Occasional papers - San Diego Society of Natural History

FOSSIL MOLLUSKS

OF SAN DIEGO COUNTY

ELLEN J. MOORE

SAN DIEGO

SOCIETY OF NATURAL HISTORY

OCCASIONAL PAPER 15

FOSSIL MOLLUSKS

OF

SAN DIEGO COUNTY

ELLEN J. MOORE

Associate Curator of Paleontology
San Diego Natural History Museum

f

San Diego Society of Natural History

Balboa Park, San Diego, California

Occasional Paper 15

1968

CONTENTS

Page

Introduction 5

Acknowledgments 8

Classes of moUusks 8

Pelecypods (clams) 8

Gastropods (snails) 8

Cephalopods 12

Scaphopods (tusk shells) 12

Terminology 12

Geologic age and description of fossil mollusks 15

Jurassic 15

Cretaceous 15

Eocene 25

Pliocene 33

Pleistocene 56

References 73

YEARS AGO

ERA

PERIOD OR EPOCH

APPROXIMATE AGES
OF FOSSIL MOLLUSKS

10,000-

30,000 -

100,000

300,000 -

1,000,000

3,000,000

10,000,000

30,000,000

CENOZOIC

100,000,000

300,000,000

1,000,000,000 1

3,000,000,000 -

MESOZOIC

PALEOZOIC

HOLOCENE

PLEISTOCENE

PLIOCENE

MIOCENE

PRECAMBRIAN

OLIGOCENE

EOCENE

PAL EOCENE

CRETACEOUS

JURASSIC

TRIASSIC

PERMIAN

PENNSYLVANIAN

MISSISSIPPIAN

\ DEVONIAN
SILURIAN
ORDOVICIAN
, CAMBRIAN

PLEISTOCENE
100,000

PLIOCENE
5,000,000

EOCENE
45,000,000

. CRETACEOUS
W 80,000,000

4 JURASSIC

^ 140,000,000

Table 1. Geologic time scale and the ages of fossil mollusks in San
Diego. Time-scale boundaries from Harland and others (1964).

INTRODUCTION

Many times in the geologic past, the area that is now San Diego
has been partly or wholly beneath the sea. The most recent time in
which that occurred was about 100,000 years ago, toward the end of
the Pleistocene Epoch, and the oldest for which we have a fossil
record was in the Jurassic Period, about 140 million years ago
(Table 1). These submergences are recorded by sedimentary rocks
containing marine fossils. Such fossils may be collected in and near
San Diego from rocks of those ages and of Cretaceous, Eocene, and
Pliocene age, about 80,000,000, 45,000,000, and 5,000,000 years old
respectively.

A fossil is a trace or a remnant of an animal or plant preserved
from a past geologic epoch. Remnants of animals that lived in the
present, or Holocene Epoch, are not technically fossils, even if they
represent extinct species. For example, the last passenger pigeon is
not a fossil. The youngest fossils are those of organisms that lived in
the Pleistocene Epoch, which ended approximately 10,000 years ago.

The age of a fossil may be determined by its position in a rock
sequence. The fossils in a given rock layer or bed are generally
younger than those in underlying beds. Geologic age can also be deter-
mined by radioisotope dating — by ascertaining the extent to which
radioactive isotopes, such as carbon- 14 and potassium-40, of known
decay rate and original concentration, have decayed in the enclosing
rocks.

Shell middens, disposal piles accumulated by Indians, are very
common in the San Diego area. Most of the shells in these middens
are not fossils, but unfortunately, some can be mistaken for fossils,
especially when they roll down cliffs and come to rest on rocks con-
taining true fossils. Since Pleistocene rocks may contain fossil shells
of species that are not yet extinct, this can cause confusion.

One of the first fossils from California to be described was a
Pliocene oyster, Ostrea vespertina, which was named in 1854 by
Timothy A. Conrad, a famous paleontologist at the Academy of Natu-
ral Sciences of Philadelphia. This oyster occurs in Pliocene rocks in
San Diego and also in the Imperial Valley.

Among the publications on fossil moUusks of the San Diego area
are those of Marcus A. Hanna on the Eocene fauna of the La Jolla
area, those of Leo G. Hertlein and U. S. Grant IV on the Pliocene
fauna of San Diego; the Pleistocene fauna is treated in papers by
W. K. Emerson, E. P. Chace, W. O. Addicott, Frank Stephens, and
J. W. Valentine.

Not all of the fossil mollusks found in the San Diego area can be
described and illustrated in this guide. Those species chosen for in-
clusion are common in the area, highly distinctive, or were first col-
lected in or near San Diego.

In this guide the dimensions of fossil shells are given in centi-
meters, which can be converted to inches by means of a conversion
scale on the outside back cover. The fossils have been photographed
at their natural size when possible. For some very small or large shells,
however, this was not practical. The small shells are magnified to
make them easier to identify, and the large ones are reduced to accom-
modate a page. If x 2 appears after a fossil name, the shell is twice as
large in the photograph as is the actual specimen. If x ^ appears with
the name, the image is half the size of the specimen.

A person who intends to collect fossils should bear two things in
mind. The first is that a permit is required to collect on government
land, and the permission of the owner on private land. The second is
that the locality at which each specimen was collected should be
recorded. A fossil is of most scientific value if the precise locality
from which it came is known. The locality description should be so
worded as to enable another collector to find the locality with as little
trouble and as much certainty as possible. Just "Pacific Beach" is not
much help, whereas ''2000 feet north of Crystal Pier, Pacific Beach,
San Diego County, California, in cliff 20 feet above tide level at
2:00 p.m.. May 15, 1968," is more useful. If it is possible also to
describe the locality by latitude and longitude, as it can be measured
on a topographic map, such precision is most helpful. A paleontologist
also records his name, the date, and the age of the rocks from which
the specimen was taken, if the age is known.

The first step in identifying a fossil is to determine what kind of
an animal or plant was fossilized. Is it a sand dollar, a clam, a coral,
a seed, a leaf, or the tooth of a shark. Usually this is obvious, but
sometimes even the experts are stumped. Books of a general nature

are the most useful source for preliminary identifications. Examples
of such books are:

Moore, R. C, Lalicker, C. G., and Fischer, A. G., 1952, In-
vertebrate fossils : New York, McGraw-Hill Book Company, Inc.,
766 p., illus.

Moore, R. C., ed., 1953 to date. Treatise on invertebrate
paleontology : Geol. Soc. America and Univ. Kansas Press, pts. A
through X, illus.

Shimer, H. W., and Shrock, R. R., 1944, Index fossils of
North America : New York, John Wiley and Sons, Inc., 837 p.,
303 pis.

The next step is to go to a paper on the fossil fauna of the area
from which your fossil came, such as Hanna (1927) on the Eocene
of La JoUa and this book, or to a monograph on the particular type of
organism, such as Hertlein and Grant (1960) on brachiopods, or
Keen (1958) on mollusks. By comparison with pictures in the books,
the identification of the fossil can usually be narrowed down to one
of two or three species. Then the description is checked, and a further
refinement to a specific name can be made.

