrensis, Lucina, 13, 14, 15

Tellina, 2

pectinata, 2

tcnuisculpta, Lucina, 2, 3

Parvilucina, 3, 12 (fig.), 15

Phacoides, 2, 3

trisulcata, Cavilinga, 3

Cavilucina, 3

Linga, 3

Lucina, 2, 3

Parvilurina, 3

Phacoides, 2, 3

tuomcyi, Phacoides, 10

Parvilucina, 13

Venus, 2, 3

pcnsylvanica, 2

wacamawensb, Parvilucina, 13

Phacoides, 10

19 U. S. GOVERNMENT PRINTING OFFICE: 1»72 484-922/28



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