MOLLUSKS OF THE TROPICAL EASTERN PACIFIC PARTICULARLY FROM THE SOUTHERN HALF OF THE PANAMIC-PACIFIC FAUNAE PROVINCE (PANAMA TO PERU) Panamic-Pacific Pelecypoda By AXEL A. OLSSON PALEONTOLOGICAL RESEARCH INSTIimTION ITHACA, N. Y. 1961 MOLLUSKS OF THE TROPICAL EASTERN PACIFIC PARTICULARLY FROM THE SOUTHERN HALF OF THE PANAMIC-PACIFIC FAUNAL PROVINCE (PANAMA TO PERU) 4; =g Panamic-Pacific Pelecypoda By AXEL A. OLSSON March 10, 1961 PALEONTOLOGICAL RESEARCH INSTITUTION ITHACA. N. Y. Library of Congress Catalog Number: 61-9722 w Printed in United States of America Norton Printing Company ACKNOWLEDGMENTS Acknowledgment is here extended to the many institutions and fiiends who through their generous aid have contributed so substantially to the completion of this study. The author received three grants from the Amer- ican Philosophical Society, two for field work in Ecuador and Panama (No. lis J, 1952; No. 154 J, 1954) and one for study at the British Museum (Natural History) (No. 124, 1953), with a second visit in 1959. The author is under deep obligations to the authorities of the British Museum (Natural History) and especially to W. J. Rees, formerly in charge of MoUusca, and the late Guy L. Wilkins for permission to examine and photograph many of the types of Pacific Coast mollusks from the Cuming Collection as well as facilities to study the radula slides from the unexcelled Gwatkin Collection. For the 1959 visit, the author wishes to thank I. C. J. Galbraith and S. P. Dance for similar privileges. Here in the United States, the author is under obligations to Harald Rehder and J. P. E. Morrison for their assistance, re- ceived on so many visits to the United States National Museum, as well as to Wendell P. Woodring, of the United States Geological Survey, when questions as to fossil determinations came up for review or discussion. The author wishes to express his appreciation of the assistance received from the authorities of the Academy of Natural Sciences in Philadelphia where this work was first started, particularly to the late H. A. Pilsbry with whom the author was so closely associated for many years and to R. Tucker Abbott, now at the same institution. The author is grateful to L. G. Hertlein for the loan of specimens of rare species of Pacific shells from time to time. On various surveys and trips along the coast of Central America and South America, the author has been accompanied by many geologists and engineers too numerous to mention here. In Costa Rica and Panama, the author was accompanied by R. A. Terry on many arduous trips, mainly for geological investigations but on which collections of both fossil and marine molluscan shells were generally secured. Notably amongst these expeditions in Panama were the ones to the Darien and the Pearl Islands; the Los Santos Province and to the Burica Peninsula, all in 1935. During parts of 1935 and 1936, the author accompanied by O. D. Boggs of the International Petroleum Company travelled along the greater part of the coast of western Colombia and Ecuador between Buenaventura and the Gulf of Guayaquil, and except for stretches of mangrove, the traverse was made largely on foot. This long trek of many months offered opportunities for collecting at many remote locaHties and to assemble data on regional distribution. Smce the beginning of this study of the Pelecypoda in 1953, two major expeditions have been made to Ecuador and Panama, both aided in part by grants from the American Philosophical Society. On the first of these in 1953, the author was accompanied by two famed collectors and students of Recent mollusks, T. G. McGinty of Boughton Beach, Florida, and J. Weber of Miami. Alfred G. Fischer, at that time geologist for the Inter- national Petroleum Company and now at Princeton University, was also a member of this expedition. A second expedition to Ecuador was made in 1955 when the writer was accompanied by the late Ted Dranga and Mrs. A. Dranga. Amongst Panama Canal Zone personnel, the author is especially indebted to the late James Zetek, former Resident Manager of Barro Colorado Island Wildlife Reservation and his assistant, Mrs. A. Gomez, for many courtesies; and among local naturalists and collectors the following: Captain W. S. Bitler, USN, Mr. and Mrs. Lee Beil, Mr. and Mrs. H. John- son, Mr. and Mrs. H. B. Haskell and Mr. Stewart Jadis. Lastly, the author wishes to thank Katherine V. W. Palmer, Director of the Paleontological Research Institution for much help in the past, tracing literature references and under whose editorial guidance this work was published. Myra Keen's comprehensive work on Panamic mollusks appeared after the major part of our study had been completed; hence only occasional reference to it will be found in this memoir. DEPOSITION OF TYPES AND FIGURED SPECIMENS The holotypes of the new species described in this work have been deposited at the Academy of Natural Sciences in Philadelphia, and where additional material is available, the paratypes of the same species will be placed in other museum collections. Unless otherwise indicated, the figured specimens, largely from my own collection, have been deposited at the Paleontological Research Institution at Ithaca, New York. Coral Gables, Florida July 1st, 1958. CONTENTS Acknowledgments 3 Deposition of types and figured specimens 4 Part I. Introduction 7 General statement 7 Historical review 9 Coastal features between Panama and the northwestern part of Peru 16 Faunal provinces 23 The Panamic-Pacific province, its limits and faunal characteristics 24 The Peruvian province, its limits and faunal characteristics 32 The Paita buffer zone with a list of its principal species 37 Bibliography 40 Part II. Panamic-Pacific Pelecypoda General statement 40 Artificial key to principal families of Panamic-Pacific Pelecypoda 43 Glossary of some common terms used in pelecypod descriptions 49 Systematic treatment 52 Order Palaeoconcha 52 Superfamily Solemyacea 52 Family Solemyidae 52 Order Palaeotaxodontida 53 Superfamily Nuculacea 53 Family Nuculidae 53 Family Nuculanidae [[ 58 Family Nucinellidae '...' 71 Order Eutaxodontida 73 Superfamily Arcacea 73 Family Arcidae 73 Family Glycymeridae 103 Limopsidae 109 Order Dysodontida (Anisomyaria) 110 Superfamily Mytilacea 110 Family Mytilidae 110 Family Dreissenidae 139 Family Juliidae (Opistobranchia Sacoglossa) 141 Order Isodontida 143 Superfamily Pteriacea 143 Family Pinnidae 143 Family Pteriidae 145 Family Philobryidae 147 Family Isognomonidae 149 Superfamily Pectinacea 149 Family Spondylidae 150 Family Plicatulidae 153 Family Pectinidae 155 Family Amusiidae 168 Superfamily Limacea 169 Family Limidae 169 Superfamily Ostracea 171 Family Ostreidae 171 Superfamily Anomiacea 175 Family Anomiidae 175 Order Heteredontida 179 Superfamily Astartacea 179 Family Crassatellidae 179 Superfamily Carditacea 184 Family Carditidae 184 Family Condylocardiidae 190 Superfamily Sphaeriacea 191 Family Corbiculidae 191 Superfamily Lucinacea 199 Family Diplodontidae 199 Family Lucinidae 206 Superfamily Chamacea ~ 222 Family Chamidae 222 Superfamily Cyrenoidacea 227 Family Cyrenoididae 227 Superfamily Erycinacea 228 Family Erycinidae 229 Family Kelliidae 231 Family Montacutidae 233 Family Galeommatidae 239 Family Sportellidae 241 Status uncertain 243 Superfamily Cardiacea 243 Family Cardiidae 243 Superfamily Veneracea .257 Family Veneridae 257 Family Petricolidae 314 Family Cooperellidae 318 Family uncertain, Genus Halodakra 319 Superfamily Mactracea 320 Family Mactridae 320 Family Mesodesmatidae 334 Superfamily Tellinacea 336 Family Donacidae 336 Family Sanguinolariidae 347 Family Semelidae 358 Family Tellinidae 375 Order Adapedontida 419 Superfamily Solenacea 419 Family Solenidae 419 Superfamily Myacacea 422 Family Myacidae 422 Family Hiatellidae 425 Family Corbulidae 426 Family Gastrochaenidae 439 Superfamily Pholadacea 441 Family Pholadidae 441 Family Teredinidae 451 Order Anomalodesmacea 452 Superfamily Anatinacea 452 Family Pandoridae 452 Family Thraciidae 457 Family Periplomatidae 460 Superfamily Poromyacea 464 Family Cuspidariidae 464 Family Poromyidae 466 Family Lyonsiidae 467 Family Verticordiidae 469 New genera and subgenera proposed in this work 471 Plates 474-558 PART I. INTRODUCTION 1. GENERAL STATEMENT This work on Panamic mollusks deals with the genera and species of the Pelecypoda known principally from the southern half of the great Panamic-Pacific zoogeographic province or more precisely from the region ex- tending from Costa Rica southward to northern Peru. This large faunal region in its fullest development begins in the Gulf of California in north- western Mexico and extends southward to northern Peru or along a coast- line of more than 4500 nautical miles. In spite of its great length, its molluscan fauna is remarkably uniform throughout and efforts to divide the province into smaller subregions, not strictly ecological in character, have so far failed. It is in the southern half of the province (which includes Panama) where the Panamic fauna attains its most typical development, and where the majority of its species were first discovered and afterwards named. It is also the region so fully explored by Hugh Cuming at the beginning of the 19th century, the great era of oceanic exploration and conchological description. Shell collecting in Panama and Ecuador may be at times rewarding in the large number of species obtainable at a few special localities where optimum conditions of environment exist, and where large tracts of sea bottom become uncovered during periods of abnormally low or minus tides. To the geologist and especially to the invertebrate paleontologist familiar with West Indian, Caribbean, and South American Tertiary fossils, the living mollusks of the Panamic-Pacific region have a special meaning. During the greater part of Tertiary time and more especially in the Miocene and early Pliocene, the tropical West Atlantic and the tropical East Pacific constituted a single zoogeographical province or faunal region (West Tethyan), its species for the most part of Atlantic origin. Channels or sea- ways across parts of northwestern Colombia, Panama, and Costa Rica were then open affording free communication between the Pacific on the one hand and the Caribbean or West Atlantic on the other; hence the Miocene mollusks of the West Indian-Caribbean region are related and in many cases identical with those from rocks of the same age in Ecuador and north- ern Peru. Towards the end of the Pliocene and more fully in the Pleistocene, the isthmian straits were closed by an uplift forming a final land connection between North America and South America. This period of earth disturbance, world-wide in scope, appears to have culminated in the mid-Pleistocene, the time of maximum glaciation in the Northern Hemi- sphere and of a general lowered sea-level elsewhere (see K. K. Landes, 1952). It seems likely that large tracts of the shallower parts of the Carib- bean Sea were then drained, resulting in extinction of many species and forcing others to retreat into the deeper portion of the basin. As compared to its richness in the Miocene, the present-day Caribbean mollusks appear strangely modified and greatly impoverished; on the other hand. 8 AXEL A. OLSSON the Panamic-Pacific molluscan fauna has remained fundamentally unchanged. The living Panamic-Pacific mollusks are, therefore, a part of a larger relict fauna, once more widely distributed, left isolated in the Pacific zone by the isthmian land uplift of Pleistocene times. This aspect of the origin and affinities of our Panamic mollusks was forecast by early paleontological studies but its full significance and bearing on the Recent faunas were not until now so fully understood. In this work the main attention will be focused on the neritic species of the Pelecypoda or those which live along a bottom environment of 100 meters (300 feet) or less. This belt of shallow water has sometimes been called the "littoral zone". This is the zone of strong daytime illumination or of light penetration (the Photo zone) suitable for the growth of green plants on which in the ultimate analyses all life in the sea depends. Today the term "littoral" is generally used in a more restricted sense, or for the small area laid bare by tidal changes (intertidal zone) and to the immediate strand line along which a limited number of marine species live. To the larger region of shallow waters extending from extreme low tide to the edge of the continental shelf, the term "neritic" is employed, a name proposed by Haeckel to complement the expression "oceanic" or the environment of blue waters of the open sea. For the same region of shallow water, Ekman proposed the term "shelf zone". Modern methods of classification and the naming of animal and plant species (taxonomy) commenced with the adoption of the binomial system of nomenclature introduced by Linnaeus, that of the animal kingdom dating from the publication of the 10th edition of Systema Naturae in 1758. Many excellent works on mollusks had appeared before the Systema but lacking in a uniform method of species naming, their interest to the average student is largely historical. After Linnaeus, the second half of the 18th and the first half of the 19th century, witnessed a feverish activity in exploration and in the naming of new species of mollusks from all parts of the world. In this haste of species making, many new names were proposed without adequate description or illustration so that their subsequent identi- fication was both difficult and uncertain. It was fortunate for the science of malacology that interest in shells was sufficiently broad that the prepa- ration of a fine series of well-illustrated monographs or Iconographs was soon begun. Some of these works on conchology, such as that of Chenu's magnificent Conchological Illustrations in four large folio volumes, are the finest colored illustrations of shells ever produced. At the same time, studies on the soft parts of the animal were started, and the importance of the radula in classification discovered. A careful survey of any large family of mollusks will generally show the need for closer generic differentiation and for a revision in classification. Many families of mollusks, as defined at present, are of composite or polyphyletic origin, the genera placed together for convenience or in sharing a few common characters. Such families on close study will be broken apart or divided into smaller categories such as subfamilies which generally means PANAMIC-PACIFIC PELECYPODA 9 the lower taxa must also be divided, and often new ones proposed. This condition has been the case in the Arcidae, Veneridae, and the Olividae. Other large families are more compact, such as the Tellinidae and Conidae, and efforts to divide them even into clearly defined genera have been less successful. The author is strongly opposed to name changing for mere priority reasons or to give undue recognition to works of questionable value, thereby replacing generic names well established by long usage and scientific authority. 2. HISTORICAL REVIEW The collecting of plant specimens, mainly for the purpose of discrimi- nating those with food or medicinal value began shortly after the Spanish Conquest, but the first serious studies projected along modern scientific lines in tropical America was that of the French Mission sent out by the Academie des Sciences in 1735-44 for the purpose of obtaining an exact measure of a degree of the meridian at the equator and from which the size and figure of the earth could be calculated in conjunction with observations of a similar character at other points of the earth's surface. Members of this mission included C. M. de la Condamine, Pierre Bouguer, and Louis Godin as geodesist and Joseph de Jussieu as botanist. No marine shells were obtained by this group. This mission was followed in the opening years of the 19th century by the famous journey of Alexander von Humboldt and Aime Bonpland who travelled through the greater part of northern South America from eastern Venezuela to Peru. No other expedition to South America accomplished so much in the whole realm of science or left as lasting impression of good will in the lands through which these distin- guished visitors journeyed. During the last stages of this remarkable expedi- tion, Humboldt and Bonpland traversed southern Ecuador and reached the upper Amazon or the Maranon at Tompenda situated above the cataracts known as the Ponga de Retema. This was a point of some geographic significance because of an earlier astronomical fix made by Condamine. From this place on the upper Amazon, Humboldt and Bonpland began the ascent of the Peruvian Andes which they crossed in the latitude of Cajamarca and Cotumaza and finally reached the coast at Trujillo from which point they continued on southward to Lima. As the two travellers descended the last slopes of the Andes and approached the coast, they entered into a strange land which became increasingly more arid, the slopes of the mountains beyond the narrow limits of the valley floor devoid of plant growth aside from a few straggling bushes and cacti. This was the travellers' introduction to the great coastal desert of Peru which begins in the north near the Ecuadorian border and extends far southward into middle Chile. Gaining the coast, they noticed that the air held a feeling of coldness, the sky overcast, and the nearby landscape at times obscured by a blanket of mist (garua) which drifted inland from the sea, tainted with a scent of ammonia arising from offshore rocks and islands, whitened with guano. Humboldt speculated deeply on this unusual climatic set-up 10 AXEL A. OLSSON in latitudes so near the equator, quickly sensed its cause, attributed it to the cooling effects of a stream of cold waters swept northward along the Peruvian coast by an oceanic current. As far as known, Humboldt's descrip- tion and accurate diagnoses of the Peruvian current (now sometimes called the Humboldt Current) is the first mention of this important oceanic stream in the literature. Humboldt secured a few shells along the Peruvian coast, others in Mexico, which were described by Valenciennes a few years later. Humboldt's achievements in South America attracted widespread attention in Europe and several other expeditions were shortly organized. The first of these expeditions to South America was one sponsored by the Museum National d'Histoire Naturelle de Paris who selected Alcide d'Orbigny to serve as a travelling naturalist and to explore the southern half of the continent thus complementing in some respects the work accomplished by Humboldt in the north. D'Orbigny at the age of 24, was excep- tionally well qualified for this task, both in the fields of zoology and in geology. He sailed from France, the 31st of July, 1826, and about a month later, landed at Rio de Janeiro at a time of war between Brazil and Argentina. Over the next six