A fossil mollusk collected in the San Diego area can be dated
on the basis of the maps in this book that show the distribution of
rocks of various geologic ages. When you have determined the age,
compare the fossil with illustrations of fossils of the same age in this
guide. If a similar one is found, a check against the description, to
see if it agrees with your specimen, helps to strengthen the identifica-
tion. For fossils not illustrated in this book, those of Cretaceous age
should be checked in Anderson (1958), of Eocene age in Hanna
(1927), of Pliocene age in Hertlein and Grant (1960) and Grant and
Gale (1931), and of Pleistocene age in Grant and Gale and in books
on modern shells such as Keen (1958) or Abbott (1954). The Treatise
on Invertebrate Paleontology is also of particular help in the identifi-
cation of fossils; parts I, J, K, L, M, and N are devoted to mollusks.

The San Diego Museum of Natural History welcomes gifts of
fossils, especially with adequate collecting data. Some are retained in
the study collections used by specialists, some are put on exhibit,
some are added to teaching collections used by students, and some
may be exchanged with other museums and universities.

ACKNOWLEDGMENTS

It is a pleasure to acknowledge the assistance of my colleagues at
the San Diego Museum of Natural History. Edward C. Wilson, for-
mer curator, was particularly helpful and encouraging. The photo-
graphs of all but the Cretaceous fossils were taken by Dallas Clites,
and the drawings in plates 1, 2, and 3 were made by Anne Acevedo.
Arnold Ross, Curator of Invertebrate Paleontology, read the manu-
script as technical critic.

Leo G. Hertlein of the California Academy of Sciences kindly
provided photographs of Cretaceous fossils, read the manuscript as
technical critic, and also assisted me in other ways. The geologic maps
were prepared by George W. Moore, U. S. Geological Survey. Ed-
ward C. Wilson, Los Angeles County Museum, Edwin C. Allison,
San Diego State College, and Warren O. Addicott, U. S. Geological
Survey, read the paper as technical critics, and Frank C. Calkins,
U. S. Geological Survey, read it as a critic of style. I am indebted to
all of these people.

CLASSES OF MOLLUSKS
PELECYPODS (clams). — A clam usually possesses two similar
shells or valves that are hinged and that the living animal can open
and shut at will (Plate 1). The shells are kept open by the tension of
an elastic ligament at the hinge except when they are closed by the
contraction of muscles attached to the insides of the shells. The im-
pressions or scars left on the shells where the muscles were attached
can usually be seen in fossil clams (Plate 17a). On some, one scar is
at the front or anterior end and one at the rear or posterior end of
the shell. The outside of the shell may be smooth or may be marked
or sculptured with radial ribs, concentric lines, or spines, not all, how-
ever, occurring on one specimen as on the composite drawing on
Plate L

GASTROPODS (snails). — Most snails have a single shell that
is spirally coiled (Plate 2). Many have a calcareous or chitinous plate
(operculum) that is used to close the aperture of the shell, and occa-
sionally these are also found as fossils. A few snail shells are coiled
flat in one plane like watch springs. The shells may be sculptured
either with spines, nodes, axial ribs, or spiral cords.

muscle
scar

pallial line
crenulafions

teeth

EXTERIOR

spine

radial rib
interspace

Plate 1. Terminology for clam shells.

concentric
ine

10

spines

concentric
ribs

height

T

spire

body
whorl

aperture
siphonal canal

width ^

Plate 2. Terminology for snail shells.

11

\

/'

Plate 3. Cross-section of Nautilus shell, x >^.

12

CEPHALOPODS. — This group includes the squid and octopus,
which have no external shell, and other forms that do have them;
among these are the chambered Nautilus (Plate 3), which lives today,
and ammonites (Plate 6), which became extinct at the end of the
Cretaceous.

The cephalopod shell is like a cone, either straight as in some fossil
species or coiled in one plane. The animal lives only in the larger end,
and builds a wall or partition between that and the rest of the shell.
When it has outgrown its chamber it moves forward and builds a new
partition behind its body. The shell thus consists of many chambers,
or rooms, each one larger than the one formed before it, and all empty
but the youngest and largest.

The partition between two rooms, which is called a septum, is at-
tached to the inner surface of the shell along a line called a suture
r Plate 4). The outline of this suture is important in the classification
and identification of cephalopods. The nautiloids have simple septa and
therefore simple sutures; the septa and sutures of ammonites are
fluted and convolute near their edges; these convolutions may be ex-
tremely intricate. The compartments in any individual are all con-
nected by a slender tube called a siphuncle (Plate 3). The siphuncle
and sutures can often be seen in fossil cephalopods, and these features
immediately separate them from the gastropods, which have no such
structures.

SCAPHOPODS (tusk shells). — The shell of a scaphopod is a
slightly curved tapering tube, open at both ends (Plate 4). Most
present-day species of the Scaphopoda live in deep water.

TERMINOLOGY

In scientific terminology, fossil and living mollusks bear two Latin
names, as do all animals and plants. The first, or generic name is the
genus, that of cats and their relatives being Fells. The second, or
specific name is the species, as domestica for house cats. The generic
name is capitalized and the specific name lower-cased; both are itali-
cized. A mountain lion is in the genus Felts, but differs in species from
the domestic cat; its full name is Fells concolor. The Latin name is
usually followed by the surname of the person who first described the

13

nautiloid suture

ammonoid suture

tusk shell

Plate 4. Cephalopod suture types and tusk shell.

14

Torrey PInes\ (
State Park \ "V^.,

Cretaceous

Point Loma

^
^

Imperial Beach

0 12 3 4 5 Miles

.'■■'■ 'l ■'■ ■■

0123456 78 Kilometers

^...i— - - — ^"^ *"" Tijuan

Plate 5. Area at San Diego underlain by Upper Cretaceous rocks
shown by shading.

15

species, as in Felis concolor Linne. If this person's name is in paren-
theses, it indicates that he originally assigned the species to a different
genus than the one to which it is now assigned. A name in parentheses
between the generic and specific names designates a subgenus, a sub-
division of the genus. A subspecies is indicated by a third Latin name,
not in parentheses.

GEOLOGIC AGE AND DESCRIPTION
OF FOSSIL MOLLUSKS

JURASSIC

Buchia piochii, an oyster-like fossil, has recently been collected
from rocks of Late Jurassic age northeast and southeast of Del Mar
(Fife, Minch, and Crampton, 1967). These are the oldest known fos-
siliferous rocks in the San Diego area.

CRETACEOUS

Marine fossiliferous Cretaceous rocks — sandstone and shale — are
exposed and accessible at low tide on the west side and at the southern
end of the Point Loma Peninsula. Fossiliferous Cretaceous rocks are
also exposed north of False Point, which lies south of the La JoUa
business district, and on the north side of Mt. Soledad (Plate 5).
These rocks are of Late Cretaceous age (Hertlein and Grant, 1944),
and contain fossil mollusks (clams, snails, and cephalopods), and also
brachiopods (lamp shells) and microscopic foraminifera — protozoans.
The most spectacular of these fossils are the cephalopods.

