HARVARD UNIVERSITY

LIBRARY

MUSEUM OF COMPARATIVE ZOOLOGY

BULLETINS

OF

AMERICAN PALEONTOLOGY

VOL . XXVI

1940-41

Paleontological Pesearch Institution

Ithaca, New York U. S. A.

I^/H

JUL 15 1941

V

CONTENTS OF VOLUME XXVI

Bulletin No. Plates Pages

95. Marine shells of the southwest coast of Florida

By Louise M. Perry ._ . 1-39 1-260

96. Some fossils from the Edwards formation of Texas

By William Clyde Ikins and Stephen Edmund

Ciabaugh s .... 40-41 261-282

97. Upp*r Cretaceous corals from Cuha

By John W. Wells ..... .. 42-43 283-300

98. Cretaceous and Eogene corals from northwestern

Peru

By John W. Wells 44-46 301-326

99. Some palmate Lagenida? from the Lower Creta-

ceous Washita Group

By Alfred R. Loeblich, Jr. and Helen Tappan 47-49 327-356 100. The geology and paleontology of the Cuenca- Azogues-Biblian region, provinces of Cafiar and Azuay, Ecuador By Ralph A. Liddle and Katherine V. W.

Palmer 50-58 357-418

Index 419-420

,/L*' zoology "/;>

AUG 20 1940

J-/4JKA *^-

BULLETINS

OF

American paleontology

*

VOL . XXVI

NUMBER 95

19^0

Paleontological Research Institution

Ithaca, New York U. S. A

NOTE : Vol. 25. „ot yet published

BULLETINS OF AMERICAN PALEONTOLOGY

Vol. 26

No . 95

Marine Shells of the Southwest Coast of Florida

By Louise M. Perry

Illustrations by W. Hammersley Southwick August 12, igj-o

V U.KONT(U,uGllAI, RESEARCH INSTITUTE! IN

Ithaca, New York U. S. A.

Vtt,

Copyright, 1940, by the PALEONTOLOGICAL RESEARCH INSTITUTION

Printed in the United States of America

It is perhaps a mare fortunate destiny to have a taste for collect- ing shells than to be born a millionaire.

r. i.. s.

INTRODUCTION

Some fifth of a century ago when 1 first saw a Florida beach, with its multitudes of shells they seemed worthy of attention only as adding variety to the general attraction of the seashore ; but within a few tides times the lion's paw, the angel's wing, the fighting conch and the calico shell had acquired individuality and stimulated an interest that must enrich any experience which includes them.

The abundance and variety of southern Florida's molluscan fauna is unexcelled by any other in America, and by but few areas of like extent anywhere. This circumstance is due to a combina- tion of ecological factors related to latitude, sufficient bathy- metric range for slight differences of water temperature, charac- ters of sea bottom, and some local modifications of salinity due to drainage of fresh water from the Okeechobee basin and other areas. The littoral region has many genera characteristic of sand, mud and weedy bottom. Oysterbars, sandbars and mangrove- fiats, and in deeper water rock and coral reefs and outcroppings of hardpan have their peculiar associations of molluscs and other marine animals. Species native to a more southerly province overlap some which have a more northerly range, and some genera common on the southern Atlantic Coast are established along the Gulf Coast without continuity of any of their species around the southern tip of the Florida Peninsula.

All descriptions apply to specimens which were taken alive or in such fresh and perfect condition that a local station may rea- sonably be assumed. All measurements refer to average sizes, adult shells, and all illustrations are of recently collected speci- mens.

The study collections upon which the descriptions are based has been placed in the Thomas R. Baker Museum at Winter Park, Florida.

6 Bulletin 95 6

The 'List of Marine Mollusca from Labrador to Texas', by Charles W. Johnson (Boston, 1934) is used as the basis of classi- fication and nomenclature. Free use has been made of available conchological literature.

Acknowledgment of valuable assistance is made with pleasure to Dr. Henry A. Pilsbry, to Dr. Paul Bartsch, to Dr. Harold A. Rehder, to Richard F. M,cLean and Jeanne S. Schwengel. Thanks are due to George W. Underhill and George W. Underhill, Jr. for skillful use of boats and dredges.

Dr. Eugene W. Gudger has been kind enough to read the manuscript and offer many helpful suggestions.

L. M. P. Sanibel Island, Florida.

Marine Shells S. W. Fla. : Perky

GENERALIA

Shelled molluscs belong to one of the most ancient groups of animal life. Five hundred million years ago there lived in the Cambrian period of the earth's geologic history snails with shells so complex and perfect that their presence can be explained only by the existence of ancestral forms in a period far more distant. These fossil remains are of great importance in the study and chronological interpretation of the earth's geologic past. Their presence in stratified rocks determines the periods in which suc- cessive layers of sediment were deposited in ancient seas, and the evolution of primitive molluscan shells may be traced through these sedimentary deposits to the shells of Recent families and genera. Certain shells from Tertiary deposits in the Okeechobee and Caloosahatchee basins are of types which persist in the living molluscan fauna of Florida waters.