years, D'Orbigny travelled through a large part of south- ern Brazil to Argentina, then into Bolivia, Chile, and finally to Peru, often through wild, unexplored, and at times dangerous country. He finally reached Lima and while there met M. Fontaine, a countryman of his and a physician on the French warship, the Griffon then anchored in the road- stead of Calloa. The two close friends roamed the countryside and dredged for mollusks in the harbour. After a stay of about 10 days, D'Orbigny departed for France while Fontaine continued his collecting of both shells and fossils as far north as Paita. The work of D'Orbigny on the natural history of South America is monumental in its scope, the results published in five magnificently il- lustrated volumes ("Voyage dans I'Amerique Meridionale") issued from 1835 to 1847. The volume on the mollusks is a work of 758 pages (quarto) and illustrated by an atlas of 85 (82 colored) plates many of the figures showing the extended animal. This is the largest single work devoted ex- clusively to South American Mollusca, but as far as the marines are concerned, it deals mainly with southern species from Peru, Chile, and the Argentine. The visit of Charles Darwin to South America as naturalist and geologist aboard HMS Beagle commanded by Captain Fitz Roy followed that of D'Orbigny or with a small overlap. The two naturalists did not meet in the field. Although Darwin's work led to important results in the fields of geology and paleontology and in laying the foundation for his later studies in evolution, Darwin paid no particular attention to Recent mollusks, his chief interest in shells was their occurrence in high level terraces and as indicators of uplift along certain parts of the coast of Chile and Peru in relatively Recent times. PANAMIC-PACIFIC PELECYPODA 11 By far, the largest collection of shells ever assembled by one man was that of Mr. Hugh Cuming. The Cuming Collection, although somewhat depleted by sale and by trade, was acquired by the British Museum (Natural History) in 1865 when it was reputed to have contained about 19,000 specimens. Reeve in the preface to volume 20 of the Conchologica Iconica stated that the collection (Cuming) for its richness and com- pleteness then rivaled all other collections of marine shells in the world together. In recent years, most of its type specimens have been segregated, although others may still remain to be identified and picked out of the general systematic collection amongst which they had been distributed. Mr. Hugh Cuming, an Englishman by birth, went to Chile about 1819, and resided in Valparaiso with some interruptions until 1831. He apparently prospered in his business connections so well that he was able to retire early and from then on to devote his time and fortune to the collecting of shells on a large scale. He built a yacht, named the Discoverer, which was fitted out especially for the collecting and dredging of marine specimens. He made his first trip to Juan Fernandez off the coast of Chile, then to Easter Island, and still further afield. On his second voyage which lasted two years, he explored the coast of Peru, then northward to Ecuador, Panama, Costa Rica, Mexica, and finally to Galapagos. Cuming returned to London in 1831 where his interest in shells took on a still larger field, leading to the organization of an expedition to the Philippines. Much adverse criticism^ has been directed against Cuming mainly from envious zoologists who were denied access to his material or on the grounds that his locality labels were faulty and unreliable. This criticism may be partly true, but it should be remembered that Cuming was not a trained naturalist, and it is hardly fair to judge him by modern standards of field collecting. There has been little reluctance on the part of systematists from describing new species without locality records or many to base new species on scarcely recognizable material or without suitable illustration.- The Cuming Collection contained only the choicest specimens avail- able, and its new species were described for the most part by the ablest conchologists of the time. Probably its greatest defect is that specimens were added to it from time to time, as better ones were secured, replacing some of the older ones. Cuming was in residence in Valparaiso at the time of the great earthquake of November, 1822, when his home was destroyed. An account of this quake was read before the Geological Society of London by Captain Fitz Roy of the Beagle who described the great tidal wave which swept in after the earth shocks, causing widespread damage. Ac- cording to a note by Dall, tradition relates that Cuming's interest in col- 1. Gray, the most severe critic of Cuming, although then connected with the British Museum and contemporary of Sowerby and others, did not name directly any of Cuming's shells. 2. Darwin held Cuming in high esteem and often appealed to him for identification or for information on habitat station with respect to shells obtained from elevated terraces along the Chilean coast. Mr. S. P. Dance of the British Museum (Natural History) has through diligent search of museum records and correspondence unearthed much new information on Cuming, his life and accomplishments. 12 AXEL A. OLSSON lecting was then aroused by the quantity of shells and other products of the sea carried ashore by the great wave. We have unfortunately no account of the collecting activities of Cuming during his Pacific voyages or if any records were kept, they have since been destroyed. Most of the new species were described by Broderip, the two Sowerbys, Hanley, Reeve, and Deshayes, the most eminent con- chologists in England at the time and published mainly in the Proceedings of the Zoological Society of London. It is largely from the supplementary remarks accompanying these descriptions that some information on the localities visited by Cuming can be obtained. These locality citations show that Cuming collected extensively and at such places as Tumbez in north- western Peru; and in Ecuador at Isla del Muerte and Puna Island in the Gulf of Guayaquil, at Santa Elena, Xipixapa (Jipijapa [Puerto Callo]), Salango, Isla la Plata, Manta (Montecristi), Bahia (Bahia de Caraques), Atacames. Northward, he continued on to Panama, collecting at the Pearl Islands, and then on to Costa Rica and Mexico. From my own experiences along the coast of Peru and Ecuador, the locality citation for Cuming's shells have proved correct with the possible exception of one or two species, the same forms being common at the places mentioned; a good example is Litharca lithodomus. This species was described from a few specimens collected by Cuming at Montecristi (present-day Manta) and stated as found in holes in stones, pierced by Pholades at low water. The specimens were apparently taken alive as borne out by the appearance of the shells in the British Museum. Litharca is fairly common at Manta, living in deep bores in sandstone ledges between softer shales uncovered at low tide. Elsewhere Litharca is extremely rare and known only from a few drift valves. During the 18th and a considerable part of the early 19th century, the nations of Europe vied with each other in organizing expeditions of oceanic exploration to distant lands, much of it connected with the opening up of new trade routes and the determination of geographic points neces- sary for the tracing of trustworthy, navigational charts. Several such ships fitted out by the French and British, touched at points along the west coast of South America and then continued their journey on across the Pacific and around the world. The accomplishments of the French ships in particular were often of a high order and through their finely illustrated reports, we have the first real account of the geology and natural history of many places. The drawings of Quoy and Gaimard for instance, in color of the living, fully expanded mollusks published in the plates of the "Voy- age of the Astrolabe", are unexcelled and have not often been equalled since. On March 9, 1823, the French ship La Coquille anchored in the Bay of Paita and remained there until March 23d. Messrs. Garnon, Lesson, and Gaudichaud served as naturalists aboard this vessel. During the stay at Paita, excursions were made through various parts of the surrounding country as far as the village of Amotape in the Chira Valley. Notice was taken of the fossiliferous calcareous formation (the tablazo beds capping PANAMIC-PACIFIC PELECYPODA 13 the cliffs behind Paita) which they compared with the Calcaire Grossier of the Paris Basin. Fossils collected by this group were later described by D'Orbigny. The next French ship to visit Paita was the La Bonite which arrived there on July 25th, 1836. On this vessel, Messrs. Eydoux and Souleyet served as zoologists and Chevalier as geologist. Chevalier explored the environs of Paita and gave the first correct description of the geology accompanied by a structural section. He considered the capping tablazo limestones as much younger than the Calcaire Grossier and com- pared it rather with the falaise of Touraine and with Pampean formation of Buenos Aires. After leaving Paita, the La Bonite touched in at Santa Elena in Ecuador and then sailed for the Sandwich Islands. Due to the death of Eydoux at Martinque in 1841 of yellow fever, the description of the La Bonite mollusks has remained unfinished. Roughly of the same date as the La Bonite, is the voyage of HMS Sulphur, an English ship commanded at first by Commander Kellett and afterwards by Captain Sir Edward Belcher, the latter taking a particular interest in the collecting of shells in which he was assisted by Richard B. Hinds, the ship's surgeon. After a visit to Callao and Paita, the Sulphur began a survey of the coast from the Gulf of Guayaquil northward to Panama. Dredging was carried on in the Gulf of Guayaquil with gratifying results ("we on one occasion spent a forenoon in the Bay of Guayaquil in using the dredge, and the results gave upwards of fifty species, and at other times, I have repeatedly enumerated between twenty and thirty species from a single cast"). It is reported that the cabin of Captain Belcher soon became so filled with marine products as to take on the aspects of a museum. The many new species discovered on the voyage of the Sulphur were after- wards described in a special work devoted to the zoology of the voyage, the author of the names given to the mollusks was Hinds. Since the Sulphur dredged in waters of moderate depth and often some distance from shore, many special species were discovered which have remained rare to the present-day. By now, Panama had become known for its many fine shells, and its location as a transhipment point between the Atlantic and Pacific made it a convenient stop-over for travellers, some of wham brought back shells. This was true in particular during the late 40ths and 50ths when traffic across the isthmus was greatly augmented by miners and adventurers enroute to the newly discovered gold fields in California. During this period, several collectors visited Panama, the most important being Colonel Ezekiel Jewett who had served under General Scott in the Mexican wars. Jewett spent ten weeks in Panama in the early part of 1849 or about two years ahead of the visit there of C.B. Adams. Afterwards he collected in California and at Acapulco and Mazatlan. It is reported that Jewett's collection of Panama shells was large but as a result of an almost continuous change of residence along with the transmission of specimens for identifi- cation, the material became mixed and its labels deranged or lost. A list of species from the Jewett Collection was published by Philip Carpenter. 14 AXEL A. OLSSON Later Jewett returned east, became interested in Paleozoic fossils of New York State, of which he amassed an unsurpassed collection and in this way he became associated with James Hall and finally awarded the post of Curator of the State Museum at Albany. The name of C. B. Adams will always remain closely associated with Panamic shells. Adams was a professor of zoology at Amherst College in Massachusetts and in his earlier years had collected extensively in Jamaica, B.W.I. , describing many species of both land and marine moUusks from there. On a leave of absence from teaching, Adams went to Panama, landed at Chagres on November 22, 1850 which at that time was the usual starting point for crossing the isthmus. With two companions, he started upriver by canoe and reached Las Cruces on the 25th. There they secured horses and rode the remaining few miles into Panama City where he secured lodging at the American Hotel. Adams stayed at Panama five weeks, col- lected assiduously, and kept copious notes recording species abundance and habitat station. Adams' account of his stay in Panama and of the collecting conditions met with there then are of high scientific, as well as historical value, and have often been quoted in part as an illustration of the exuber- ance of life which is sometimes developed in tropical waters where abundant food and suitable environment attain their optimum conditions. The material gathered by Adams was shipped to Amherst filling eight large cases and when unpacked and sorted was found to contain 30,920 specimens of 515 species of mollusks of which 157 were afterward described as new, a large part of these new species being small or minute forms over- looked or ignored by the earlier collectors. Adams' Panama paper was pub- lished in 1852 but unfortunately the new species were not figured so that their identification until recently was difficult and uncertain. The Adams Collection was on loan at the Academy of Natural Sciences of Philadelphia for some time where the author had an opportunity to examine it closely. The collection has since been acquired by the Museum of Comparative Zoology at Harvard College, and a paper illustrating its type specimens was published by Ruth Turner in 1955. A large collection of Mexican marine shells was made by Frederick Reigen, a Belgian, while in residence at Mazatlan between 1848 and 1850. This collection was sent to Liverpool and was eventually acquired by P. P. Carpenter. The shells selected by Carpenter, augmented by a large number of small or minute forms picked from the debris washed from" Chama and Spondylus became the subject of a report published as a cata- logue by the British Museum in 1875. More than 600 species of marine mollusks are covered in this work, the descriptions composed in Latin and accompanied in most cases by fairly copious notes. A large number of new species were described, mostly minute forms, and being unaccompanied by figures, the Mazatlan Catalogue has been difficult to use so that in many respects it retarted rather than advanced our knowledge of Pacific Coast shells for a long time. In full justice to Carpenter, no one was better qualified to monograph the Pacific Coast mollusks. Carpenter was already fully PANAMIC-PACIFIC PELECYPODA IS familiar with the Cuming's Collection in the British Museum and the lack of illustration in the Mazatlan Catalogue was partly offset by the duplicate collections which he arranged and deposited in the museums at Washing- ton, D.C., Albany, and Montreal. There is also at Washington, a set of plates of fine, camera-lucida drawings of the majority of the species described in the Mazatlan Catalogue. The main Mazatlan Collection is in the British Museum (Natural History) where it is readily available, the larger specimens are glued on glass plates, the smaller species such as Caecum and the vitrinellids on glass slivers placed in vials. Since many of the minute species were obtained from the pickings of Spondylus, and the like, the specimens are often broken and worn and being stuck down and in some cases deeply embedded in glue, only a single surface is exposed, and a critical study of the shell is difficult. In 1891 and again in 1904-05, the United States Fish Commission steamer Albatross under the direction of Alexander Agassiz, carried on extensive dredging operations along the coasts of Mexico, Panama, Ecuador, Peru, and around the Galapagos Islands. As the Albatross mollusks were taken mostly in deep water they do not embrace many forms proper to the Panamic-Pacific province. The report on the mollusks was prepared by Dall and published as a separate bulletin of the Museum of Compar- ative Zoology at Cambridge, Massachusetts. This report is the first general account we have of the deep-sea mollusks of the eastern Pacific, the Ch-allenger of the British Expedition having entered this region for a brief spell only and taken but a few hauls. Being mainly deepwater species, the Albatross forms do not particularly concern us in this work, but several closely allied species are known as fossil in Panama and Ecuador. At the request of the Peruvian government, R. E. Coker connected with the United States Bureau of Fisheries spent several years in Peru, and reported upon the marine resources of that country, including studies on the nesting habits of the guano birds. Coker assembled large collections of marine invertebrates which were distributed amongst several specialists to work up, Dall reporting on the mollusks. ("Report on a Collection of Shells from Peru, with a Summary of the Littoral Marine Mollusca of the Peru- vian Zoological Province," Proc. U.S. Nat. Museum, vol. 37, No. 1704, 1909) In this important paper, Dall besides describing the Coker material, also complied a checklist of Peruvian marine mollusks, largely from the literature, thus bringing the subject up-to-date. The paper also contains a discussion of the Panamic and Peruvian faunal areas and a bibliography. Between 1929 and 1931, H. N. Lowe, a Californian, collected assiduously along the coast of Mexico, San Salvador, Costa Rica, and Panama. An account of his experiences in the field was published in the Nautilus and in the Proceedings of the Academy of Natural Sciences. The latter paper in collaboration with Pilsbry also contains a section devoted to the description of the many new species secured as well as copious notes on many others. The paper is illustrated with a series of 17 plates. 