16 Cretaceous

CEPHALOPOD

Pachydiscus (Neodesmoceras) catarinae (Anderson and Hanna),
Plate 6.

This is a large form, flat-coiled, about 50 cm in its greatest overall
diameter, with the largest individual whorl about 22 cm across. Low
rounded ribs radiate from its center. The figured specimen was inked
to show the sutures. It has been collected from the Cretaceous rocks
at Point Loma and is also found in central California and in Baja
California, Mexico.

Plate 6. Cretaceous ammonite.

Pachydiscus (Neodesmoceras) catarinae (Anderson and Hanna),
X Vs.

Cretaceous

17

wm

^* '^3

\

18 Cretaceous

GASTROPOD

Haliotis lomaensis Anderson, Plate 7a

If this species, which is about 80 million years old, is correctly
assigned to the genus Haliotis, it is the oldest fossil abalone in the
world. It is very small; the figured specimen from the Cretaceous
rocks of Point Loma is 1.3 cm long, 0.9 cm wide, and 0.3 cm high.
The specimen figured is the only one known of the species. Since
it was described in 1902, the specimen has been kept in San Francisco.
At the time of the earthquake and fire of 1906, it was fortunately
housed in the collections of the California State Mining Bureau in the
nearly unscathed Ferry Building, and therefore escaped the fate of
some other scientifically priceless type specimens when the Market
Street building of the California Academy of Sciences was destroyed.
The specimen is now in the collections of the Academy at its head-
quarters in Golden Gate Park. The much larger abalones that live on
the Pacific Coast today comprise several species in the same genus,
Haliotis.

PELECYPODS

Crassatella lomana Cooper, Plate 7b

This species has a thick shell that is smooth except for concentric
lines. The specimen figured is the one on which the species is based,
and is therefore called the holotype. It was collected at Point Loma
and also occurs at other localities in California.

Plate 7. Cretaceous snail and clam.

a) Haliotis lomaensis Anderson, x 5.

b) Crassatella lomana Cooper, x 1.

Cretaceous

19

20 Cretaceous

Coralliochama orcutti White, Plate 8

This unusual clam belongs to a group known as the rudistids. The
right valve is greatly elongated; the left valve is much smaller and
lies across the right valve to form a lid. This creature is believed to
have lived in an upright position as illustrated. The figured specimen,
whose total length is 25.5 cm, was collected at Punta Banda, Baja
California, Mexico, and is deposited at the California Academy of
Sciences. This species also occurs in the Cretaceous rocks of Point
Loma and La Jolla, and at other localities in California.

Plate 8. Cretaceous clam.

Coralliochama orcutti White, x 1

Cretaceous

21

22 Cretaceous

Cordis sp. aff. C. peninsularis Anderson and Hanna; Plate 9a

This clam is generally round in outline, and its shell is smooth
except for concentric lines. The first specimen described of Corbis
peninsularis was from Baja California. The illustrated specimen from
Point Loma is identified as Corbis sp. aff. C. peninsularis. The aff.
stands for affinis meaning it is similar to, but not identical with the
original specimen of Corbis peninsularis and may prove to be a dif-
ferent species.

Inoceramus sp., Plate 9b

This clam has not yet been identified specifically because it is rep-
resented only by poorly preserved specimens. It is distinguished by
concentric folds on the shell, the thinness of the shell, and its outline.
The illustrated specimen — broken — is about 5 cm long and was
collected in the Cretaceous rocks at Point Loma.

Plate 9. Cretaceous clams.

a) Corbis sp. aff. C. peninsularis Anderson and Hanna, x 1

b) Inoceramus sp., x 1.

Cretaceous

23

24

Eocene

Torrey P'"®^1^^'
State Park ^E^

0 12 3 4 5 Miles
01234 5678 Kilometers

Tijuana

Plate 10. Area at San Diego underlain by Eocene rocks shown
by shading.

Eocene

25

EOCENE

Fossil mollusks in the Eocene rocks exposed in the La Jolla
quadrangle, just north of San Diego, were studied and illustrated by
Marcus A. Hanna (1926). Isolated patches of these rocks occur as far
south as Mission Valley, and some of them overlie the Cretaceous
rocks on the Point Loma Peninsula (Hertlein and Grant, 1944). Dis-
tribution of the Eocene rocks is shown in Plate 10. They can most
readily be seen in the sea cliffs at Torrey Pines State Park and in
Rose Canyon.

One of the most common fossils seen in exposures of Eocene
rocks at the north end of San Diego is an oyster, Ostrea idriaensis
Gabb, It is so common in some places that it occurs in nearly pure
layers in the rocks (Figure 1).

m^-.^^

Figure 1. A richly fossiliferous layer within Eocene rocks that crop
out north of the area of plate 10 in the San Dieguito River
valley, east of Del Mar.

26 Eocene

GASTROPODS

Amaurellina moragai lajollaensis Stewart, Plate 11a

This snail is of moderate size and has a large, rather round body-
whorl, on which there is a shelf. Incised spiral lines may be seen to
cover the entire shell of a well-preserved specimen.

The figured specimen is from Rose Canyon, in San Diego, but this
species has also been found in Eocene rocks at other localities in
California.
Ficopsis cooperiana Stewart, Plate lib

This species has a large body whorl with three rows of nodes —
one on the edge of each flat surface. The spire is relatively short, and
there are two rows of nodes on each whorl. Basket-weave sculpture
can be seen on well-preserved specimens but is not shown on the
figured specimen, which is from the Eocene rocks in Rose Canyon.
This species is also found in Eocene rocks at other localities in
California.

Ficopsis remondi crescentensis Weaver and Palmer, Plate lie

The entire shell of this snail is sculptured with spiral and radial
threads of equal weight and spacing, forming a delicate basket- weave
pattern. It has a large body whorl and a shelved spire. A flat surface
on the body whorl, marked off by two slightly heavier spiral threads,
can be seen just below the shoulder. The figured specimen was col-
lected from the Eocene in Rose Canyon. The species also occurs in the
Eocene rocks elsewhere in California, and in Oregon and Washington.

Loxotrema turritum Gabb, Plate lid

This is a rather small shell with a turreted spire and with the body-
whorl overlapping at the suture. The body whorl is smooth near the
suture and is sculptured with spiral cords near the base of the shell.
The figured specimen came from the Eocene of San Clemente Canyon,
but this species, which is the only one known in the genus, occurs in
Eocene rocks at other localities in California and in Oregon.
Megistostoma gabbianum (Stoliczka), Plate lie

The body whorl of this snail is large and its spire is hidden. The
sculpture consists of irregular spiral threads. The specimen figured
came from the Eocene of Rose Canyon. This species, which is the
only one known in the genus, is also found in the Eocene rocks of
Oregon and Washington.

%

a

27

e

Plate 11. Eocene snails.

a) Amaurellina moragai lajollaensis Stewart, x 1^.

b) Ficopsis cooperiana Stewart, x 1}^.

c) Ficopsis remondi crescentensis Weaver and Palmer, x 1;^

d) Loxotrema turritum Gabb, x 2.

e) Megistostoma gabbianum (Stoliczka), x l^^.

