Gulf Research
Reports

Volume 1, Number 1

Ocean Springs, Mississippi
April, 1961

Gulf Research Reports

Volume 1 Issue 1

January 1961

The Marine and Brackish Water Mollusca of the State of Mississippi

Donald R. Moore

Gulf Coast Research Laboratory

DOI: 10.18785/grr.0101.01

Follow this and additional works at: http:/ / aquila.usm.edu/ gcr

Recommended Citation

Moore, D. R. 1961. The Marine and Brackish Water Mollusca of the State of Mississippi. Gulf Research Reports 1 (l): 1-58.
Retrieved from http://aquila.usm.edu/gcr/voll/issl/l

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Gulf Research
Reports

Volume 1, Number 1

Ocean Springs, Mississippi
April, 1961

A JOURNAL DEVOTED PRIMARILY TO
PUBLICATION OF THE DATA OF THE
MARINE SCIENCES, CHIEFLY OF THE
GULF OF MEXICO AND ADJACENT
WATERS.

GORDON GUNTER, Editor

Published by fhe

GULF COAST RESEARCH LABORATORY
Ocean Springs, Mississippi

SHAUGHNESSY PRINTING CO.. BILOXI, MISS.

MAP OF THE MISSISSIPPI COAST

THE MARINE AND BRACKISH WATER MOLLUSCA

of the

STATE OF MISSISSIPPI

by

Donald R, Moore

GULF COAST RESEARCH LABORATORY

and

DEPARTMENT OF BIOLOGY,
MISSISSIPPI SOUTHERN COLLEGE

- 1 -

TABLE OF CONTENTS

Introduction Page 3

Historical Account Page 3

Procedure of Work Page 4

Description of the Mississippi Coast Page 5

The Physical Environment Page 7

List of Mississippi Marine and Brackish Water Mollusca . . Page 11

Discussion of Species Page 17

Supplementary Note Page 52

Summary Page 55

Bibliography Page 57

- 2 -

INTRODUCTION

The study of marine life of the Gulf of Mexico has progressed
slowly as compared to other regions of the United States. Much of
this lack of progress is probably due to the absence of universities
in the coastal area, and the absence of large populated centers where
marine research would be encouraged. The early work was done by
travelers and expeditions from places remote to the Gulf. Only in
the present century has there been any attempt to establish marine
laboratories on this seaside. Most of these laboratories have been
located in rather remote, inaccessible places, and have usually suf-
fered from inattention by the parent institution. In recent years,
however, the search for oil, industrial growth of coastal cities, and
the development of beach resorts have brought new roads and more
people to the coast. During the same time the Gulf fishing industry
expanded enormously, and, in value, became the largest fishery of
the several important fishing regions of the United States. For in-
stance, according to Fisheries Industries of the United States for
1956, the Gulf coast produced more in pounds and value than the
Pacific coast, and more in value than the New England states. This
new growth has stimulated a demand for more scientific knowledge
of the Gulf and its waters.

The scientific study of the Mollusca of the Gulf of Mexico has
been carried on in the past in museums far from this region. The
bulk of this work has dealt mainly with taxonomy, and even the
geographical distribution of most species is poorly known. The writ-
er’s purpose in the present work is to give a brief history of prior
work on Mollusca along the Mississippi coast, to identify the species
found in the area studied, and to discuss what is known of the dis-
tribution, abundance, and habits of many of the species. The work
was done at the Gulf Coast Research Laboratory in Ocean Springs,
Mississippi, and was carried on concurrently while the writer was
engaged in other duties and activities. Most of the specimens were
collected near the Laboratory or around Horn and Ship Islands, but
both ends of Mississippi Sound received attention, and it is believed
that the collections are representative of the entire area. The writer
did not attempt to work in fresh water, and limited the marine col-
lections to the area inside a line drawn one mile south of the bar-
rier islands.

The writer would like to thank those who have given freely of
advice and help. In particular, he would like to thank Dr. Gordon
Gunter of the Gulf Coast Research Laboratory, Drs. J. F. Walker
and R. A. Woodmansee, Mississippi Southern College, Dr. Hugh Ber-
nard, Shell Development Company and Dr. R. R. Priddy of Millsaps
College.

HISTORICAL ACCOUNT

Some shallow water mollusks of the northern Gulf of Mexico
were first described by European zoologists in the latter half of the
eighteenth and early part of the nineteenth centuries. Two Europeans,
LeSueur and Rafinesque, came to this country in the early 1800’s,
and published some of their findings in American journals. Thomas
Say was the first American to describe material from the Southern
states. He made a collecting trip to Georgia and Florida in 1818, and

- 3 -

described a number of species which are common on the Mississippi
coast. He was followed by T. A. Conrad who visited Alabama in 1833.
Conrad was mainly interested in fossils, but some of those he de-
scribed are found living in our coastal waters at the present time.
The first publication specifically mentioning Mississippi marine mol-
lusks is Whiles (1854), who listed one species of squid under Crus-
tacea.

Many people began to collect and write about Gulf mollusks after
the Civil War. Most of this activity, however, was centered on the
west coast of Florida, and the central Gulf states were almost com-
pletely neglected. The first faunal list of species from the Mississippi
coast was a very short one published by Stearns (1894). The next
list of Mississippi mollusks was published by Vanatta (1904) on a
collection from Horn Island. He listed thirty-five species, but did
not indicate exactly where or how they were collected. Cary (1906)
enumerated seventy-three species from the coast of Louisiana. This
list is mentioned here because many of the specimens came from the
same molluscan fauna as that found on the Mississippi barrier islands.

Nothing more was published on Mississippi mollusks, except oys-
ter reef survey work by H. F. Moore (1913), until a series of short
papers was published by various authors from 1952 onwards. Kosso
(1952) listed six species of pelecypods found in Mississippi Sound,
but which did not occur around Grand Isle, Louisiana, Ward ef al.
(1953) published a list of thirteen names, and Tolbert and Walker
(1953), in a brief note discussed the general biology and distribution
of Mississippi Mollusca. A paper by Walker (1953) listed the marine
invertebrates, including mollusks, that had been collected by students
and workers at the Gulf Coast Research Laboratory. He listed forty-
seven species, but four names have been since dropped by the writer
for the following reasons. One species was placed in three different
genera, but all three names referred to the same animal. Another
species was divided into two subspecies that are not believed to be
valid. Another species is not found in the Gulf of Mexico, and was
apparently based on a misidentified specimen. The most recent pub-
lication, D. R. Moore (1957), discussed the occurrence and distribu-
tion of the minute pelecypod, Cana dalli.

In addition to the published reports, a checklist of the marine
invertebrates was mimeographed by the Gulf Coast Research Labor-
atory in the summer of 1955. It contained a list of seventy mollusks,
but eight of these were duplications or misidentified, or came from
deep water some distance offshore and outside of the region treated
in this paper.

PROCEDURE OF WORK

The specimens studied by the writer v/ere collected by every
means possible. Many specimens were picked out of beach drift, and
samples of beach sand were examined under the low power micro-
scope. Many animals were captured in trawls or taken in bottom
samples during work on board the Laboratory vessel, “Hermes.”
Other collections were made by skin diving, and by screening sand
in shallow water near shore. The writer is indebted to several
people who brought in material from collecting trips. W. J. Demoran
and J. Y. Christmas of the Laboratory staff brought in a great deal
of valuable material collected during the course of their field work,

- 4 -

and among the summer teaching staff, Dr. R. A. Woodmansee and
Dr. H. J. Bennett were particularly helpful.

Activities of the living animals were observed in some cases,
but, for many species, only empty shells were collected. The most
important part of the work was the taxonomy of the local animals,
and the identity of some species is still in doubt. As might be ex-
pected, it was the small species that proved to be difficult, and a
great deal of literature was consulted in order to make determina-
tions. The major reference works utilized include de Blainville
(1325), H. and A. Adams (1858), Fischer (1880-87), Tryon (1881), Thiele
(1928-35), Morton (1958), Abbott (1954), Smith (1937), Perry and
Schwengel (1955), “John sonia” (1941 to 1959), Johnson (1934), Clench
and Turner (1950), Dali 1890-1903), Olsson, Harbison, Fargo and Pils-
bry (1953). A host of shorter papers and monographs were also con-
sulted.

Specific determinations were based almost entirely on the shell
alone, since very few marine mollusks have had their soft anatomy
described, although the general classification of mollusks is based
almost entirely on the soft anatomy of the animals.

DESCRIPTION OF THE MISSISSIPPI COAST

The Gulf coast of Mississippi occupies a short stretch of coast
line east of the delta of the Mississippi River. It is entirely a mud
and sand environment except for pilings and a few rocks brought in
by man. The major physiographic feature is Mississippi Sound, an
elongate body of water partially enclosed by a series of* barrier is-
lands. The Sound is approximately eighty miles long by ten miles
wide, and averages about ten feet in depth. The axis of the Sound
is almost due east and west. The eastern end is at Grant's Pass near
the lower end of Mobile Bay and the western end terminates at
Grand Island, Louisiana, at the east end of Lake Borgne. Most of
the bottom is mud, but this is replaced by sand close to the barrier
islands and in some places along the mainland. However, several
oyster reefs provide a firm substratum in the mud region. The
eastern one-fifth of Mississippi Sound lies in Alabama.

The barrier islands lie along the southern flank of Mississippi
Sound. They arc long and narrow, and are oriented generally east
and west. Although subject to a certain amount of shifting, the
main part of the islands have been in existence for a considerable
period of time, and all of them have considerable areas forested with
Caribbean pine. From east to west, the first barrier is Dauphin Is-
land, Alabama It is approximately twelve miles long, but is very
narrow except for three miles at the east end where the width is
about a mile. This end forms the west side of the mouth of Mobile
Bay. A causeway has been built from the mainland to the island,
and it is now readily accessible to the public. Four miles to the west
of Dauphin lies Petit Bois, a smaller island about six miles in length.
The Alabama-Mississippi boundary cuts the island, with the larger
portion lying in Mississippi. From Petit Bois to Horn Island is less
than two miles. The channel between the two islands is known as
Horn Island Pass and serves the port of Pascagoula. Horn Island
is twelve miles long, and averages about a half mile in width.
About half of the island is forested. The next in the series. Ship

- 5 -

Island, lies nearly five miles to the west of Horn Island. Much of
the interval is made up of shallow banks, but Dog Keys Pass, just
west of Horn Island, is a natural deep water pass, used mostly by
shrimpers and menhaden boats. Ship Island is actually two islands
connected by a narrow sand spit. The eastern portion is roughly
triangular, and much of it is wooded. The western portion is elon-
gate, low and flat, and without any wooded sections.

Cat Island lies four miles to the west of Ship Island. The body
of water between these islands is Ship Island Pass, and a deep water
ship channel is maintained through the pass and up the Sound to
the city of Gulfport on the mainland. Cat Island differs from the
other islands in that it is T shaped, although apparently, it was
originally aligned with the other islands in an east-west direction.
It appears that as the Mississippi Delta built out to the eastward,
the Chandeleur Island arc was formed. The only direction that waves
from the open Gulf can come on to Cat Island at the present time
is from the ESE. The eastern part of the island now runs NNE by
SSW and is long and narrow. This part of the island is thus at right
angles to the direction of the waves, and was obviously formed by
their action. Cat Island is the last of the barrier islands, for the
remaining islands at the southwest end of the Sound are part of
the Mississippi Delta system. The water around these islands is very
shallow, but Cat Island Channel, between Cat Island and the delta
islands, is more than forty feet deep in some places.

It can be seen that the writer is of the opinion that the Mis-
sissippi barrier islands were formed before the Chandeleur Islands.
Dr. Hugh Bernard, of the Shell Development Company, has informed
the writer (personal communication) that radiocarbon dating of shells
gives an age of five to six thousand years for the Mississippi islands,
and approximately half that age for the Chandeleurs.

The deep passes between the barrier islands are located close
to the western tip of each island. Since waves from the open Gulf
cannot come from the southwest because of the Mississippi Delta, all
waves must come from the southeast quadrant. Each wave, when
coming oblique to the beach, tends to move sand down the beach
in the direction the wave is traveling. Each island has extended
sand spits to the westward, and has displaced the tidal flow at the
same time. The increased flow of water around the end of the spit
has dug out fairly deep channels very close to shore, with depth
ranges from about twenty to fifty feet. There is often an off-shore
bar, however, where the depth is reduced to ten or twelve feet.

A number of smaller islands are found in Mississippi Sound close
to the mainland shore. An exception is Round Island which is mid-
way in the Sound between the mouth of the Pascagoula River and
Horn Island. The two largest islands near the mainland are Isle
Aux Herbes just south of Coden, Alabama and Deer Island which
lies across the mouth of Biloxi Bay. Round and Deer islands are
high, sandy and extensively wooded with pine; the remaining islands
are low and marshy.

The shore of the mainland is often quite irregular, and indicates
some degree of submergence. It is low, marshy and irregular along
the east Mississippi and west Alabama coast, but much of the interval
between Pascagoula and Waveland is a high sandy ridge. From
Waveland westward to the Louisiana boundary it is once again low

- 6 -

and marshy. Biloxi Bay is long and narrow, and the inner seven
and one-half miles is oriented east and west. The remaining three
and one-half miles, east of U. S. 90 Highway bridge, runs in a NW-
SE direction. Deer Island lies across the mouth of the bay, leaving
a narrow channel along the eastern section of the city of Biloxi, and
a wider channel between the east end of the island and Marsh Point
on the mainland. The outer bay is shallow, much of it being less
than six feet deep at low tide. The narrow channel in the inner
bay, however, may be as much as thirty feet deep. Three small
streams empty into the inner bay. They are: Old Fort Bayou, Biloxi
River, and Bernard Bayou. Davis Bayou empties into outer Biloxi
Bay opposite Deer Island, and it is here that the Gulf Coast Re-
search Laboratory is located.

Bay St. Louis is only fifteen miles or so to the west of Biloxi
Bay. Its shape, however, is much different. From the mouth to the
northern shore is about six and one-half miles. The shape as seen
on a chart is roughly that of a mushroom, with the top somewhat
displaced to the westward. Two rivers, the Jourdan and the Wolf,
empty into the bay on the west and east sides, respectively. The
bay is quite shallow except at the mouths of the rivers where depths
of ten to twenty feet are reported.

In addition to the streams flowing into the two bays mentioned
above, a number of small streams flow directly into the Sound. The
two most important rivers on the Mississippi coast are the Pearl and
the Pascagoula. The latter empties into the Sound near the Alabama-
Mississippi border. The Pearl flows into Lake Borgne about four
miles west of Grand Island Pass, which in turn flows into the west
end of Mississippi Sound. In 1902 the United States Supreme Court
set the offshore boundary between the states of Louisiana and Mis-
sissippi as the channel, determined by depth, from the mouth of the
Pearl River to the Gulf of Mexico.

The climate of lower Mississippi is moist and humid, and the sal-
inity of the Sound is kept lower than the open Gulf by the inflow of
fresh water from streams.

THE PHYSICAL ENVIRONMENT

Many factors influence the variety and numbers of marine an-
imals. The substratum, depth of water, waves and currents, salinity,
temperature, and turbidity, all have a vital influence on the marine
fauna.

Students of coastal animal communities usually rely heavily on
salinity as the chief limiting factor. Thus Gunter (i945, 1950) related
the presence or absence of animals largely to salinity. His studies,
however, were based mainly on motile organisms. Most Mollusca
are not capable of rapid movement, and might be excluded from an
area by the grain particle size of the substratum or by the absence
of plants where turbidity is unusually high. While not the only lim-
iting factor, salinity is probably second only to temperature as a
physical condition in most areas.

The terms, marine and brackish water, are somtimes used here
to define general salinity conditions. The writer considers in this
work that marine waters have a salinity of more than 25 parts per
thousand, and that brackish waters have a lower salinity.