16 AXEL A. OLSSON In more recent years, much additional collecting of Panamic mollusks has been made under both professional and private auspices. In the former class belong the extensive explorations carried out throughout the eastern Pacific by expeditions sponsored by the New York Zoological Society under the direction of William Beebe and that of the Templeton Crocker Expedi- tion, the combined moUuscan material worked up by L. G. Hertlein and A. M. Strong of the California Academy of Sciences and pubHshed in various issues of Zoologica and in the Bulletin of the American Museum of Natural History. In these papers, the authors have described a large number of new species and extended the range of many others. Their revision of Panamic Pelecypoda is especially important. The hobby of shell collecting and study amongst the Panama Canal Zone personnel has expanded greatly since the war, and the author is extremely indebted to many of the local naturalists who have contributed specimens, extended their hospitality, or guided him on many a trip to the beach. James Zetek, former resident manager of Barro Colorado Wildlife Refuge, has been an ardent collector of both land and marine mollusks for many years, and science is indebted to him for the discovery of many fine species described by Dall, Pilsbry, and others. Walter D. Clark, a former postmaster in the Canal Zone, ranks also as a good collector and through his discoveries contributed many new species described in the main by Maxwell Smith. Captain W. S. Bitler, USN, formerly stationed in the Zone, carried on extensive dredgings in the vicinity of Panama City and around the Pearl Islands and to whom the author is indebted for many specimens of Oliva and Olivella containing the soft parts for radular extraction. 3. COASTAL FEATURES BETWEEN PANAMA AND THE NORTHWESTERN PART OF PERU Panama is naturally the center of the faunal province bearing its name as well as by its historical associations. The extraordinary abundance of marine mollusks at certain places in the vicinity of Panama City was emphasized through the writings of C. B. Adams, and it has often been debated whether shell life is still as abundant there as formerly. There is little doubt that the construction of the canal resulted in great destruction of marine life through its disturbances of the sea bottom, pollution, and other factors, at least locally, but perhaps in some measure mitigated through the creation of other environmental sites favorable to marine growth such as the building of the Amador causeway of rock ballast, amongst which many species live and breed. The entrance to the canal requires almost constant dredging of the ship channel and much mud from this source drifted on the tide has silted in considerable parts of the bay opposite Old Panama, covering its bottom with a layer of black mud leaving only a narrow beach at the upper tide level which can be safely traversed on foot. Beach collecting at Old Panama is usually good and such fragile species as Ha/rvella elegans, Pandora panamensis, and Nucidan-a PANAMIC-PACIFIC PELECYPODA 1? polita, rare at most other localities, are common here, as well as a host of smaller forms, all of which must find congenial living quarters in the slimy- mud outside. For the newcomer to Panama and to most of the shelters in residence in the Canal Zone, the favorite localities for collecting are Palo Seco (near the Leper colony) and Venado Beach. Both places are on the west side of the canal; both offer expansive mud flats, sand bars, rocky- areas exposed at low water. Collecting is always best at night with a strong lantern, as many shy mollusks, which in the daytime lie buried in the mud or hidden under rocks, are then active and appear on the surface. A shelling spree in Panama at midnight at the right season and under proper guidance is an unforgettable experience, well worth the tramp through mud, with sore back, and general exhaustion which is sure to follow the next day. Almost any part of the long coastline of Panama offers good collecting of some sort but places as productive as Venado Beach are few. Perhaps the best locality in Panama outside of Venado Beach is Biicaro at the southern end of the Los Santos Peninsula, but at present difficult of access. MoUuscan records from western Colombia are scanty as much of its coastline has not been well explored, its northern part from Buenaventura to the Panama border not readily accessible by ordinary means of trans- portation, while its southern half is almost one continuous line of mangrove swamps. Our molluscan records for this coast are confined largely to the general vicinity of Tumaco, in Narino in southwestern Colombia. Good collections of shells were obtained on Isla del Gallo, a small island in the mouth of the Rio Patia, and also from the mud flats exposed at Tumaco. To the naturalist, the highly diversified coast of Ecuador offers un- limited opportunities for faunal studies for nearly its whole length. The man- grove swamp environment of southern Colombia continues into north- ern Ecuador, covering the banks of the numerous esteros around Punta Mangle with heavy forest growth and reaching into the lower portions of the Santiago and Cayapas river systems. There are, however, a few open spots near Puerto Limones where some collecting is possible. At Tola, at the mouth of the Cayapas, the coast changes gradually to a sand beach as the land behind it becomes higher. This condition continues on to Rio Verde and then to Esmeraldas with diminishing patches of man- grove so, except for short stretches, travel by car or truck on the beach is feasible at low water. Similar conditions continue past Esmeraldas to Atacames (a Cuming locality) and Galeras, although at times, large scale land slides off the cliffs at Punta Gorda render a continuous traverse along the shore impassable by any means. The Galeras Peninsula must be crossed in the rear by a foot trail, its shore lined with rock cliffs rising sheer from the waters' edge and are passable only with great difficulty. At San Francisco, a small settlement on the south side of the peninsula, mangrove again makes its appearance in force and extends past Mompiche to Coji- menes. Cojimenes is a small village at the mouth of the river of the same name and at present an outlet for bananas shipped by small boats to 18 AXEL A. OLSSON Esmeraldas for export. At this place, car travel in a southerly direction again becomes possible, partly along the beach to Jama and from there inland to Bahia. The road from Jama to Bahia is exceedingly rough and can be travelled only during the dry season. The shore can be followed on foot with some difficulty from Jama southward to Cabo Pasado, past Punta Borracho composed of fossilferous Pliocene beds which are subject in wet weather to much slumping, covering the narrow beach with a thick mass of impassable mud. Cabo Pasados, so named because of its position just below the equator, is a small settlement and port offering some shelter and anchorage for small boats. South of the Cabo, the shore is precipitous and impassable on foot. Bahia de Caraques, the third most important city along the west coast of Ecuador, lies at the head of the poorly defined Bahia de Manta, at the mouth of the Rio Chones and the gateway to a rich agricultural hinder- land. At Bahia, and for a considerable distance to the west, there are alternating stretches of sand beach and shelving flats of soft rock flanked by high cliffs of Tertiary formations. As seen so frequently along the coast of Ecuador, the soft rocks at water level are riddled with the borings of pholads and worms so thick that a fresh sample of the rock cannot be secured, the hammer or pick sinking to the hilt in the soft mass when struck. From Bahia the coastal trend is almost due south to Charapoto near the mouth of the small Rio Puertoviejo and then more westerly on to Jaramijo and Manta. This long stretch of beach is usually passable by car or truck but the trip must be well timed so as to pass the mouth of Rio Puertoviejo at the lowest stage of the tide, there being no bridge. The beach route is sometimes closed by slides near the Bahia end; then the much longer inland road to Montecristi, Puertoviejo, and Rocafuerte must be taken. Manta is the largest city on the coast of Ecuador and, until lately, its most important port. (Esmeraldas, because of the banana trade, now ranks first in Ecuadorian export). At Manta and along the coast east to Jaramijo and west to San Mateo are some of the best collecting grounds met with in Ecuador but subject to great seasonal variation. The environs of Manta are semiarid, since this section of the coast is affected by the cooling influence of winds from the Humboldt Current far out to sea, hence the ravages of the "aguaje" is felt here as strongly as at Santa Elena. At such times, the region is deluged with torrential rains, the waters of the bay become rough and stormy, the waves lashing the shore with destructive effects both to the life in the shallows and to nearby objects on land. At normal times shells are plentiful at Manta, and a large number of species have been recorded from here. Rock borers are plentiful, amongst which is the interesting Litharca lithodomus, first taken here by Cuming. Travel by car from Manta south towards Guayaquil or Jijijapa is over inland roads, first to Montecristi, and then forking towards the various destinations. A collector or naturalist wishing to follow along the coast must do so either on foot or in the saddle. West of San Mateo the PANAMIC-PACIFIC PELECYPODA 19 coast trend becomes more southerly until Cabo San Lorenzo is reached, a commanding headland formed of chert and igneous rocks. In this direction, the land rises, and the shore is lined with high cliffs, some of which are impassable even at lowest tide. The heights behind San Lorenzo are fairly wet or humid, and there are small strips of cultivated lands, and good water in springs or small streams is more plentiful. The more flourishing aspect of the country side is shown by the fresher, greener vegetation, and especially by the large clumps of bamboo, poles of which are cut and carried to Manta and other points for general construction. The shore south of San Lorenzo IS for the most part a rock platform planed off by wave action. At Punta Blanca, about five miles below San Lorenzo, the shore cliffs are formed of beds of Pliocene age full of beautiful fossils, many of which are the same as Recent species. This rocky shore ends at Punta Canoa, replaced by a narrow sand beach awash at high water. Callo, the port of Jipijapa (center of Montecristi Panama Hat industry) sits at the head of a large coastal indentation, widely open to the north- west, protected only by some outlying rocks and a small island. This is the commencement of the next, large coastal bulge known as Salango, the ocean end of a range of rugged mountains known as the Cordillera de Chongon and Colonche. Along the projected extension of this range out to sea in a northwesterly direction is the small Isla la Plata formed for the most part of igneous rocks and chert, its top shows remnants of several, wave-cut terraces or tablazos, covered locally with a thin veneer of Pleisto- cene deposits. The island is the type locality for many species, first collected by Cuming. Shell collecting is difficult as the shore line is preciptious and there is only one landing spot. Strong currents sweep past the island on both sides. Salango, already mentioned, may be reached by a dry-weather road running between Jipijapa to Puerto Lobos and Machililla, or from Manglar- alto if approached from the south. This is an extremely rugged area, the coast indented by many small coves between jagged, rocky points. At the head of some of the coves there are small beaches, usually with habitations. The small villages of Lobos and Machalilla have such location. Salango is also one of Cuming's locality, referred to by the authors of his species. Because of its general remoteness, Salango has not received the study from naturalists that it deserves. South of Salango, the trend of the coast becomes southeasterly form- ing the northern arm of the large, open bay of Santa Elena. In this stretch are the villages of Manglaralto and San Pedro, the region still semihumid, with a fine fringe of cocoanut trees along the beach and small stands of mangrove, the last such met with on the west coast of Ecuador. Passing Punta Ayanque, the climate undergoes a marked change and becomes semi- arid, increasingly more southward to Santa Elena. Shortly below Puerto Palmar, the outlet for Colonche, the coast swings outward towards the southwest and opens into the more sheltered part of the bay of Santa Elena. 20 AXEL A. OLSSON Distributed along this section of the Santa Elena Peninsula are the small villages of La Libertad, San Antonio, and Salinas, which become resort towns for the Ecuadorians during the rainy season in the interior. The small town of Santa Elena, lies inland a few miles from the shore. The Santa Elena Peninsula is the type locality for many of the species taken by Cuming and by other visiting naturalists; most of these records probably refer to the small stretch of coast between La Libertad and La Puntilla. Collecting along the beach at Santa Elena is unpredictable. At times the shore is smothered under a blanket of shells, at other times quite bare. At San Antonio and other places, fishermen setting nets for langosta (crayfish) often bring in a load of Murex and other large gastropods; the crayfish is reserved for sale in Guayaquil, the moUusks consumed by the local population. Excellent beach drift has been obtained along the north side of the peninsula, rich in small species. The rocky coves around La Puntilla (now a military reservation) and at the nearby Punta Camera on the south side of the peninsula are good collecting spots at all times. The extreme western point of the Santa Elena Peninsula is known as La Puntilla, a long, narrow neck composed of hard cherty and igneous rocks and cut into by several levels of tablazo. Passing this point, the south shore of the peninsula is deflected sharply towards the southwest to form the northern shoreline of the Gulf of Guayaquil for more than 60 miles. This is an open coast pounded by strong surf and except for a short stretch of rocky cliffs at the west (Punta Ancon and P. Camera), it is mainly a soft sandy beach flanked behind by cliffs of Tertiary and tablazo beds, the seaward margin of a large plain which extends far inland. At the eastern end of this long stretch of monotonous coast, are the small resort villages of Playas and Posorja; across the Estero de Morro is the large well-wooded island of Puna, situated in the entrance to the Guayas River and a pilot station for steamers ascending the river to Guayaquil. The banks of the Guayas River and the numerous esteros connected with it are lined with a magnificent stand of tall mangrove trees, the same growth continuing on southward along the Jambeli channel and the coast of Rio de Oro almost to the Peruvian border. Anadara grandis and A. tubercidosa, found here in great abundance, are sold in the market places in Guayaquil, and the large piles of their shells seen everywhere on shore testify to the im- portance which these mollusks must play in the food economy of the native population. Outside in the open sea of the Gulf of Guayaquil is the small, rocky island of Santa Clara or "El Muerte" frequently mentioned in mollus- can and natural history reports. Beyond the Jameli Channel the coast trend turns sharply to the southwest and continues in this direction past the Peruvian border near Tumbez to Cabo Blanco, forming the much longer southern limb of the Gulf of Guayaquil. This is also the north end of the great coastal desert of Peru which becomes increasingly more arid towards the south. At the Peruvian-Ecuadorian border, the climate is still sufficiently wet to support a fairly good growth of small trees and bushes nourished by yearly rains PANAMIC-PACIFIG PELECYPODA 21 while the Tumbez Rivier, rising far back in the Andes, is a permanent, fast flowing stream. In the lower reaches of the Tumbez River, where its waters are rendered brackish by the tide, its banks are lined with a sub- stantial growth of mangrove. This is the most southerly occurrence of this plant along the west coast of South America at this time. In the Pleistocene, the climate or northwestern Peru was at times more humid than at present, with mangrove extending at least two degrees or about 120 nautical miles further south as shown by the occurrence of its fossil leaves in clay beds near Talara and by specimens of Anadara grandis and A. tuberculosa at Sechura, and near Lagunitas; these mollusks as shown above occur in abundance only where mangrove conditions exist. During the climatic dis- turbances known as the invasion of "The El Nino" or the Aguaje, mangrove seedlings from the inner reaches of the Gulf of Guayaquil drift southward on the current. They become stranded in lagoonal areas along the coast, take root, and are established for a short time. Botanists have shown that the maintainence of successful growth of mangrove is dependent upon a mini- mum amount of annual rainfall even though other ecological factors are favorable. At the mouth of the Tumbez River (Puerto Pizarro), the shore is formed by a sandy beach grading into mud flats and good collecting is generally obtained there. Tumbez is the type locality for many fine species obtained by Cuming. Good collecting is also generally available at Zorritos, especially if dredging can be done. Further west and south along the coast are numerous collecting spots mentioned as locality records in Part II of this work under the names: Punta Picos; Boca Pan; Caleto Mero; Caleto Sal; Mancora; Pena Negra; and Cabo Verde. The location of these places is shown on the Tumbez and Piura sheets of the American Geographical Society 1: 1,000,000 map of South America. This section of the Peruvian coast is readily accessible, being followed by the Pan-American Highway. Cabo Blanco at the southwest end of the Gulf of Guayaquil is the most northerly member of a series of three large, bulging headlands which so well characterize this part of the northwest coast of Peru, The Cabo itself is a low ridge of sandstone but immediately behind it the land climbs rapidly to El Alto (an oil camp) situated on a high terrace plain (Talara and Mancora tablazo), a full thousand feet above the sea. Cabo Blanco is a famous fishing camp for marlin and other sport fish in the waters offshore. Passing southward of Cabo Blanco and its near neigh- bor Restin, the shore has a nearly due south trend and is formed mainly by a sand beach as far as Punta Nautilus, a small patch of sandstone rocks famous for its fossil nautiloids found there in abundance, A short distance further south is the oil town of Lobitos, lying in a small bay protected from the south by Punta Capullana. Punta Capullana is also the north boundary of the La Brea-Parinas estate of the International Petroleum Company, the largest oil producing property in coastal Peru. After crossing the wide, sandy stretch of the lower Parinas Valley with its green Algarroba (Honey Mesquite) trees scattered along its dried-up stream channel, there is 22 AXEL A. OLSSON a stretch of sandy and rocky coast and then comes the small covelike harbor of Talara. Much changed from pioneer days, Talara today is an important, modern city with its refinery, shops and fine homes of the oil workers in this part of Peru. About five miles south of Talara is the town of Negritos, now less important than in former times, overlooking