Emanuel Mendes DaCosta1, one hundred and sixty-three years ago wrote :

The study of shells or testaceous animals is a branch of Natural History, though not greatly useful in human economy, yet perhaps by the infinite beauty of the subjects it treats of, is adapted to recreate the sences and insensibility to lead the amazed admirer into the contemplation of the glory of the Divinity in their crea- tion. The British conchologist George Perry, expressed a like feel- ing in the introduction of his 'Conchology, or the Natural History of Shells', published at London in 1811. The sentiment was not unique, for the symmetry and beauty of shells have suggested many forms in art and architecture, and in some parts of the world their use as objects of utility, ornament and symbolism is presently continuous with the practice of early man. North American Indian tribes which practiced totemism used shells (Cxprcca moneta) in their ritual of death and resurrection and so recently as eighteen forty-eight to the eighties, Maplewood Insti- tute for Young Ladies, at Pittsfield, Massachusetts, listed Conch- ology in its regular curriculum as a subject of cultural value to its students.

1 Ills, of Fossil and Kecent Shells

8 Bulletin 95 8

Certain elementary principles must be understood before an intelligent approach can be made to the study of shells. It is a matter of common knowledge that animals differ widely in ap- pearance and anatomical structure. These differences form the basis of classification of all animal forms first into two principal groups invertebrates and vertebrates, or those forms without a backbone and those possessing one. These groups are divided into phyla (Gr., phylon, meaning race or tribe). Each phylum is sub- divided on the basis of anatomical structure into groups which show the increasingly closer relationships which establish class, order, family, genus and species.

The phylum Mollusca (Lat, mollis, soft, having reference to the soft body), is fifteenth on the scale of increasing complexity of structure among the invertebrates. It has, perhaps, more than 100,000 species, a greater number than any other group of animals excepting the Arthropoda, which includes the insects and crusta- ceans.

Molluscs have no supporting skeleton, but with few exceptions they have developed a protective calcareous structure, the shell,2 which has evolved into a number of highly differentiated forms. The shell is a part of the animal, and failure to consider this re- lationship and the relationship of molluscs to other animal species, deprives the student of one of the great advantages and pleasures of his avocation.

The shell is secreted by a specialized part of the mollusc's body called the mantle, which envelops the soft structures like a closely wrapped cape, and whose external, secreting surface is in intimate contact with the internal surface of the shell. The se- creted shell substance consists of about five per cent of an organic matrix called conchyolin impregnated with mineral salts taken from the sea water, principally carbonate of lime and small amounts of magnesium. The conchyolin, which is elaborated and secreted by the mantle, provides a framework for deposition of the mineral salts, and in an unimpregnated state forms an external

2 Dr. Samuel Johnson 's Dictionary gives eight meanings for the word ' ' shell ' '. The second is ' ' The covering of a testaceous or crustaceous animal." The word is of Saxon origin scyll or scell meaning rough, homespun.

Marine Shells S. W. Fla. : Perry

covering for the shell which affords protection against chemical injury from corrosive substances which the water may hold in solution; it is called the epidermis or periostracum. Differences in structural arrangement of the shell elements produce differ- ences in quality and appearance of the shells viz. opaque, por- celaneous, polished.

A rudimentary shell is present when the young mollusc leaves the egg capsule, or is developed very soon thereafter, this nucleus rapidly increases its size by the addition of new shelly matter but is generally lacking in features which characterize older shells. Sculpture is formed and color and pattern are added by the secret- ing edge of the mantle, and any injury to this soft organ may re- sult in some degree of deformity of the shell and partial loss of pattern and color. Alternating periods of growth and inactivity are often defined by an axial ridge or varix which represents the outer lip of a previous aperture in univalve shells, and in lines or ridges of growth parallel to the margin of bivalve shells. All irregularities about the apertures and margins of shells are pro- duced by corresponding irregularities in the edge of the mantle, and remain as sculptural features of the shell as new growth pro- ceeds. Immature shells often differ from adult specimens of the same species; juvenile shells are usually thin, have thin lips and are lacking in the color and finished sculpture that ornament the adult shell. These differences are sometimes so marked that the identity of young shells has been unrecognizel and independent specific rank given them.