- 7 -

The salinity of the Mississippi coast varies with the amount of
fresh-water runoff in the southern half of the state. There appears
to be a seasonal variation with the highest salinities in the late fall
and lowest in the summer, but this varies from year to year. A
series of salinity readings taken during the years 1956-57 are given
in Table L The figures are in parts per thousand and were computed
from specific gravities measured on a chain gravitometer. There
are some anomalies in the salinity table, for more dense waters were
sometimes found at the surface. In no case, however, is the difference
in density very great, and may have been caused by both turbulence
and by human error. It should be noted that in shallow Gulf coastal
waters surface salinities higher than bottom salinities are fairly com-
mon (Cf. Gunter, 1945, Collier and Hedgpeth, 1950). The stations are
described in the following paragraphs and their location is given in
Figure I.

TABLE /. Surface and bottom salinities at Gulf Coast Research
Laboratory Stations. Station I is between Marsh Point and Deer
Island in the Bay of Biloxi. Station II is at the mouth of the Bay of
Biloxi, Station III is half way across Mississippi Sound from Station
II to Dog Keys Pass. Station IV is in the outside part of Dog Keys
Pass. These salinities were computed from specific gravities measured
on a chain gravitometer, and are given here in parts per thousand.

Date

I

II

III

IV

12/15/56

Surface

28.44

25.33

33.32

Bottom

27.72

28.68

33.32

2/9/57

Surface

11.91

9.58

19.21

26.53

Bottom

11.85

11.23

19.94

25.72

3/23/57

Surface

19.25

21.91

25.88

28.51

Bottom

19.25

23.88

26.54

27.20

4/6/57

Surface

6.56

9.17

8.66

27.36

Bottom

9.17

15.99

27.41

29.99

4/22/57

Surface

5.64

10.39

12.88

Bottom

4.07

6.65

16.68

6/15/57

Surface

17.42

20.16

23.08

27.68

Bottom

17.42

21.66

25.68

27.75

Station I was located between the tip of Marsh Point and Deer
Island, II at the mouth of Biloxi Bay, III halfway between Station
II and Dog Keys Pass, and Station IV was in Dog Keys Pass.

It can be seen in the above table that there is a gradient from
low salinity in the mainland bay to high salinity in the barrier is-
land pass. The salinity at Station TV, however, was still somewhat
lower than oceanic water, which is generally about 36.5 parts per
thousand in the Gulf of Mexico. Many marine animals can live
where the salinity ranges down to about 25 parts per thousand, but
the number of species falls off rapidly at lower salinities. The Mol-
lusca are no exception to the general rule, and most of the species
were found only around the barrier islands. A few species are con-
ditioned to low salinities; they are invariably confined to the inner

- 8 -

- 9 -

bay or outer bayou region, or possibly brackish water ponds on the
barrier islands.

Very wet or very dry periods can, of course, displace the salinity
gradient seawards or landwards. The summers of 1953 and 1959 had
unusually heavy precipitation, and salinities dropped to less than 1.0
at the Gulf Coast Research Laboratory. In the Sound, on the north
side of Ship Island, surface salinities as low as 11.5 were encountered.
Many animals that are capable of moving about undoubtedly descend
to deeper, more saline water at such times, but sessile forms, and
some others, sometimes suspend all activity until the fresh water is
dispersed.

The temperature of Mississippi coastal waters fluctuates over a
fairly wide range with the greatest variation occurring in the bays
and bayous during the winter months. Summer temperatures do not
usually show much variation between stations, for cool fresh water
runoff helps to keep temperatures down close to the mainland. A
series of temperature readings taken at the four stations already
mentioned in Table I are given in Table II.

TABLE II. Surface and bottom temperatures in degrees Centigrade
at the Gulf Coast Research Laboratory Stations described in the
legend of Table I.

Date

I

II

III

IV

12/15/56

Surface

18.3

18.4

19.0

Bottom

18.3

17.0

19.0

1/26/57

Surface

14.4

14.4

14.8

Bottom

14.3

14.0

14.8

2/9/57

Surface

24.5

21.6

18.0

21.1

Bottom

24.0

21.9

17.0

16.0

3/9/57

Surface

12.4

12.5

14.1

18.0

Bottom

11.9

12.7

14.3

17.4

6/15/57

Surface

29.4

30.1

30.4

30.4

Bottom

29.5

29.6

30.15

29.7

The temperatures for February 9, 1957 were taken near the end
of a period of unusually warm weather and are not typical of the
usual Mississippi winter. The winter temperatures in Table II are
probably higher than average, for during a cold wave the surface
temperatures drop to 4.0° centigrade. Surface temperatures taken
at Ship Island Lighthouse, Bumpus (1957), during the years 1930-32
had a mean of approximately 11° for the month of January. As
these temperatures were taken at 8 a. m. and 6 p. m., they would
reflect the daily average better than the temperatures in Table II
which were taken between the hours of 9 a. m. and 3 p. m.

The remaining physical conditions, except the substratum, have
not been studied in the Mississippi area. Turbidity is high and for
long periods at a time Sccchi disk measurements are less than one
meter. This, of course, discourages macrospic plant life, and nearly
all of the attached algae and “grass” is found in shallow water on
the north side of the barrier islands. Currents are mainly tidal or
wind driven, so are usually of rather short duration. Waves are

- 10 -

apparently of little consequence except during high winds. The bot-
tom slopes very gradually from the barrier islands southward, and
acts as a dampener for large waves.

The substratum of Mississippi coastal waters has been investi-
gated more thoroughly than the waters above it (Priddy ef al. 1955).
The bottom consists of mud or sand, and oyster reefs provide some
natural hard bottom. Man has provided hard bottom in the form
of pilings for docks and piers, rock jetties, and rocks in shallow
water around Fort Massachusetts and the old quarantine station on
Ship Island. Most of the man-made hard substratum is along the
mainland where few species of mollusks are able to utilize it. The
rocks at Ship Island, however, provide a habitat for a number of
species that would not otherwise be found here. Another type of
hard bottom consists of broken shell in the passes. Trawling in Dog
Keys Pass usually produced a number of worn valves of Dinocardium
robusfum, and assorted worm tubes; bryozoans and small mollusks were
usually found on these shells. Priddy (op. c/f.) disregarded the infin-
itesimal hard bottom and gave the following estimates for the type
of substratum in Mississippi Sound: sand 5 per cent, clay-mud 80 per
cent, and silt or sandy silt 15 per cent.

The type of substratum has a great deal of influence on the mol-
luscan population, for many species that are at home in sand can-
not exist in mud. The oyster is a notable exception, but it needs
some hard structure to fasten onto when the time comes for the
young to settle on the bottom. Most pelecypods found living along
the mainland shore are living in muddy sand, or, especially among
the Pholadidae, in sandy mud or firm silt.

Most of the bottom of Mississippi Sound appears to be mud, and
the surface layer is fine unconsolidated material which is easily
stirred up by waves. Most mollusks are unable to keep fine material
from clogging their gills; hence they are excluded from most of the
area under discussion. On the other hand, the sand found on the
barrier islands is often coarse, and probably permits some species to
live there that are not to be found west of the Mississippi River,
where the sand is much finer. One such species is the minute pel-
ecypod Cuna dalli, which is smaller than some of the sand grains as-
sociated with it.

In general the conditions of the Mississippi coast are quite sim-
ilar to those found on the Georgia and Carolina coasts. Much of
the invertebrate populations are identical, and it is obvious that the
two areas were not separated by the peninsula of Florida until rel-
atively recent times. For this reason, the coast from south Texas
to Cape Hatteras, North Carolina (excepting south Florida) is con-
sidered to be a single biogeographic area, the Carolinian Province.
The climate is warm temperate, and the tropical element is scanty.
Only those forms that are able to withstand rather wide extremes
of temperature during the year can survive on the Mississippi coast.

LIST OF MISSISSIPPI MARINE AND
BRACKISH WATER MOLLUSCA

The following classification is essentially the same as that em-
ployed by Morton (1958), which differs slightly from that of Thiele

- 11 -

(1928-35), mainly in the addition of the class Monoplacophora, and
in the subdivision of the Opisthobranchia and the Pelecypoda. He
also adds a fourth order to the Cephalopoda, the deep sea Vampyro-
morpha. The large family Pyramidellidae has also been removed
from the Prosobranchia, and placed under the order Cephalaspidea
in the class Opisthobranchia on the basis of a number of anatomical
resemblances. Two of the six classes of living mollusks, Monoplaco-
phora and Amphineura, are not found on the Mississippi coast. The
two existing species of Monoplacophora were described in 1957 and
1959 from deep water in the eastern Pacific, and this class is not
likely to be found in the shallow waters of the northern Gulf of
Mexico. The Amphineura, however, are well represented in the Gulf,
but seem to be excluded from Mississippi coastal waters, possibly
by low salinities.

Class Gastropoda
Subclass Prosobranchia
Order Archaeogastropoda
Family Fissurellidae
Diodora cayen&nsis Lamarck 1822
Lucapinella limatula Reeve 1850
Family Neritidae
Neritina reclivata Say 1822

Order Mesogastropoda
Family Littorinidae
Littorina irrorata Say 1822
Family Rissoinidae
Rissoina chesneli Michaud 1832
Family Vitrinellidae
Cyclostremiscus trilix Bush 1883
Episcynia multicorinafa Dali 1889
Solariorbis blokei Rehder 1944
Solariorbis mooreana Vanatta 1904
Teinostoma biscaynense Pilsbry & McGinty 1945
Family Caecidae
Caecum cooper/ Smith 1860
Caecum cf. glabrum Montagu 1803
Caecum pule helium Stimpson 1851
Meioceras nifidum Stimpson 1851
Family Cerithidae
A/ob/na cerithidiaides Dali 1889
Bift/um varium Pfeiffer 1840
Seila adamsi Lea 1845

Family Cerithiopsidae
Cerithiopsis greeni C. B. Adams 1839
Family Triphoridae
Triphora nigrocincta C. B. Adams 1839
Family Epitonidae
Epitonium rupicolum Kurtz 1860
Epifonium angulafum Say 1831
Family Eulimidae
Melanella intermedia Cantraine 1835

- 12 -

Family Calyptraeidae
Crepidul a convexa Say 1822
Crepidula farnicafa Linne 1767
Crepidula maculosa Conrad 1845
Crepidula plana Say 1822
Family Strombidae
Strombus alatus Gmelin 1790
Family Naticidae
Natica pusilla Say 1822
Polinices duplicafus Say 1822
Sinum perspeciivum Say 1831
Family Cassididae
Phalium granulatum Born 1780

Order Neogastropoda
Family Muricidae
Murex fulvescens Sowerby 1834
Thais haemastoma Linne 1767
Family Columbellidae
Anachis avara Say 1822
Anachis obesa C. B. Adams 1845
Mitrella lunata Say 1826
Family Buccinidae
Cantharus cancellarus Conrad 1846
Family Melongenidae
Busycon perversum Linne 1758
Busyc on spiratum Lamarck 1816
Family Nassariidae
Nassarius acutus Say 1822
Nassarius vibex Say 1822
Family Fasciolariidae
Fasciolaria hunteria Perry 1811
Family Olividae
Oliva sayana Ravenel 1834
O livella sp.

O livella mufka Say 1822
O livella pusilla Marrat 1871
Family Volutidae
Scaphella junonia Shaw 1808
Family Cancellariidae
Cancellaria reticulata Linne 1767
Family Terebridae
Terebra concava Say 1827
Terebra dislocata Say 1822
Terebra salleana Deshayes 1859
Family Turridae
Kurtziella cerinella Dali 1889
Rubellatoma diomedea Bartsch and Rehder 1939
Nannodiella melanitica Bush 1885

Subclass Opisthobranchia
Order Cephalaspidea
Family Acteonidae
Acteon punctostriatus C. B. Adams 1840

- 13 -

Family Atyidae

Haminoea antillarum d’Orbigny 1841
Haminoea succinea Conrad 1846
Family Retusidae
Retusa canaliculate i Say 1822
Family Acteocinidae
Cylichna bidenfat a d’Orbigny 1841
Family Gastropteridae
Gadropteron rubrum Rafinesque 1814
Family Pyramidcllidae
Odostomia impressa Say 1822
Odostomia seminuda C. B. Adams 1839
Odostomia sp.

Turbonilla conradi Bush 1899
Turbonilla sp.

Order Anaspidea

Family Aplysidae
Aplysia willcoxi Heilprin 1886

Order Thecosomata
Family Cavolinidae
Cavo/ina longirostris LeSueur 1821
C resis acicula Rang 1828

Order Nudibranchia
Family Polyceridae
Polycera hummi Abbott 1952
Family Corambidae
Corambella baratarioe Harry 1953
Family Arminidae
Armina tigrina Rafinesque 1814
Family Scyllaeidae
Scyllaea pelagica Linne 1758
Family Flabellinidae
Eubranchus sp.

Subclass Pulmonata
Order Basommatophora
Family Ellobiidae
Melampus bidenfatus Say 1822

Class Scaphopoda

Family Dentaliidae
Dentalium texasianum Philippi 1848
Dentalium eboreum Conrad 1846

Class Pelecypoda
Order Protobranchia
Family Nuculanidae
Nuculana acuta Conrad 1831

- 14

Order Taxodonta
Family Arcidae

Anadara brasiliana Lamarck 1818
Anadara ovalis Bruguiere 1792
Anadara transversa Say 1822
Noetia ponderosa Say 1822

Order Anisomyaria
Family Mytilidae
Amygdalum papyria Conrad 1846
Brachidontes recurvus Rafinescue 1820
Lithophaga bisulcata d’Orbigny 1846
Modiolus demissus Dillwyn 1817
Muscu/us lateralis Say 1822
Family Pinnidae
Atrina seminuda Lamarck 1819
Atrina serrafa Sowerby 1825
Family Plicatulidae
Plicatula gibbosa Lamarck 1801
Family Pectinidae
Aequipecten irradians Lamarck 1819
Family Ostreidae
Crassosfrea virginica Gmelin 1792
Osfrecr equestris Say 1834

Order Heterodonta

Family Crassatellidae
Crassinella lunulata Conrad 1834
Cuna dalli Vanatta 1904
Family Carditidae
Cardita floridana Conrad 1838
Family Corbiculiidae
Polymesoda caroliniana Bose 1801
Family Diplodontidae
Diplodonta punctata Say 1822
Family Lucinidae
Lucina amiantus Dali 1901
Lucina floridana Conrad 1833
Lucina multilineata Tuomey & Holmes 1857
Family Chamidae
Chama co ngregata Conrad 1833
Family Leptonidae
Kellia suborbicularis Montagu 1804
Mysella cuneata Verrill 1898
Mysella planulata Stimpson 1851
Family Cardiidae
Dinocardivm robustum Solander 1786
La&vicardium laevigatum Linne 1758
Laevicardium mortoni Conrad 1830

- 15 -

Family Veneridae
Callocardia texasiana Dali 1892
Chi one cancellata Linne 1767
Chi one grus Holmes 1858
Chione intapurpurea Conrad 1849
Dosinia discus Reeve 1850
Gemma gemma Totten 1834
MacrocalHata nimbosa Solander 1786
Mercenaria mercenaria Linne 1758
Parastarte triquetra Conrad 1845
Family Petricolidae
Petricola pholadiformis Lamarck 1818
Family Tellinidae
Macoma constricta Bruguiere 1792
Macoma mitchelli Dali 1895
Strigilla mirabilis Philippi 1841
Tellidora cristata Recluz 1843
Tellina alternata Say 1822
Tellina iris Say 1822
Tellina fexana Dali 1900
Tellina versicolor DeKay 1843
Family Semelidae
Abra aequalis Say 1822
Abra lioica Dali 1881
Cumingia tellinoides Conrad 1831
Seme/e nuculoides Conrad 1841
Semele proficua Pultney 1767
Family Donacidae
Donax variabilis Say 1822

Family Sanguinolariidae
Tagelus plebeius Solander 1786
Tagelus divisus Spengler 1794

Order Adapedonta
Family Solenidae
Enis minor Dali 1900
Family Mactridae
Labiosa plicaiella Lamarck 1818
Mactra fragilis Gmelitl 1792
Mulinia lateralis Say 1822
Rangia cuneata Gray 1831
Spisula solidissima Dillwyn 1817
Family Mesodesmatidae
Ervillia concentrica Gould 1862
Family Corbulidae
Co rbula sp.