the sea with nearby Punta Parinas and Punta Balcones, the most westerly points of all South America. Continuing southward past Punta Parinas with its light beacon perched on its shoulder and the nearby Punta Balcones, another long stretch of open sand beach is encountered which trends to the southeast past Portochuelo and the mouth of the Chira River, and thence to Colon. The coast then curves towards the west to form the next large bay "the Bay of Paita", widely open to the north but affording safe anchorage opposite its southern shore. The old city of Paita, founded in early colonial days, sits in a small gap at the base of high cliffs at the junction point of two con- trasting rock formations. To the east of the city, there are high cliffs of the Chira shales capped by heavy beds of tablazo sands and coquina limestones; to the west by much older slates and schists, both rock formations, in spite of their great differences in hardness are planed off more or less evenly by a marine sea-transgression and overlain by a variable thickness of Pleistocene deposits of the Mancora tablazo forming a plain of wide extent. At this place the tablazo plain is elevated about 200 feet above the sea. Collecting along the shore at Paita is generally poor, but Paita is the type locality of many species, for the most part, dredged in the bay outside. The middle bulge in the coast of northwestern Peru is that of the Paita Peninsula bounded on the north by the Bay of Paita and on the south by the deep Bay of Sechura. The peninsula is a broad, irregu- larly shaped area, its basement formed of ancient slates, schist, seamed with quartz veins and intruded by large masses of granodiorite. Near the middle of this area rise the Paita Mountains, a group of small, barren peaks which attain an elevation of about 400 meters above sea level. Elsewhere, the general surface of the pninsula is a flat plain or tablazo, barren for the most part of any vegetation. Along the west side of the peninsula, there are seg- ments of Tertiary rocks infaulted between the slates and where these softer beds come to the shore, they have been eroded into deep, picturesque coves and small bays between the much harder slates which jut seaward in jagged, rocky points. In this section is located the small village of Yasila, easily accessible from Paita. Yasila is a good locality for Eocene fossils, and at times may offer collecting possibilities for marine shells. The south side of the peninsula is rugged, the shore lined with high cliffs of Cretaceous rocks overlain by a massive bed of tablazo limestone. This is a good locality for Cretaceous fossils. Nearby is the small fishing settlement of Tortuga. PANAMIC-PACIFIC PELECYPODA 23 South of the Paita Peninsula and between it and the third major headland of the coast, that of the Illescas Peninsula, is the large open Bay of Sechura. Like its much smaller neighbor to the north (Bay of Paita), the outline of its shore is shaped like that of a large fish hook, its sharp, barbed end at Punta Aguja pointing northwest, its long shank forming the seaward margin of the great Sechura desert stretching far inland. At both its northern and southern ends, the shores of Sechura Bay are rocky lined with high, steep cliffs; in between the long stretch of the inner bay is an open sandy beach. Bayovar at the south end, is a small, abandoned settlement, at one time the port and terminus of a small railway to some sulphur deposits at Revantazon at the southeast end of the Illescas Mountains. West of Bayovar towards Punta Aguja, the shore is rugged, formed for the most part of schist and other metamorphic rocks. The beach at Bayovar is generally strewn with shells, many species of which attain a larger size here than they do in the north. This condition is well illustrated by Mexicardia frocera which often has a height of 100 mm. or more. The beach is also covered with the dead valves of Anomia peru- viana, large banks of which must lie off shore. Aequipecten purpuratus is as large here as so commonly seen south of Lima. During the severe aguaje of 1925, the shore at Salinas was swept by strong waves and large quantities of marine life of all sorts cast upon the beach. Many seabirds, deprived of their normal source of food, died in large numbers or wandered around on shore in a starved condition. 4. FAUNAL PROVINCES Using the mollusks as a basis. Woodward, a century ago, arranged the coastal or shallow-water faunas of the eastern Pacific into five main geo- graphic provinces, his data for the most part being the list of species com- piled by D'Orbigny. Dall in 1910, followed Woodward's classification with only a few, minor changes. In 1936, Schenck and Keen suggested some modifications of the same system for the west coast of the United States, and placed the main boundaries at somewhat different points. They further indicated that the faunal provinces were not so sharply limited as first believed but were separated by wide belts of overlap or transition in which the species were more or less mixed. It will be seen later that an overlap or transitional zone separates the tropical Panamic-Pacific fauna from that of the cooler water Peruvian fauna along the northwest coast of Peru. Detailed studies along the Pacific coast of Central America and South America may perhaps show the need for other modifications or for the recognition of sub- regions, as for instance around the Galapagos Islands. From the north southward, the main faunal or zoogeographic provinces U AXEL A. OLSSON generally recognized along the Pacific Coast of North America, Central America, and South America are as follows: 1. The Aleutian or Oregonian Province Extends from the limit of floating ice in Bering Sea south to Point Concepcion in California. 2. The Californian Province From Point Concepcion south to Cape San Lucas at the southern end of the peninsula of Lower California. 3. The Panamic Province (the Panamic-Pacific) From the head of the Gulf of California (about lat 30° 30' N.) south to Cabo Blanco in northwestern Peru (lat 4° 15' S.) A tropi- cal zone with average surface temperatures between 80 and 85 degrees Fahrenheit except where modified by upwellings of cooler waters. 4. The Peruvian Province From Punta Aguja at the southwestern end of Sechura Bay in northwestern Peru (lat 5° 40' S.) south to near Chiloe Island, Chile (near lat 42° S.). Temperature of the surface waters con- trolled by the Humboldt Current and extensive submarine up- wellings. Temperature range between 58 to 65 degrees Fahrenheit. 5. The Magellanic or Patagonian Province From Chiloe southward to Cape Horn and thence northward along the coast of Argentina. The geographic points selected as marking the boundaries between the main faunal provinces are certain prominent capes or headlands where the coast generally shows a marked change of trend. It is usually in the vicinity of such headlands that major shifts in oceanic circulation frequently occur, resulting in marked differences in the temperature of the surface waters on either side. Usually, the change from one faunal zone to another is gradual, producing a transitional or overlap zone with a mixed assemblage of species spread over a belt of many miles. a. THE PANAMIC-PACIFIC PROVINCE ITS LIMITS AND FAUNAL CHARACTERISTICS Largest in areal extent, the middle Province or the Panamic is also the richest and most diversified in its faunal makeup. As the Republic of Panama, from which the name "Panamic" is derived, borders on both the Atlantic (Caribbean) and the Pacific, the term "Panamic-Pacific" more clearly denotes the Pacific side and will be used in this work in place of the single term "Panamic". PANAMIC-PACIFIC PELECYPODA 25 The northern hmits of the Panamic-Pacific faunal region can be drawn closely since it lies at the head of the Gulf of California at approximately lat 30° 30' N. and about long 114° W. From this point, the province extends in a southeasterly direction, its waters bathing the coast of Mexico, Guate- mala, Nicaragua, Costa Rica, Panama, western Colombia, Ecuador, and northwestern Peru, or for a distance of about 4500 statute miles. It may also be somewhat expanded so as to include the waters around such off- shore islands as Tres Marias, Cocos, and the island archipelago of the Galapagos. At the south, its limits cannot be fixed so closely and opinion has varied as to its location. For geographic reasons, the south boundary seems best placed at Cabo Blanco at the lower end of the Gulf of Guaya- quil and the most westerly point of the South American continent. For the same reason, the north border of the Peruvian Province is placed at Punta Aguja (Dall location) at the southwest end of the Bay of Sechura, thus leav- ing between the two faunal regions a transitional zone about 120 nautical miles wide, here called the "Paita Buffer Zone" after the city and Bay of Paita situated near its middle point. The Panamic-Pacific faunal region is essentially a tropical one as would be expected from its geographic location, but at many places strong up- wellings occur which materially lower the temperature of the surface waters. Such belts of relatively cooler waters are met with frequently in the Gulf of Panama and off certain sections of Costa Rica. They periodically appear along the coast of Ecuador and when severe or of long duration may bring to those sections of the coastal lands a climatic upset similar to that of the Humboldt Current much further south in Peru. In Ecuador, as in Peru, the winds blowing steadily from the sea onto a more highly heated land, become dry and desiccating, and produce belts of aridity along the coast, in some cases nearly as barren and desert as in Peru (Santa Elena, Isla la Plata, Manta). Where the coast trend offers shelter from the sea winds, the climate is more humid and wet, the hills are clothed with vegetation, and the shore itself lined with mangrove (the inner section of the Gulf of Guayaquil. Manglaralto, Salango). Although the waters of the Panamic-Pacific Province are somewhat cooler than would normally be expected in these latitudes, its fauna is essentially a tropical one but much less so than that of the Indo-Pacific, as shown by the general absence of reef corals and in the mollusks by the fewer species of Conus, Cypraea, and others. It is probably due to this factor that so few Indo-Pacific species have been able to establish themselves along the mainland coast although many such species have been able to do so on some of the off shore islands as reported by Hertlein. In spite of its great length, the fauna of the Panamic-Pacific Province is remarkably uniform throughout with many of its most common species ranging from the Gulf of California southward to Peru. This fact is partic- ularly well illustrated by the Pelecypoda as shown by the tabulation on page 26. These percentages are based upon existing data and can be expected to change as the range of some species becomes better known. AXEL A. OLSSON Percentage of known species ranging from Gulf of California to Ecuador or to Peru Family Arcidae » Percentage 73 Glycymeridae „ ^^ Mytilidae ....^ - - 58 Pinnidae - .„ 33 Pter ii d ae _ Diplodontidae Lucinidae „. .» „ ^....^....^. 75 ..„ 37 .45 Chamidae .. ..~ - .. .>... „. 57 Card iid ae — Veneridae » -.. 55 53 Petricolidae Mactridae ^...12 .„ 50 Tellinidae 44 ......50 Corbulidae „ My acid ae ».. .~ . .. .- -....~.. 50 75 Pandoridae — Thraciidae - - _ Periplomatidae „ Pholadidae 42 ..„ ....25 ....„....--.-13 ..„58 Exclusive of the cephalopods, nudibranchs, sea hares and the pteropods, the remaining groups of Panamic-Pacific mollusks have been conservatively estimated at about 2200 species. This estimate compiled some time ago is as follows: Gastropoda -....„ „ 1662 species Pelecypoda „ 496 species Scaphopoda — 14 species Amphineura ....„ _ 27 species Total 2199 species Gastropoda As would be expected, this class of the Mollusca contains the largest number of species, about three times all others combined. The number esti- mated above will no doubt be increased when such large families as the Turridae, Columbellidae, Caecidae, and Pyramidellidae are fully known. Other families may be reduced in the number of valid species attributed to them after revisional studies are made. The gastropods include some of the finest and most interesting of Panamic mollusks. The Cancellariidae are well represented (about 33 species) with such fine species as C. (Pyruclia) solida, probably the largest PANAMIC-PACIFIC PELECYPODA 27 species of the genus attaining a length of nearly three inches; the group of C. (Euclia) cassidijormis, also of large size; and the small C. (Aphera) tessellata, these three species have closely related forms amongst the Carib- bean Miocene fossils. Other interesting and striking cancellarids are: C. (Ovilia) cumingiana-, C. (Narona) clavatida and the mitralike C. (Hert- leinia) mitrijormis. Of special interest is the rare C. (Perplicaria) clarki described by Maxwell Smith from Venado Beach, in the Canal Zone, the only other known species in the subgenus is C. perplexa from the Caloosa- hatchee Pliocene of Florida. Species of the Terebridae (about 35 species) are plentiful throughout the province, some species have a great range, others are more restricted; two of the largest species, T. robusta and T. strigata, are common on mud flats. T. luctuosa, related to T. cinerea of the Caribbean, is plentiful on sandy beaches; of a similar habitat is T. acicidata, common in Peru. The family Olividae (with about 28 species) contains a large number of interesting forms distributed amongst three main genera. The largest and finest species of the family is the Oliva porphyria (the Pan- ama Tent Olive), quite localized in its distribution but ranging from the Gulf of California to Panama and the Galapagos Islands. Another large Olive is Oliva incrassata (angulata) found on sand bars exposed at low tide; this species has closely related forms in the Caribbean Miocene. Oliva spicata (0. polpasta and several other names) is the commonest species at most localities. Abundant at many places in Panama and Ecuador is the small Oliva undatella, usually with a varied color pattern, and because of its size, often referred to Olivella but with the shell and radular characters of Oliva. Agaronia with two or more closely similar species is often seen along beaches at low tide feeding on the smaller Olivellas. Olivella has many species, many of which are local. Olivella (Lamprodoma) volutella is especi- ally common in Panama on slimy mud flats and exhibits a wide range of coloration from pure white to nearly black. Olivella {Pachy oliva) columel- laris and 0. semistriata are typically open beach species and may occur in countless numbers at favorable localities. The Conidae are represented by about 33 species. Conus fergusoni and C. patricius are the largest forms, each often reaching a length of four inches or more; both species have fossil rela- tives in the Caribbean region. C. purpurascens is the commonest of all Pan- amic cones and has the widest range, extending into northwestern Peru: in the Caribbean, this species is represented by the similar C. ranunculus. C. dalli is a relatively rare species, the only member of the C. textilis group and probably a recent arrival from the Indo-Pacific region; it has no fossil rela- tives in the American Tertiary. The turrids, because of their large number, are the poorest known of all Panamic gastropods, and new species can be expected in any dredge haul taken at new localities. The genus Polystira is represented by two species, P. picta and P. oxytropis, both fairly common from dredgings in waters of a few fathoms depth; both species have allied forms as fossil in the Pacific and Caribbean zone. Characteristic of the Panamic fauna are the dark-colored species of Crassipira found abundantly 28 AXEL A. OLSSON under rocks at low tide, A large variety of turrids can generally be found along Amador and Farfan Beach where they have been washed out of the mud dredged from the ship channel and pumped onto the neighboring shore. The Nassariidae is a large family with an indefinite number of species (present estimate about 51); they include N. myristicata, N. luteostonna, and N. pagoda, all common at Panama. Amongst the buccinids, there is the curious Northia northiae which at night can often be seen plowing its solitary way just below the surface with only the tip of its siphon showing. It has related forms in the Caribbean Miocene, Phos or its allied genera are repre- sented by several fine species; the largest is Cymatophos panamensis (clarki), first described as fossil, later found in the Recent fauna. The Mitridae are well represented and include some of the most sought for species (about 20); they include the magnificent M. belcheri, often dredged off the Pearl Islands and which has lately shown up in the Gulf of California; in Peru, M. swainsoni is often cast up on the beach; it has a nearly smooth surface and a dark- colored periostracum. The commonest of the shore Mitras are M. lens and M. tristis, both found under rocks at low tide. Amongst the Muricidae (about 75 species in its widest meaning) are several showy species, often common at favorable localities, Murex elensis, Muricanthus radix, and M. nigritus, Hexaplex brassica and H. regius are often taken in large numbers by the fishermen at Santa Elena, Ecuador, the conchs entangled in the nets set out for crayfish (langosta). The Cypraeidae contain relatively few species and most of these are small; the largest, C. cervinetta is perhaps best considered as only a sub-species of the Caribbean C. zebra {exanthema). Characteristic amongst CypraeaAWie shells are Trivia radians and Jenneria pustulata, both found under rocks. Amongst the Cymatiidae are two species of Distorsio (decussatus and constrictus) with similar forms in the Caribbean, the large Cymatium tigrinum, formerly common in Panama, and several Bursa. With the exception of the Scotch bonnet, the Semicassis centiquadrata, the other members of the family Cassididae are relatively uncommon. Special mention should be made of Malea ringens, one of the most characteristic of present- day Panamic gastropoda, but represented in the Caribbean Miocene by hardly distinguishable forms. This species extends south to the Lobos Islands in Peruvian waters where it grows to a large size. Along the Ecuadorian coast, M. ringens is relatively rare, replaced by the smaller, heavier shelled M. crassilabris Val., which the author regards as a good species. Pelecypoda The pelecypods are probably the best known of Panamic-Pacific mollusks, and in addition to this study, the class has been revised by Hert- lein and Strong in a series of excellent papers published in Zoologica be- tween 1940 and 1950. Two other important papers have also appeared, one PANAMIC-PACIFIC PELECYPODA 29 on the Mytilidae by Tron Soot-Ryen and the other on the Arcidae by Helen