Actual attachment of the mollusc to its shell is effected by means of strong muscles. In gasteropods, one powerful muscle is firmly fixed to the columella near the apex of the shell ; in the pelecypods one or two muscles are attached at opposite points in the two valves, contraction of these muscles keeps the valves tightly closed.

Color is present only on the surface of shells and is believed to be influenced by food and exposure to light. Shells from warm and shallow waters are usually more brightly colored than shells of species inhabiting the colder depths, and in must fixed bivalves the upper, exposed valve is the more highly colored.

10 Bulletin 95 10

Molluscs have well developed systems for nutrition, respiration, circulation, excretion and reproduction all under the control of a nervous system. Many of them have organs of special sense ; in some instances even a structure analogous to the ear, which keeps the animal in touch with its surroundings and aids in maintaining its equilibrium. Man}- molluscs are sensitive to light and respond actively to any change in its intensity ; some possess compound eyes with structures definitely comparable to those of the eyes of higher vertebrates.

Dr. Paul Bartsch, of the U. S. National Museum, claims for the Mollusca first rank in complex organization and intelligence among the invertebrates, and in consideration of the squid and octopus, believes that they surpass some groups of the lower verte- brates.

The food habits of molluscs are varied. Some gasteropods are predatory and carnivorous, others are vegetarian ; some are para- sitic upon starfish, sea cucumbers, corals, sponges and other mol- luscs ; some pierce the egg capsules of their own and other species to prey upon the contained ova and embryos. The food of the pelecypods consists of minute plants and animals taken into the digestive tract with indrawn currents of water.

In some groups of molluscs the sexes are separate, in which case the male is usually the smaller. In other groups the molluscs are bi- sexual and there are some examples of true hermaphroditism.

Phosphorescence is a property of certain molluscs. The Roman naturalist Pliny remarked this emission of light, and wrote of the Dactylus (pholads), 'it is the property of these fish to shine brightly in the dark, when all other lights are removed, and the more moisture they have, the brighter is the light they emit. In the mouth even, when they are being eaten, they give forth their light and the same too when in the hands ; the very drops, in fact. that fall from them on the ground or on the clothes, are of the same nature. Hence it is beyond a doubt, that it is liquid that possesses this peculiar property, which, even in a solid body, would be ground for considerable surprise'.3

3 Historia Naturalis, Book IX, Chapter 33.

11 Marine Shells S. W. Fla. : Perry 11

There is little definite knowledge of the age attained by mol- luscs. The great size of some gasteropods presupposes many years of life, and the enormous valves of the East Indian Tridacna are the growth of man's three score years and ten, and more. Some of the pelecypods reach reproductive maturity within twelve months and oysters are known to live for fifteen years.

The phylum Mollusca is divided into five classes :-Amphineura , Pelecypoda , Scaphopoda , Gasteropoda , Cephalopoda. Further subdivision expands each class through order and family, to genus and species. Shells of genera belonging to the Amphineura, Pelecypoda, Scaphopoda and Gasteropoda are considered in this manual.

The system of scientific nomenclature in general usage is bi- nomial. Latin or Greek words are generally used for generic and specific names. Occasionally proper names, names of localities, or words from a language other than Greek or Latin are chosen, but are always given in Latinized form.

Each genus possesses a distinctive name, always capitalized viz. Oliva. The name of a species consists of the name of its genus, followed by its own distinguishing name, both in italics ; next is appended the name of its author whose original published description or definition clearly established the species, viz. Oliva sayana Ravenel. Variations of a species sufficiently well defined and constant to merit subspecific distinction as a variety are given a third name which is interpolated between the specific name and the name of the sponsor, viz. Oliva sayana citrina Johnson.

The terms genotype, holotype and paratype are used in refer- ence to the establishment of genera and species. As defined by Schenck and Mc Masters , Procedure in Taxonomy, 1936, the genotype is the single species upon which a genus is based. The holotype is the single specimen taken as 'the type' by the orig- inal author of a species. The paratype is a specimen other than the holotype, used as the basis of a new species.

12 Bulletin 95 12

COLLECTION AND PREPARATION OF SPECIMENS

Shells of many probably most of the molluscs whose habitat is the nearby sea bottom may be found at some time on the open beaches. Shore collecting is profitable in proportion to the regu- larity and persistence of the search, it will afford a considerable variety of excellent specimens and at any time a happy coincidence of time and tide may bring a rare treasure to the hand of the col- lector.