28 Eocene

Nerita triangulata Gabb, Plate 12a

This is a small snail with the spire visible but not elevated above
the body whorl. The shell is scultpured with rather strong spiral ribs.
The figured specimen is from the Eocene of Rose Canyon, and this
species occurs in Eocene rocks at other places in California.

Pseudoperrisolax blakei praeblakei Yokes, Plate 13b

This is a snail of moderate size, which has a long siphonal canal
and bears a strong shelf on the body whorl. There are small nodes
along the edges of this shelf and on the shoulders of the whorls of the
spire. The figured specimen was collected in the Eocene rocks of Rose
Canyon, and this species has also been collected from Eocene rocks in
the Coalinga area of California.

Scaphander (Mirascapha) costatus (Gabb), Plate 12c

On all species of Scaphander the spire is sunken and completely
covered by the body whorl. The shell is elongated and somewhat cylin-
drical. It is sculptured with flat spiral ribs and narrow interspaces.
The figured specimen is from the Eocene rocks in Rose Canyon. This
species is also found in Eocene rocks at other localities in California
and in Oregon and Washington.

Sinum obliquum (Gabb), Plate 12d

This snail has a large body whorl and a very small, squat spire.
Sinum is most easily distinguished by its squatness and by its spiral
sculpture of irregular incised lines. The figured specimen, which is
1.2 cm high and 1.8 cm wide, was collected in the Eocene of Rose
Canyon. This species occurs in Eocene rocks at other localities in
California, and also in Oregon and Washington.

Turrit ella uvasana applinae Hanna, Plate 12e

Most species of Turritella have slim, high-spired shells sculptured
with spiral ribs of varying diameters and spacings. This species is
distinguished by its rounded whorls and rather widely spaced and
moderately strong spiral ribs. It was originally described from speci-
mens found in the Eocene of Rose Canyon, which is thus the type
locality for the species. The figured specimen is from the Eocene of
San Clemente Canyon. This species is found also in Eocene rocks at
other localities in California.

Eocene

29

^?^^:

c

4

./

Plate 12. Eocene snails.

a) Nerita triangulata Gabb, x 2.

b) Pseudoperrisolax blakei praeblakei Yokes, x 1>^,

c) Scaphander (Mirascapha) costatus (Gabb), x 2.

d) Sinum obliquum (Gabb), x 2.

e) Turritella uvasana applinae Hanna, x 1.

'30 Eocene

PELECYPODS

Acila (Truncacila) decisa (Conrad), Plate 13a

This is a small clam of triangular outline. Its most distinctive
feature is the bifurcation of the radial ribs, which somewhat resembles
the part in one's hair. The beaks are very small; the interior of the
shell is pearly. Acila all have taxodont dentition — a row of small
teeth alternating with sockets along the hinge. The figured specimen
came from the Eocene of Rose Canyon. The same species occurs in
the Paleocene of California and the Eocene of the Coast Ranges else-
where in California and in Oregon and Washington.

Corhiila rosecanyonensis Hanna, Plate 13b

This is perhaps the smallest fossil clam known from the Eocene
of San Diego; the figured specimen, which is of average size, is only
1.0 cm long and 0.8 cm high. It is triangular in outline and sculptured
with concentric lines. Rose Canyon, from which the figured specimen
was collected is the type locality for the species. This species is found
also in Eocene rocks in other localities in California.
Macrocallista horni (Gabb), Plate 13c

This species is rather small, the figured specimen, which was col-
lected in Rose Canyon, being 2.6 cm long and 2.0 cm high. It is oval
in outline, bears small beaks turned in toward the anterior margin, and
is sculptured with concentric ridges. This species is also found in
Eocene rocks in other localities in California.
Nemocardium linteum (Conrad), Plate 13d

Nearly square in outline, this shell is somewhat polished. It bears
fine radial ribs covering three- fourths of its area and coarse ribs on
the remainder. The presence of these coarse ribs, which are on the
posterior quarter, is a distinguishing feature of the genus Nemocar-
dium. The figured specimen came from the Eocene rocks of Rose
Canyon; the species is also found in the Eocene of Oregon.

Venericardia (Pacificor) horni (Gabb), Plate 13e, f

This is a large thick shell of somewhat oval outline with a heavy,
massive hinge plate. The outside of the shell is sculptured with broad
rounded ribs separated by narrow incised interspaces. The beaks curve
strongly toward the anterior end of the shell. The figured specimen
came from the Eocene rocks of Rose Canyon; the species is also found
in the Eocene of Oregon.

31

Plate 13. Eocene clams.

a) Acila (Truncacila) decisa (Conrad), x 2.

b) Corbula rosecanyonensis Hanna, x 3.

c) Macrocallista horni (Gabb), x 2.

d) Nemocardium linteum (Conrad), x 1.

e, f) Venericardia {Pacific or) horni (Gabb), x 1,

32

Pliocene

Pliocene

Torrey Pines \ I
State Park \ "V""

La Jolla

Pacific Beach

Mission Bay

Ocean Beach

Point Loma

0 12 3 4 5 Miles

1 I ' I l' I 'l I ' I l'
0123456 78 Kilometers

Plate 14. Area at San Diego underlain by Pliocene rocks shown
by shading.

Pliocene 33

PLIOCENE

Fossils in the Pliocene rocks of the San Diego area have been
studied by Leo G. Hertlein and U. S. Grant IV; their papers on the
distribution of the Pliocene rocks in San Diego (1944) and on the
fossil sand dollars and brachiopods found in those rocks (1960) are
very useful. In 1931, U. S. Grant IV and Hoyt R. Gale published a
catalogue of the Pliocene and Pleistocene fossils of California, and
that book contains illustrated descriptions of many mollusks of those
ages collected in or near San Diego. Leo G. Hertlein and U. S. Grant
IV have in preparation a monograph on the pelecypods of the Pliocene
rocks of San Diego. This will be a significant contribution to the
knowledge of the fauna of these rocks.

William H. Dall (1874) when serving as paleontologist and con-
chologist at the U. S. National Museum, identified Pliocene fossils
taken from a well in Balboa Park. This was one of the first Pliocene
localities to be definitely established in California. Pliocene rocks are
exposed at Pacific Beach and over a large area that lies south of
Route 8 and east of Route 5 and extends across the International
Boundary (Plate 14).

GASTROPODS

Crepidula prince ps Conrad, Plate 15b

A smooth, rather flat shell, without a spire this species has a beak
that curves toward the right if the beak end of the shell is held nearest
the viewer. All species of Crepidula have a deck or shelf across part
of the aperture on the under side of the shell.

The incomplete specimen figured, which is 3.0 cm high and 6.0 cm
long, was taken from the Pliocene rocks at Reynard Way in San
Diego. This species occurs in Miocene rocks in California and Pliocene
and Pleistocene rocks in California, Oregon, and Washington.