Rest, both papers reporting on collections of the Allan Hancock Pacific Expeditions. Several families of the bivalves, such as the Arcidae (31 species), Mytihdae (25 species), Veneridae (62 species), Tellinidae (54 species), and Donacidae (36 species) have more species than they do in the Western Atlantic. As this class of the MoUusca will be treated at some length in the systematic section of this work, only a few of the more striking features of Panamic bivalves will be noted here. Many species could be cited as being characteristic of the Panamic-Pacific fauna as known today, but as in the case of the gastropods, the larger number of these forms have identical or closely related species in the Tertiary faunas of the Caribbean and West Indian region. The Nuculacea of the Panamic region, as elsewhere, comprise a large number of small forms of no particular interest with the exception of the following: the genus Adrana with its peculiar, flattened, bladelike shell (some of which attain large size) are particularly characteristic of the Panamic fauna, and several species appear in numbers on certain favorable, sandy beaches; Nuculana {Politoleda) polita, notable for its large size and curious surface markings, is always common on the beach at Old Panama. Among the true taxodont moUusks, the Panamic Arcidae deserves notice; its species are numerous and occupy a wide variety of ecological stations. Amongst the true arks. Area pacijica and A. mutabilis, are relatively less common than their twin forms in the Caribbean fauna. The most important of all Panamic bivalves in the food economy of the region are the two Anadaras, A. tuberculosa and A. grandis. Both species are intimately associ- ated with a mangrove mud environment. A. tuberculosa, and its near ally A. similis, live buried in the mud amongst the mangrove roots; A. grandis in the nearby esteros or mud banks just outside. The range of A. grandis and A. tuberculosa is, therefore, coextensive with that of the mangrove itself (Rliizophora mangle). The most interesting of all Panamic arks is Litharca lithodomus, a true rock borer, in which the shell has become greatly lengthened or pholad in shape. The anterior side is much the longer, wedge-shaped at the end while the posterior side towards the open end of the bore is short. This ark drills circular holes in hard layers of sandstone, often six inches or more deep. This curious species is a member of the true Arcinae. Although discovered by Cuming nearly 150 years ago, it long remained one of the rarest and least known of Panamic mollusks. Restricted to the Pacific Coast today, is the unsymmetrical Noetia reversa but with almost identical forms in the Miocene of the Caribbean region. Another Noetia is N. olssoni which is closely allied to A^. centrota of the Caribbean. As an additional illustration of the close alliance of the present-day Pacific molluscan fauna with that of the Miocene Caribbean mention may be made of the rare Sheldonella delgada of which the only other known species is S. maoica, common in the Miocene of Santo Domingo. As in most tropical faunas, the Pectens are comparatively few in number. Of these, the only 30 AXEL A. OLSSON common one is Aequipecten circularis which shows a wide range of colora- tion. A. purpuratus, so common in Peruvian waters, has been recorded on good authority from Panama and elsewhere but is rare, and its distribution irregular. Pecten vogdesi, although first described under the name P. denta- tus, presumably from Santa Elena, Ecuador, appears to be largely restricted to the Gulf of California. Like the Pectens, the oysters are relatively unim- portant in the faunal makeup, although some interesting species are repre- sented. Amongst them is Ostrea iridescens, a purely marine form which sometimes grows to a large size. It is much sought for by the natives, but its flavor is strong, probably due to a high iodine content. Another purely marine species is the Ostrea jischeri, a pycnodonta, with a peculiar, porous, or honey-combed texture, relatively rare but widely distributed through the whole faunal province. The smaller 0. columbiensis is often seen in the markets of Ecuador. The most interesting of the Anomiidae is the large Placuanomia cumingii, similar to the P. plicata of the Miocene of the Carolinas. As presently interpreted, Spondylus appears to have three species in the Panamic fauna but the distinctions between them are ill-defined due to incomplete data and the great variability of its characters due to fixa- tion. In contrast with the Caribbean fauna, the Lucinidae are poorly repre- sented in the Pacific zone either in the Recent or fossil state. Codakia has two fine species but both rare. C. distinquenda attains a much larger size than any species of the genus is the Caribbean. Of unusual interest is D. punctata, an Indo-Pacific species recorded from the Pearl Islands and from the Galapagos. There are two species of Afwdontia, but they are rare and have been seldom collected. Amongst the Crassatellidae and Carditidae are several fine species which give color and character to the Panamic fauna. Eucrassatella gibbosa, with its coarse, heavy shell, is common at some localities. Cardita tricolor is the commonest member of its family and shows a wide range of coloration. Conspicuous because of their large size are the relatively rare C. cuvieri and C. megastrophia. There are two species of Carditamera. C. radiata, largely restricted to Panama, is a form closely related to C. arata of the East Coast or Atlantic Miocene. As in most warm water or tropical faunas, the Tellinidae are represented by a large number of species, and other new ones will no doubt be discovered with further exploration. Some of these tellinids are brightly colored, as for instance, those belonging to the genus Tellinidella. Conspicuous in the fauna are the several species of Fhrimetis and especially the numerous forms of Eurytellina. Of special interest is Psammothalia cognata, a species fairly common in Panama and extending to Peru, nevertheless, it has remained rare in most collections; a few years ago, specimens were obtained in dredgings off the gulf coast of Spanish Honduras which appeared to be identical with typical P. cognata from the Pacific Ocean. To the Donacidae belong some of the finest species of the family; Iphigema altior, found in more or less brackish- water situations, is closely allied to the West Atlantic /. brasUiana; several species of Donax, common on sandy beaches such as D. asper, D. peruviana, and D. panamensis, are current items of food amongst the native population; PANAMIC-PACIFIC PELECYPODA 31 Indian graves or huacos in coastal Peru are thickly covered or literally snowed under a blanket of whitened shells of D. peruviatia. The Veneridae, with about 62 species, ranks as the largest family of Panamic bivalves, and such species that are sufficiently abundant, are much sought for as food along the entire coast. Perhaps the largest and finest species in the family is Periglypta muLticostata, and in a few places, as in the Pearl Islands, it is sufficiently common to be gathered for food. Another large clam, but rare at most localities, is Ventricolaria isocardia, similar to V. rigida of Florida. Tivela hians is plentiful in northwestern Peru on sandy beaches and is gathered in large numbers by the natives. It is often commensal with a small sea anenome. The genus Hysteroconcha, with but one species in the Caribbean, has four in the Pacific zone, the largest and commonest is H. lupanaria with long spines and usually purplish coloration, while in H. brevispinosa, the spines are short, often reduced to mere stumps, and the color is white. Amongst the Chiones, C. compta, a. large, thick-shelled species, like an overgrown C. cancellata, is most common in the south. In the allied genus Chionopsis are several fine species such as C. amathusia, C. gfiidia, C. jamaniana, and C. ornatissima with highly intricate surface sculpture. Other equally characteristic Panamic venerids are Notochione cokcmbiensis, a thick-walled shell with coarse ribbing and variable color markings and the Nioche asperrima with a fine cancellate sculpture like that seen on some Codakias. Protothaca grata, showing an endless variation in coloration, is collected in quantities from gravel bars exposed at low water along the coast of Ecuador. Dosinia ponderosa, the largest species of the genus and a hangover from the Miocene, is common at many places and ranges throughout the whole province and southward into the Peruvian. The Mactridae have several fine species; HarveUa elegans and Tumbezi- concha trachoides have thin fragile valves marked with strong, concentric or oblique undulations, and appear to range through the entire province wherever suitable conditions of environment occur. Another thin-shelled, fragile species is the Raeta undidata, common along the coast of north- western Peru and ranging far southward into the Peruvian Province; else- wihere the species is rather rare but extends northward to the Gulf of California. Mactrellona alata and M. exoleta, together with M. clisea, are met with along sandy beaches, the two former species also living in the Caribbean region. The Micromactras form a group of several species, often difficult to separate properly from each other. Rock boring mollusks such as the Lithophagas and the Pholadidae are especially common along certain parts of the coast of Ecuador, and in some stretches where the shore is formed of soft rock formations, they thereby contribute substantially to shore line erosion. Amongst the Corbulidae, may be mentioned the large Panmmcorbula inflata with subequal, convex valves, and a hinge showing vestigial lateral teeth; it is found principally in muddy, brackish- water situations. Other interesting species of the family are Caryocorbula ovulata, C. ameystina, Tenuicorbtda tenuis, and the curious Serracorbula tumaca with serrated margins. 32 AXEL A. OLSSON Scapho'poda Of the classes of the Panamic Mollusca, the scaphopods with about 14 species are the least known (Dentalium, 11 species and Cadtdus, 3 species). As noted by Pilsbry and Sharp (1897), the shallow-water Scapho- poda of the eastern Pacific are closely related to forms from the Antillean Tertiary and Recent faunas, whereas, the offshore, deep-water species belong mainly to what seems to be endemic West American, and have no allies in Antillean or Oriental seas. Characteristic of the West Coast species are Dentaliums of the subgenus Tesseracme, unknown by any living species in the present-day West Atlantic. They were well represented there during the Miocene and Pliocene periods. A Dentalium related to D. pretiosum (Antalis group) is encountered in beach drift along the Santa Elena Peninsula in Ecuador, Only two scaphopods are known so far from north- western Peru, namely D. (Graptacme) splendidwn and Cadulus (Gadilia) perpusillus; both species are also found in Ecuador. Amphineura The chiton fauna of the Panamic-Pacific Province seems relatively small in the number of species, probably because of incomplete explora- tion. The common large chiton along the surf line in Panama and Ecuador is C. stokesi, gathered by the natives for food and bait. Other shore species in Panama are Chaetopleura lurida, Ischnochiton adamsi, and the lovely Tonicia crenidata. Acanthochites hirundinijormis has been obtained at Manta and Santa Elena, Acanthopleura echinata, primarily a cold-water species of the Peruvian Province, occurs as far north as Cabo Blanco. THE PERUVIAN PROVINCE ITS LIMITS AND PAUNAL CHARACTERISTICS The Panamic-Pacific and the Peruvian faunal provinces border along the northwest coast of Peru between the Gulf of Guayaquil and Punta Aguja at the end of the Illescas Peninsula (about lat S° 40' S,). In this region, the continent of South America projects the furthest west forming a series of massive headlands separated by deep re-entrants or bays. There are three of these coastal bulges, namely, Cabo Blanco-Punta Parinas in the north; the smaller peninsula of Paita in the middle; and the Illescas Peninsula in the south, the whole spread over a distance of about 120 nautical miles. The bays between these headlands, two in number (Paita and Sechura) are asymetrical in shape and widely open to the north. The bays of Manta and Santa Elena along the Ecuadorian Coast are similarly shaped. Geologically, the headland areas are structural highs, the bays between them synclinal. Cabo Blanco-Parinas bulge is underlain by Tertiary rocks, while the peninsulas of Paita and Illescas by more ancient rocks, the two latter, represent the deeply eroded cores of old mountain uplifts. The sea lying off this portion of the Peruvian coast is the meeting ground of two major oceanic currents; that of the Equatorial Counter Current from the north, which after bathing the coasts of western Colombia and PANAMIC-PACIFIC PELECYPODA 33 Ecuador with its warm water is here deflected westward into the open Pacific, and the mighty Peruvian or Humboldt Current streaming up from the south is similarly deflected on a more westerly course. As a result, the waters off the coast of northwestern Peru are in a constant tumult or conflict, as the drift of the two streams meet and join, the mixing zone shifting its position continually, sometimes to the south or far to the north. At times, the Equatorial stream is the more powerful and is able to push its way southward bringing waters warmer than usual into the coastal zone. This disturbance is known to the Peruvians as "El Nino" since it commonly appears during the Christmas season or simply as "the Aguaje". Although the El Nino is felt somewhat each year, its duration is usually short but at more or less cyclic intervals, it can be very severe, upsetting the normal climatic conditions of the coastal land and bringing catastrophic destruction to life in the sea. The winds which blow normally from the sea or from the southwest, then become northerly or easterly, bring heavy, torrential rains, converting the dry quebradas into rushing streams and covering the otherwise dry and barren land with a lush growth of vegetation. The most severe of the El Nino distrubances in recent years was in 1925: a lesser one in 1953. Although the Peruvian Province extends well into the tropics and with- in a few degrees of the equator, its fauna is essentially one of cool or temper- ate waters, maintained partly by the Peruvian Current and by strong, in- shore upweHings from depths. The Peruvian Current (or Humboldt Current) is one of the most remarkable of oceanic streams if judged by the influence which it exerts on the coastal lands along which it flows and by the pro- fusion of marine life which it supports in its waters. The source of this mighty stream lies in the high southern latitudes of the westerly winds which propel it eastward to impinge upon the coast of southern Chile near the island of Chiloe, south of Concepcion. At this place, the stream divides into two branches, one turns to the south, flows to and around Cape Horn, the other and major branch is diverted to the north and skirts the coast of Chile and Peru. Near the city of Chiclayo (lat 6° 30' S.) the coast bends sharply towards the west, thereby turning and driving the Peruvian Current out into the open Pacific at Punta Aguja. Surface temperatures in the stream off the coast of southern Chile in the month of August average about 45° Fahrenheit and between 60 and 65° in the northern sector. The most significant feature of the Peruvian stream is its lower temperatures inshore and higher ones offshore. The maintenance of the lower temperature along the inner course of the stream is mainly due to strong upwellings rather than a direct transport of identical masses of cold water from far southern latitudes. This phenomenon of upwellings appears to be strongest in the northern part of the stream where it flows over the shallower plat- form areas which prevail there rather than in the south where the shelf zone is narrower and the dip-off into deep water is more abrupt. Research, mainly by the Schott Expedition, has shown that this rise of cold submarine water to the surface comes from relatively shallow depths of 30 to 400 34 AXEL A. OLSSON meters only. It brings to the surface an abundant supply of mineral salts and nitrogenous compounds favorable to the growth of an extraordinarily rich planktonic fauna and flora which in turn gives support to vast schools of anchovies and other small fish. These are the main source of food for the vast swarms of guano birds seen along the Peruvian coast south of Sechura. Through most of the year conditions in the path of the Peru- vian Current are fairly stable but during the summer months of the Southern Hemisphere upsets in circulation may occur, the upwellings may diminish or cease entirely, and the invasion of a southward flowing, inshore current, the "El Nino" and the accompanying phenomenon known as the "Aguaje" or Callao Painter sets in as already mentioned. In most years, the effects of the El Nino are relatively unimportant and of short duration but during some years, spaced roughly at 7 and 35 year intervals, the cli- matic upset of the El Nino may be great. In the Aguaje of 1925, the tem- perature of the surf at Negritos in northwestern Peru rose sharply from an average of about 65° to about 80° and remained so for several weeks. At the same time, surface water temperatures in the harbor of Callao were reported as high as 80 degrees. Such a sharp rise in the temperature of the sea water, if prolonged, results in a catastrophic destruction of most forms of marine life along large parts of the Peruvian coast as well as an upset in the climatic pattern on land. At such times, the decomposition of the vast quantity of dead marine life, much of it cast upon the beach, generates volumes of hydrogen sulphide that blackens the walls of houses and hulls of ships which are painted with white lead (the Callao Painter). Evidence of the southward flowing El Nino current in 1925 was demon- strated by the large numbers of sea-snakes stranded on the beach at Negritos and of mangrove seedlings rooted in tidal lagoons and flats as far south as Sechura. An estimate of the size of the molluscan element in the Peruvian fauna is still difficult to make as many records in the literature cannot be relied upon with full confidence. Fully half of the species so far known from Peru and middle Chile are littoral forms such as the limpets, chitons, and other rock perching types and show that the offshore species are known only in an imperfect manner. The first compilation of the mollusks of Peru and Chile was made by Alcide d'Orbigny and published in the "Voyage dans I'Amerique Meridionale" (1835-1843). In this list D'Orbigny recorded 251 species as living along the coast from southern Chile to the Peruvian-Ecua- dorian border. Of this number, 89 species were listed from Paita or from Tumbez, and of which only one species was also known to occur at Callao. These northern species are members of the Panamic-Pacific and the Paita Buffer Zone, leaving only 163 species for the restricted Peruvian fauna as then known. In 1909, our knowledge of the Peruvian fauna was greatly advanced by Dall through his work on the Coker Collection as noted in an earlier section of this paper. The compilation following was prepared largely for this occasion and is based on our own collections and observations and on such records in PANAMIC-PACIFIC PELECYPODA S5 the literature which seem acceptable. Only the shell-bearing types of mol- lusks are included in this analysis. Total number^ of species of moUusks known at the present time along the coast of Peru southward to the Island of Chiloe, Chile. Gastropods .