Family Gastrochaenidae
Rocellaria stimpsonii Tryon 1861
Family Pholadidae
Borneo truncata Say 1822
Cyrtopleura co stata Linne 1758
Diplothyra smithii Tryon 1862
Family Teredinidae
Bankia gouldi Bartsch 1908

- 16

Order Anomalodesmata
Family Lyonsiidae
Lyonsia floridana Conrad 1849
Family Pandoridae
Pandora trilineata Say 1822

Class Cephalopoda
Subclass Coleidea
Order Deeapoda

Family Loliginidae
Lofigo pealei LeSueur 1821
Lolliguncula brevis de Blainville 1828

Order Octopodidae

Family Octopodidae
Octopus vulgaris Lamarck 1798

DISCUSSION OF THE SPECIES

Unfortunately, little can be said concerning many of the species
beyond a simple statement as to where they occurred, and their
probable abundance For some species, however, the writer has
gathered additional information concerning habits and life histories.
The same classification as that of the systematic list of species is
followed, but some of the higher categories, such as Subclass are
left out,

FISSURELLIDAE

The shells of this family are secondarily bilaterally symmetrical.
They are limpet shaped, and have either a slit or a hole in the
shell. The animal is primitive, and retains a pair of gills in the
mantle cavity.

Diodora cayenensis. This keyhole limpet was taken only in small
numbers in Dog Keys Pass living on pieces of old shells and other
debris. It will probably be found in any similar habitat along the
coast. Maximum size about 35 to 40 mm.

Lucapinella limafula. This species is very similar to the preceding
one. However, the shell is much more depressed, and the animal
is not enclosed by the shell as in Diodora c ayenensis. A further dif-
ference between the two is that the internal callus around the ap-
ical slit is truncate posteriorly in D. cayenensis and is rounded in L.
limatula . The animal of the latter differs from the former in the pos-
session of papillae at the apical slit, three before and four behind.
One live specimen on broken shell from Dog Keys Pass. Maximum
size about 20 mm.

NERITIDAE

The columella in this family is shelf like, and is somewhat sim-
ilar in some respects to that found in Crepidula . Unlike Crepidula,
however, the animals are active browsers. This is the only family
in the Archaeogastropoda that has penetrated fresh water,

Nerifina reclivata. The river snail is usually found in shallow
water in low salinity bayous and bays. It has been collected as
far down Biloxi Bay as the U. S. 90 Highway bridge. It is also

- 17 -

abundant on the west side of Mobile Bay about two miles south
of the mouth of the Fowl River. The eggs are laid in flat oval
cases, half a dozen or so at a time. The shell is rounded, smooth,
green in color, and with many narrow, wavy, black axial lines.
Maximum size about 15 mm. This species was erroneously reported
to live on vegetation above the surface of the water by Parker (1956).

LITTORINIDAE

This is a family of rather simple appearing snails that has
moved out of the sea, yet must stay close to salt water. The eggs
are shed into the water, and there is a free swimming veliger.

Littorina irroraia. This is an extremely abundant species in the
marshy areas along the mainland. It leaves the water after a pel-
agic larval existence, but must remain in a damp habitat at the
water’s edge. It is usually found living on the salt water marsh
grass, Spariina, or on the rush, ./uncus, but is sometimes found on
bridge pilings or other man-made structures. It has been observed
copulating in July and August.

The shell is dull tan in color, with sculpture of many spiral
cords. The aperture is rounded and is closed entirely by the corne-
ous operculum. Maximum size about 25 mm.

RISSOINIDAE

In this family, the shells are elongate, white, and variously
sculptured. They are most abundant in shallow warm seas.

Rissoina chesneli. This little snail has not been reported on the
northern Gulf coast before. It is elongate, white in color, and has
about a dozen axial ribs per whorl. Maximum size is about 4 mm.

Several specimens, one living, were taken in shallow water on
the north side of Horn Island.

VITRINELLIDAE

The vitrinellids are minute, white, depressed snails and are
among the smallest gastropods known.

Cyclosiremhcus trilix. Members of this family are minute, flat and
disk like. The w r horls are added on a more or less horizontal plane.
This species has a minute projecting apex and the whorls are angled
on the shoulder, base, and periphery. A few specimens have been
found in beach drift on the barrier islands. Maximum diameter
about 2 to 3 mm.

Episcynia multicarinato. This species is not as flat as the other
members of the family in this region, and is more trochoid in shape.
In addition, there is a finely toothed carina on the periphery of the
whorls. Maximum diameter, 3 to 4 mm. One specimen in beach
drift from Dauphin Island.

Solariorbis blakei. Vifrinella blakei Rehder, 1944, Nautilus 57 (3):
97, plate 9, figures 1, 2. This species is not in the genus Vifrinella as
we understand it today. The chief difference between the two gen-
era is the heavy ridge which constricts the umbilicus in Solariorbis.
This structure is very strongly developed in S. blakei , and, in this
feature, it greatly resembles the type of the genus, Solariorbis depressus

- 18 -

Lea. It also has axial wrinkles on the spire which are very similar
to those found on S. bartschi Vanatta, a species which apparently does
not range as far north as Mississippi. In some S. blakei the umbilical
ridge is exceptionally well developed and the umbilicus is closed
except for a minute oblique chink. These specimens appear at first
glance to belong to the genus Teinostoma, but, in that genus, the um-
bilicus is entirely closed by a plug of shelly material and is formed
differently from the umbilical ridge of Solariorbis.

Only two dead and broken specimens were taken in Ship Is-
land Pass, but the small size (diameter, 1 mm.) of this species makes
it easy to overlook.

Solariorbis mooreana. Vifrinella mooreana Vanatta, 1904, Proceedings
of the Academy of Natural Sciences of Philadelphia 55 (1903): 756-
759. Type locality, Crooked Island, St. Andrews Bay, Florida. This
species also has a strong umbilical ridge, and unquestionably be-
longs in the genus Solariorbis. It is larger than the preceding species
with a maximum diameter of nearly 3 mm. In addition, there are
about five to seven spiral cords on the top half of the shell, the lower
half being smooth. Several specimens have been found in beach
drift on Dauphin, Horn and Ship Islands.

S. mooreana seems to be endemic to the northern Gulf Coast, but
it appears to be known only from the five type specimens at the
Academy of Natural Sciences in Philadelphia and the material the
writer has collected. Nothing is known of the animal, but the oper-
culum is thin and circular. It is multispiral, and is light tan in color.

Teinosfoma biscaynensis. One somewhat immature specimen was
taken in Dog Keys Pass. The umbilicus is completely filled by a
callus, an important characteristic of the genus. Maximum size 1.8 mm.

CAECIDAE

The shells of this family are simple curved tubes, closed at the
posterior end by a shelly plug.

Caecum coo peri. This minute white species attains a length of
about 4 mm There are about 15 longitudinal ribs, and two or three
heavy axial rings at the anterior end. The animal appears to be shy
and retiring in strong light, and evidently prefers to live below the
well lighted zone in rather turbid coastal waters. As is the case in
the preceding two families, the small size of the individual makes
it extremely difficult to estimate abundance, but it appears to be a
fairly common species.

Caecum cf. glabrum. This species has a smooth, cylindrical, slight-
ly curved shell with a dome like apical plug. It has been known
in collections as C. glabrum for the past one hundred years or so, but
it is apparently not that species. Specimens from Dog Keys Pass
were sent to Dr. Harald Rehder, Curator of Mollusks, United States
National Museum, who replied as follows. “I have examined these
small caecids, and I thought at first that they were specimens of
Brochina glabra Montagu. This species, however, is distinguished from
most of the other species by having a conical operculum, whereas
all the others are flattened and discoid. Your specimens have the
operculum of typical Caecum, but with the shell characters of Brochina.
Whether this means that your specimens belong to a new subgenus
under Caecum or Brochina, I do not know; I will have to go into this

- 19 ^

question a little more deeply and examine more specimens, I hope
to be able to include the results of my findings in a paper I am
writing on some new and interesting marine mollusks from the Car-
ibbean and Gulf area.”

This interesting species lives in much the same habitat as C.
cooper/, and most of the writer's specimens came from trawling in
Dog Keys Pass. Maximum size about 2 mm.

Caecum pulchellum . The sculpture consists of about two dozen
axial rings. It is not common on the Mississippi coast. Maximum
size about 2 mm.

Meioceras nitidum . This distinctive little species is very bulbous
in the middle, and has an oblique, constricted aperture, Glassy,
mottled by patches of chalk white. It was only collected once, crawl-
ing on algae trawled just north of Horn Island in a depth of about
20 feet. Maximum size 2 mm.

Me/oceras lermondi Dali, 1924, was described from eleven speci-
mens from Boca Ciega Bay, on the west coast of Florida. The char-
acters appear to be the same as are found in the typical M. nifidum,
and the name should be placed in synonomy with that species.

M. nrfidum is not affected by strong light, and will crawl about
actively and feed while being observed under the microscope. It
does not eat macroscopic algae, but scrapes the surface with the
radula, picking up minute diatoms and other small attached organ-
isms. The tentacles are ciliated, and the eyes are small and black.
Evidently the reduced salinity in Mississippi Sound is responsible
for the species living in deeper water there, for the salinity is usual-
ly higher in the deeper parts of the Sound. At Miami, Florida, the
writer has collected living specimens in only an inch or two of water.
In this case, however, the salinity was very close to that of the open
sea. It is a common species in the Gulf and Caribbean wherever
there is abundant submarine vegetation.

CERITHIDAE

Elongate spiral shells, usually with a short siphonal canal.

Alabina cerHhidioides. A minute glassy species. Maximum size
about 3 mm. It does not appear to be abundant, for only a few
specimens have been found in beach drift on the barrier islands.

Bittium varium . This is a minute form which is probably the most
abundant gastropod on the Mississippi coast. Its color ranges from
light brown to black. Sculpture consists of four spiral cords crossed
by axial riblets. A varix is usually formed on the body whorl, a little
behind the outer lip. To 4 or 5 mm.

The abundance of this little gastropod is not evident unless
some sort of special collecting method is utilized. It lives in great
numbers on marine “grass,” and any method which knocks the ani-
mals off onto a cloth or screen will collect large numbers in a few
minutes where they are abundant. The numerous eggs hatch out
into free swimming veliger larvae that must often form a large pro-
portion of the inshore planktonic animals.

It has been noticed that B. varfum tends to live in somewhat
deeper water in Mississippi Sound than in other localities the writer
has examined, such as Aransas Bay, Texas. It may be that the lower
salinities of surface waters in the Sound force this species to live
in deeper water in Mississippi.

- 20

Seila adamsi. This is a very long and slender little gastropod.
There may be as many as fifteen post-larval whorls in a shell 15 mm.
long. The sculpture consists of three strong spiral cords on the
whorls and two more on the base of the shell. The color is brown.

The species appears to be fairly common in the deeper part of
Dog Keys Pass, for all of the specimens collected were picked out
of shell debris brought up by the trawl.

CERITHIOPSIDAE

This group is similar to the preceding family, but all of the
species are small. The larval whorls are very slender, and the post
larval shell expands rapidly. This gives the apex a somewhat mam-
millated appearance and is quite distinctive. The exterior of the
shell has a beaded appearance.

Cerifhiopsis greeni. This species looks superficially very much like
Bittium varium . However, there is no varix, and the shell has a more
beaded appearance. It attains a size of 4 or 5 mm.

The species listed up to this point are all herbivores as far as is
known at present. Cerifhiopsis , however, feeds on sponges and must
be classed as a carnivore, although its feeding techniques are prob-
ably little changed from that of a typical herbivore. All of the spec-
imens of C. greeni were collected from the north side of Ship Island.
The under side of some rocks at both the old Quarantine Station
and at Fort Massachusetts is covered by a sheet of encrusting yel-
low sponge which is, as yet, unidentified. C. greeni was fairly com-
mon on this sponge, but has not been found anywhere else.

TRIFORIDAE

The triforids are very similar to the preceding family, but differ
in being coiled to the left. They are all small shells and have simi-
lar habits to Cerifhiopsis.

Triphora nigrocinda. A shell very similar to Cerifhiopsis greeni. The
sinistral coiling of T, nigroernefa, however, makes it extremely simple
to tell them apart. The only other sinistrally coiling species in this
region is very large and has a quite different appearance.

It has been collected on a gray encrusting sponge underneath
rocks at both the old Quarantine Station and at Fort Massachusetts.
Although found at the same localities, there was no mixing with
C. greeni. The latter was confined to yellow sponge, and T. nigrocinda
was found only on gray sponge. It was not as abundant as C. greeni ,
but was still fairly common.

In addition, two living specimens were collected in a trawl haul
from a deep channel just north of Horn Island. Most of the catch
was algae of various types, but there may have been sponges on
the bottom that were not picked up by the trawl.

EPITONIDAE

Elongate, usually white, and with numerous blade like axial ribs.

Bpitonium angulofum. A white shell that attains a length of 20 mm.
The ribs are angled near the posterior end.

- 21 -

Occasional specimens are found in shallow water around the
barrier islands.

Epitonium rupicolum. Shell brown. Ribs are very low and fine ex-
cept for an occasional heavy one. There is a thick varix on the outer
lip, and a spiral rib on the base of the shell. One specimen, with
hermit crab, was taken on the north side of Horn Island.

CALYPTRAEIDAE

The shell is more or less limpet shaped and is open ventrally.
The columella has been modified to form an internal shelf. The
single gill is greatly enlarged and modified to serve as a food gath-
ering organ as well as for respiration, and in this respect bears some
resemblance to the pelecypods.

Crepidula convexo. A small highly arched form, dark brown in-
side and out. The shelf edge is almost straight. Seldom more than
15 mm. in length.

This species is fairly common on the “grass” flats on the north
side of the barrier islands. It is often found living on the blades of
turtle grass, and this appears to be its principal habitat, at least in
this area.

Crepidula fornicata. This is a large white form with brownish
blotches, The edge of the shelf is strongly sinuate. It reaches a
length of about 60 mm.

This is the largest and best known American Crepidula. In some
localities it is considered a pest, for large numbers together can com-
pete with oysters for food. C. fornicata is not very numerous in Mis-
sissippi Sound, and it is not a pest in these waters.

Crepidula maculosa. This species is very similar to the preceding
one, and grows almost as large. The edge of the shelf, however, is
straight or nearly so. Like C. fornicata , it is not very common on the
Mississippi coast, and only a few specimens have been found.

Crepidula plana. This snail differs from the other Crepidulas in
being white in color, and having a low, flattened, or even concave
outline. It is usually found inside old gastropod shells along with
various species of hermit crabs. It is a common species from the
middle of Mississippi Sound, the grass flats north of the barrier is-
lands, in the passes, and offshore. Salinities along the mainland ap-
pear to be too low for it to occur there.

STROMBIDAE

Rather large animals with heavy shells. The eyes are extremely
well developed for gastropods, and the foot is poorly developed. The
animal moves by thrusting the long narrow operculum into the
ground, then pulling itself forward.

Strombus alatus. This snail has a fairly heavy shell with an extra
notch in the outer lip near the siphonal canal. There is a single
row of nodules on the shoulder just below the suture, and the spire
is fairly well extended and pointed. It attains a length of around
100 mm.

Dead shells occupied by hermit crabs are fairly common around
the barrier islands, but the writer has seen only one live specimen.
This was collected by W. J. Demoran on a shallow grass flat near
Fort Massachusetts, Ship Island, on October 14, 1956.

- 22 -

Young specimens resemble the Conidae (cone shells), and are
often mistaken for members of that family. However, the absence
of a creeping foot, and the well developed eyes are stromboid char-
acters not found in the Conidae.

NATICIDAE

The shell in this family is rounded, and has a very low spire.
The genera Natica and Polinices differ mainly in the operculum which
is calcareous in Natica and corneous in Polinices . The two Mississippi
forms also differ greatly in size.

Natica pusilla. This is a small brown and white species with a
slightly extended spire. Maximum size about 3 mm.

Sand bottom, shallow, high salinity water, and wave action or
currents appear to be habitat requirements. These snails are car-
nivores, and feed on small clams living in the sand. A small hole is
drilled by the radula through one valve close to the umbone. After
the hole is drilled through, the proboscis is inserted and the radula
rapidly rasps away the flesh of the clam.