Megasurcula carpenteriana (Gabb), Plate 15d, e

The body whorl is larger than the spire on this species, and each
whorl of the shell overlaps the spire. The shell is sculptured with
spiral threads and lighter radial threads. A moderately heavy spiral
thread usually alternates with a much finer one. Small nodes project
from the whorls of the spire just above the suture. The canal is
notched at the basal margin. The figured specimen came from the

34 Pliocene

Pliocene rocks exposed on Reynard Way, and this species is also
found in the Pliocene of Balboa Park, in the Pleistocene at Pacific
Beach, and the Pleistocene of Baja California, Mexico.

Nassarius (Caesia) grammatus (Dall), Plate 15f, h

This snail has a fat shell and is sculptured with equally spaced
radial and spiral threads that produce a basket-weave pattern. There is
a deep groove near the base of the shell and a notch at the end of the
recurved canal. This was a carnivorous animal that drilled holes in
clams or snails and then ate their flesh.

This species is found in Pliocene rocks from northern California
to San Diego, California. The figured specimen came from Reynard
Way.

Opalia varicostata (Stearns), Plate 15a

The cone-like form and sculpture of evenly spaced, heavy radial
ribs identify this snail. Variants of this species with a smooth, ribless
shell also occur. The aperture is almost round and the outer lip is
thickened. Very fine spiral lines may be seen on well preserved speci-
mens. The figured specimen is from Pacific Beach. This species has
also been found in the Pliocene of Fresno County, California.

Sinum scopulosum (Conrad), Plate 15g

This species has a large fat body whorl and a small spire. The shell
is sculptured with irregular flat spiral threads and interspaces of about
equal width. The figured specimen, which is 1.7 cm high and 2.4 cm
wide, was collected at Reynard Way in San Diego.

This species occurs in the Miocene of California, Oregon, and
Washington and in the Pliocene of California and Oregon. It probably
is the same species as the one called, by some authors, Sinum cali-
fornicum. The modern species lives in the sea between the latitudes of
central California and Baja California, Mexico.

Plate 15. Pliocene snails.

a) Opalia varicostata (Stearns), x 1^.

b) Crepidula prince ps Conrad, x 1.

c) Terehra (Strioterebrum) martini English, x 1^,
d, e) Megasurcula carpenteriana (Gabb), x 1.

f , h) Nassarius {Caesia) grammatus (Dall), x 1.

g) Sinum scopulosum (Conrad), x 1^.

Pliocene

35

36 Pliocene

Terehra (Strioterebrum) martini English, Plate 15c '

This is a slim-shelled snail with a tall spire, and each whorl is
sculptured with fine radial threads that twist toward the suture. There
is a collar bounded by an incised line a little below each suture. A
notch is present on the posterior margin of the outer lip. The specimen
illustrated is 3.1 cm high and 0.9 cm wide and was taken on Reynard
Way, San Diego. This species is found also in the Pliocene of the
Los Angeles area.

PELECYPODS

Anadara (Anadara) trilineata (Conrad), Plate 16a, b

This fossil clam is oval or sub-triangular in outline and is sculp-
tured with grooved radial ribs. It has taxodont dentition (teeth in a
row). A flat triangular area between the beaks is sculptured with
chevron-like grooves; Plate 16a shows this feature.

This species is found in the Pliocene of California, Oregon, and
Washington. The figured specimens are from Reynard Way, San
Diego.

Plate 16. Pliocene clam.

a, b) Anadara (Anadara) trilineata (Conrad), x 1,

Pliocene

37

\

?-,3- .y,-

I ^

i ^

38 Pliocene

Dosinia ponderosa (Gray), Plate 17a, b

This clam is round and moderately large; it has a rather thick
shell that is sculptured with equally spaced concentric grooves. The
beaks are small and point toward the anterior end of the shell. The
specimen figured came from a locality near the Mexican-United States
boundary and one-half a mile from the ocean.

This species may be collected from the Pliocene in Balboa Park
and could formerly be collected from the Pleistocene at 26th Street in
San Diego. It also occurs in the Pleistocene of Baja California and
is living today from Baja California to Peru.

Plate 17. Pliocene clam.

a, b) Dosinia ponderosa (Gray), x 1.

Pliocene

39

^'K

40 Pliocene

Lucinoma annulata (Reeve), Plate 18a, b, c

Almost circular in outline this clam is sculptured with rather widely
spaced concentric ridges. In order to show the hinge plate and the
interior of the valves, a modern specimen (Plate 19a, c) is figured in
addition to the fossil specimen (Plate 19b). The fossil specimen was
collected near the south base of Mount Soledad. The modern specimen
came from San Pedro, California.

This species is found in the Pliocene and Pleistocene rocks of
California and has been collected from both in San Diego. It lives
today in the sea from Alaska to Baja California, Mexico.

Lucinisca nuttalli (Conrad), Plate 18d

This is a small, very pretty shell, distinguished from other lucinids
in the Pliocene of San Diego by its basket-weave sculpture of concen-
tric and radial ribs, equally spaced.

The figured specimen was collected in Balboa Park. Fossils of this
species are found in the Pliocene and Pleistocene of the San Diego
area and in the Miocene elsewhere in California. It lives in the sea
today from Santa Barbara, California, to Manzanillo, Mexico.

Miltha xantusi (Dall), Plate 18e, f

This shell is almost flat and has small but prominent beaks. It has
an anterior and a posterior indentation, both demarcated by a radial
ridge; the posterior indentation is at the margin of the shell. The sur-
face is sculptured with fine radial threads.

This species has been found in the Miocene and Pliocene of Cali-
fornia and lives off Cabo San Lucas, Baja California, and in the Gulfo
de California, Mexico, today at a depth of 60 meters or more. The
figured specimen is from Pliocene rocks in Balboa Park.

Plate 18. Pliocene and Holocene clams,
a, c) Lucinoma annulata (Reeve), x 1.
b) Lucinoma annulata (Reeve), x 1}^.
d) Lucinisca nuttalli (Conrad), x 1^.
e, f) Miltha xantusi (Dall), x 1.

Pliocene

41

e

42 Pliocene

Panope (Panope) abrupta (Conrad), Plate 19

This clam has a moderately thick shell and often reaches a large
size. The specimen figured, which is near the middle of the size range,
is 11.2 cm long and 6,6 cm high. Two distinguishing features of the
species are the square truncation at the posterior end and the large
gape of the shells.

This species, which was formerly called Panope generosa, has been
collected from rocks of Miocene to Pleistocene age in California, Ore-
gon, and Washington. It lives in the sea today from Alaska to Baja
California, Mexico. The figured specimen came from Pliocene rocks
in Balboa Park.

Plate 19. Pliocene clam.