„ Pelecypods ... Scaphopods Chitons — 274 species — 248 species 2 species 45 species Total ,.569 species This total of 569 species may be broken down as follows: Species found in northwestern Peru (largely Panamic-Pacific and Paita Buffer species) which do not range south of Punta Aguja, and of these the majority of which do not pass Cabo Blanco. Gastropods Pelecypods Scaphopods Chitons .121 species .178 species 2 species 2 species Total 303 species Panamic-Pacific and Paita Buffer species ranging south of Punta Aguja. Gastropods Pelecypods Chitons ,....57 species „...32 species ..„ 5 species Total ...94 species Species restricted to the Peruvian Province as a whole. Gastropod s — 1 61 species Pelecypods 80 species Chitons 45 species Total 292 species Species known only from Peru. Gastropods 133 species Pelecypods „ ~ 60 species Chitons „ 26 species Total .219 species 3 The above compilation is the best possible at the present time. Additions to the mollusks of northwestern Peru may be expected as the families of some small gastro- pods are worked up, of which good collections are at hand. 36 AXEL A. OLSSON At the present time nearly 600 species of shell-bearing mollusks are known from the coastal waters of Peru and Chile. Of this number, about 397 species or roughly 69 percent are Panamic-Pacific species which range southward into Peruvian waters, the majority of which (about 53 percent) do not pass Punta Aguja. The overflow of some of these northern forms south of Punta Aguja into the Peruvian faunal province is small and most of these species are known only from its northern sector. Shells collected at Lobos de Tierra, the most northerly of the two guano islands just south of Punta Aguja, are largely the same species as found in Sechura Bay at Bayovar. Lobos Island fauna, therefore, must be considered an outlier of the Paita Buffer Zone. Several Panamic species occur at Lobos Island and probably find their southern limit of range at that place, such as Malea ringens, Fusinus dupetithoursi, Cancellaria chrysostoma, and Cypraea cervinetta. It seems likely that these species do not extend much further south. Mexicardia procera and Raeta undulata range south to Bahia de la Independencia (lat 14° 15' S.) below Paracas. These vigorous north- ern species are much larger in size than they attain along the coasts of Ecuador and Panama. Semele corrugata, common at Paracas and Bahia, is also common in the Paita Buffer Zone. Pecten purpuratus, the common scallop of the Peruvian markets, is plentiful in Sechura Bay but is rare north of the Gulf of Guayaquil. Concholepas concholepas is perhaps the most characteristic species of the Peruvian Province. It seems to find its northern limits at Lobos de Tierra, but all the specimens seen from there are small. Oliva peruviana, Thais chocolata, and Turbo magnijicus are wide spread and find their northern limits in the Paita Buffer Zone or in the Gulf of Guayaquil. Amongst other characteristic Peruvian mollusks are Trochita trochiformis, several large mytilids (Aulacomya, Choromytilus, Semi- mytUus), and clams (Protothaca thaca and P. domheyi). The chitons are numerous in the south, A cantho chiton echinata and Enoplochiton niger are especially common, the former known also from Paita. Amongst the other invertebrates are several species of barnacles, of which Balanus laevis is especially common in the south, bunched in large clusters on boulders or perched on the shell of Concholepas in a crowded mass. Of special interest also along the coast of mid,dle Peru is a colonial polychaete worm {Gun- narea) which forms large encrustations of closely packed, vertical, cal- careous tubes. Such reeflike masses, often mistaken for coral heads, are found in the Mancora tablazo at Paita and Cabo Blanco in northern Peru, far north of their present-day known occurrence and show that these Pleistocene deposits were laid down in waters as cool as those which now wash the shore of Peru much further south. The deficiencies in the Peruvian fauna amongst the mollusks are as striking as some of its redundances. There are no Tellinidae or Lucinidae. Species of Conus and Terebra are lacking although a few forms are known from Panama-Pacific and Paita Buffer Zones in northwestern Peru. The fauna of the Peruvian Province is one of temperate or relatively cool waters and its penetration along the coast northward into the tropical PANAMIC-PACIFIC PELECYPODA J7 zone is due entirely to presence of the Peruvian Current. A cessation of the flow of this stream or of the submarine upwellings which accompany it, would permit the southward invasion of much warmer waters from the west or the open Pacific and from the north. The Peruvian fauna would be forced to retreat southward and the more aggressive, Panamic-Pacific species would move in to take its place. This faunal shift, back and forth, has occurred repeatedly. THE PAITA BUFFER ZONE WITH A LIST OF ITS PRINCIPAL SPECIES As seen from the previous discussion, the northern or Panamic-Pacific and the southern or Peruvian faunas meet and to a certain extent inter- mingle along the coast of northwestern Peru between Cabo Blanco at the south end of the Gulf of Guayaquil and Punta Aguja at the western tip of the Bay of Sechura. This is an overlap region of about two degrees of lati- tudinal spread or about 120 nautical miles. The marine species of this overlap region belong properly neither to the Panamic or the Peruvian faunal provinces, hence the name of the "Paita Buffer Zone" is here pro- posed, its name taken from the city or bay of Paita located in its central portion. Both on land and in the sea, this is truly a transitional region. At Tumbez, and throughout most of southwestern Ecuador, the country is covered with a good growth of small trees, bushes, and cacti. Along the banks of the many esteros or inlets, there are stands of tall mangrove, a flora maintained by a fairly heavy and regular rainfall during the summer months. Further south in Peru, this zone of semiarid vegetation retreats deeper inland, following the base of the Amotape Mountains or retained only on some of the higher hills. In the vicinity of the coast, the climate, tempered by the winds blowing in from a colder sea, are dry and dessicating, the rainfall sparse and irregular in normal years. Beyond Cabo Blanco, desert conditions set in rapidly and plant growth becomes less plentiful or confined largely to river and quebrada bottoms where some moisture re- mains in the subsoil. At Paita, Sechura, and points further south, desert conditions become more strongly intensified. Interesting accounts of the bird life along this transitional zone in northwestern Peru have been given by R. C. Murphy in several papers and books. Some of the northern or tropical sea birds which find their southern limits of range in the Paita Buffer Zone are: The West Indian ?e\ican( Pelecanus occidentalis), the Caribbean Man-O-War bird (Fregata), the Roseate Spoonbill, and several others. The common gannet in the Paita Buffer Zone is the Blue-Footed Booby (Sida nebouxii) but which ranges somewhat further south, nesting in large numbers on the islands of Lobos de Tierra. Regular visitors in the Paita Buffer Zone from the south, especially in the early months of the year, are the large Peruvian pelican (Pelecanus thagus), a strictly marine species, the Piquero (Sula variegata), the White-breasted Cormorant or Guanay (Phalacrorax bougainviUei) , and the Kelp Gull (Larus dominie anus) . The Peruvian Penguin {Spheniscus humboldti) is rare in the Paita Buffer Zone but has been observed in the Bay of Sechura. The sea lion (Otaria juhata) was formerly common at 38 AXEL A. OLSSON Balcones Point near Negritos but has been driven away by being con- stantly shot at by trigger happy sportsmen. Among fishes, the Black Marlin (Makaina marlina) and the Sailfish (Istio-phorus greyi) do not normally extend south of this region. Below is given a list of the principal species of mollusks of the Paita Buffer Zone. The species marked with an asterisk (*) are southern forms from the Peruvian Province; unmarked species are Panamic, the latter predominating greatly in number. The island of Lobos de Tierra, the largest and most northerly of the guano islands along the coast of Peru and lying about 80 kilometers south of Punta Aguja, although in the middle of the Peruvian stream, has a molluscan fauna similar to that of the Bay of Sechura. For this reason it is considered an outlier of the Paita Buffer Zone. Rictaxis venustus (d'Orbigny) Paita, also Mancora BuUaria aspersa (A. Adams) Negritos, Paita, Bayovar, Lobos de Tierra, also Paracas Peninsula Umbractdum ovalis ( Carpenter) Bayovar Cancellaria cassidijormis Sowerby — - Negritos Caticellaria chrysostoma Sowerby Negritos, Lobos de Tierra *Oliva -peruviana Lamarck _ Negritos, Paita, Bayovar, Lobos de Tierra OliveUa columellaris Sowerby .„ _ — Negritos, Paita, Bayovar *Marginella curta Sowerby „ .Negritos, Paita, Bayovar, Lobos de Tierra Mitra swainsoni Broderip Yasila, Paita Cantharus (Triumphis) distortus (Gray) _ Lobitos, Paita Cantharus vibex B roderip — Lobitos Columbella paytensis Lesson Negritos, Paita, Bayovar Hexaplex brassica (Lamarck) „ Bayovar, Lobos de Tierra Murex squamosus (Broderip) Bayovar, Lobos de Tierra, Paita *Concholepas concholepas (Bruguiere) _ Lobos de Tierra *Thais chocolata (Duclos) Negritos, Paita, Bayovar, Lobos de Tierra Thais haemastoma (Linne) (biserialis Blainville) Negritos, Paita, Bayovar Thais callaoensis (Gray) Negritos, Paita, Bayovar, Lobos de Tierra Purpura patula pansa Gould Lobos de Tierra Fusinus dupetithouarsi (Kiener) Bayovar, Lobos de Tierra Fusinus panamensis Dall - ......Lobitos, Bayovar Epitonium statuminatum ( Sowerby ) — — Paita Cymatium parthenopeum (von Salis) [costatum Born] „ Bayovar, Lobos de Tierra Cymatium wiegmanni ( Anton ) Bayovar Bursa ventricosa (Broderip) — Bayovar, Lobos de Tierra, also Paracas Cypraea (Trona) exanthem^a Linne - Lobos de Tierra, Bayovar, Negritos Trivia radians (Lamarck) — Negritos, Lobos de Tierra Malea ringens (Swainson) .....^Negritos, Paita, Bayovar, Lobos de Tierra Ficus decussatus ( Wood ) „ Negritos Turritella goniostoma Valenciennes Bayovar, Paita, Negritos, Lobos de Tierra PANAMIC-PACIFIC PELECYPODA 89 *Turritella broderipiana d'Orbigny _ Paita, Yasila, Bayovar Architectonica nobilis Roding „ Negritos Crucibulum scutellatum (Wood) ™. Bayovar, Lobos de Tierra Crucibulum spinosvm (Sowerby) — » Paita, Negritos, Bayovar Crepidula onyx Sowerby [arenata Broderip] Bayovar, Paita, Lobos de Tierra Pdinices panamensis (Recluz) Bayovar, Negritos Sinum concavum (Lamarck) Bayovar, Lobos de Tierra *Acmuea viridnla (Lamarck) Lobos de Tierra *Turbo magnijicus Jonas Negritos, Paita, Bayovar, Lobos de Tierra ChloTostoma melaleucos (Jones) Bayovar *Fissurella peruviana Lamarck Lobitos, Bayovar Fissurella macrotrema Lamarck Paita, Tortuga, Lobos de Tierra Diodora inaequalis (Sowerby) Negritos, Lobitos Nucula paytensis A. Adams Negritos, Paita, Bayovar *Glycymeris ovata (Broderip) Bayovar, Lobos de Tierra Axinactis inaequalis (Sowerby) Bayovar, Lobos de Tierra Ostrea (Alectryonia) megodon Hanley Bayovar, Lobos de Tierra Anomia peruviana d'Orbigny Bayovar, Paita, Lobos de Tierra Aequipccten purpuratus (Lamarck) ...Negritos, Paita, Bayovar, Lobos de Tierra Aequipecten circularis (Sowerby) - Negritos, Paita, Bayovar, Lobos de Tierra Pteria sterna (Gould) -.... - - Negritos, Paita, Bayovar Mytella speciosa ( Reeve) - Negritos *Serrmnytilus nonuranus Pilsbry and Olsson Nonura Bay (P. Aguja), Paita, Negritos Modiolus pacificus Olsson - ••••" raita Adula solenijormis (d'Orbigny) - Mancora, Paita Chama pellucida Sowerby - - ^.....Bayovar Mexicardia procera (Sowerby) Negritos, Paita, Bayovar, Lobos de Tierra Dosinia ponderosa (Gray) - Negritos, Paita, Bayovar Cyclinella subquadrata ( Hanley) Bayovar Tivela hians (Philippi) .- Negritos, Paita, Yasila, Bayovar Hysteroconcha lupanana (Lesson) Negritos, Paita, Yasila, Bayovar Chione compta ( Broderip) Bayovar Iliochione subrugosa (Wood) Negritos, Paita, Bayovar Nioche asperrima ( Sowerby) Bayovar Petricola denticulMa Sowerby Paita, Bayovar, Negritos Mactra velata Philippi Negritos, Paita, Bayovar Raeta undulata (Gould) _ - Negritos, Bayovar, also Paracas Donax peruvianus Deshayes Negritos, Paita, Yasila, Bayovar *Tagelus dombeii (Lamarck) Negritos, Paita, Bayovar, Lobos de Tierra *Semele corrugata (Sowerby) Bayovar, Lobos de Tierra, also Paracas Cryptomya calif arnica ( Conrad ) ......Negritos Periploma planiuscuLa Sowerby - - • Negritos 40 AXEL A. OLSSON Entodesma (Agriodesma) sechurana Pilsbry and Olsson . — Bayovar *Acanthopleura echinata (Barnes) Negritos, Yasila, Paita, Lobos de Tierra BIBLIOGRAPHY Ekman, Sven. 1853. Zoogeography of the sea. London. Keen, A. Myra. 1958. Sea shells of tropical West America. Stanford, Cali- fornia. Landes, Kenneth K. 1952. Our shrinking globe. Bull. Geol. Soc. America, vol. 63, No. 3, pp. 225-240. Lowe, Herbert N. 1932. Shell collecting in west Central America, Nautilus, vol. 45, No. 3, pp. 73-82. Murphy, T. C. 1925. Bird Islands of Peru. New York. . 1925. Equatorial vignettes. Natural History, vol. 25, No. 5, pp. 431-449. . 1932 Review of Gerhard Schott, 1931 "The Humboldt and Nino currents". Geographical Record, vol. 22, pp. 140-150. . 1926. Oceanic and climatic phenomena along the west coast of South America during 1925. American Geographical Society, vol. 16, No. 1, pp. 26-54. . 1936. Oceanic birds of South America. Vols. 1 and 2. Macmillan Co. New York. Olsson, Axel, A. 1924. Notes on marine mollusks of Peru and Ecuador. Nautilus, vol. 37, pp. 121-131. Presbrey, E. W. 1913. Collecting in Panama. Nautilus, vol. 26, No. 11, pp. 121-125. Rost, Helen. 1955. A report on the family Arcidae (Pelecypoda). Allan Hancock Pacific Exped., vol. 20, No. 2, pp. 173-248, pis. 11-16. Schenck, H. G., and Keen, A. M. 1936. Marine molluscan provinces of western North America. Proc. Amer. Philos, Soc, vol. 76, No. 6. Soot-Ryen, Tron. 1955. A report on the family Mytilidae (Pelecypoda). Allan Hancock Pacific Expedition, vol. 20, No. 1, 174 p., 10 pis. PART II. PANAMIC-PACIFIC PELECYPODA Phylum MOLLUSCA Class PELECYPODA GENERAL STATEMENT The MoUusca as a separate branch or phylum of the Invertebrata is divided into six smaller groups called Classes of which the Pelecypoda is one. All members of the Pelecypoda are aquatic, living in fresh, brackish, or marine waters, at all depths, and under many environmental condi- tions. Of the marine sorts, the many kinds of hard-shelled clams (venerids), the soft-shelled clams (myads), the mussels (mytilids), the scallops (Pec- PANAMIC-PACIFIC PELECYPODA 41 tens) may be cited as examples. From all other classes of the Mollusca, the pelecypods are distinguished by their bivalved shell, formed of two, cal- careous valves placed on the sides and thus enclosing and protecting the soft, vital organs of the animal within. The two valves are joined in a flexing, hingelike fashion along their dorsal margins. They differ from most other mollusks in the absence of a true head and of a mouth provided with biting parts, the pelecypods being wholly plankton and detritus feeders. As in all other mollusks, the shell of the Pelecypoda is secreted by a fleshy sheet or mantle which covers the soft parts of the animal within. This mantle arises from the back in the shape of two lobes, one on each side, each lobe being closely applied to the inner surface of the valve and directly attached to it along a line near the ventral margin; this is the pallwl line, usually indicated by a more or less continuous linear impression extending from one adductor scar to the other. Each lobe of the mantle functions in the secretion of the shell through the addition of thin, indi- vidual layers to its inner surface thus increasing its thickness and weight, and by similar secretions around the ventral margin adding to its size; therefore, the oldest and thickest part of the shell is located at the beaks while its growth in size is shown by the many small concentric lines (growth lines) which cover its surface, sometimes uniformly distributed, or in con- centric bands or ribbons set apart by deeper impressed lines or by thickened ribs or varices which indicate halts or interruptions in shell growth (resting marks.) The teethlike projections along the dorsal margin, together with the elastic ligament, hold the valves together and form a hingelike structure. The ligament may be considered as a fundamental character of the Pele- cypoda (possessed by no other group of the Mollusca) universally present amongst them, although in some cases in a modified or degraded form. The primary function of the ligament is to open or to spread apart the ventral margins of the valves which takes place on relaxation of the adductor muscles. Structurally the ligament is composed of two bands which differ in composition and in the mechanics of operation. In the Veneridae and Tellinidae, these two bands are united in a single structure forming an inner and outer layer. In this case, the ligament is spoken of as "external" and it is visible from the outside just behind the beaks. Therefore, the position of the ligament generally behind or in the rear of the beaks furn- ishes a means of orientation of the whole shell or of an individual valve. In some other families, such as the Mactridae, Myacidae, and the Corbulidae, the two bands of the ligament are widely separated and attached to dif- ferent parts of the hinge plate. In this case, the upper band of the ligament (here called the tensUium,) is much diminished in size and its importance in the opening of the valve much reduced. The scar of the tensilium in this case is placed high on the hinge plate well above the hinge teeth. The larger part of the ligament is now formed by the inner layer or resiliimi, and its attachment to the hinge plate is placed lower, between the hinge teeth, generally in a special groove or pit called the resilifer or chondrophore. The 42 AXEL A. OLSSON latter name is used if the resilifer has the shape of a spoon or a projecting armlike process. The ligament is now considered "internal" since it lies con- cealed within the hinge