Collecting is best at low tide. Large shells are oftenest found along the beaches near high-water mark and wherever there is an accumulation of sea-wrack. After a quiet tide man}' minute shells lie among the fine detritus left by the ebb tide in ridges along the beach and in any small depressions in the sand. Living molluscs are often washed ashore and many individuals of very small species cling to the rough surface of stranded shells or hide within the cavities of sponges and among the branches of hydroid colonies and seaweed. Pieces of water-logged wood, wave worn shells and lumps of coral are worth careful examination for speci- mens of such boring genera as Martesia, Litliophagus and Gas- trochcrna. Ritpellaria, Coralliophaga and Modiolus may be found in cavities not of their own making. A bread sponge may harbor a colony of the uncommon Ostrea per mollis. Specimens of a para- sitic Mclanella may be found attached to the tough integument of holothurians (sea cumbers), and the dainty Erato maugerice may share space on the rough valves of Atrina with several dif- ferent species of other small univalves and attached bivalves.

The shell of one living Atrina rigid a, picked up at random after a windblown tide, yielded the molluscs listed below together with egg cases of Anachis avara similis, Cantharus tinctus and Muri- cidea multangula, and many individuals of other invertebrate groups :

Anachis avara similis, Anachis obesa, Anomia simplex, Area occidentalis, Cantharus tinctus, Ischnochiton papulosa, Monili-

13 Marine Shells S. W. Fla. : Perry 13

spira monilis, Rubellatoma diomedea, Crepidula fornicata, Erato mauger'ne, Modiolaria lateralis, juvenile specimens of Murex rufus and pomum, Ostrea virginica floridana and Urosalpinx perru- gatus.

At the fortnightly times of high tides coincident with the changes of the moon, the ebb exposes a wide extent of beach and leaves dry for a short while many bars and flats of inland waters. At such times specimens of many littoral species may be found alive and perfect, and localities may be explored which are inac- cessible in ordinary circumstances. Old pilings of wood or cement and clumps of living and dead oyster shells should be examined ; logs and stones turned over ; but always and everywhere any object that has been moved should be replaced in its original position ; do not expose to drying and needless death the many small creatures that have been disturbed by the search.

Beyond the limits of the beaches search for living molluscs must be based upon some knowledge of their habits and stations stations having reference to the particular conditions of environ- ment which are congenial to various species. Association of cer- tain species of molluscs with definite characters of environment is almost invariable. Thus species of Cerithidca, Cerithiuni, Mar- ginella, Melongcna, Anomalocardia, Polyinesoda and several small Tellinas coinhabit tidal salt flats and the intertidal zone of inside waters. Littorina, Melampus and Truncatella live about salt marshes, often out of water for long periods. Ostrea and Modio- lus live about the mangrove fringes of the flats and bayous and are out of water at extreme low tide. Barnea truncata is likely to be found in black mud near mangroves, while Barnea costata lives in deeper water, usually where there is an admixture of gravelly bottom with a substratum of marl or silt.

On grassy bottom are found Modulus, Pyrene, Cerithiuni, Bit- tiunt, Rissoina, Marginclla, Smaragdia and at certain seasons, Pecten. On sandy bottoms, living buried beneath the surface with siphons extended upward into the water are Chione, Venus, Transenella, Pitar, Macrocallista, Lucina, Tellina, Mactra, Tage- lus; and preying largely on these bivalves Natica, Polynices, Terebra, Conus, Xassarius, Murieidea and Urosalpinx move

14 Bulletin 95 14

freely about. Wherever Venus mercenaria is found there also are Busycon and Fasciolaria. Eupleura is often associated with a bottom weed known commonly as 'rolling moss'.

Dentalium, Corbula, Nucula, Nnculana, Lyonsia and Cuspi- daria are found in soft, oozy bottoms beyond low tide mark, although Lyonsia is also found in shallow water. On outcrop- pings of hardpan and about reefs associated with corals, corallines and sponges are found Murcx, Cancellaria, Leucozonia, Xeno- phora, Trivia and Mac id ope plum junonia, with Chania, Pscudo- eliauia, Echinochaina, Spondylus and Ostrea sprcta and limacella. Pccten gibbus is a Gulf species, apparently living in large, scat- tered and migratory colonies in from three to seven fathoms of water. After a northwest blow it is frequently one of the most abundant shells on the beach. With this Pccten are associated Pecten rarencli and Pccten ciccac, but in relatively small numbers, and in depths of five fathoms and more are Pecten nodosus and jragosus. Pecten gibbus irradians is a common bay species. In many localities it is sufficiently abundant to be dredged for the market.

Many species, among them Caniharus tinctns, Muricidea mul- tangula and ostrearwn, Fasciolaria gigantea, tulipa and c'istans, Strombus pugilis, Murcx rujus, Chionc cancellata and some of the Lucinidee are .common at varying depths both in inside and open waters.