The eggs are iaid in a small simple circular sand ribbon, 7 or 8
mm. in diameter. The capsules in a specimen examined under the
microscope each contained only a single veliger larva. The larvae
were not observed after hatching, but are probably planktonic for
some time before taking up a more sedentary existence on the bot-
tom. Egg cases have been noted in June and July. It is found in
small numbers just offshore on the Gulf side of the barrier islands,
and in the passes between the islands. Collections of living material
have been made so far at depths of about eight to twelve feet just
off the Gulf side of Ship Island opposite Fort Massachusetts, and in
about six feet on the shallow bar between Ship and Horn Islands.
It has not been found on the north side of the barrier islands,

Polinices duplicatus . Very similar to Natica pussilla in shape, but
there are no spots or blotches, and the size is much larger. Maximum
size about 75 mm.

This is a much better known animal than the preceding species.
Although usually buried to an inch or so beneath the surface of the
sand, it leaves a large easily followed trail. There is usually a
small mound at the end of the trail where the animal is feeding or
resting. This species is responsible for a large proportion of bored
clam shells found on the northern Gulf beaches.

The eggs are deposited in a sand ribbon which has a character^
istic “collar” or constriction near the dorsal edge. There may be
more than one egg in each capsule, and the young hatch out as vel-
iger larvae. Very young post-larvae have glassy shells, and may be
confused with the Vitrinellidae. The aperture, however, is rather
elongate whereas in vitrinellids it is usually circular.

P. duplicatus is fairly common, for a carnivore, in the sand around
both sides of the barrier islands. It is also found living in sandy
areas along the mainland, and live specimens have been taken in
one to three feet of water at Biloxi, the west end of Deer Island,
and off Belle Fontaine Point. Although the species is rarely found
in mud, one specimen was taken at the Laboratory Station III in
Mississippi Sound.

Sinum perspectivum . The shell is white, very depressed, and with

- 23 -

a broadly open, oblique aperture. There is no operculum. Maximum
size of the shell is about 35 mm., but the animal may be up to
100 mm. long. In both Nafica and Polinices the animal is somewhat
modified for locomotion beneath the surface of the sand. A head
“shield” is developed by the anterior portion of the foot and the
head for plowing through sand. When expanded, the body nearly
surrounds the shell, and apparently in Polinices , this is accomplished
partially by the intake of water into spaces within the foot. The
animals in both genera are able to retire within the shell, and the
aperture is entirely closed by the operculum. Smum has evolved much
further for a life beneath the surface. The shell is almost entirely
internal, and the animal is much too large to withdraw within. The
animal is white with no trace of color, and is considerably depressed
and oval in outline when seen from above. Little is known concern-
ing its habits.

This snail is rare on the Mississippi coast and only three speci-
mens were collected during a four year period. One was taken at a
depth of about fifteen feet off the south side of Ship Island. Another
was taken in twelve feet of water about two miles from the west
end off the north side of Horn Island. One specimen was found in
a trawl haul two miles south of the east end of Deer Island, not far
from the mainland shore.

CASSIDIDAE

Rather large gastropods for the most part, whose chief dis-
tinguishing feature is the deposition of shelly deposits on the ventral
surface (parietal wall) of the shell. In some species it forms a flat
shield by this process in which the edges are more or less free from
the main part of the shell.

Phalium granulotum . The shell has a short pointed spire, a long
narrow aperture, spiral sculpture of numerous impressed lines, and
a heavy varix or rib on the outer lip. In addition, there is a parietal
shield, and five or six spiral rows of brownish spots. Maximum size
about 90 mm.

This species appears to be strictly marine, and has not been
found in Mississippi Sound. Moore (1956) reported that specimens
he observed at Pensacola, Florida, were feeding on the sand dollar,
Mellita qoinquiesperforata . Except for this single observation, little is
known concerning habits and life history of the species. Living spec-
imens appear to be rare on the Mississippi coast, perhaps because of
somewhat reduced salinities. Most shells seen by the writer were
occupied by hermit crabs.

MURICIDAE

The “rock shells” are usually spiny, and possess three or more
varices on each whorl. Some genera, however, do not have varices,
and may or may not have spines.

Murex fulvescens. An exceptionally spiny species. The spines are
located on the varices, which number about six or seven to the
whorl. Maximum size is close to 200 mm.

This species is a common offshore form, but is usually rare in
shallow coastal waters. Three records for Mississippi are known.

- 24 -

One was collected on an old wreck a short distance north of Ship
Island by W. J. Demoran, and two others were trawled in Dog Keys
Pass. Occasionally dead shells occupied by hermit crabs are also
found.

The egg capsules have not as yet been described or figured.
These are usually attached to the shell of another M. fulvescens, for,
since they live on muddy or sandy bottom, a hard substratum ;for
the attachment of the capsules is rare. The capsules are tall and
slender, and a little wider than thick. Measurements for one typical
specimen are: height, 14 mm., width, 5 mm., thickness, 2.5 mm. The
escape port is oval, and has a large diameter of about 0.6 mm. There
is a thin flattened ridge around the distal end. The ridges do not
meet on one side, but turn when about 2 mm. apart, and descend
vertically. They gradually become smaller, and disappear about one-
third the way down the capsule. There are also two smaller ridges
on the sides of the capsule giving it something of a football shape
in cross-section. There is no color to the capsule, but the eggs are
purple. There are over a hundred eggs to the capsule, and they
undoubtedly hatch out as a planktonic veliger. The capsules from
which these observations are made were collected some distance off-
shore during the first week of July 1957.

Thais haemasfoma. The shell of the oyster drill is quite variable.
The result is that many names have been applied during a span of
nearly two centuries. According to Clench (1947), there are two sub-
species in the northern Gulf, T. h. tloridana and T. h. haysoe. They are
both found in the same region, however, and certainly do not fit
into the recognized definition of subspecies. The two forms are ap-
parently ecological variants found under somewhat different physi-
cal conditions. The form hoysae is found in the Sound on oyster
reefs and along the mainland on jetties, pilings, and other man made
structures. The form flondana is found on rocks and pilings around
the barrier islands.

The biology and habits of the oyster drill have been investigated
by Burkenroad (1931) and others. They have found that the female
lays many egg capsules, and that each capsule contains several
hundred to more than a thousand eggs. The resulting veligers that
hatch out are very small, and apparently remain in the plankton for
some time, perhaps ,for as long as two months.

Young postlarval specimens have been figured and discussed by
Craven (1883), Crosse (1885), and Dautzenberg (1889). Dautzenberg
commented that the larval portion of his specimen was very similar
to Sinusigera colbeauiona Craven. A monograph had been published
by Craven (1877) on larval muricids under the mistaken impression
that these were adult gastropods, so, naturally, no attempt was made
to relate the larval form to the adult shell.

The larval shell is a typical sinusigera, originally named as a
genus by d’Orbigny. Sinusigera larvae have part of the outer lip
projected in a claw like extension some distance in advance of the
remainder, and are typical of many Muricidae which have planktonic
larvae. Full grown larvae have been found in the months of June,
July, and August. The writer has collected them in shallow water
close to the beach clinging to drifting pieces of grass. This appears
to be the mechanism by which the young are carried inshore to the
brackish water bays and sounds. The gentle breezes during the

- 25 -

26

summer months almost always blow toward the shore. Bits of
seaweed and grass are gently pushed to shore, and, where there
are passes, into brackish waters. Countless numbers undoubtedly
perish on the open beaches, but enough reach favorable habitats to
be regarded as serious pests wherever there are oysters.

Description of the full grown larval shell.

The shell is light brown, and measures 1.6 mm. by 1.1 mm. There
are five whorls which are smooth except for extremely minute
punctae on the body whorl. In addition, there are six or seven mi-
nute ridges on the siphonal canal, and two spiral cords on either
side of the periphery. There are also exceedingly minute, numerous,
very short axial riblets just below the suture.

The middle portion of the outer lip bears a slender, hooked pro-
jection. A smaller projection is close to the end of the siphonal
canal. Larval growth terminates in a thin blade like varix which
stands up above both the larval and post larval shell.

COLUMBELLIDAE

These animals have small slender shells, and the family, like
the preceding three, is carnivorous.

Anocfi/s ov ora. This is a small slender shell with about a dozen
low axial ribs. There are also weak spiral incised lines which are
stronger on the siphonal canal. The narrow aperture is almost half
the length of the shell. Maximum size about 14 mm.

Puffer and Emerson (1953) refer to A. avara as a herbivorous or-
ganism, and Keen (1958) states that columbellids may be seen plow-
ing about on the floor of a tide pool , . . searching’ for the minute
organisms on which they feed. Both of these statements are at
variance with the writer’s observations. At Miami, Florida, Nifidella
ocellata Gmelin, another columbellid, was seen feeding on small Is-
ognomon sp., a pelecypod attached to hard substratum with a byssus.
There was no sign of a drilled hole, and, apparently, the proboscis
was simply forced between the two valves of the pelecypod.

At Port Aransas, Texas, the writer fed snails to A. ovora. As with
Nifidella , there was no attempt to bore a hole. Instead, the proboscis
was forced past the operculum, and the snails were rapidly con-
sumed. Instead of being a harmless herbivore, it is possible that
A. avara is an oyster predator on very young oysters on reefs in
waters of fairly high salinity.

This species is common on the Sound side of the barrier islands,
especially on grass flats or other habitats where the little herbivor-
ous snail, Biffium vorium, is present. It has also been taken in the mid-
dle of the Sound on mud bottom, but here it was living on hydroid
or bryozoan colonies. None have been found along the mainland.

Anachis obesa. This little shell is similar to A. avara, but is usu-
ally solid brown and is much smaller. There are fairly numerous
axial ribs and incised spiral lines in the spaces between the ribs.
The narrow aperture is about half the length of the shell, and the
outer lip ends in a large rounded varix. Adults are usually about
4 mm. long .

It appears to be about as common as A, avara, and is found in
the same habitats.

Mitrello lunata. This is a small smooth species about the same size

- 27 -

as A. obesa* The aperture is shorter and there are brownish markings
on a greenish gray background. The only sculpture is a few incised
lines on the siphonal canal,

M. lunata is found in the same area as the two preceding species,
but does not appear to be as common.

BUCCINIDAE

These are fairly large gastropods simple in appearance. Some
genera look very much like Thais and related muricid genera; how-
ever, the operculum is different. The nucleus in this structure is
lateral in the Muricidae, but is terminal in the Buccinidae.

Confhorus cancellarus . The shell has a simple fusiform shape. The
inside of the aperture is white, and there is a prominent knob on
the columella where the siphonal canal begins. Sculpture consists
of low axial ribs which bear spiral cords. Maximum size about
35 mm.

C. cancellarus is apparently able to do well on both mud and sand
bottom. It is a common species in the southern half of the Sound,
in the passes, and a little distance offshore from the Gulf side of
the barrier islands. It is usually found in water more than ten feet
deep. It seems to prefer turbid conditions.

The egg capsules are rather common objects during March,
April and May, They often wash up on the beach attached to hy-
droid colonies, worm tubes, and clam shells. Some have been found
fastened to the shell of living Thais haemasfoma. The capsules, which
have never been described, stand about 3 mm, high. There are
four little spine like projections around the distal end. At one side
of the top is an oval escape port, about 0.7 mm. in larger diameter.
At the opposite side is an oval groove which runs down the side of
the capsule. A dozen or more eggs hatch out while still in the vel-
iger stage. The freshly liberated veligcr swims by means of a pair
of ciliated oval lobes. The entire animal is transparent, and the in-
ternal organs can be observed easily under the microscope. The di-
gestive tract is well developed; and food particles can be seen ro-
tating in the anterior portion of the stomach. The stomach at this
stage resembles that of the lower herbivorous prosobranchs, and the
cilia which produce the rotating movement are probably lost soon
after the young snail assumes a more sedentary carnivorous existence.

The veligers swim about freely during the first day or so after
hatching.

After that, however, they begin to avoid any light source, and
are probably ready to take up a bottom crawling life shortly there-
after.

MELONGENIDAE

Large carnivorous gastropods with a long slender siphonal canal.

Busycon perversum. This is the largest gastropod found on the Mis-
sissippi coast. The animal is sinistral, and all of the organs, includ-
ing the shell, are opposite to those found in dextral species. Maxi-
mum size about 300 mm.

Since this is the only large sinistral species in this area, it is
easy to identify. (The only other sinistral species, Triphora nigrocineta.

- 28 -

\

is even smaller than the freshly hatched young B. perversum.) It is
a fairly rare species, and is usually taken while trawling. It has
been collected in the Sound about two miles north of Fort Massa-
chusetts, and in Dog Keys Pass.

Busycon spiratum. This is a similar but smaller species than B.
perversum. Since it is dextral, it cannot be confused with the sinistral
species. Until recently, it has been known as Busycon pyrum Dillwyn,
but spirotum is the older name. This species has a channeled suture,
a feature that has caused it to be confused with B. canaliculafa Linne
an Atlantic species not found in the Gulf of Mexico.

Living B. spiratu pi appear to remain some distance offshore along
the Mississippi coast, but occasional hermit crab shells are taken
in shallow water around the barrier islands.

NASSARIIDAE

Small scavangers with long siphons. The siphon is naked, not
being protected by a siphon al canal.

Nassarius acutus. This species has a small, rather long spired
shell and rather large axial ribs crossed by spiral cords. The outer
lip swells into a rather heavy varix, and the siphonal canal is hardly
more than a notch. It reaches a size of about 6 mm. and is light
brown in color.

This species, like Confhoros cancellarus, seems to prefer deeper
and turbid conditions. It has not been found living on a mud sub-
stratum, however, it is one of the most common carnivores on sand
bottom around the barrier islands in water usually more than six
feet deep.

Nassarius vibex . This is a slightly larger species than acufus. It is
colored bluish gray, and, in the adults, has a heavy parietal shield
over much of the ventral part of the shell.

N. vibex, in contrast to N. acufus, lives in very shallow water in
protected areas. The snails often bury in the sand just below the
low tide level, and come out in large numbers when a dead fish
strands on the shore. The eggs are laid in a gelatinous ribbon, and
hatch out in the veliger stage.

Live specimens have been collected near the lighthouse on Ship
Island, and along the north shore of Horn Island.

F ASCIOLARIID AE

Large elongate fusiform species that may be smooth or sculptured.

Fasciolarh hvnteria. Until recently this was known as Fasciolaria
distans Lamarck. It is smooth, and has a color pattern of widely
spaced, distinct, brown lines.

A few dead shells are found around the barrier islands.

OLIVIDAE

Small, slender, brightly polished shells with the soft parts mod-
ified for plowing through the sand. The two Mississippi genera are
distinguished by the possession or lack of an operculum, absent in
Oliva and present in O/ivello.

Oliva sayano. This is a slender, polished shell with a long nar-

- 29 -

row aperture. There is a siphon al notch and a long naked siphon
as is usual in the sand burrowing Neogastropoda. Maximum size
about 80 mm., but specimens are seldom more than 50 mm. long on
the Mississippi coast.

O. soyona lives buried beneath the surface of the sand and is a
common species in shallow water along the Gulf side of the barrier
islands. It is a scavenger and has been taken feeding on dead fish.
They are sometimes caught on a hook and line as they attempt to
eat the bait. It is not known whether they actively attack living
animals, or if they swallow small organisms living in the sand.

Young shells of O. sayana look very much like Olivella, but they
have a longer aperture which does not open as widely at the an-
terior end as it does in Olivella . Specimens under six or seven mm,
differ mostly from Olivella in the larger size of the apical whorls.

This species is found in the Sound near the passes, but it does
not venture very far from high salinity waters and clean sand
bottom.

Olivella sp. This is a thin, slender species. The color is white
with brown markings. Maximum size about 12 mm.

A few specimens have been collected in Dog Keys Pass and
on the Gulf side of Ship Island.

Olivella motica * This is a fairly large, fat, brightly colored species.
Maximum size about 16 mm.

The specimens collected so far were trawled in Dog Keys Pass.
Specimens collected several years ago in south Florida have dried,
and bits of the remains of the animals have accumulated in the
small box in which they were kept. One somewhat larger mass ap-
pears to have been the stomach contents of one specimen. This
mass consists of one minute pelecypod and several ostracods, and
apparently this constitutes typical food of Olivella „

Olivella pusilla. This looks very much like a miniature Oliva savana.
However, the aperture is only half the length of the shell, and the
nucleus is rounded and not protruding. Maximum size about 7 mm.