plate. In the case of the Mactridae, the resilifer has the shape of a large, pear-shaped depression or cup in the middle of the hinge plate, between the cardinal teeth, and below the main fulcrum of the hinge. This internal position places the resilium under compressional strain while the valves are held shut by the pull of the adductor muscles. In structure, the resilium is fibrous or lamellar, often showing a pearly or silky luster along a fractured surface; it is always impregnated with lime giving to it a grayish color and resistance towards alkaline solutions; in some families of the Anomalodesmacea, particularly, the Lyonsiidae and Periplomidae, the middle portion of the resilium is often replaced so com- pletely with lime as to form a shelly plate (the lithodesma), its purpose is to strengthen the whole. The outer band or tensilium is usually much thinner, often a mere skinlike membrane, brown in color, and of a chiti- nous or hornlike nature. Like the periostracum, of which it is a continuation, it is acted upon by strong, alkaline solutions. The mechanical action of the outer layer of the ligament is mainly tensional or by its contraction pulls the valves open by a shortening of the space above the fulcrum of the hinge. The name "tensilimn" is here proposed for this outer part of the ligament, to complement or conform in principle of naming with the resilium (Dall), whose mechanics of operation is resistance to compression. Hence, the ligament is under both tensional and compressional strain when the valves are tightly closed. In most pelecypods, the dorsal margin of the valves bears small rough projections or teeth which fit into sockets and form a swinging or hinge union. These structures are called hinge teeth, and their shape and distri- bution forms a set pattern characteristic for each family and genus. Illus- trations of various hinge patterns will be found amongst the plates of this work. The teeth set under the beaks and which appear to radiate out from there are called cardinal teeth; those more removed or placed along the sides are known as lateral teeth. In some families, the teeth may degenerate, be- come partially or wholly obsolete as in some genera of the Lucinidae. A taxo- dont hinge is one composed of many small teeth arranged in a more or less unbroken series (Nuculidae, Arcidae); this type of hinge has sometimes been considered as the more primitive. A cyclodont hinge is one without a definite plate, the teeth arising as hooks or prongs from the margin; this type of hinge generally shows evidence of torsion (Cardiidae). The most advanced type of hinge is found in the Mactridae and Veneridae and is knowrrf as teleodont; this type has well-developed cardinal and lateral teeth seated on a definite platform-like plate. Some groups have an edentulous hinge or one without any teeth; this type is characteristic of some borers. On the inside of the valve, there are several impressions which repre- sent the attachment scars of various muscles. Most pelecypod shells have two adductor muscle scars (Dimyarian) located at the anterior and posterior ends of each valve. The two adductor scars may be of nearly equal size, PANAMIC-PACIFIC PELECYPODA 4S or the posterior one is much larger (Heteromyarian). In some other forms, such as the scallops and oysters, there is but one adductor scar (Monomyar- ian); observation will show that this scar is not exactly in the middle but nearer the posterior side and hence is an aid in deciding whether the valve is right or left. The pallial line, already mentioned, is a more or less con- tinuous linear scar or series of small impressions marking the line of attach- ment of the mantle to the valve. It is generally placed close to the ventral margin. The pallial line may be developed as a simple, curved Une between the adductor scar (an entire pallial line), or it may show an inflexion at the posterior end (pallial sinus). A large pallial sinus indicates that the clam possessed large, extrudable siphons such as in Mya. ARTIFICIAL KEY TO THE PRINCIPAL FAMILIES OF PANAMIC-PACIFIC PELECYPODA.-* I. Monomyarian. Each valve with a single adductor scar only; this scar is placed slightly behind or posterior of the middle. A. Shell permanently attached to the substratum (sea bottom, rocks, other shells) either by direct cementation or anchored by a byssal plug or by byssal threads. a. Attachment by direct cementation by the umbone or beak, the at- tachment area producing a distinct scar. 1. Attachment by the left valve which is generally the larger, the shape usually irregular due to distortion, the valves alike or unlike in surface sculpture. No teeth or other interlocking devices along the hinge margin. Ostreidae 2. Valves pectiniform, attached generally by the right valve, often with a ribbed or spinous sculpture. Hinge provided with stout, interlocking teeth or crura on each side of a deep, resilifer. Spondylidae b. Attachment by means of a solid byssal plug passing through a slit or circular hole (foramen) in the beak and umbone of the right valve; this opening sometimes closed off by later calcification, the shell becoming free. 3. Valves irregular, ostreiform, but with a subnacreous, platty or micaceous texture, and a subtranslucent or silvery luster. Anomiidae c. Shell anchored by a byssus or a bundle of horny or silky threads passing through a gap or notch along the anterior margin of the right valve. Shell often aviculiform or with the ends unequally winged or emarginated. Inner layer pearly. *A few small families arc not included in this key, as they are unimportant, their characters are obscure so that their inclusion would make the key too complex for general use. 44 AXEL A. OLSSON 4. Hinge line straight, the cardinal area grooved by a series of ver- tical pits for the attachment of the ligament. Isognomonidae 5. Hinge line straight, the cardinal area narrow, elongated and simple, with a single resilifer under the beak. Pteriidae B. Shell free or attached only in the earlier stages of growth. Porcel- laneous, never pearly. 6. Valves almost bilaterally symmetrical, and nearly equilateral, pectiniform, with well-developed anterior and posterior ears. Hinge line straight, the resilifer a pit under the beak. Surface smooth or with radial ribs; often brightly colored. Pectinidae 7. Valves oblique, inequilateral and often gaping on the sides, the lateral wings less perfectly developed. Color usually white, smooth or with radial ribs, often scabrous. Limidae n. Dimyarian. Each valve has two adductor scars placed near the anterior and posterior ends of the shell. C. The adductor scars are of unequal size (Anisomyarian), the anterior one is always small and sometimes partly effaced by the advancing or growing margin of the hinge area. Byssiferous. 8. Shells usually growing in clusters, attached to rocks, piling. Valves mytiliform or modioliform, the beaks small and placed at or close to the anterior end, the surface plain or ribbed, white, brown or bluish-black, covered with a smooth or bristly periostracum. In- terior pearly. Mytilidae 9. Shell elongate, narrowed, and pointed anteriorly, fan-shaped, brown or horn-colored, flexible around the wide margins. Seden- tary forms buried in sand or gravel, the shell held in a vertical position by the byssus. Pinnidae D. Adductor scars are more or less alike in size and shape. Da. Hinge structure formed by numerous, small vertical or > — shaped teeth, on one or both sides of the beak, continuous or in- terrupted in the middle (taxodont). Daa. No cardinal area. The ligament attached to a central resilifer under the beak. 10. Shell rounded or ovate (nuculiform). Interior pearly. Ligament internal. Nuculidae 11. Shell elongated, the posterior side narrowed and rostrated, por- cellaneous. An external ligament is present. Nuculanidae PANAMIC-PACIFIC PELECYPODA 45 Dab. Cardinal area well developed. Substance of shell porcellaneous, the surface with plain or strong sculpture. With or without an anchoring byssus. Daba. Shell inequilateral and often inequivalve. Hinge line straight. 12. Surface with ribbed sculpture, often unequally developed in the two valves. Arcidae Dabb. Valves nearly symmetrical, the sides subequal. Hinge line arched or curved. 13. Ligament spread over the greater part of the cardinal area. Glycymeridae 14. Most of the cardinal area bare, the small ligament internal and lodged in a triangular pit or resilifer under the beak. Limopsidae Db. Hinge concentrated, usually composed of a few, strong teeth which fit into sockets. Dba. Hinge torsional, the teeth hook-shaped, curving outward from be- low the beaks. Cyclodonta. 15. Shell cordate or heart-shaped, convex, the valves equal. Surface smooth or ribbed. Cardiidae Dbb. Hinge not torsional, the teeth seated on a platform along the margin. The teeth below the beak are called cardinals; those spaced along the margins are known as laterals. Teleodonta. Dbba. The ligament is external, usually placed behind the beaks. Dbbaa. Interior of the shell showing a deep pallial sinus. 16. Shell cordate or heart-shaped, the valves alike in sculpture and convexity, the umbones usually prominent, ending in prosogyrate beaks, the anterior side usually shorter. Veneridae 17. Shell lenticulate, elongated, thinner and generally inequivalve, the umbones flattened, inconspicuous, the posterior end of shell shorter, flexed, and sometimes rostrated. Surface smooth, with concentric growth incrementals, more rarely radially ribbed. Pallial sinus deep, the margin of the valves usually smooth. Tellinidae 18. Similar to the last but the shell often razor-shaped, thin or of medium weight, generally equivalved, gaping posteriorly (except Heterodonax). Color white, pink, or maculated and rayed with purple, the periostracum coarse and thick. Ligament external, at- tached to a stout nymphal plate which rises prominently behind the beaks. Sanguinolariidae H AXEL A. QLSSON 19. Shell wedge-shaped, the posterior side shorter, often flattened and with subtruncated margin, the texture solid. Surface smooth and pohshed, usually showing fine radials which crenulate the margins. Mostly beach shells. Donacidae 20. Shell elongated, razor-shaped, the beaks submedian or close to the anterior end. Surface with growth line sculpture, sometimes cut by oblique lines. Solenidae 21. Mostly rock borers with subovate to subelongate valves, often deformed. Surface with ribbed or concentric sculpture, sometimes with zigzag markings. Hinge similar to the Veneridae. Petricolidae Dbbab. Pallial line entire, no sinal inflexion. Dbbaba. Shell permanently attached to the substratum. Hinge with large, irregular-shaped teeth, 22. Shell solid, porcellaneous, generally irregular in shape, attached by the umbone of either valve. Sculpture formed by ribs and con- centric lamellae. Generally strongly colored. Chamidae Dbbabb. Shell free not attached at any time. Dbbabba. Mostly fresh-water or brackish species, the surface covered by a thick, coarse periostracum, generally destroyed over the beaks and umbones which are deeply corroded and chalky. 23. Shell generally cordate or rounded, equivalve, with anterior beaks and umbones, the hinge provided with both cardinal and lateral teeth. Pallial line mostly entire, sometimes with a small posterior sinus. Color white, often with pink or purple shading. Corbiculidae Dbbabbb. Marine species, the surface of the umbones and beaks generally not corroded. 24. Shell cordate, veneriform, equivalve with prominent umbones and recurved, prosogyrate beaks, solid. Surface often with ribbed sculpture and fluted margins. Carditidae 25. Shell subovate, cordate, convex to depressed. The dorsal areas are frequently set-off by differences in contour and sculpture. Hinge teeth variable, often become obsolete. The anterior ad- ductor scar is generally long and narrow, lying within the cir- cumference of the pallial line. Lucinidae 26. Shell similar to the Lucinidae in shape but generally smaller and thinner. Cardinal teeth conspicuously double or bifid. Adductor scars of equal size. Diplodontidae PANAMIC-PACIFIC PELECYPODA 47 Dbbb. Ligament almost wholly internal and divided into two unequal parts, the larger section or resilium lodged in a chondrophore (resilifer) or an excavated, cup-shaped pit in the hinge plate between the hinge teeth or carried on a projecting arm, Dbbba. Pallial line entire, no posterior sinus. 27. Shell elongated or subrectangular, solid, the posterior side often pointed, rostrated. Crassatellidae Dbbbb. Pallial sinus strong. 28. Shell ovate or trigonal with high, full umbones and prosogyrate beaks, thin or solid, the color generally white. Resilifer is a deep, cup-shaped chondrophore in the middle of the hinge plate between the cardinal teeth. Posterior-dorsal area usually well defined by an angle, ridge or elevated frill. Valve margins smooth. Mactridae 29. Shell subcircular to subelliptical, convex or depressed, the posterior side sometimes flexed. Surface smooth or with elaborate sculpture of ribs, lamellae. Pallial sinus large and deep. Resilifer an oblique groove in the hinge plate, similar in both valves. Semelidae Dc. Hinge structure relatively simple, the teeth small, irregular in shape or wholly wanting. Dca. Substance of the shell porcellaneous, the ligament either external or internal; if internal, the resilium is attached to a spoon-shaped chondrophoral arm often simulating a large tooth which projects outward from the hinge plate in the left valve (asthenodont). Nestlers, rock borers or living buried in sand or mud. Dcaa. Ligament external. 30. Species with both large or small shells, the valves gape strongly behind, the surface sculptured with crude or wrinkled concentric lines, occasionally rayed. Borers or nestlers in rock, shell, or coral. Saxicavidae Dcab. Ligament internal. Resilifer carried on a chondrophoral arm in the left valve which fits into a wide gap in the right valve, with the resilifer scar within, under the umbone. 3L Valves more or less equal in size, shape and convexity, the umbones rather low. PaUial sinus usually large and deep. Myacidae 32. Shell usually small, the valves alike or unequal in size, often rostrated or pointed posteriorly. Chondrophoral plate resembles a cardinal tooth. Corbulidae Deb. Shell typically nacreous, rarely subporcellaneous, the surface layer often earthy, chalky, or granulose. Ligament internal, the resilium lodged in a chondrophore which is similar in both valves. ( Anomalodesmacea ) . 48 AXEL A. OLSSON Dcba. Shell generally small, rounded to corbuliform, rostrated, the pallial line simple. Chondrophore small. 33. Shell small, rounded or depressed, with noded radial riblets. In- terior bright and pearly. Verticordidae 34. Shell corbuliform, elongated, the anterior side short, rounded and convex, the posterior side narrowed, produced, and pointed. Cuspidariidae Dcbb. Shell small or medium-sized, the chondrophore larger, the pallial sinus sinuous. A lithodesma often present. Dcbba. Mostly nestlers, the shell often quite irregular in shape. 35. Shell sometimes paper thin or heavy, generally with a peeling periostracal cover. Lysonidae Dcbbb. Not nestlers, the shell with a more regular form, the periostracum more closely adherent. 36. Shell subporcellaneous and often quite thin, inequivalve, the right valve larger, surface with rude sculpture, earthy, or pustulose. Thraciidae 37. Valves hatchet-shaped, generally depressed, with a pearly surface. Hinge with strong crural ridges. Pandoridae 38. Shell usually rounded, the right valve larger and convex, the left smaller and depressed, pearly. Hinge without crural ridges, the chondrophore a large, spoon-shaped process. Periplomatidae Dd. Hinge margin without any teeth, and the ligament is atrophied or obsolete. Dorsal margin smooth, reflected, or rolled over the um- bone to which it may be closely appressed. Borers in rock, wood, shell, or burrowing deeply in a sand or clay bottom. (Adesmacea). The shell is generally white, thin, open or gaping at the ends and along the dorsal and ventral margins or these spaces may be cov- ered by accessory calcareous plates. There is generally within the umbonal cavity a slender projecting arm or myophore (apophysis) to which the foot muscles were attached. 39. Typically borers in wood, the shell small and much reduced in size. Bore lined with a heavy calcareous, wormlike tube, generally much contorted. Teredinidae 40. Shell larger and more perfectly formed, with open gaps or these spaces covered with accessory plates. Shell thin, the surface marked with coarse, scabrous ribs usually set apart in well-defined areas. Borers in rock, wood, shell, or simply in the sea bottom. Pholadidae PANAMIC-PACIFIC PELECYPODA 49 GLOSSARY OF SOME COMMON TERMS USED IN PELECYPOD DESCRIPTIONS Adductors. The valves of a pelecypod are closed by the pull of a special set of internal muscles known as adductors; the attachment of these muscles to the inside of the valve leave rounded or elongated impressions or scars (adductor scars), one or two in number; if there is only one scar (monomyarian) as in Ostrea or Pecten, this impression is placed slightly behind the middle; if there are two scars (dimyarian), they are located at the anterior and posterior ends (anterior and posterior adductor scars). Amphidectic, With the ligament developed on both sides of the beaks. Anisomyarian. With two adductor scars, of which the anterior one is much smaller than the other (Heteromyarian) Beak. The tip or oldest part of the shell above the hinge margin; generally pointed and often coiled or curved. Byssus. A bunch of horny threads, loose or in compact form, secreted by a special gland of the foot and by means of which some species are anchored to the sea floor or other objects. Cardinal area. The surface of the valve between the beak and the hinge margin, often of a triangular shape and partly or wholly covered by the ligament. Ostrea, Area. Cardinal teeth. The middle members of the hinge teeth and which lie under the beak and seem to radiate out from there. Cartilage. Obsolete name for the resilium; extensively used in French works on conchology. Conchiolin. The organic constituent of the shell; left after the lime has been dissolved away by acid. Cordate. Shaped like a heart. Often applied to such shells as Cardium, Cardita, Venus. Dimyarian. With two adductor muscle scars. Dorsal area or slope. The upper surface of the shell between the dorsal margin and the umbonal slope; it is best differentiated if the posterior umbonal slope is carinate or by marked differences in sculpture. Edentulous. Hinge line without teeth. Equilateral. Valve with both ends alike. Equivalve. A shell with both valves alike in shape, convexity and sculpture. Escutcheon. A depressed or flattened area (shield-shape) along the pos- terior dorsal side, on one or both valves, and set off from the rest of the shell surface by a ridge or line, or by a change of sculpture. External hgament. The visible part of the ligament, usually shows as a rounded, brown mass just behind the beaks. Foramen. A round hole or fissure in the lower valve for the passage of the byssal plug. Anomia. Heterodont. Hinge with both cardinal and lateral teeth. Heteromyarian. Same as Anisomyarian. 