A seasonal variation in numbers of individuals is evident in the case of some genera notably Pecten, Oliva, Murcx and Fasciola- ria, probably coincident with the spawning period when they seem to seek more shallow water. Spawning of molluscs is observed in the Florida region from November to midsummer, but the season of reproductive activity for individual species is not continuous through this long period. There seems also to be a difference in the abundance of certain pelecypods from year to year as suggest- ed by the presence of their shells on the beaches in great numbers, or their almost total absence for several years ; notable examples of this circumstance are Pccten muscosus, Chionc cancellata, Spisida solidissinia similis, and Area occidcntalis.

For eollecting beyond beach limits some equipment is necessary.

15 Marine Shells S. W. Fla. : Perky 15

Convenient containers are needed for shells, and pails for living material nonmetal if animals are to be kept alive for any length of time. Jars and vials should be provided for rare, small or deli- cate specimens some containing fifty per cent alcohol if it is de- sired to preserve the animal. Forceps, knife and pocket lens are useful.

Work in shallow water at low tide requires a long-handled shovel and a sieve approximately in size twenty-four by eighteen inches, by some three inches in depth. Its bottom should be of good wire screen, sixteen squares to the inch. It is well to have the bottom reinforced with heavier and larger mesh screen. Place a shovelful of sand or mud in the sieve and wash thorough- ly, examine what remains for small molluscs ; many of these and other small sand-dwellers will be seen. Repeat this digging and sifting at successive depths in the same spot in order to learn what species live near the surface and which ones burrow more deeply. Continue this process at increasing distances out from shore and in bottoms of different character. Slightly different conditions within a circumscribed locality will afford congenial stations to various species of molluscs. In protected inside waters with varying depths and character of bottom a great number of species find favorable circumstances and attain prefect development.

The frame of a crab net rather tightly covered with good qual- ity fine-meshed net or coarse scrim is very useful for collecting these species which live among grass or seaweed. The net should be used with a scooping movement, just escaping bottom.

Baited traps may be set and left for twenty-four hours, at least overnight since many molluscs are nocturnal feeders. When set in water deep enough to cover the trap, the location should be marked by a buoy. Shrimp, crab and fish are best for bait, though dead molluscs and bits of meat will attract carrion feeders. Sand fleas (Hippidse) have proven exceedingly attractive bait to Olii'a.

Dredging is the only method of taking living shells of other than shallow water species. By this means material is secured which is otherwise inaccessible, or at best represented by occasional beachworn specimens. The type of dredge shown in the frontis- piece is satisfactory for general work ; the cutting blades should

16 Bulletin 95 16

be at an angle of about one hundred and sixty-five degrees with the bottom of the dredge and the dimension between top and bot- tom not less than ten inches. Scallop dredges and tangles have also been used successfully, and a short section of cast iron pipe with a perforated bottom and suitable means of attachment for chains and tow rope is advantageous for learning characters of bottom. Dredges are drawn behind a motor boat with a stout rope twice or three times as long as the depth of water the deep- er the water the greater the proportionate length of the tow rope. Five or six feet of galvanized iron chain is attached to each arm of the dredge and joined with a swivel to the towing rope. When dredging is undertaken in depths of water exceeding four or five fathoms a weight should be attached to the tow rope about ten feet ahead of the dredge A float should also be attached to the dredge to mark its location in case the tow rope should break.

Everything that comes up in the dredge should be carefully in- spected. Starfish, sea urchins, sea cucumbers, hydroids and sea- weeds may be placed in a pail of fresh water for a time small molluscs that may be upon them will fall to the bottom of the con- tainer. Dead shells of Atrina afford lodgment to many chitons and small gasteropods ; Erato is often found in the crevices of compound zooid colonies, Sininia clings to gorgonians and exact- ly matches them in color. Ptcrict and Pinctada are attached by a byssus to other shells, to each other, sometimes in large num- bers of all sizes together. Pecten nutscosits is almost always cov- ered by a growth of sponge which is firmly established upon the scaly ribs of the bivalve shell. It is interesting to observe that the brilliant yellow and orange colored specimens of this Pecten are generally embedded in sponge of a purple tint.

It is essential to note and record carefully the locality and depth of water from which specimens are secured, and it is also well to record the date. Specimens which cannot be assigned to a definite locality have no value to a collection.