Panope {Panope) abrupta (Conrad), x 1,

Pliocene

43

I

44 Pliocene

Pecten (Lyropecten) cerrosensis Gabb, Plate 20a, b

This fossil Pecten is one of the largest known in the San Diego
area; the figured right valve is 19 cm long and 17.5 cm high. The
figured specimen bears 21 large rounded ribs, separated by spaces of
nearly the same width as the ribs. The entire surface is sculptured
with threadlike ribs. Coarse tooth-like hinge processes are present on
the hinge plate. This species is rare in San Diego, but several speci-
mens exist in the collections of the California Academy of Sciences,
San Francisco, and in the Los Angeles County Museum of Natural
History. The shell figured here is the right valve of a double- valved
specimen collected in Chula Vista by a student and subsequently do-
nated to the San Diego Museum of Natural History. The species has
also been collected from Pliocene rocks at other localities in California.

Plate 20. Pliocene clam.

a, b) Pecten {Lyropecten) cerrosensis Gabb, x 1%.

Pliocene

45

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t

«f

x,^

v^ b

'*fti5;£'

46

Pliocene

Pecten (Patmopecten) healeyi Arnold, Plate 21a, b '

This is one of the largest clams found in the Pliocene of the San
Diego area. The actual dimensions of the figured specimen are 18.8 cm
wide and 17.0 cm high; the photograph is one half as large. The right
valve is moderately convex and bears 18 square-cornered, medially
grooved ribs separated by spaces of the same w^idth. The left valve is
nearly flat and bears 17 somewhat rounded ribs, between which there
are wider spaces divided in some cases by a smaller rib.

This species was first collected from the Pliocene of San Diego and
has also been found in the Pliocene of the Los Angeles area and in
Baja California, Mexico. The figured specimen is from Pacific Beach.

Figure 2. Laminated Eocene sandstone at lower left overlain by more
easily eroded Pecten-htdirmg Pliocene rocks at Tourmaline Surfing
Park, Pacific Beach.

Plate 21. Pliocene clam.

a, b) Pecten (Patinopecten) healeyi Arnold, x y

Pliocene

47

-'^^

-^S.

\

.0'

48 Pliocene

Pecten (Pecten) stearnsi Dall, Plate 22a, b

This is a moderate-sized Pecten with a flat left valve and a moder-
ately convex right valve. The left valve has rounded ribs; the right
valve has flat-topped ribs that are medially grooved. The right valve
figured is 9.8 cm wide and 7.7 cm high; the left valve, which is broken,
is 9.0 cm wide and 8.1 cm high; each bears 24 ribs.

Young individuals of species of Pecten that have light shells can
propel themselves efficiently by opening the valves to take in water,
then closing them to squirt the water out through openings at the ears.

This species was first collected at Pacific Beach, as the figured
specimen was, and has since been found in the Pliocene of the Los
Angeles area and of Baja California, Mexico. It has also been collected
in the Pleistocene at San Pedro, and a form that may be identical with
it is living today.

Plate 22. Pliocene clam,

a, b) Pecten (Pecten) stearnsi Dall, x 1.

Pliocene

49

50 Pliocene

Pec ten (Argopecten) subdolus Hertlein, Plate 23a, b'

This form has low rounded ribs on both valves, and the valves are

moderately and equally inflated. The anterior ear on the right valve is

somewhat winglike.

The species was first collected at Pacific Beach, as was the figured

specimen. It has also been collected in the Pliocene of Baja California

and is presumed to be extinct.

Pecten (Pecten) bellus hemphilli Dall, Plate 23c, d

The right valve, which is convex, bears high rather flat-topped
ribs; on the left valve, which is flat, the ribs and the interspaces are
square-cornered. There are 14 ribs on the right valve and 12 on the
left valve of the specimen figured. This subspecies was first collected
from the Pliocene of San Diego, and has since been found in the
Pliocene of the Los Angeles area and in Baja California, Mexico. It
is believed to be extinct.

Saccella taphria (Dall), Plate 23e, f, g

This is a small shell with a recurved and pointed end. The small
double-valved specimen is 1.6 cm long and 1.0 cm high. The valves
when closed are almost as wide as they are high, and the shell is
sculptured with equally spaced concentric ridges. In this genus the
hinge bears teeth alternating with sockets, as is shown in the figure
representing the interior of the shell, Plate 23g.

Both specimens came from the Pliocene of Balboa Park. At Pacific
Beach this species occurs in both Pliocene and Pleistocene rocks, at
Spanish Bight in the Pleistocene. At other places in California it is
found in rocks of Miocene to Pleistocene age, and it lives today in
coastal water from Bodega Bay, California, to Banco de Arena, Gulfo
de California, Mexico.

Plate 23. Pliocene clams.

a, b) Pecten (Argopecten) subdolus Hertlein, x 1,
c, d) Pecten (Pecten) bellus hemphilli Dall, x 1.

e, f, g) Saccella taphria (Dall), x 2.

Pliocene

51

52 Pliocene

Saxidomus sp. aff. S. nuttalli Conrad, Plate 24a, b

This is a moderately large clam, the specimen figured being 12.3
cm long and 9.1 cm high. It has a thick shell sculptured externally with
concentric threads of shell bunched together at irregular intervals. The
muscle scars are shown in the internal view (Plate 24a). The shells
are said to gape as they do not completely close at the posterior end.
The figured specimen was collected from the Pliocene in Balboa Park,
San Diego.

The Pleistocene form is believed to differ slightly from the modern
species, because it is more truncated at the posterior end, and because
the hinge plate and teeth do not exactly match those of modern
specimens.

Plate 24. Pliocene clam,
a, b) Saxidomus sp. aff. ^. nuttalli Conrad, x 1

Pliocene

53

4

54

Pleistocene

Torrey Pines
State Park

La Jolla

Pacific Beach

Crown (Ba
Point

Mission Bay
Ocean Beach

Point Loma

0 12 3 4 5 Miles

1 . ■■ l' I 'l I'l .'

0123456 78 Kilometers

Plate 25. Area at San Diego inundated by the sea in late Pleistocene
time shown by shading. Dashed line marks edge of artificial fill.

Pleistocene

55

Plate 26. Pleistocene rocks.

a) A thick Pleistocene section near Del Mar Racetrack contain-

ing a shell bed marked by hammer.

b) Pleistocene moUuscan shells in Carmel Valley, near Del Mar.

56 Pleistocene

PLEISTOCENE

So far as is known, the marine fossiliferous Pleistocene in the
vicinity of San Diego is of late Pleistocene (Sangamon) age (Wahr-
haftig and Birman, 1965, p. 340). It is widely distributed west of
Highway 5 (Plates 25 and 26) and is well exposed in the upper parts
of cliffs along much of the coastline. It is overlain in places by shell
middens left by the Indians, and shells from the two sources are not
always readily separable; but many of the shell middens are underlain
as well as overlain by soil, none are consolidated, and some may con-
tain artifacts.

The Pleistocene fossils described and illustrated below were all
collected at Spanish Bight, west of San Diego, which was a bay .that
once intervened between North Island and Coronado Island but which
has now been almost completely filled, to extend the land area for
construction.

GASTROPODS

Acteon traski Stearns, Plate 27a

A rather small shell, the figured specimen of this species is only
2.0 cm high and 1.0 cm wide. It is sculptured with fine spiral ribs, and
the spaces between them are finely pitted. The spire is about half as
high as the body whorl.