The specimens collected came from trawling about one-half
mile south of Ship Island. It is apparently fairly abundant a little
distance offshore.

VOLUTIDAE

Large, brightly colored shells. Western Atlantic species are gen-
erally smooth or polished, with little or no sculpture.

Scaphell a junonia. The shell is white or cream colored, and is fur-
ther provided with about a dozen spiral rows of large brown spots.
The aperture is long and narrow. The animal is active, mottled
black and white, and does not have an operculum.

S. junonia usually lives outside the area covered in this study. It
is mentioned here because occasional strays probably wander inshore
to within a mile or so of the barrier islands. A few shells are found
on the beach after storms.

CANCELLARIIDAE

Small to medium sized gastropods, typically with both axial
and spiral sculpture.

- 30 -

Cancellaria reticulata. This is a medium size gastropod with both
axial and spiral sculpture. The color is white except for large
brown blotches. The columella has three folds, the posterior being
the sharpest and most prominent.

C. reticulata appears to be very rare on this coast. One specimen
was taken by trawling in Dog Keys Pass.

TEREBRIDAE

Terebra concava . This is a fairly small species with a maximum
size of approximately 20 mm. There are numerous short axial ribs
just below the suture; but the remaining two-thirds of the whorl is
smooth and concave.

This species does not appear to be common in this area, for only
a few specimens have been collected in Dog Keys Pass.

Terebra dislocata. There are numerous short axial riblets below
the suture; below these is a spiral groove, and on the remaining
two-thirds of the whorl are equally numerous axial ribs which do
not line up with the riblets below the suture. Maximum size about
50 mm.

This is a fairly common species on clean sand bottom around
the barrier islands wherever the salinity does not drop very low.

Terebra saileana . This has been known until recently as Terebra
cinerea Gmelin, but Abbott (1954) pointed out that T. cinerea is a
West Indian species with somewhat similar shape and structure.
The shell of T. saleana is a bluish gray color, and attains a size of
about 30 mm. There are numerous, low, rounded, axial riblets just
below the suture, but the remainder of the whorl is smooth except
for a few fine, interrupted, spiral lines.

This is the most common Terebra on the Mississippi coast. It
lives in shallow water on the Gulf side of the barrier islands, and
during calm summer weather it moves up into the zone occupied by
the surf clam, Donax variabilis.

TURRIDAE

The shells of this family are usually long and slender, and usu-
ally have a distinct oval notch at the posterior end of the aperture.

Kurtziella c erinella. This is a small species with a slender, elon-
gate shell which appears to be rather common in this area. The
sculpture consists of nine or ten axial ribs per whorl, and many
fine, rough, spiral cords that give the shell a frosted appearance.
Maximum size about 8 mm.

Specimens have been found in beach drift from the south side
of the barrier islands, and from bottom debris trawled in Dog Keys
Pass.

Rubellatoma diomedea. This is a slender shell with about ten
rounded axial ribs on the body whorl. The coloration consists of
two spiral brown bands with a pale zone in between. Maximum
size about 10 mm.

One dead specimen was taken about one half mile south of
Ship Island opposite Fort Massachusetts.

Nannodiella molanitica . This little shell has a very heavy varix
which makes the spire look very slender. The anal notch is large

- 31 -

and is angled off about ninety degrees from the main axis of the
shell.

One dead specimen was taken in Dog Keys Pass.

ACTEONIDAE

In this family of primitive opisthobranchs, the shell is very
similar to those found in prosobranchs. The animal has an opercul-
um and even retains the figure 8 nervous system.

Members of this family have thin, diaphanous shells. They are
burrowing forms and have a well developed head shield.

Acteon punciostrialus. This is a small white species with revolv-
ing, punctate, incised lines on the lower portion of the whorls.
Greatest length attained is about 6 mm.

A dead specimen was obtained in a bottom sample from Ship
Island Pass.

Haminoea antillarum. This species has a greenish, rounded shell
with a rather wide aperture. The animal is larger than its shell, and
does not seem to be able to retract entirely within it. Maximum
size about 18 mm,

A few live specimens have been collected on grass flats in one
to three feet of water on the north side of Horn Island. There is no
radula, but there is a gizzard-like organ provided with three stout
plates for crushing small shelled organisms.

Haminoea succinea. This is very similar to the preceding species,
but the shell is smaller and narrower. The sides of the shell are
almost straight, not rounded as in H . antillarum. Maximum length
about 10 mm.

About twenty living specimens were collected in July, 1959, in
water approximately four feet deep near Fort Massachusetts, Ship
Island.

RETUSIDAE

This family consists of small white shells in which the narrow
aperture is about as long as the shell. Although members of this
family are burrowers, the animals can retract completely within
the shell. The radula has been lost.

Retusa canaliculata. The minute larval whorls, when present, are
at right angles to the main axis of the shell. Spire moderately long.
Maximum size about 5 to 6 mm.

This is a fairly common species around the barrier islands in
sand, but it is usually overlooked due to its small size. Their diet
consists of Foraminifera, which are swallowed whole and crushed
in the gizzard. Apparently these snails can exist in salinities down
to 20-25 parts per thousand, for several live specimens were brought
up in a bottom sample two miles south of the east end of Deer
Island.

ACTEOCINIDAE

The small shells of this family are very similar to the preceding
one, but the animals do have a radula.

Cy/ichna bidenfafa. This species is slightly smaller than R. canal-
iculata, and differ in that as the shell grows the whorls extend up

- 32 -

over the spire and completely cover it. Thus, the aperture is as
long as the entire shell. Maximum size about 3 mm.

A few specimens have been found in beach drift on Ship Is-
land. It, too, is a sand dwelling foram feeder, but it has not been
found in lower salinity water near the mainland.

GASTROPTERIDAE

This peculiar family has an entirely internal shell, and swims
with two large wing-like flaps.

Goifropteron rubrum. This little species has a head shield, as is
common with burrowing forms, but is also provided with wing-like
parapodia. The minute shell is internal, and a narrow foot enables
the animal to crawl on the bottom. Maximum size about 25 mm.,
but the Mississippi specimens are all considerably smaller than that.

All specimens were taken in plankton tows made by J, Y.
Christmas during the first four months of 1959. They have not ap-
peared in the plankton at other times. A few specimens were taken
in the Sound, but most were captured in the open Gulf to the
south of the barrier islands.

PYRAMIDELLIDAE

The Mississippi members of this family are small, white, and
rather elongate. They are ectoparasites, and one species has been
found to be a common parasite of the commercial oyster.

Odostomia impress o. A small elongate species with spiral sculpture
of four revolving ridges. A generic character is the single revolv-
ing ridge on the columella. Maximum size range about 5 mm.

This species is usually found associated with its host, the com-
mon oyster, Crassostrea virginka . It is usually overlooked due to its
small size, but the writer has found as many as seven on one oys-
ter. It is not found in very low salinities, but it appears to do well
down to 20 parts per thousand and probably down to 15 parts per
thousand. It is fairly common on oysters in Mississippi Sound. It is
listed in the Grand Isle Checklist (Behre, 1950) as O. trifida Totan.

Odostomia seminudo. The shell is not quite as elongate as is that
of O. impressa, and there are fine axial lines which gives the spiral
ridges a somewhat knobby appearance. It attains a length of 4 mm.

One specimen has been collected from Dog Keys Pass.

Odostomia sp. This is a slender minute species with numerous
axial riblets, and with several spiral ridges on the base of the shell.
Maximum size about 1 mm.

This species is rather common in sand and debris from the
bottom of Dog Key Pass. As yet, it has not been related to any
described species of Odostomia from the western Atlantic. It is only
known from Dog Keys Pass.

Turboniila conradi. In the genus Turbonilla, the larval whorls are
pimple-like, and are generally set at a considerable angle from the
main axis of the shell. There is no ridge on the columella. Usually,
there are numerous axial riblets and fine incised spiral lines. T.
conradi is typical in these respects, and has about a dozen spiral lines
to the whorl. It is a very slender shell that attains a length of
about 10 mm.

- 33 -

One specimen came from a depth of approximately 25 feet, just
south of Ship Island.

Turbonilla sp. This is a much stouter species than T. conradi. It
is the same length, but has only half the number of spiral lines per
whorl.

The taxonomic confusion reigning at present in the genus Tur-
bonilla has produced great difficulties in identification. For the pres-
ent, at least, this species will be left nameless until a name can
be applied to it with some certainity.

Two specimens were trawled in Dog Keys Pass.

APLYSIDAE

This is a family of large naked herbivorous gastropods.

Aplysia wiflcoxi. This is a rather large animal that attains a
length of 200 mm. The head bears four tentacles. The last pair is
large, and stand nearly vertical; from this it is easy to see how
the name “sea hare” came into being. There is an elongate crawl-
ing foot, and a pair of fleshy parapodia meet over the back. The
shell is thin flexible noncalcified plate over the viscera, and is com-
pletely internal. The color is a mottled brown.

One specimen was collected at the east end of Deer Island on
October 4, 1957, and seven small specimens were trawled off the
north side of Horn Island in June of 1959. It is apparently not
abundant on this coast.

CAVOLINIDAE

This family of “sea butterflies” has shells that have lost their
spiral coiling, and appear to be bilaterally symmetrical.

Cavatina longirostris. The shell of this species is made up of two
convex plates which are united posteriorly. The lip of the ventral
plate is long and slender, and protrudes considerably beyond the
dorsal. The foot is divided into two lobes which propel the animal
through the water. It reaches a length of 9 mm.

A few specimens have been collected in beach drift on the bar-
rier islands.

Cresis acicula. This is a slender tube which is closed at one end.
Maximum size about 30 mm.

This species is found in beach drift, and has also been taken
alive in a plankton tow in Dog Keys Pass. It has been reported be-
fore in the inshore waters of the Gulf by Moore (1958).

POLY CERID AE

Slug-like nudibranchs with non-retractile branchiae in a circle
near the posterior end of the dorsum.

Polycera hummi. This is a rather small species which may reach
a length of about 20 mm.

One live specimen was collected off the Biloxi beach in four
feet of water by Captain L. Arbon, of Keesler Air Force Base.

CORAMBIDAE

Small nudibranchs in which the oval dorsum covers the entire
animal.

- 34 -

Corambello barafariae. The only projections on the dorsal side
are the retractile rhinophores. The branchiae consist of two pair of
plates between the dorsum and the foot at the posterior end of the
body. Maximum size about 4 to 5 mm.

Several specimens have been found on rocks near Fort Massa-
chusetts on Ship Island. It is easily overlooked due to small size
and inconspicuous appearance, and actually may be fairly abundant.

ARMINIDAE

The branchiae in this family are ranged on each side of the
body beneath the lateral edges of the dorsum.

Armina tigrina. The dorsum is black with numerous narrow white
longitudinal stripes. Maximum size about 50 mm.

Specimens have been taken several times in trawls in Dog Keys
Pass, once in the Sound about one mile north of Dog Keys Pass,
and once about a mile south of the west end of Horn Island. Sev-
eral specimens were also taken in the middle of the Sound on two
different trawling trips.

SCYLLAEIDAE

In this family large numbers of minute branchiae are found
on the dorsal surface.

Scyllaea pelaglca . This is a mottled brown white species with a
very narrow foot and with two pair of dorsolateral extensions of
the dorsum. Maximum size about 40 mm.

This species, which is strictly pelagic, lives on the oceanic
drafting algae, Sorgossvm. It has been found once by the writer on
the beach at Ship Island after a gale in June, 1956. This is only an
occasional visitor at our shores, but it probably washes ashore dur-
ing nearly every strong wind from the south and south-east.

FLABELLIDAE

This family has no branchiae. Instead, a series of club shaped
cerata are ranged down the dorsum.

Eubranchus sp. There are four rows of cerata on this brightly
colored little nudibranch. Maximum size about 6 to 8 mm.

Nudibranch taxomony south of New England is almost entirely
neglected. Until more work is done, it is best to leave this species
nameless. Specimens usually show up in aquaria in the Gulf Coast
Research Laboratory during the winter months. They apparently
come through the salt water system in the veliger stage.

ELLOBIIDAE

This is a family of small primitive pulmonates living in salt
marshes and mangrove swamps.

Me/ompus bidentatus . This is a small cone shaped species with a
low spire and long narrow aperture. There are two plicae on the
anterior portion of the columella and a half dozen denticles on the
inside of the outer lip. Maximum size about 12 to 14 mm.

This species was found to be abundant along the edges of the

- 35 -

small boat harbor in Ocean Springs. It has also been found in
marsh grass along the edge of Davis Bayou and along the edge of
ponds on Horn Island. It appears to be a detritus feeder, and the
fecal pellets, oddly enough, have sand grains interspersed at inter-
vals.

DENTALIDAE

This family has slender curved shells shaped like an elephant’s
tusk. They are open at both ends, the posterior opening serving as
an exit for respiratory currents.

Dentalim texosianum. A small white species which is hexagonal in
cross section. Largest size attained is approximately 35 mm. It is
very thick shelled.

This species has been found in beach drift on both Ship and
Dauphin Islands. It does not appear to be very common.

Dentalium eboreum. This is a very slender and thin shelled species,
and is circular in cross section. Maximum length about 60 mm.

One specimen has been found in beach drift from Dauphin Is-
land.

NUCULANIDAE

This family contains the most primitive pelecypods found on
the Mississippi coast. The shells are small, white, and have many
sub-equal teeth in the hinge.

Nuculana acula. This species has a yellowish white shell with
concentric ribs. The anterior end is rounded, but the posterior is
longer and pointed. Maximum size about 10 mm.

Specimens have been found in beach drift from the barrier is-
lands, and three live specimens were found in a bottom sample
from near the east end of Deer Island. It is a rather abundant
species qffshore in shallow Gulf waters.

ARCIDAE

In this family, the species are usually larger than in the pre-
ceding family, and the hinge is straight or nearly so, and has many
more teeth. Although most species are white, a few are colored.

Anadara brasttana. This species is white, has 26 to 28 radial ribs,
and, on the ribs, there are strong bar-like beads. The left valve
overlaps the right. Maximum size about 60 mm.

This species is common in the beach drift on the Gulf side of
the barrier islands. It apparently does not penetrate very far into
the Sound.

Anadara o vafis. This species has 26 to 35 square smooth ribs,
and is rounded in outline. Maximum size about 60 mm.

This species has a greater resistance to lowered salinity than
the other arcids in this region. One large live specimen was taken
in a trawl off the west end of Belle Fontaine Point, and other live
and dead specimens have been collected at the Gulf Coast Research
Laboratory Station III, in the middle of the Sound. In addition,
young specimens are often found in grass and algae from the grass
flats on the north side of the barrier islands. It is also a common
shell in beach drift on the barrier islands.

Andara transversa. This little shell is transversely oblong in shape,

- 36 -

and has 30 to 35 ribs on each valve. The left valve overlaps the
right valve. The ribs on the left valve are usually beaded, but are
seldom beaded on the right valve. Greatest length is about 25 to
30 mm.

This little clam is very abundant in grass and algae on the
north side of the barrier islands, and attached to various objects
in the deeper waters of the Sound. It, too, is found in beach drift
on the barrier islands.

Noefia ponderoso . The posterior muscle scar is raised on a weak
flange. The ribs, 27 to 32 per valve, are square and are split down
the middle. The periostracum is black and exceptionally thick.

N. ponderosa is a fairly common shell on the barrier island
beaches but apparently does not live in the Sound.

MYTILIDAE

The mussels are thin shelled elongate pelecypods which attach
to objects by means of a byssus.

Amygdalum papyria. This is a smooth, very thin shelled species
colored pale green and light brown. It builds a nest for itself with
a large supply of byssus threads. It reaches a maximum size of ap-
proximately 30 mm.

This little mussel lives on mud bottom in the Sound. It has
been trawled at Gulf Coast Research Laboratory Station III, and
has also been found on Biloxi beach after stormy weather. Small
dead specimens have also been found in a bottom sample in outer
Biloxi Bay, between Marsh Point and Deer Island.