Cleaning shells has no fascination comparable to the satisfaction of collecting them, but this work must be done thoroughly if the specimens are to be preserved and enjoyed in a permanent collec- tion. Boiling best accomplishes removal of the soft parts. Many collectors prefer to place specimens in warm water and bring to

17 Marine Shells S. W. Fla. : Perry 17

the boil, allowing from two to thirty minutes boiling according to the size of the shells. Highly polished shells should be dropped into boiling water and permitted to remain not more than three minutes. After the shells are sufficiently cool to be handled the soft parts may be removed by gentle traction, taking care not to leave a pait of the animal in the apex of a univalve shell; in such event a few drops of ten per cent solution of formaldehyde left in the shell for a few days will deodorize and harden what soft parts remain. Small specimens may be placed as collected in fifty per cent alcohol and the hardened animal tissue subsequently removed from the shell with an appropriate instrument. Very small shells may be washed clean and left to dry without removal of the animal parts, or placed in a jar of fresh water, shaken well from time to time and the water frequently renewed until the macerated soft parts are washed away.

After removal of the animal, mechanical cleaning is next to be undertaken by scrubbing with a fairly stiff brush and by the use of some small, sharp instrument to remove calcareous deposits, worm tubes, barnacles, etc., care must be exercised to avoid in- jury to delicate sculpture. Immersion in one of the several com- mercial cleaning fluids similar to Javelle water, effectively aids mechanical cleaning by loosening the attachments of limy encrus- tations. Muriatic acid is useful but must be handled with care on account of its corrosive and destructive properties. A solution of one part of commercial acid to three parts of fresh water is sufficiently strong for general use. Shells should not be permitted to remain for more than a few seconds in the acid bath before washing and careful inspection ; the bath may be repeated if de- sired or further application of acid made with a brush interrupted by frequent thorough rinsings. The hands should be protected from contact with the acid.

After specimens are thoroughly cleaned and dried, a film of very thin oil may be applied to preserve the surface lustre. Shells which have naturally a very high polish may have their surfaces protected by a thin coating of colorless lacquer or an aqueous solu- tion of gum arabic, though this is not necessary. The epidermis and valve ligaments may be kept from excessive drying by soaking

18 Bulletin 95 18

the shell for a time in a weak solution of calcium chloride, equal parts of glycerine and water or some other hygroscopic agent. The operculums of univalves should be glued to bits of cotton and ad- justed in proper relation to the apertures of the shells from which they were removed. Bivalve shells may be closed and so main- tained until the hinge is dry enough to resist opening, otherwise the valves are quite certain to become separated.

Chitons are best handled by placing them in a vessel of sea water as collected until the}- can be extended on a firm surface and held flat by binding or light pressure until well dried ; or they may be left in a shallow dish of sea water until quite relaxed when the water is poured off and the chitons allowed to dry slowly. Unless some such method is followed chitons will contract themselves into a veritable ball from which it is impossible to reduce them without injury.

The characteristic specific features and the intrinsic beauty of shells are best exhibited in well prepared specimens, but every col- lection should include a few shells of each species in the undis- turbed natural condition, with epidermis intact and incrustations and barnacles unremoved.4

Some definite plan of classification should be adopted for the cabinet, and each group of specimens should be clearly labelled with the name, the date and the locality in which they were col- lected.

4 The scientifical collectors, or naturalists, are always desirous of having the shells in their rough state, or just as they are fished. This method, though extremely useful, is not to be absolutely followed ; not only because their beauties would be lost, but also on account that the different species could never be truly defined. However, as a medium, I would advise all collectors to have some shells of each genus in their rough state, while the others should display their beauties by all the accomplishments of art. Emanuel Mendes DaCosta, 1776.

19 Marine Shells S. W. Fla.: Perky 19

SYSTEMATIC DESCRIPTIONS

Class AMPHINEURA

The foundation of this distinct class of the Mollusca is the com- plete bilateral symmetry of its members. The name Amphineura (from the Greek combining form, amphi, both, on both sides; and neuron, nerve) refers to the balanced arrangement of the nervous system. The two orders of this class, the Aplacophora not bear- ing plates and the Polyplacophora bearing many plates, are based upon the absence or the presence of a shell, and the naked molluscs of the first order are the simplest and most lowly organ- ized members of the phylum Mollusca.

The Polyplacophora or chitons have a multivalve shell which covers and protects only the dorsum of the animal's flattened and elongated body. The unprotected ventral surface is equipped with a broad, suckerdike muscular foot, admirably adapted for creep- ing and for adhering tightly to the firm surfaces of rocks, shells and corals over which most chitons browse in search for their vegetable food of algse and diatoms. Chitons are native to all seas, usually at moderate depths. They are sluggish creatures, generally nocturnal in habit and appear to avoid light by hiding during the daytime in crevices, dead shells and under rocks. Some are said to return to a chosen resting place after each feeding excursion. Their size ranges between five and one hundred and fifty millimeters.

The sexes are separate. Some species lay their eggs singly or in unattached strings, some others retain the ova within the mantle cavity until the shell is formed.