This species lives today in the sea at depths up to 30 meters off
southern California and possibly as far south as Panama.

Calliostoma dolarium (Holten), Plate 27b

This shell is pearly inside, as are all species of Calliostoma, and
each whorl is sculptured with spiral cords, some of which are slightly
beaded.

This species, formerly cited as Calliostoma canaliculatum (Martyn),
is found in the Pliocene of Pacific Beach as well as in the Pleistocene

Plate 27. Pleistocene snails.

a) Acteon traski Stearns, x 2.

b) Calliostoma doliarium (Holten), x 1.
c, d) Crepidula adunca Sowerby, x 2.

e, f) Crucibulum spinosum (Sowerby), x 2.

g) Epitonium (Nitidiscala) indianorum (Carpenter), x 1^.

h) Jaton f estiva (Hinds), x 1.

Pleistocene

57

.-*^

^

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^i

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Ll

%

g

58 Pleistocene

of Spanish Bight. It is living in the sea today from Sitka, Alaska, to
San Diego, California, and is usually found offshore on kelp.

Crepidula adunca Sowerby, Plate 27c, d

A low, rather flat, quite thin shell this species has the apex or beak
near one of its margins and bears a shelf that covers about a third of
the aperture. The beak is small and slightly curved.

This species lived in California during the Pliocene, and Pleisto-
cene fossils are found at Point Loma and near the Mexican border as
well as at Spanish Bight, from which the figured specimen came. It
lives in the sea today from British Columbia to Baja California,
Mexico.

Crucihulum spinosum (Sowerby), Plate 27e, f

The apex is twisted a bit to one side and the shell is dome shaped.
The shell is sculptured with radial wrinkles bearing tubular spines. A
cuplike shelf is attached to the interior of the shell at one side.

The figured specimen is from Spanish Bight. Fossils of this species
are found in the Pliocene of Balboa Park and in the Pleistocene along
Pacific Beach. It was also formerly collected from the Pleistocene at
the foot of 26th Street, San Diego. It is now living in the sea from
southern California to Chile, clinging to other shells and stones at
depths of as much as 60 meters.

Epitonium (Nitidiscala) indianorum (Carpenter), Plate 27g

This lovely slender shell has numerous whorls and a round aper-
ture. The figured specimen is 2.3 cm high and 0.9 cm wide. Each whorl
bears pointed radial ribs that stop at the boundary of the whorl and
are slightly bent backwards.

This species first appeared in California in the Pliocene. It also
occurs in the Pleistocene near the Mexican border and lives in the
sea today from Alaska to Baja California. A picture of a shell of this
species is used to decorate the cover of this book.

Jaton f estiva (Hinds), Plate 27h

On each whorl of this shell are three prominent ribs that are leaf-
like near the shoulder, and between each pair of them is a heavy,
rounded node. The siphonal canal is moderately long and turned back
at the base.

Pleistocene 59

This species has been collected from the Pliocene and Pleistocene
at various places in California, the Pleistocene in Baja California, and
lives today in the sea ofif southern California and Baja California,
Mexico, on rocky or mud bottoms to a depth of 150 meters.

Nassarius (Caesia) cerritensis (Arnold), Plate 28a

This is a slender, high-spired species with coarse ribs that are
rather widely spaced. The shell has a small hole drilled by another
snail, which probably then ate this animal's flesh. The driller of the
hole may have been another Nassarius, all species of which are carni-
vorous and drill holes in clams or snails. They are also scavengers.

This species is living today in the sea from Long Beach, Califor-
nia, to Bahia Magdalena, Baja California, Mexico.

Nassarius (Caesia) fossatus (Gould), Plate 28f

A large, fat shell, this species has noded ribs along the shoulder of
the body whorl, which is higher than the spire.

This species has been found in the Pleistocene of San Diego. It
now lives in the sea from Vancouver Island, British Columbia, to Isla
Cedros, Baja California, Mexico.

Nassarius (Demondia) mendicus (Gould), Plate 28d

A high, slender spire and sculpture of numerous ribs help to dis-
tinguish this species. The spire is as high as the body whorl. Its sculp-
ture is finer than that of Nassarius cerritensis and coarser than that of
Nassarius perpinguis.

This species occurs in the Pliocene in Balboa Park, and in the
Pleistocene at Pacific Beach and near the Mexican border as well as
at Spanish Bight. It lives in the sea today from Kodiak Island, Alaska,
to Bahia Magdalena, Baja California, Mexico.

Nassarius (Caesia) perpinguis (Hinds), Plate 28e

This Nassarius has a spire of moderate height and is finely and
evenly sculptured with radial and spiral ridges that produce small
nodes where they meet.

This species has been collected from the Pliocene in Balboa Park
and from the Pleistocene along Pacific Beach and near the Mexican
border. It lives now in the sea between Puget Sound, Washington, and
Bahia Magdalena, Baja California, Mexico.

60 Pleistocene

Olivella biplicata (Sowerby), Plate 28g, i

A very small spire and a relatively large body whorl help to dis-
tinguish this little shell. Its surface is smooth, with no ornamentation,
and the whorls lap over one another like the pages of a twisted maga-
zine. The neat hole on the front of the body whorl was drilled by a
carnivorous snail in order that he might eat the soft parts.

This species has been collected from the Pliocene in Balboa Park
and at various Pleistocene localities in San Diego. It lives today from
British Columbia to Baja California, Mexico, on beach sand and in
sandy bays but sometimes in water as much as 50 meters deep.

Polinices (Neverita) recluzianus (Deshayes), Plate 28b, h '

This snail is one of the largest found in the Pleistocene of San
Diego. It has a very large body whorl and a relatively low spire. It is
somewhat oval in shape; the shell is thick, smooth and not sculptured,
and there is a large plug near the aperture.

This species may have lived as long ago as the Oligocene, but in
San Diego it is collected from both the Pliocene and Pleistocene, and
it lives today from Monterey, California, to the Islas Tres Marias,
Mexico, in shallow water and at depths of as much as 50 meters.

Terehra (Strioterebrum) pedroana Dall, Plate 28c

This shell has a slim spire about twice as high as the body whorl.
The whorls are sculptured with fine spiral bands and grooves, and
with radial ridges each of which ends in a node on the shoulder of
the whorl.

This species has been collected from the Pliocene in Balboa Park
and in the Pleistocene at several localities in San Diego. It lives today
in shallow water oflf southern California and Baja California, Mexico.

Plate 28. Pleistocene snails.

a) Nassarius (Caesia) cerritensis (Arnold), x 1^.

b, h) Polinices (Neverita) recluzianus (Deshayes), x 1,

c) Terehra {Strioterebrum) pedroana Dall, x 2.

d) Nassarius (Demondia) mendicus (Gould), x 3.

e) Nassarius (Caesia) perpinguis (Hinds), x 1^.

f) Nassarius (Caesia) fossatus (Gould), x 1^.
g, i) Olivella biplicata (Sowerby), x 2.