Brachidonfes recurvu s. This is a grayish black species with num-
erous wavy ribs. The anterior end is strongly hooked. Maximum
length about 60 mm.

This mussel is often found on oyster reefs, and in some places
must be a serious competitor with the oyster for food. Although
usually found attached to oysters, any hard substratum will do if
other conditions are favorable. It is found in roughly the same
area as the common oyster in Mississippi Sound and in the bays
and bayous along the mainland.

Lithophaga bisulcata . This is a slender light brown cylindrical
species that burrows into calcareous structures. The anterior end
is rounded, but the posterior end is pointed. An oblique indented
line divides each valve into two sections. Maximum size about
45 mm.

This is probably the species listed in the Grand Isle Checklist
as L antillarum d’Orbigny, a common species in the southern Gulf,
but not known north of south Florida. Being forced to bore into
shells by the lack of calcareous rocks, L. bisulcata is not too success-
ful in this area. Living specimens have been found in shell debris
trawled in Dog Keys Pass, and in oyster shell from an old wreck
off the north side of Ship Island. It does not penetrate far into
lower salinity waters, and is not found living in the Sound except
close to the barrier islands.

Modiolus demissus . This is a large shiny dark brown mussel, with
many strong radial bifurcating ribs. It is similar to Brachidonfes re-
curvus, but does not have the hooked anterior end, and the habitats
of the two species are also quite different. Maximum size about
100 mm.

- 37 -

This species is large enough to be of commercial importance if a
demand were to develop that would make collecting them worthwhile.
In the Mississippi area, it is usually found at lower salinities than is
B. reevrvus. It lives intertidally among the roots of the marsh grass,
Spartino, and is common in the bays and bayous of the mainland.
The byssus is firmly attached to the main stem or root of the grass,
and it is difficult to remove the mussel without some sort of dig-
ging tool. It is sometimes quite abundant, but in a very narrow
restricted environment.

Muscufus lateralis . This is the smallest of the family in Missis-
sippi. It is characterized by radial ribs on either side of a central
smooth area. Maximum size about 8 mm.

This is a marine species which is, however, found in the Sound
on the rocks and grass flats on the north side of the islands. It is
usually overlooked due to its small size, but is probably fairly
abundant on the grass flats.

PINNIDAE

This is a family of large thin shelled bivalves. The anterior
end is reduced, narrow, and pointed, the posterior is large and
rounded. It lives buried in the sand or mud with just the tips of
the posterior ends of the valves protruding.

Atrina seminuda. This species has a few (5 to 16) radial ribs
which may be smooth or carry spines. The spines, if present, arc
fairly large. Maximum size about 240 mm.

This is not a common species on the Mississippi coast. One
fresh dead specimen was collected in a depth of about 10 feet of
water on the north side of Horn Island during the summer of 1959.
A live specimen was collected in shallow water near Fort Massa-
chusetts a few weeks later,

Atrina serrato, This is a more thin shelled species than the pre-
ceding. The sculpture consists of about 30 inconspicuous ribs which
carry many fine imbrications. Maximum size about 300 mm.

A few specimens are found from time to time in deeper water
along the north side of the barrier islands. It must be fairly
abundant just offshore on the Gulf side of the barrier islands, for
many are washed ashore after strong winds and high waves.

PLICATULIDAE

This is a family of small attached, oyster-like, bivalves. The
ligament, however, is internal, and there is a hinge tooth on each
side of it.

Plicatula gibbosa. There are five to seven strong radial ribs which
give the valves an interlocking margin. Maximum size about 30 mm.

One live specimen was taken in the trawl at Dog Keys Pass.

PECTINIDAE

The scallops have a rounded outline except for the straight
hinge line. They are unusual pelecypods in that they can swim and
have eyes on the edge of the mantle.

Aequipecten irradians. This scallop has 12 to 21 radial ribs. The

- 38 -

dorsal valve is mottled brown and gray, but the ventral is usually
pure white. Maximum size about 75 mm.

This is the common edible scallop on the Atlantic and Gulf
coasts. It is quite common on the west coast of Florida and there
is a small fishery in Tampa Bay, however, it is not abundant on the
Mississippi coast. A few specimens can be found on the barrier is-
land grass flats occasionally, and on October 14, 1956, W. J. Dcmoran
collected about 35 specimens near Fort Massachusetts. There appear
to be extensive beds of this scallop in the Chandeleur Islands, but
no report has been published as yet on their abundance.

OSTREIDAE

This family of attached bivalves contains the edible oysters,
but not the so-called pearl oysters,

Crossosfrea virginica. This is the common edible oyster that is
of such economic importance. Oysters are extremely variable in
size and shape; a result of varying environmental conditions. The
outside of the shell is usually a dirty gray, and the inside is white
with purple muscle scar. Maximum size close to 300 mm.

The value of the Mississippi oyster fishery catch in 1957 was
$185,402. This figure is based on the production of the large oyster
houses, and does not include those taken by individuals working on
a small scale. In addition to the living oysters, dead reefs are
dredged to provide large quantities of calcium carbonate for var-
ious industrial purposes on the Gulf coast. Large quantities of fresh
shell are utilized for drains, driveways, and similar purposes.

The most extensive oyster reefs on the Mississippi coast are in
the Sound off Pass Christian, but scattered patches are common in
the bays and bayous. Another fairly extensive reef is at the east
end of the Sound between Point Clear and Dauphin Island in Ala-
bama waters. Oysters are common on pilings and other man made
structures, and in the southern portion of the Sound. Large oysters
have been found on pilings close to Horn Island and on the re-
mains of an old wreck close to Ship Island. They have also been
found on the remnants of an old dock jutting into the Gulf on the
east end of Ship Island. It is an abundant species, but its numbers
have declined due to fishing pressure and other causes.

Os/rea equesfris. This little oyster is a high salinity form so it is
not often found with the commercial oyster. It differs from C.
virginica in that the muscle scar is near the center of the shell and
is not colored. The interior of the shell is not white, but is usually
grayish or greenish. There is a row of denticles on each side of
the hinge.

A few specimens have been trawled in Dog Keys Pass attached
to broken shell.

CRASSATELLIDAE

This is a family of rather primitive burrowing clams without
siphons. The ligament is interior, and there are two or three strong
hinge teeth in each valve.

Crossinella lunulata . This is a small, compressed, subtriangular
species with two cardinals and one lateral in each valve. Dorsal

- 39 -

margins are straight and about 90 degrees to each other. Concen-
tric sculpture consists of about 15 coarse, well developed ribs.

This little sand dweller appears to be rare in this region. It
occasionally washes ashore on the Gulf side of the barrier islands,
and two live specimens have been brought up in bottom samples
in Dog Keys Pass.

Cono dalli. This clam is one of the smallest species to be found
on the Mississippi coast. The shell is subtriangular, and has fine
concentric sculpture. There are three cardinals in each valve and
an internal ligament. The two muscle scars are subequal, and the
pallial line is simple. The color is purple. Maximum size about 2 mm.

This little clam was reported as being extremely common on
the beaches of Dauphin Island by Moore (1957). Since then it has
been found living in shallow water at the west end of Horn Is-
land. It lives at a depth of several millimeters in fairly coarse
sand. Some of the sand grains are larger than adult C. dalli, but
this does not appear to impede the movement of the little clam.

The writer collected living specimens for study by running his
fingers through the sand, then picking up individual clams that
were brought to the surface by the disturbance. Some were kept
alive in the Laboratory for a few days, but did not do well in still
water and soon died. For the first two or three days, however,
they were quite active, and ploughed around in the sand several
millimeters beneath the surface. While being observed by the writer,
one gave birth to a single young. This young specimen, which was
approximately 300 microns in length, immediately began to burrow
into the sand.

C. dalli, appears to be confined to the northeastern Gulf between
Apalachicola, Florida and eastern Louisiana. West of the Mississippi
River, the grain size of the sand is much smaller, and seems to be
unsuitable for the existence of the species. The Gulf coast of Flor-
ida to the east of the Apalachicola area is protected from wave
action by the broad shallow shelf, and open wave swept beaches
are not to be found. C. dalli , apparently, will not survive in this type
of environment. Where the environment is favorable, however, such
as the area between Dauphin Island and Sand Island at the mouth
of Mobile Bay, C. dalli can live in vast numbers.

CARDITIDAE

Small, heavy, thick ribbed, elongate clams.

Cardita floridana. This species is twice as long as high, and has
about 20 strong beaded radial ribs. Maximum size about 35 mm.

Single valves are found occasionally in beach drift from the
barrier islands, but none have been found living in this area.

CORBICULIDAE

This is a family qf fresh or brackish water clams. They are
usually oval in shape, and have two or three cardinal teeth in each
valve.

Polymesoda caroliniana. The shell is oval and is covered with a
fuzzy periostracum. There are three small, nearly vertical cardinal
teeth in each valve. There are also two lateral teeth in each valve.

- 40 -

About a dozen specimens were collected by geology students
in the summer of 1958 from mud thrown on the bank of Fort
Bayou by dredging operations. This locality is several miles up the
bayou from Biloxi Bay, where the salinity is always quite low. It
is common in Halstead Bayou, a small marsh drainage stream near
the Laboratory.

DIPLODONTIDAE

This is a family of rounded, inflated white clams with a pair
of cardinal teeth in each valve. They do not ordinarily drill holes,
but like to nest in holes and cavities left by other animals.

Diplodonfa punctata. This species is quite inflated, pure white, and
has very fine concentric sculpture. Maximum size about 18 mm.

Five living examples of this species were taken in a small brick
pile about 100 feet east of Fort Massachusetts on Ship Island. Rosso
reported a Dipladonta (1952) from the same locality. He thought that
it was D. soror C. B. Adams, but, if his species is the same as the
writer’s, it does not fit the description of D. soror.

LUCINIDAE

This family consists of thin, usually white clams without si-
phons and weak or obsolete hinge teeth. The anterior muscle scar
is long and narrow.

Lucina amiantus. This is a small obese species sculptured with 8
or 9 wide radial ribs. Across the ribs run numerous small concen-
tric riblets. Maximum size about 8 mm.

Shells of this little clam are fairly common in beach drift from
the barrier islands, but it has not been collected alive by the writer.
It may live in deeper water a little distance offshore.

Lucina floridana. This is the largest Lucina found in the region.
It is thin and compressed and with no sculpture except occasional
growth rings. Maximum size about 45 mm.

This is a fairly common species in the grass flats on the north
side o,f the barrier islands. The grass flats three to four miles from
the west end of Horn Island have been an especially good collect-
ing area.

Lucina multilineata. This species is similar to L. amiantus , but is
without the radial ribs. It often continues growing after a rest per-
iod which causes a concentric hump in the shell. Maximum size
about 8 mm.

Single valves are fairly common in beach drift from the barrier
islands.

CHAMIDAE

Members of the Chamidae have heavy inequivalve shells that
are fixed to the substratum.

Chama congregata. This is a fairly thick species which is at-
tached by the left valve. The fixed valve is larger and deeper than
the upper valve. There is one hinge tooth in each valve, and num-
erous small denticles are found all around both valves.

As yet, only one small live specimen from Dog Keys Pass has
been collected.

- 41 -

LEPTONIDAE

This is an odd family of small clams. The foot in many has
reacquired a flattened sole, and they glide around like typical gas-
tropods. There is a special anterior inhalent siphon, but the water
is expelled behind in the usual manner. Some are commensal or
parasitic.

Kellia suborbicufaris. The shell is glassy, thin, and inflated. The
outline is rounded, and there is one tooth in the hinge of each valve.
Maximum size about 2 mm.

One live specimen measuring 1 mm. was found in sand and
shell debris from Dog Keys Pass.

Mysella cuneata. There are two cardinal teeth in the right valve,
none in the left. It is distinctly triagonal in outline. Maximum
size about 3 mm.

Single valves have been found in shell debris brought up by
the trawl in Dog Keys Pass.

Mysella planulata . This species is oval oblong in outline. The
anterior end is longest. Maximum size about 3 mm.

This species has been found in beach drift from Dauphin Is-
land and Horn Island, and also from shell debris in Dog Keys Pass.

CARDIDAE

The hinge in this family usually consists of a strong cardinal
and two laterals. The shells are usually much inflated, and may be
quite large.

Dinocardium robustum. This is by far the largest of the family in
this area. It is ovate, inflated, and bears about 35 radial ribs. Maxi-
mum size about 100 mm.

Dead shells are common on the barrier island beaches, and many
have been taken in the trawl in Dog Keys Pass. The trawl, how-
ever, does not dig into the sand, and only one live specimen has
been collected by this device. D. robustum seems to be fairly abund-
ant around the passes, and off the barrier islands. It apparently
does not penetrate into Mississippi Sound, or, if it does, only a
short distance from the passes.

Laevicardlum laevigatum . Fairly large, inflated, smooth and ob-
scurely ribbed, this species may be up to 60 mm. in size.

A few dead shells have been found in the grass flats on the
north side of Horn Island. Live ones have not been collected.

Laevicordium mortonl. This is a smaller but similar species that
differs from 1 . laevigatum in the color pattern of brown zig-zag mark-
ings and minutely pimpled concentric ridges. Maximum size about
25 mm.

Occasional living specimens are found in shallow water (2 to 4
feet) on the Sound side of Horn and Ship Island.

VENERIDAE

This is a family of many species of burrowing clams. The
shells are solid and porcelaneous, and have three diverging cardinal
teeth in each valve.

Callocardia texasiana. This is a white, thin shelled species with
fine concentric sculpture. Maximum size about 80 mm.

- 42 -

Abbott (1954) states “Uncommon, if not rare. Found on the
beaches, but its biology and habits are unknown,"

About a dozen live specimens have been collected in trawls in
Mississippi Sound. All specimens were living in soft mud in the
central part of the Sound, either between Biloxi and Ship Island or
between Bell Fontaine Point and Dog Keys Pass. The reason for the
distribution found is that the Laboratory vessel “Hermes" usually
goes to either Horn or Ship Island on field trips. Trawling almost
anywhere on mud bottom in the deeper parts of the Sound should
produce these clams. It is easy to see why clams living in this sort
of environment are not often found on the beach. It is propably
fairly common both in offshore and inshore waters in similar local-
ities in the northern Gulf.

Chione c ancellata. This is a medium size ovate shell with both
concentric and radial ribs. Maximum size about 45 mm.

A few single valves have been found around the barrier islands,
but no live or even fresh dead specimens have been collected.
Possibly it was once established here, but died out due to adverse
physical conditions.

Chi one grus. This is a small oblong species with 30 to 40 fine
radial ribs which are crossed by very fine concentric threads. There
is purple color on the hinge at both ends. Size about 8 mm.

This species is apparently common, but is usually overlooked
due to its small size and to its habits. The writer has not found it
burrowing in sand or mud; instead, it has been found living in sea
weed on rocks and similar habitats.

Chione intapurpurea. This species is very similar to C. eancellafa,
but it has concentric sculpturing only. The lower edges of the ribs
bear many small bars which line up to give the impression of radial
ribs. Maximum size about 40 mm.

Single valves are fairly common on the barrier island beaches,
but only one live specimen has been taken in Dog Keys Pass.

Dasinia discus . The shell is circular, compressed, and white with
a thin yellowish periostracum. Sculpture consists of numerous, fine
concentric ridges, about 50 to the inch. Maximum size about 70 mm.

Both single and fresh double valves arc commonly washed up
on the barrier island beaches. It apparently does not live in the
Sound.

Gemma gemma. This is one of the smallest members of the family.
The shell is sub trigonal, somewhat inflated and has numerous fine
concentric riblets. Maximum size about 3 mm.

This specimen is superficially similar to Cuno dalli , but has an
external ligament and a large faintly impressed lunule. It is like
C. dalli in that it broods its young, which emerge as replicas of the
adult. It is often pure white, but some specimens are purple which
increases the resemblance to C. dalli

This little clam lives in sand on both sides of Mississippi Sound.
A number of live specimens have been taken by screening sand on
the east end of Deer Island. Other specimens have been collected
close to shore on the north side of Horn Island. It does not appear
to be common here.

Macrocollisfa nimbosa. This is an elongate compressed species
without sculpture. The exterior is glossy, smooth, pale brown with
broken radial bands of darker color. Maximum size about 130 mm.