In some tropical countries the muscular foot of large chitons is used as food. Natives of some of the West Indian islands call it 'sea beef, and either eat it uncooked or make of it the chief ingredient in a savory loblolly. In the far north chitons are a reputed cure of seasickness, but only when swallowed alive.

20 Bulletin 95 20

The remarkable ellipsoidal shell of the chitons covers only the dorsum of the animal. It is multivalvular, consisting of eight, thin plates or valves, transversely wide, gently arched from side to side and longitudinally keeled in the midline. Each valve articu- lates with the valve next behind it with a slight overlap toward the posterior end. All the valves are held together and in rela- tion to each other by a girdle of tough, leathery tissue which surrounds the entire periphery of the articulated valves. The overlap of the valves facilitates bending and the chiton's defens- ive attitude is assumed by approximating end to end for protec- tion of the vulnerable body. Just so in the early Dark Ages armor plates were fastened to leather, often by rivets ; the leather foundation gave flexibility to the coat of mail.

When the valves are separated, which is easily done by a short soaking in fresh water, the head and tail plates are seen to differ from the six intermediates. The anterior valve is roughly semi- circular with a median elevated apex. The posterior valve is much like the intermediates, but slopes abruptly to a rounded margin. The intermediate valves are rectangular in outline and show three more or less well defined areas upon their outer sur- face ; along the keeled mid-ridge of the shell is the jugal or dorsal tract, on each side are the pleural tracts, which in some genera are demarcated from the lateral tracts by an oblique line from near the center of the posterior valve margin toward the outer end of the anterior margin ; the sculpture of these areas is important in diagnosis. The valves of most chitons have projecting plates at the free edges which are covered by, and serve as attachment for the girdle.

The structure of the valves is highly interesting ; there are two layers ; a quite compact inner stratum and an outer, superficial layer which is perforated by many minute canals perpendicular to the surface, which contain specialized sense organs. In some species these organs have the form of eyes, possessing cornea, lens, pigment layer and retina.

-1 Marine Shells S. W. Fla. : I'kkky

Species of three genera belonging to this class are described.

Order POLYPLACOPHORA

Family ISCHNOCHITONID/E

Genus ISCHNOCHITON Gray, 1847

Ischnochiton"' papillosa C. B. Adams Plate 1, fig-. 1

Length, 6—8.5; breadth, 5 6 mm. Color mottled olive green or brown. The sides slope gently and convexly from a moderately keeled mid-ridge. An umbo, central and rounded, on posterior valve. Central and lateral areas of intermediate valves are ill defined, uniformly and thickly dotted with minute papillae. The narrow girdle is covered with fine overlapping scales and bears small tufts of shining spicules at each end and on each side. In- terior of the shell white.

/. papillosa is often found with Chcvtopleura apiculata adhering to dead shells of Atrina.

Genus CHCETOPLEURA Shuttleworth, 1853 Cha?topleura'; apiculata Say Plate 1, fig. 2

Length, 17 25; breadth, 10 16 mm. Color varies through buff to ashy-gray or brown, either unicolored or regularly pat- terned in a darker shade. Occasional specimens are uniformly red or orange color. The dorsum is sharply keeled, the sides slope rather abruptly and are convex. Well marked oblique lir.es separate central from lateral areas on each intermediate valve. The central areas bear finely beaded longitudinal riblets. The lateral areas are clearly defined and irregularly dotted with numerous rounded tubercles. The girdle is narrow, with scat- tered, transparent hairs. Interior white, greenish or grayish.

Family ACANTHOCHITIOCE

Genus ACANTHOCHITES Risso, 1826

Acanthochites7 pygmaea Pilsbry Plate 1, fig. 3

Length, io 20; breadth, 5 10 mm. Color pale or deep olive or gray-green. Less oval and a little more slender than Chceto- pleura apiculata. Dorsal areas well marked, rather fiat and mod- erately keeled. The sides are fiat and sloping and quite evenly covered with small papillae. The girdle partly covers the valves

5 Gr., ischno, slender, chiton, a girdle; Lat., papilla, nippl<

6 Gr., chaites, haired, pleura, side; Lat., apicvlus, dim. of apes

7 Gr., akantho, thorn; Lat., pygmwus, pygmy

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Bulletin 95

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and bears nine small tufts of silvery bristles, evenly spaced, on each side, and a sparse beard of bristle on each end.