Pleistocene

61

:i

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-yj}^

i#.H

62 Pleistocene

SCAPHOPOD

Dentalium neohexagonum Sharp and Pilsbry, Plate 29a

A long, curved tube characterizes this shell and all shells of the
genus Dentalium. It is rather thin and has seven flat sides separated
by low ribs. The figured specimen is 3.5 cm long, 0.3 cm wide at the
greatest diameter, and 0.1 cm wide at the least diameter.

This species has been found in the Pliocene of Balboa Park and
Pacific Beach and in the Pleistocene at several localities in San Diego.
It also occurs in the Pleistocene of the Los Angeles area and in Baja
California, and lives in the present sea from central California to
Central America.

PELECYPODS

Amiantis callosa (Conrad), Plate 29b, c

This is an ovate, porcelain-like shell that is thick and sculptured
with heavy concentric ridges. The beaks are small and are turned
toward the anterior end of the shell. The pallial sinus and muscle
scars can be seen on the interior of the figured shell, Plate 30b.

This species has been collected from rocks of Miocene to Pleisto-
cene age in California, from Pleistocene deposits in Baja California,
and in the present sea from Santa Barbara, California, to Cabo San
Lucas, Baja California, Mexico.

Plate 29. Pleistocene tusk shell and clam.

a) Dentalium neohexagonum Sharp and Pilsbry, x 1
b, c) Amiantis callosa (Conrad), x 1.

Pleistocene

63

64 Pleistocene

Florimetis biangulata (Carpenter), Plate 30a, b

A large shell, this species has two folds at the posterior end, as is
indicated by its name bi (two) angulata (angled). It is subrounded in
outline, and the exterior is sculptured with fine threads.

This species has been collected in California from rocks of Miocene
to Pleistocene age, in Baja California from the Pliocene and Pleis-
tocene, and in the present sea from Point Conception, California, to
San Quintin, Baja California, Mexico. It occurs in the Pliocene at
Pacific Beach and in the Pleistocene at Spanish Bight and near the
Mexican border.

Plate 30. Pleistocene clam.

a, b) Florimetis biangulata (Carpenter), x 1.

Pleistocene

65

^

66 Pleistocene

Pandora (Heteroclidus) punctata Conrad, Plate 31a, b

This thin, pearly little shell is flat and somewhat similar in form
to the side of a wooden shoe. The beaks are near the posterior end of
the shell. Inside the shell, small pits can be seen where the animal was
attached to it.

This species occurs in Pliocene and Pleistocene rocks elsewhere in
California and in the Pleistocene at Spanish Bight and near the Mexi-
can border, and it lives today from Vancouver Island to Golfo de
California, Mexico.

Leptopecten latiauratus (Conrad), Plate 31c, d

This very small Pecten is 1.3 cm high and 1.2 cm wide, and both
valves are 0.6 cm thick. The right and left valves are equally convex.
The two ears on the left valve are almost equal in size and alike in
shape; the anterior ear on the right valve looks like part of a fan and
is bordered by a deep groove. Both the right and the left valves are
sculptured with low, rounded ribs. This clam attaches itself to rocks
by secreting long tough filaments.

The figured specimen was collected at Spanish Bight. The species
also occurs in the Pleistocene at Point Loma, formerly at the foot of
26th Street, and near the Mexican border. It lives today from central
California to Golfo de California, Mexico.

Petricola (Petricolaria) parallela Pilsbry and Lowe, Plate 31e

A long, slender, thin shell, this species has noded radial ribs on
the anterior end. The posterior two-thirds of the shell is sculptured
with fine radial lines that do not have nodes. Petricola lives in holes
that it bores into hard clay or in holes that it finds in the rocks.

The figured specimen was collected at Spanish Bight. The species
has also been collected at Tecolote Creek, San Diego, and it lives today
from Laguna Scammon, Baja California, to Nicaragua at depths up to
15 meters.

Plate 31. Pleistocene clams.

a, b) Pandora {Heteroclidus) punctata Conrad, x 1.
c, d) Leptopecten latiauratus (Conrad), x 3.

e) Petricola {Petricola) parallela Pilsbry and Lowe, x 1>^.

Pleistocene

67

^^^||^^^gjMmm||[|MJ||MJ|i^^

•

68 Pleistocene

Tagelus (Tagelus) calif ornianus (Conrad), Plate 32a

Being very long in proportion to its height, this clam resembles
a closed jackknife and is therefore commonly called the jackknife clam.
The shell is thin, and its exterior surface is sculptured with fine con-
centric threads. When the valves are closed, the shell gapes.

This species occurs in the Pliocene and Pleistocene of California
and in the Pleistocene of Baja California, Mexico. It has been found
in the Pliocene in Balboa Park and in the Pleistocene at Spanish Bight,
near Tecolote Creek, and formerly at 26th Street, in San Diego. It
lives today from Monterey Bay, California, to Golfo de Tehuantepec,
Mexico.

Trachycardium (Mexicardia) procerum (Sowerby), Plate 32b, c

This shell is somewhat heart shaped in profile, and both valves are

strongly convex. It is sculptured with many subrounded ribs separated

by square-cornered interspaces. The beaks are centrally located and

curve inward. The interior margin is crenulated.

This species has been found in the Pleistocene at the foot of 26th

Street in San Diego and in Baja California. It lives today from Baja

California to Peru.

Yoldia cooperi Gabb, Plate 32d, e

Although this shell looks a little like shells of Pandora (Plate 31 ),
the genera may be instantly told apart if the interior can be seen,
because Yoldia has a row of many small teeth alternating with sockets
along the hinge, whereas Pandora has but one to three radiating teeth.
The exterior of Yoldia cooperi is sculptured with incised concentric
lines that tend to be bunched at the pointed posterior end. The beaks
are located two-thirds of the distance from the anterior end.

In the San Diego area this species has been found in the Pleisto-
cene only, but elsewhere in California it occurs in rocks of Miocene
and Pliocene as well as Pleistocene age. It lives today from San Fran-
cisco Bay to San Diego.

Plate 32. Pleistocene clams.

a) Tagelus {Tagelus) calif ornianus (Conrad), x 1.
b, c) Trachycardium {Mexicardia) procerum (Sowerby), x 1.
d, e) Yoldia cooperi Gabb, x 1.

Pleistocene

69

*^

X

,x

h""

e

70 Pleistocene

Tresus nuttalli (Conrad), Plate 33, Plate 34

This is one of the largest of the Pleistocene clams; the specimen
figured is 15.0 cm long and 9.8 cm high but is only of moderate size
for the species. The shell is thick and is truncated at the posterior end,
and if the two valves are together and closed it gapes at the posterior
end. The pallial line and muscle scars can be seen in the interior view.
Plate 34.

This species has been collected from Miocene, Pliocene, and Pleis-
tocene rocks in California and from the Pleistocene of Baja California.
It lives today off central and southern California and Baja California,
Mexico.

Plate 33. Pleistocene clam.

Tresus nuttalli (Conrad), x 1.

Pleistocene

71

72

Pleistocene

\

Plate 34. Pleistocene clam.

Tresus nuttalli (Conrad), x 1,

73

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