- 43 -

Three or four live specimens have been found in shallow water
on the north side of Ship Island near Fort Massachusetts. It ap-
pears to be rather rare in Mississippi waters as it seems to prefer
shallow protected sandy areas where many would be found if it
were at all abundant.

Mercenaria mercenaria. Large ovate-trigonal and thick shelled, this
species has long been known as the hard shell clam or quahog.
There are three cardinal teeth in each valve, and the middle cardinal
in both is split. External sculpture consists of numerous concentric
growth rings which usually coalesce to form irregular flat topped
ribs.

Although common in some Gulf localities, this species appears
to be rather rare in Mississippi. A few live samples have been col-
lected on the north side of Horn and Ship Island in sand. Several
beds of M. mercenaria have been reported from the Chandeleur Is-
lands, Spaulding (1906), but it is not known if these beds still exist.
Since this species is the chief constituent of clam chowders, the dis-
covery of large beds could be of commercial importance.

Parasfarte triquefra. This little clam is about the size of Gemma
gemma , but is different in appearance. The shell is higher than long,
and the exterior is smooth and highly polished. The color is some
shade of brown. Maximum size about 3 mm.

One quite fresh valve was collected in shallow water on the
north side of Horn Island. It was neatly drilled by some small pred-
atory gastropod. A few worn dead valves have also been found in
shallow water on the north side of Ship Island.

PETRICOLIDAE

Members of this family are usually elongate, and burrow into
rock and clay. The hinge teeth are similar to the Veneridae, but
there are no laterals.

Petricola pholadiformis . This is an elongate, fragile, chalky white
species. There are numerous radial ribs, an external ligament, and
long pointed cardinal teeth. This clam has considerable similarity in
appearance to some of the Pholadidae, especially to Cyriopleura costata
Linne and to Pholas campechiensis Gmelin.

Single valves are fairly common in beach drift on the barrier
islands. The writer has not collected living samples, but Dr. J. F.
Walker has collected living specimens from the Gulf side of the
eastern half of Ship Island, and a graduate student, Bennie Rohr,
has found living material at Belle Fontaine Point on the mainland.

TELLINIDAE

Members of this family have long slender separate siphons,
and a long and powerful foot. The shells are usually compressed
and elongate, and the sculpture, if present, is made up of very fine
ridges.

Macoma co nstricta. This is a medium sized, ovate species with a
somewhat pointed posterior end. This end is also strongly twisted to
the right. The color of the shell is white, but it is covered by a
thin grayish periostracum when alive.

This is a euryhaline species which lives in sand on both sides

- 44 -

of Mississippi Sound. Although it may live just off the beach in
some Texas localities, it does not appear to do so on the Mississippi
coast It is apparently most abundant on the mainland side of the
Sound in such sandy areas as the east end of Deer Island and Belle
Fontaine Point. A few specimens have also been taken at the tip
of Marsh Point in Biloxi Bay.

Mocoma mitchellL This is a small elongate clam with a nearly
straight ventral line having a slight twist to the right. Live speci-
mens have a thin periustracum which gives a smooth, glossy irides-
cent sheen to the shell. The maximum size is about 20 mm.

This species is common in muddy bottom in Davis Bay where
it was collected in numbers, by the author and Dr. J. P. E. Morri-
son. It should be found in mud or muddy sand in many localities
along the mainland.

Strigilla mirabilis. This is a white, oval, inflated clam with pe-
culiar sculpture. There are many fine, oblique cut lines which meet
the ventral edge at an angle of about 45 degrees. Maximum size
about 9 mm.

This is a common species in the beach drift on the barrier is-
lands. It does not appear to live in the Sound.

Tellidora c ristata. This is a white, compressed, ovate species with
sawtooth crenulations on the dorsal margins. Maximum size about
40 mm.

Only one valve of this species was collected at Laboratory Sta-
tion III.

Tellina aliemoia. This is an elongate solid species with an elon-
gate somewhat pointed and twisted posterior end. Sculpture con-
sists of numerous, evenly spaced concentric grooves. Color is whit-
ish to pink. Maximum size about 70 mm.

Single valves have been trawled from time to time in Dog Keys
Pass, but live specimens have not been taken. However, this is a
large powerful burrower, and is not easily captured.

Tellina iris This species is somewhat elongate, thin shelled and
has fine wavy oblique lines. There are two weak white internal
ribs present at the posterior end. Maximum size is about 12 mm.

One live specimen was trawled in Dog Keys Pass.

Tellina texana . This species was listed on the Laboratory Invert-
ebrate Checklist as T, sayi Dali, a synonym of T, texana. The writer
believes that specimens of Mocoma mitchelli were probably identified
as this species.

Tellina versicolor. This clam looks very much like a small T. alter-
nate, but has a shorter posterior end. Live specimens are iridescent.

Two specimens were brought in by trawl in sand and shell
debris about one half mile south of Fort Massachusetts on Ship
Island.

SEMELIDAE

Members of this family are very similar to the Tellinidae, but
have an internal resilium as well as an external ligament. The
slender separate siphons are extremely long.

Abra aequalis. The shell is white and rounded with small pointed
umbos. There is a groove on the anterior margin of the right valve.
Maximum size about 12 mm.

This little clam has been found in considerable numbers in

- 45 -

beach drift from the barrier islands. It has not been collected in
the Sound.

Abra lioica. This is a somewhat smaller, very similar species
which lacks the groove on the anterior margin of the right valve.
Maximum size about 8 mm.

It is sometimes rather abundant in barrier island beach drift.

Cumingia tel/inoide a. This species is oblong, thin and slightly
pointed at the posterior end. It looks very much like a Tellina.
Maximum size about 20 mm.

The writer has not found this species, but it is included because
it is on the Laboratory Checklist.

Semele nuculoides. This is a small white species with an elongate
anterior end, with the umbos very close to the posterior end. Very
fine concentric ridges make up the sculpture. Maximum size ap-
proximately 6 mm.

This little clam has been taken in Dog Keys Pass and Ship Is-
land Pass. It has also been found in barrier island beach drift. It
is probably fairly abundant in a depth of two fathoms or more, but
it is easily overlooked due to its small size.

Semele proficua. This species is almost round in outline with the
beaks almost central. There is a small pushed in lunule. The sculp-
ture consists of fine concentric lines and microscopic radial striations.

Two live specimens were collected by W. J. Demoran at the
old wreck off the north side of Ship Island. These specimens were
found in a dead oyster shell several feet above the bottom. This
appears to be an unusual habitat for the species, but it is the only
habitat found for B. proficua on the Mississippi coast.

DONACIDAE

Members of this family are usually cuniform in shape with a
short thick posterior end and a long tapering anterior end. The
American species all live in the surf zone on open beaches.

Do nax variabilis . This clam has an almost straight ventral mar-
gin. The inner edges of the valve are denticulate. The color is ex-
tremely variable and usually bright. The siphons are quite short.
Maximum size about 25 mm.

This is the common surf clam from North Carolina to Texas.
It lives along the beach in the area where the waves wash back
and ^orth. In this habitat it is usually protected from predatory
snails, although the writer once found one being bored by a Polinicus
duplicatus on a Texas beach. During the summer Terebra saleana moves
into the same zone, but it is not known whether or not it feeds
on Donax. The most serious predators seem to be the small beach
birds, the sand pipers.

Although the vast majority of this species are found on the
Gulf beaches, an occasional rare specimen is found on the Sound
side of the islands. In addition, another species, Donax tumidus , is
probably present just off the beach in knee deep water. Specimens
which differ slightly from typical D. variabilis have been collected at
Ship Island.

SANGUINOLARIIDAE

In this family the siphons are long and separate as in the Tell-

- 46 -

inidae and Semelidae. They have a strong foot and can burrow
rapidly into the sand. They resemble razor dams, but the beaks
are located near the center of the dorsal margin.

Tagelus plebeius. This is an elongate species with parallel ventral
and dorsal margins. The anterior and posterior margins are blunt-
ly rounded. The color is white, but the exterior is covered by a
brownish periostracum Maximum length about 80 mm.

The habitat favored by T. plebeius in Mississippi is muddy sand
bottom and turbid water. It is common in the Sound along the
mainland shore, but is seldom seen or collected alive due to the
speed that it can burrow into the sand. It has been collected many
times, however, by students using shovels and screens. The east
end of Deer Island has proved to be a good collecting spot. It does
not appear to be as common in the southern part of the Sound.

Tagelus divisus. This species is very similar to the preceding one,
but it is a little more slender. Internally, the valves are strength-
ened by a weak radial rib. Maximum size approximately 40 mm.

One valve was trawled in Ship Island Pass in January, 1956.

SOLENIDAE

Members of this family are elongate, slender burrowers in sand.
They are similar in appearance to Tagelus , but the beaks are usually
displaced toward the anterior end of the shell.

Ensis minor. This is the Gulf coast “razor clam.” The shell is
long, slender, and slightly curved. The beaks and hinge teeth are
at the extreme anterior end. The shell is covered with a pale green-
ish periostracum. Maximum size approximately 70 mm., but spec-
imens which might belong to this species have been found offshore
in deeper water in sizes ranging to 145 mm.

E. minor is a common species in shallow water on both sides of
the Sound. It is more common than Tagelus plebeius, and appears to
thrive in a somewhat wider range of salinity and turbidity.

MACTRIDAE

Members of this family usually have an external ligament as
well as an internal resilium supported on a chondrophore.

Labiosa plicatella. This is a large, oval, thin shelled species. The
anterior end is longest, and the sculpture consists of large concentric
ribs which appear as grooves on the inside of the shell.

The valves of this clam are easily broken by rough weather,
but a few wash up on the beach. The writer has never seen a
living specimen, or even a dead one with both valves attached. It
appears to be strictly marine, and does not live in the Sound. A
closely related species, Labiosa lineafa Say, has been found at North
Island, Chandeleur Islands, and should be found in Mississippi in
the future.

Moc/ro fragilis. This species is oval, thin, and smooth. It is pure
white, but is covered by a thin brownish periostracum. The pallial
sinus is rounded, and extends about halfway to the anterior muscle
scar. Maximum size about 100 mm., but Mississippi specimens are
usually only half that size.

It is a common species in shallow water on the Sound side of

- 47 -

the barrier islands. Most of the specimens the writer collected came
from the extensive grass flat area on the north side of Horn Island
in depths of from 2 to 6 feet. It has not been found along the main-
land shore, and appears to be scarce on the Gulf side of the barrier
islands.

Mulinia lateralis. This little shell does not have an external liga-
ment, and there are two long slender laterals in each valve. It is
very similar in appearance to young Spisula solidissima , but the lateral
teeth are smooth whereas in S. solidissima there arc minute vertical
ridges on the laterals. M. lateralis is usually trigonal in shape, but
there is some variation. The color is white, but a thin brownish
periostracum covers the exterior of the shell. Maximum size about
15 mm.

This clam lives in sand in the protected waters of bays and la-
goons. Somehow the common name “Surf clam” became associated
with this species, and both Abbott (1954) and Morris (1951) use this
name. However, the writer and other interested people have searched
in vain for this clam in the surf zone.

This clam is distributed in Mississippi on both sides of the
Sound in shallow water on sand or muddy sand bottom. It does
not appear to do well if the salinity becomes low, but it has been
found living in the Laguna Madre of Texas where the salinity was
over 70 parts per thousand.

Rangjo cuneata. This is a very thick, heavy, obliquely ovate
species. The external ligament is absent, and the beaks are sep-
arated and rolled in toward each other. Long serrated lateral teeth
extend over both the anterior and posterior adductor muscles. The
exterior is white, but is covered by a fairly heavy brownish perios-
Iracum. There is a small, distinct pallial sinus. Maximum size
about 60 mm.

R. cuneata lives in fresh to brackish water in the bays and tidal
bayous where the salinity seldom goes above 15 parts per thousand.
No specimens have been found as yet in the Sound, where the water
is too salty, but seven live specimens were collected by Dr. J. F.
Walker in a brackish water lagoon on the north side of Ship Island
in July, 1949.

Spisula solidissima. This is a large handsome clam which, super-
ficially, resembles Mactra fragilis. However, it has long slender lateral
teeth which bear tiny vertical ridges. The pallial sinus is small,
and reaches no more than one fourth of the distance between the
muscle scars. Maximum size about 180 mm.

This handsome clam is found living on both sides of the barrier
islands in fairly shallow water. Although fair numbers of shells
are found, it does not seem to be very abundant on the Mississippi
coast. The Gulf coast form is usually considered a subspecies of
the north Atlantic form, but it may prove to be a distinct species.

MESODESMATIDAE

These are oval or wedge shaped shells with short posterior ends.
There is no ligament, but the internal resilium is supported by a
chondrophore in each valve.

Ervilia concentrica. This little clam is somewhat elongate, and is
elliptical in outline. Sculpture consists of numerous fine concentric

- 48 -

ridges. The color range is white, yellow, and pale pink. Maximum
size about 8 mm.

This small species has only turned up as single valves in bar-
rier island beach drift. It does not appear to be very numerous,
but it is easily overlooked.

CORBULIDAE

Small, solid clams that look very much alike. The Corbulidae
are unusual in that one valve completely overlaps the other in most
species. They are usually concentrically ribbed, and have a single
conical hinge tooth in the right valve.

Corbula sp. One live specimen was collected from the east end
of Ship Island; length 6 mm. The taxonomy of the West Indian
members of the genus is still confused and the identity of this
specimen has not yet been made.

GASTROCHAENIDAE

Members of this family bore into rocks or into the shells of
larger mollusks. The shell is chalky white, and gaps widely at the
anterior end.

Rocellaria stimpsonii. The surface sculpture consists Only of incre-
mental lines The anterior border is reflected outward, and there is
no interior rib. Maximum size about 15 mm.

This clam appears to be fairly common in rocks and shells
around the barrier islands. When individuals bore through a thin
shell they form a flask shaped shelter of calcareous material. Sev-
eral of these curious little structures have been found in shell
debris from Dog Keys Pass.

PHOLADIDAE

This is a family of boring pelecypods A burrow is started when
the young pholad settles to the bottom, and it remains there for
the rest of its life. There are no teeth in the hinge, but there is
an accessory plate over the hinge area. Thin membranes unite the
valves above and below the accessory plate.

Borneo iruncata. This is a thin shelled species with long dark
colored siphons. The anterior end is somewhat pointed, and the
posterior is abruptly truncate. Maximum size of the shell is ap-
proximately 60 mm. The siphons cannot be retracted within the
shell.

This species appears to be rather rare in Mississippi waters. Two
live specimens were collected in July, 1958, by Dr. H. J. Bennett
and his Marine Zoology class at the east end of Deer Island.

Cyrtopleura costaio. This is the large and handsome “Angel Wing.”
The shell is usually white, elongate, and rather thin shelled, but is
not as fragile as B. fronca/a. There are about 30 radial ribs which have
projecting scales on the anterior portion of the shell. The valves
gape considerably, and the animal is much too large to fit inside
the valves. Maximum size of the shell is 200 mm., but the entire
animal when relaxed in its burrow may be 400 mm, long. It usually
burrows in mud, but has been found by the writer living in fine
sand.

- 49 -

C. costata is found in very shallow water along the mainland
shore of the Sound. An especially good collecting ground has been
at the east end of Deer Island, but even here it does not seem to
be abundant. Single valves are found in beach drift on the bar-
rier islands, but no living specimens have been seen in that area.

Diplothyra smithii. This is a small, rounded clam that is usually
found boring into oyster shells. The shell is widely gaping in young,
but this open space is covered by a shelly callus after the animal
reaches maturity. The exterior of the valve is divided by a sulcus,
and the anterior half is sculptured by fine concentric ridges and in-
distinct radial ribs. The posterior half has growth lines only. Max-
imum size is 15 mm.

This species is easily overlooked, but is fairly common in the
saltier parts of the Sound.

TEREDINIDAE

This is a family of worm like pelecypods (the “Shipworms”) that
burrow into wood. The minute shell is at the deep end of the bur-
row, and a shelly lining for the tube is secreted by the mantle for
protection. Two plume-like pallets at the posterior end of the ani-
mal can close off the burrow.