This chiton is usually found in shallow water, adhering to dead shells, or crawling in sand near shore line, an unusual habit for a member of this group.

dorsal border

HgameJital area posterior lateral teeth

lunular area cardinal teeth

anterior adductor tear

anterior border

yallwl li

posterior adductor scar

-posterior border pallial sinus

- ventral border

Fig. i. Diagram showing the characteristic features of a pelecypod Class PELECYPODA

The class Pelecypoda (Gr., pelekys, axe; podos, foot) is in- ferior to the Gasteropoda in numbers of genera and species, but in numbers of individuals it surpasses all other divisions of the Mol- lusca. Along parts of the North Atlantic Coast where Mya aren- aria finds congenial circumstances, the littoral area may be almost paved with successive generations of this bivalve mollusc. On the Gulf beach of Sanibel Island, Florida, wind and tide pile up great banks of shells which consist preponderatingly of Noctia ponder- osa, and from time to time incredible numbers of young Chione cancellata are washed ashore. Less frequently living Barnca cos- tata are stranded on the beach by hundreds when some unusual tidal current has undermined a colony of them.

Pelecypoda are without distinct heads and the organs of special sense are not highly developed. The mantle conforms to the shape of the shell. It covers the viscera and contains between its

23 Marine Shells S. W. Fla.: Perry 23

two lobes the gills and mouth parts; its posterior edges are modi- fied to form simple or tubular openings the siphons- through which currents of water are received into and expelled from the animal's body. Those genera which burrow most deeply have the longest siphons, but in almost every instance the siphons may be completely withdrawn into the shell8. Most pelecypods possess a flexible, muscular foot well adapted for digging and limited loco- motion; in many genera there is a special gland in the foot whose viscous, adhesive secretion hardens on contact with water to form a byssus. The byssal threads issue from between the valves of the shell and become attached by their distal ends to some solid sup- port. The byssus usually consists of hue, silken-like threads (Atrina and Mytilus), in some species of the genus Area it re- sembles thin kid-skin, or it may become thick and solidified in other species of this genus. In many of the pelecypods a byssus is present in juvenile but not in the adult stage, and in certain genera a byssus appears during the late embryonic development.

The food supply of pelecypods is the microscopic plant and ani- mal life of the seas. Currents of water pass through the siphons into the mantle cavity to be depleted of their content of nutriment and oxygen ; the waste water, bearing the products of excretion, is expelled in the same manner.

Most pelecypods are unisexual, some are true hermaphrodites, but a number of species have been found to exhibit alternately male and female phases of reproductivitv.

Bivalve molluscs generally bury themselves in sand or mud. Members of some genera bore into wood, concrete, shells "or coral into almost any nonmetallic substance and remain imprisoned in these burrows for the duration of their lives (Teredo, Martes- ia) . A few genera, as Modiolaria, attach themselves to the tissues of other animals, though never as parasites, while others are truly parasitic.

Anomia, Chama, Ostrea and Spo&idylus are attached by one valve. Pecten and Lima, by a rapid dapping of the valves of their shells, expel a jet of water with sufficient propulsive force to drive

8 Small pin fish in an aquarium have been seen by the author to nip off the siphons of T<ii/< In*. Tellina ami Donax as they were projected above the sand bottom into the water. At the first touch the siphons would !»■ with- drawn, when they reappeared the fish would attack again and eventually the exhausted molluscs were exposed and completely devoured.

24 Bulletin 95 24

themselves through the water for considerable distances.

The Pelecypoda have shells of two joined valves which enclose and protect their soft bodies. In some cases the relative size of the mollusc to its shell is disproportionately large as in Barnea and in other instances the valves are rudimentary, and calcareous tubes are secreted about the elongated body, as in Teredo. The two valves of the pelecypod shell are joined together by a hinge and maintained in apposition by strong muscles attached to the inner surface of each valve at opposite points. Like the gastero- pod shell, the shape of the pelecypod shell is that of a modified cone, flattened from side to side and variously distorted in other dimensions. The apex of each valve is the beak or umbo ; the umbos generally point forward with the tips close together and are usually anterior to the hinge ligament. In a few genera, they are directed backward, notably Donax and Nucula.

An equilateral shell has the umbos at or very near the center of the upper margin of the shell (Spisula). An inequilateral shell has the umbos much nearer one end of the shell than to the other (Area). The terms equivalve and inequivalve refer to the relation of the valves to each other in regard to size. The dorsal margin is that which bears the hinge and umbos. The ventral margin is directly opposite the umbos, while the anterior and posterior margins are respectively the front and hinder ends of the shell.

Most authorities measure the length of a bivalve shell by a line from the extreme anterior margin to the extreme posterior margin ; the height or altitude is measured by a line from the umbos to a point immediately opposite on the ventral margin. Thickness or diameter is the greatest dimension between the two sides of the closed valves.

In most pelecypod shells the two valves are held together be- low the beaks by a hinge consisting of interlocking teeth depres- sions in the margin of one valve receiving the teeth from the oppo- site valve. These