Bpnkia gouldi. The pallets are about one-half inch long. The cones
have deep cups with smooth edges. The entire animal may grow
to be a length of more than 200 mm.

This species bores into wood wherever the water is brackish or
salty.

LYONSIDAE

The shells of this family are small and fragile, and have a pearly
lining on the inside of the valves.

Lyons/a floridcwa. This is a small elongate species with a short
rounded anterior, and a long rostrate posterior end. The left valve
is larger than the right, and there is a thin papery periostracum.
Maximum size about 18 mm.

The writer has taken only one specimen; it was found on the
grass flats along the north side of Horn Island.

PANDORIDAE

A family of thin compressed pelecypods with a hinge of lamel-
liform plates instead of teeth. The beaks are very inconspicuous.

Pandora friHneafa. This small clam is white and very compressed.
The right valve is flat, but the left valve is somewhat convex. The
dorsal margin is concave posterior to the beaks and slightly convex
on the anterior side. The ventral margin is nearly straight, then
curves up abruptly to the anterior and posterior ends of the shell.
The beaks are near the anterior end. Maximum size about 30 mm.

P . trilineafa has proved to be almost as rare as Lyonsia f/oridana on
the Mississippi coast. Several specimens were found on the beach
on Dauphin Island in March, 1956, but only one small specimen has
been collected farther west, in Ship Island Pass.

LOLIGINIDAE

This is a family of small, fast swimming cephalopods. The body

- 50 -

is torpedo shaped, and the fins are large and triangular. There are
two long retractile tentacles and eight short arms.

Loligo pealei. This species has a slender body and long triangu-
lar fins usually slightly more than half the mantle length. Maxi-
mum size of the entire animal, including the two tentacles, may
be 500 mm. or more.

L. pealei is a coastal marine form which does not go into waters
of low salinity. Although it has been collected in Dog Keys Pass,
none have been caught in the Sound away from the Pass. It is not
very common in Mississippi coastal waters, but trawling just off
the barrier islands will occasionally turn up a few specimens.

A similar species, Dor /leaf bis plei Blainville, has been caught about
five miles south of Horn Island, and, as it probably comes closer to
shore, it should be mentioned here. It has a more slender body, the
fins are less triangular, and there is a flap of skin along the mid-
ventral line along the length of the body. Its body dimensions are
nearly the same as those of L. pealei.

Lolliguncula brevis. This small squid is somewhat similar to t. pealei.
in appearance, but differs in its small size, short thick body, and
short rounded fins. Maximum size of the animal is 250 mm.

L. brevis is an exceedingly common squid on the northern Gulf
coast. Although all cephalopods are generally considered to be sten-
ohaline marine animals, this species is quite common in brackish
water. Gunter (1950) reported that he had found it in salinities as
low as 17.7 parts per thousand. He also reported that only nine
specimens out of a total of 276 were taken in salinities below 20.0.
Since then, he and the writer have found it to be quite numerous
in slightly lower salinities in Mississippi Sound. On April 22, 1957,
eighty L. brevis were taken in a 20 minute trawl haul at the Labora-
tory Station III in a depth of 14 feet. The salinity was 12.88 at the
surface, and 16.68 just off the bottom. The corresponding tempera-
tures were 24.0* C. at the surface, and 23.2° at the bottom.

Large numbers of this little squid can usually be found almost
anywhere in the deeper waters of the Sound, and it has sometimes
been taken in quantity in outer Biloxi Bay. The long, tapering, gel-
atinous egg cases of this squid are also quite common in the central
portion of the Sound.

OCTOPODIDAE

This is a family of benthic cepahalopods distinguished from
squids by the absence of tentacular arms and fins, and by having a
short, rounded body instead of being torpedo shaped.

Octopus vulgaris. There are two rows of suckers on the arms of
this species, and the first pair of arms are much shorter than the
others. The gill plates number 7 to 11. Maximum length is about
one meter, or a radial spread of two meters.

The Mississippi coast is a poor habitat for the octopus which
prefers to live in holes and caves in rocky areas. Nevertheless, a
total of four specimens have been trawled in Dog Keys Pass from
1957 through 1959.

On November 12, 1959, a small octopus measuring approximately
one and one-half feet long with arms outstretched was trawled by
a fisherman at about the middle of Mississippi Sound, midway be-
tween Deer Island and Ship Island. The preserved specimen was
kept by the fisherman.

- 51 -

SUPPLEMENTARY NOTE

Since the time that the work on the main body of this paper
was done, additional material has added several more records for
the area studied by the writer. In addition, Dr. J. P. E. Morrison
of the U. S. National Museum worked at the Gulf Coast Research
Laboratory for a period of nearly three weeks, during May and June
of 1960. His collecting in this area turned up five more species not
previously reported, as well as new localities for other species on
the Mississippi coast. He also made a number of helpful sugges-
tions, and supplied information not available to the author. Among
other things, he pointed out that unpublished work by Dr. Alfredo
do la Torre had established the genus Alabina Dali, 1902, as a syno-
nym of Finella A. Adams, 1860. In addition, he found A. cerithidoides
Dali, 1889, to be a synonym of Chemn/fzia dubia d’Orbigny, 1842, so
that the name of this little shell is now Finella dubia d’Orbigny with
Alabina cerithidoides Dali as a synonym.

The additional species are as follows:

GASTROPODA

PROSOBRANCHIA

HYDROBIDAE

This is a large family of small to minute fresh and brackish
water snails. They usually have a well developed spire, and a rather
heavy shell. Color is lacking, but the shell is usually covered by a
brownish coating, which gives the snail a dull and inconspicuous
appearance.

Liitoridina sphinctostoma Abbott, and Ladd, 1951. This little species
is fusiform in shape, and without sculpture except for very faint in-
cremental lines. Adults usually are covered with a more or less
thick coating of brownish material. The aperture is oval, but has a
slight groove at the posterior end. The aperture becomes abruptly
smaller at maturity, and is no longer appressed to the preceding
whorl The peristome is then complete, and immature specimens
appear at first to belong to a different species. There are slightly
over six whorls in a specimen 3 mm. long.

This snail is common in Lake Ponchartain, Louisiana, but it
has been collected in Mississippi only at Heron Bay, just east of the
mouth of the Pearl River, by Dr. J. P. E. Morrison. It lives in areas
of quite low salinity, and may be found elsewhere in Mississippi
near the lower end of the salinity gradient.

Littaridina sp. This species is about the same size as L sphinctostoma,
but does not have the reduced aperture found in the mature L sphinc-
tostoma. The peristome is not entire, and the preceding body whorl
forms the inner posterior portion of the aperture. There is an um-
bilical chink, and a 3 mm. specimen had slightly more than five
whorls.

The only known locality for this species is a pond on Horn Is-
land, where it is found with Chora, a fresh water plant known as
“stonewort.” It appears to be an undescribed species, and may be-
long to a different genus. It will be described at some future date
by Dr. Morrison.

- 52 -

OPISTHOBRANCHIA

PYRAMIDELLIDAE

Sayefia hemphilli Dali, 1883.

This is a small, somewhat elongate snail with a small, narrow
aperture. There is a single columellar tooth which continues on to
become the anterior part of the peristome. The color is light brown,
but often there is a spiral band of darker color On each whorl. There
are about five whorls to a specimen 3 mm. long.

This species has been collected in beach drift at the east end
of Deer Island.

NUDIBRANCHIA

DORIDIDAE

The branchial plumes are in an arc or circle, and can be re-
tracted into a cavity. The rhinophores are also usually retractile.
The dorsum completely covers the animal and over-hangs all the
way around.

Archidoris ? sp. This is a green, oval nudibranch whose dorsum
is covered with tubercles. The rhinophores have 14 lamellae, and are
fully retractile into deeply notched tubercles. The branchiae num-
ber 13, some of which are branched. There are spicules in the dor-
sum. The underside is colored greenish yellow. The genital pore
is located on the right side a short distance behind the head, and
the mouth region is shaped almost like a boomerang with the con-
vex side anterior. The radula is broad, and with about 84 simple
hook-lie teeth in each row. There are two black eye spots on top of
the cerebral ganglion.

The maximum size when fully expanded was about 40 mm.
long by slightly over 20 mm. wide. They are oval in shape, but are
a little broader at the anterior end.

A total of twenty specimens were collected by the writer at
Dog Keys Pass in the trawl during March and April, 1960.

AEOLIDIIDAE

Long slender nudibranchs with many cerata set in numerous
close, transverse rows. They are broadest at the anterior end, and
the foot usually tapers off to a point at the posterior. There are
four simple tentacles, none of which can be retracted into holes, and
the radula consists of a single broad plate.

Aeolidia sp.

Oral tentacles, white, very long and tapered; the anterolateral
edge of the foot with a slender pointed projection. The rhinophores
are small, smooth, and tipped with pale brownish orange. The tips
of the cerata are colored pale orange, dark brown, and white. Length
is about 40 mm.

One specimen was collected in Dog Keys Pass in April, 1960.

PULMONATA

ELLOBIIDAE

Detracia floridana Pfeiffer, 1856.

- 53 -

This is a small, almost football shaped species. There is a
single strong columellar ridge at the anterior end of the columella,
and there are eight or nine small teeth inside the outer lip. There is
a single thin blade-like lamella on the columella. The color is light
brown with darker spiral bands. The maximum size is about 8 mm.,
and there are about ten or eleven whorls.

This little snail is very similar in appearance to Me/ompus bi'denfo-
tus, but differs in its nearly biconic shape, smaller size, and salinity
range. When the two species are found together, it is always at
the lower end of the salinity range for M. bidentah/s, and D. floridana
is never found in higher salinity areas where M. bideniatus is best
established. Mississippi specimens were collected at Stark Bayou,
Heron Bayou, and Davis Bayou in May, 1960, by Dr. Morrison and
the author.

PELECYPODA
ANISOM Y ARIA
ANOMIIDAE

The shell is thin and variable in shape, and, in the Atlantic
genera, the calcified byssus passes through a hole in the attached
valve. The ligament is more or less internal and is supplemented
by an internal resilium. No hinge teeth.

Anomia simplex d’Orbigny, 1845,

The attached valve has an opening for the byssus, and there are
three muscle scars in the top valve. The attached valve is flat, but
the upper valve is quite convex. The shell is thin, and has no sculp-
ture. The maximum size is about 50 mm.

HETERODONTA

CYRENOIDIDAE

The shell is thin, inflated, suborbicular, and with a brownish
periostracum. Each valve has a pair of cardinal teeth, and there is a
long external ligament which enfolds a smaller resilium.

Cyrenoida floridana Dali, 1896.

The shell is inflated, orbicular, and is covered with a yellowish
brown periostracum. Maximum size is about 14 mm.

Two live juveniles and two dead shells were collected by Dr.
Morrison in the estuary branches of Davis Bay, It has much the
same salinity tolerance as Detracia floridana , and is confined to the
fresh water side of the marshes. It is, like Polymesoda caroliniana, us-
ually intertidal, but under cover of logs or other plant debris.

LEPTONIDAE

Lepfon ? sp.

The shell is thin, white, smooth and polished. It is equivalve,
and is almost equilateral. The valves are oval in shape and the beaks
are near the center of the dorsal margin. The maximum size is about
7 mm.

This little clam is commensal on the under surface of the abdo-
men of a large mantis shrimp, Lysiosquilla scabricauda. Like other mem-
bers of the family, it is able to glide about on its foot like a gas-
tropod, and was easily able to climb the glass sides of aquaria.

The generic designation here employed is very tentative.

- 54 -

VENERIDAE

Anomalocardia cunimeris Conrad, 1346.

This; clam is; wedge shaped with a rounded anterior end, and
with a sharp, pointed rostrum at the posterior end. There is a wide
shallow escutcheon bordered by a weak ridge. The sculpture con-
sists of rounded concentric ribs which are more prominent near the
beaks. The color is variable. Maximum size is about 20 mm.

Four single valves were screened out of sand in a salt water
pond on Horn Island by Dr. Morrison in May, 1960. They appeared
to have been dead for some time.

DONACIDAE

Donax tumida Philippi, 1849.

This is a small, obese species of surf clam. The beaks are
swollen, and the posterior end is strongly truncate. There are beaded
threads on the blunt posterior end, and a few incised, concentric
lines on the anterior end. There are usually no rays of color, and
the shell appears drab compared to the average D. variabilis.

This species lives out in deeper water than does D. variabilis , and
a few specimens have been found by diving on the Gulf side of
Ship Island.

ADAPEDONTA

MACTRIDAE

Rangianella sp. This is a small white species that is very similar
to young Mulinia lateralis . There is an internal resilium, and each valve
has a pair of lateral teeth of moderate length in addition to the
cardinals. Maximum length is about 8 mm.

This species is common in Lake Pontchartrain, but was not found
in Mississippi until May, 1960, when Dr. Morrison found it in Heron
Bay. It is being described by Dr. Morrison.

Three of the species listed in this Supplementary Note have
been reported by Parker (1956), but the remaining nine are new
records for this region. The additional species increases the total
for the area studied to 163.

SUMMARY

The Mississippi coast consists of the irregular mainland shore.
It is indented by several small bays, connecting with a long, narrow,
shallow Sound. A series of barrier islands partly separates the
Sound from the Gulf of Mexico on the south. The Sound is about
80 miles long by ten miles wide, and averages ten feet deep. About
one-fifth of the eastern end lies in Alabama, but there is no im-
portant change in the environment throughout the area

The barrier islands apparently were built up some five or six
thousand years ago after the sea level became stabilized at its pres-
ent height. The Chandeleur group, to the south were formed at a
much later date than the Mississippi islands, and Cat Island has
since reoriented itself to face the open Gulf. As a consequence of
barrier island formation, the Sound acts as a settling basin, and a
thick deposit of mud now covers most of the bottom.

- 55 -

There is a gradually declining salinity gradient from the open
Gulf to the rivers and bayous of the mainland. The salinity in the
coastal waters and the Gulf remains rather stable, but there is
considerable fluctuation near the mainland, especially in the bays
and bayous after heavy and prolonged rains. Most of the streams
flowing to the coast are small, but the Pascagoula, which flows di-
rectly into the Sound, and the Pearl, which empties into Lake
Borgne about four miles west of the vSound, are medium sized rivers
which originate some distance inland.

Other important physical factors are: temperature, which ranges
from 4° C. in the winter to 30° C. in the summer; turbidity, which
is almost always high; depth of water, from shallow depths mostly
less than 20 feet to a maximum of 50 in the passes; currents, both
tidal and wind driven, and the substratum. The bottom area of the
Sound is made up of 5 per cent sand, 80 per cent clay-mud, and 15
per cent silt or sandy silt. The very small amount of hard bottom
consists of oyster reefs, or man made structures around the shores.

Four classes of mollusks have been found on the Mississippi
coast. The classes, and the number of species in each, are as fol-
lows: Gastropoda, 80; Scaphopoda, 2; Pelecypoda, 78; Cephalapoda, 3;
total, 163. Previous published works have listed 51 of these, and
112 are new records for the area. Parker (1956) reported investiga-
tions to the east of the lower Mississippi Delta in which there was
listed a large molluscan fauna taken from the tidal marshes to a
depth of 40 fathoms. His list includes a great number of mollusks
hitherto unreported from the north-eastern Gulf. Parker’s work
was done outside of the area treated here, but, even if his list is
included, 68 of the species presently reported remain as new records
for the north-eastern Gulf. A number of species listed by Johnson
(1934) were said to live from Florida to Texas, or, more often, Gulf
of Mexico. Since many of these records are for tropical or deep
water species, they have caused considerable taxonomic confusion
among biologists working in the coastal waters of the northern Gulf.
More precise locality lists are needed.

By far the greatest number of species was found around the
barrier islands on sand bottom in waters of fairly high salinity. Salin-
ity is an important factor in connection with distribution of mol-
lusks, but the type of bottom is also important, and a few euryhaline
or partly euryhaline marine species, such as the snail, Polinices dupli-
cates, are found living around both the barrier islands and also on
sandy areas along the mainland shore. The mud bottom of most of
the Sound is rather barren, but a few species, for instance, C allo-
cardia lexasiano , appear to prefer this type of habitat. The molluscan
fauna of low salinity waters consists of a small number of species
typical of brackish water marshes and bayous.

- 56 -

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