50 AXEL A. OLSSON Hinge. The section of the dorsal margin, held together by interlocking teeth. Hinge plate. An inward widening of the margin below the beak and on which the hinge teeth are placed and sometimes the internal ligament. Hinge teeth. Toothlike projections along the hinge line. Inequilateral. The two ends of the shell unlike in shape and sculpture. Inequivalve. Shell with unlike or unequal valves. Internal ligament. Ligament when placed largely or wholly within the hinge plate and not easily seen from the outside. Isomyarian. With two subequal adductor scars; same as homomyarian. Lateral teeth. Hinge teeth in a lateral position, in front or behind the cardinal teeth or the ligament. Ligament. An element of the hinge, whose elastic reaction from compression, in opposition to the pull of the adductor muscle force the valves to open or spread apart. Lithodesma. A calcified plate placed internally or under the middle portion of the ligament. Characteristic of some genera of the Anomalodes- macea. Lunule. A lenticular or heart-shaped area lying below and in front of the beaks, usually weakly or strongly outhned by an impressed line or indicated as a more deeply impressed or sunken area. The lunule may be equally developed in both valves as in the Veneridae, or in one valve only. Mantle. The fleshy sheet which envelops the vital organs of the animal within the shell. It is attached to the shell directly along the pallial line and its secretion forms the shell itself. Monomyarian. With a single adductor muscle scar in each valve. Myophore. An armlike process or apophysis rising from the interior of the shell, usually from the umbonal cavity and serves for the at- tachment of the foot muscles. Found in Pholadidae. Nacreous. Shell with the interior having the luster of pearl resulting from the interference of light rays reflected from the surface of many, thin layers with different indices of refraction. Nymph. A ridge or lamella of shell placed above the hinge teeth, platelike or with a rugose surface and to which the external ligament is attached. Opisthodetic. Behind or facing backwards; applied mostly to the position of the ligament lying behind the beaks. Opisthogyrate. Refers mostly to the backward coil of the beaks so that they point backwards or posteriorly. Pallial line. The line of adhesion of the mantle to the shell near and gener- ally parallel or concentric with the ventral margin. Pallial sinus. An inflexion of the pallial line at the posterior end, its size usually an indication of the size of the siphons or tubular ex- tensions of the mantle which protrude at the posterior end of PANAMIC-PACIFIC PELECYPODA $1 the shell when open and through which water is taken in for aeration and feeding, and afterwards expelled. Periostracum (epidermis). The periostome or the protective external covering of shell composed mostly of organic tissue or chitin with little or no lime added to it, often having a smooth, wrinkled or bristly- surface. Dissolved by alkalines. The periostracum is most heavy in fresh-water mollusks and in some deep-water species as a protection against the corrosive action of acid waters. Porcellaneus. A smooth, porcelain-like surface as the interior of some shells (contrasted with nacreous). Prodissoconch. The embryonic shell as it emerges from the egg capsule. The shell is usually small, smooth, and is often preserved on the tip of the beaks. Prosogyrate. In front or facing forward: the forward coil of the beak so that it faces or points forward or anteriorly. Resihfer. The attachment area of the resilium. In the Mactridae, the resihfer is a cup-shaped depression in the middle of the hinge plate. In the Myacidae and Corbulidae, the resihfer is carried on a pro- jecting arm or lamina. Resilium. The inner band of the ligament, more or less fibrous in structure and composed of conchiolin charged with lime. Opens the valves through compressional release. Tensilium. The outer band of the ligament. Composed of conchiolin but without lime. Usually with a conchoidal fracture, horny. Tensional. Umbone. The surface of the valve immediately behind the beak, generally convex. Umbonal slope. The line of greatest convexity which can be traced from the beak to the anterior or posterior ventral corners of the valve. 52 AXEL A. OLSSON SYSTEMATIC TREATMENT Subclass PROTOBRANCHIA Order PALAEOCONCHA Superfamily SOLEMTACEA Family SOLElkfYIDAE The shell is elongate, soleniform, thin or moderately thick, equivalve and gaping widely at both ends, the dorsal and ventral margins straight and parallel, the anterior side longer, the surface covered by a glossy, brown to black periostracum extending beyond the free margins of the valve as conspicuous, frill-like laps. Hinge margin without teeth, the ligament internal or partly external. Pallial impressions usually weak, the posterior adductor scar bordered in front by a thickened ray. Surface smooth, plain, or radially rayed. Genus S0LE3IYA Lamarck, 1818 Type species by subsequent designation, "Solenomya" mediterranea Lamarck (=Solemya mediterranea Lamarck =Tellina togata Poli, 1791) (see Vokes, 1955, Jour. Paleont., vol. 29, No. 3, p. 534). With the characters of the family. The genus is divided by Dall into three subgenera as follows: L Ligament amphidectic, along both sides of the beak, chiefly internal, in advance of the chondrophore. Subgenus Solemya, s. s. II. Ligament opisthodetic, internal, not exposed in front of the chondro- phore. Subgenus Petrasma IIL Ligament opisthodetic, wholly internal, visible internally only where it crosses the gap between the valves. Subgenus Acharax The genus Soletnya comprises relatively rare shells, seldom collected except by dredging, the fragile shell being easily damaged by drying out, the periostracum becoming separated from the layer beneath. Most species are deepwater but one form, S. (Petrasma) panamensis may sometimes be encountered on mud flats at extreme low water. Solemya is known by several fossil species in the Oligocene and Miocene of Peru, Ecuador, Colom- bia, and Panama. Subgenus ACHARAX Dall, 1908 Type species by original designation, S. johnsoni Dall. Solemya (Acharax) johnsoni Dall Plate 1, figure 5 Solemya johnsoni Dall, 1891, Proc. U. S. Nat. Museum, vol. 1+, p. 189.— Dall, 1895, op. cit.. vol. 17, p. 712, pi. 25, fig. 1. Solemya (Acharax) johnsoni Dall, Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 376.— Maxwell Smith, 1944, Panamic Marine Shells, p. 47, fig. 612. Solemya (Acharax) agassizii Dall, 1908, Bull. Mus. Comp. Zool., vol. 43. No. 6, p. 365, pi. 16, fig. rO.— Hertlein and Strong, 1940. op. cit., pp. 375, 376.— Maxwell Smith, 1944, op. cit., p. 47, fig. 613. Solemya (Acharax) johnsoni Dall and S. (A.) agassizii Dall, Vokes, 1955, Jour. Paleont., vol. 29, No. 3, p. 538. This is a deepwater species with valves reaching a length of 150 mm.. PANAMIC-PACIFIC PELECYPODA 53 thus equalling in size some of the fossil forms. The surface is marked with from 7 to 12 wide flat rays between deep channels which show on the inside as prominent radial ribs. Woodring^, who has examined the types of S. johnsoni and S. agassizii, questioned whether there are two species in the lot as the characters men- tioned by Dall as to the number of rayed channels is variable and their count a matter of personal judgement. The type of S. johnsoni is a specimen taken off the coast of Lower California in 1,005 fathoms, that of S. agassizii from the Gulf of Panama in 1,672 fathoms. Range — In deep water from Oregon to Punta Aguja, Peru, Subgenus I'ETllASMA Dall, 1908 Type species by original designation, Solemya borealis Totten. Solemya (Petrasma) panamensis Dall Solemya panamensis Dall, 1908, Nautilus, vol. 22, No, 1, p, 2, Solemya (Petrasma) panamensis Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, p. 366 Panama Bay in 29J^ fms. — Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 377, 378. Solemya panamensis Dall, Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 141 on mud flats at extreme tide, rare, La Paz. Length of valves exclusive of periostracum 39 mm., the shell thin, elongate-oval, the posterior end more pointedly and the anterior end more bluntly rounded. Periostracum brown, glossy, recurved over the margins of the valves, not produced into long processes, though more or less broken up beyond the margins. Anterior surface of valves radiately marked with eight or nine obscure rays, the middle zone with few sparse rays, the posterior with six or seven, more closely spaced, followed by a smooth area behind the beaks. This is a smaller, more expanded, and less sharply truncate anteriorly than S. agassizii of the same length. Also easily separated by hinge differ- ences. A shallow water species, sometimes encountered on mud flats at extreme low tide. Range — Panama Bay northward to California. Or,der FALAEOTAXODONTIDA Superfamily NUCULACEA Family NUCULIDAE The shells of this family are usually small, ovate to subtrigonal, with a shiny, pearly or nacreous interior, equivalve but inequilateral, the anterior side being longer than the posterior. Surface smooth, often polished or marked with radial or concentric threads or riblets, sometimes finely can- cellate, the pattern often divaricate. Hinge plate generally heavy, curved or bent in the middle with a central resilifer or chondrophoral pit bordered on the sides by an anterior and posterior series of small but numerous taxo- dont teeth. Ventral margin of valves smooth or crenulate. Mostly small shells, often known as "Nut Shells". They are widely distributed in all seas, occurring most plentifully on a mud bottom. ^Woodring, W. P., 1938, Prof. Paper 190, U. S. Geol. Sur., p. 27. 54 AXEL A. OLSSON Key to genera of Panamic Nuculidae I. Surface smooth or with radially cancellate sculpture. Genus Nucula II. Surface with divaricate sculpture. Genus Acila Genus NUCUIiA Lamarck, 1799 Type species by monotypy, Area nucleus Linne. Recent in the European Seas Shell generally small, with closed margins, not gaping, ovate-trigonal to subcircular, with small, appressed, opisthogyrate beaks. Interior white and usually brilliantly pearly. Surface smooth but in some cases showing faint to quite strong, subcutaneous radial lineation, stronger ventrallv and giving rise to a pectinate or crenulate margin. Escutcheonal area usually somewhat elevated and pouting. Hinge taxodont, with two series of crowded chevron- shaped teeth, the anterior row longer and arched, the posterior row shorter and with fewer teeth. Chondrophore narrow, inclined obliquely foward. Pallial line simple. About 13 species of Nucula have been recorded from the Pacific coasts of northern South America, Central America, and Mexico or its adjacent waters. About half of these species are abyssal and hence do not properly belong to the Panamic-Pacific fauna. Reference to these off-shore species will be found in Hertlein and Strong. The genus Nucula is commonly divided into two sections or subgenera on basis of a smooth or crenulate ventral margin. Subgenus KTCULA s.s. Inner layer of shell with radially ribbed structure which may show on the surface either strongly or weakly as fine radial striations. Inner ventral margin of valves crenulate or denticulate. Subgenus EJOfUCULA Iredale, 1931 Inner layer of shell without a radial structure and the ventral margin of valves without crenulations. Surface smooth except for growth in- crementals. Key to species of Nucula I. Inner margin of valves crenulated; the finely ribbed structure of the inner layer transmitted to the surface and showing plainly or in- distinctly. Subgenus Nucula, s.s. A. Shell very large (30 mm. or more in length). 1. Surface smooth or finely radially striate, the umbones more strongly sculptured with narrow, wavelike, concentric riblets cut by fine radial striation. A^. iphigenia B. Shell smaller. a. Surface smooth or finely radially striated. Inner margin of valves finely crenulated. 2 „ N. declivis and subspecies b. Surface with stronger sculpture, cancellated with both concentric and radial riblets. Inner margin coarsely crenulated. PANAMIC-PACIFIC PELECYPODA 55 3. Shell very small, subcircular to subovate, depressed with low umbones. N. schencki 4. Shell larger, plump, strongly inequilateral with high, swollen umbones. N. exiqua and N. paytensis II. Ventral margin smooth. Subgenus Ennucula 5. Surface smooth N. colofnbtana Jfucnla (Nncnla) iphigenia Dall Nucula iphigenia Dall, 1895, Proc. U. S. Nat. Museum, vol. 18, No. 1034, p. 15.— Dall, 1908, Bull. Mu9. Comp. Zool., vol. 43, No. 6, p. 369, pi. 7, figs. 1, 4.— Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 386. Shell large (length 30 to 35 mm.), solid, elongate-ovate, the anterior end produced, rounded, the posterior end obliquely truncate. Surface smooth- ish over parts of the shell or with feeble, narrow, irregular concentric wrinkles, strongest on the umbones, crossed by fine, radial striations. Lunula narrow, elongate, the escutcheon small, generally limited by a line from the large posterior area, the margin somewhat projecting or elevated in the middle, smoothish. Interior brilliantly nacreous with a strong pallial line and deeply impressed adductor scars. Hinge with numerous teeth, the anterior set twice as many as the posterior. Ventral margin denticulate. Length 35 mm.; height 22.5 mm.; diameter 16 mm. (Dall). One of the largest of known Nuculas. Dredged in Panama Bay, off Punta Pinas, in 259 fathoms. A closely related subspecies (N. iphigenia azidensis Olsson* PI. 2, figs. 9, 9a) is common as fossil in the Pliocene of the Burica Peninsula, Panama. Nucula (Nucula) decliris Hinds Plate 1, figures 4, 4a Nucula declivis Hinds, 1843, Proc. Zool. Soc. London, p. 98. — Hinds, 1844, Zool. Voy. Sulphur, Moll., pt. 3, p. 63, pi. 18, fig. 8. (Habitat— ?).—Hanley, 1360, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 154, pi. 230, fig. 147. Nucula (Nucula) declivis Hindi, Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 380, pi. 1, figs. 1, 2, 3, 6, 7. Shell small (length 5 mm.), solid, inequilateral, the posterior side short, its margin abruptly truncate, relatively convex. Surface smooth with deep, irregularly spaced concentrics and fine radial striation. Length 5 mm., height 4 mm., diameter (both valves) 2.9 mm. — (Hert- lein and Strong). Nucula declivis was described without indication of locality and because of this and the small size of the original figures, there is some doubt as to its identification. Strength of the surface radial striation appears to be variable, de- pending to some extent upon the degree of weathering and wear to which the shell has been exposed. Some of our shells from Ecuador have a smooth surface on which the radial striations hardly show. Range — Gulf of California to northern Peru. Ecuador: Manta. Peru: Zorritos. Other records are given by Hertlein and Strong. «0l9son, A. A., 1942, Bull. Amer. Paleont., vol. 27, No. 106, p. 176, pi. 4, figs. 2, 5, 7. 56 AXEL A. OLSSON Nncnla (Nucnla) exiqna Sowerby Plate 1. figures 2, 2a, 2b, 10, 10a Nucula exiqua Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198. — Sowerby, 1833, Conch. Illust., Nuculae, p. 6, pi. 16, figs. 24, 24*. — Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 50. No. 17, pi. 299, fig. 136. Nucula (Nucula) exiqua Sowerby, Schenck. 1939, Jour. Paleont, vol. 13, No. 1, p, 36, pi. 6, figs. 1-8, 11. — Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, p. 381, pi. 1, figs. 4, 5.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist., vol. 107, art. 2, p. 169; Palmer, 1958, Mem. Geol. Soc. America, No. 76, p. 61, pi. 1, figs. 6, 7. Generally small, length about 6 mm., or less, plump, with high, wide umbones, and with a more or less reticulate surface sculpture formed by strong, fairly wide, concentric riblets and radially threaded interspaces. The radial threads of the interspaces are strongest on the lateral slopes of the shell, sometimes quite indistinct on the umbones. The concentric riblets are generally much stronger than the radial reticulation and on the umbones, the concentric riblets are often close-set, and with smooth summits. The dorsal areas are both well marked, strongly sculptured, each set off sharply by a changed direction of the concentric riblets, the posterior-dorsal area large, cordate, flatly depressed; there is no recognizable lunule within the anterior-dorsal area. Hinge with about 18 teeth in the anterior set and about nine in the posterior. A common and widely distributed species, perhaps intergrading with N. paytensis in the border zone. Range — Lower California to Peru. Ecuador: Manta; Santa Elena. Peru: Zorritos. Nncnla (Nncnla) paytensis A. Adams Plate 1, figures 1, la, lb Nucula paytensis A. Adams, 1856, Proc. Zool. Soc. London, p. 51. — Reeve, 1870, Conch. Icon., vol. 18, Nucula, pi. 3, fig. 23 Payta, Peru. Nucula crenulata A. Adams, var. Paytensis A. Adams, Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 50, No. 16, pi. 230, figs. 160, 161. Like N. exigua but larger, more ovate, less convex, the umbones being less prominent, the sculpture is finer and more uniformly reticulate. Dorsal areas are strongly sculptured. Range — Northern Peru. Peru: Paita; Bay of Sechura. Nucula (Nucula) schencki Hertlein and Strong Plate 1, figure 6 Nucula (Nucolopsis) schencki Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 384, pi. 1, figs. 8, 9, 10. Shell small (length 2 mm.), thin, polished and rather compressed. Dor- sal margin in front of beaks elevated and broadly rounded, the anterior end more acutely rounded, the posterior and ventral margins broadly rounded. Sculpture is formed by closely spaced concentric riblets crossed by faint radial striation, weakest on the umbones. Dorsal areas weakly defined. In- terior with faint crenulations along the margin, the hinge teeth well developed with nine in the anterior set and five in the posterior. Length 2 mm., height \.7 mm., diameter (both valves) 1 mm. — (Hert- lein and Strong). Dredged off Port Guatulco, Mexico, in seven fathoms. Range — Mexico. Subgenus ENNUCULA Iredale, 1931 (Nuculopsis Woodring, 1925. Not Nuculopsis Girty, 1911). Type species by subsequent designation, Singleton, 1932, N. obliqua Lamarck. PANAMIC-PACIFIC PELECYPODA 57 Shell ovate, inequilateral, the opistogyrate beaks placed nearer the posterior end, the posterior end hence shorter, its margin subtruncated. Anterior side usually much longer, its dorsal margin gently arched, narrowly rounded at the end. Surface smooth, the lines of growth indistinct, por- cellaneously white. Inner ventral margin smooth. Hinge with the posterior set of teeth shorter and fewer in number than the anterior. Chondrophore narrow and strongly oblique. Ifucnla (Ennucnla) colombiana Dall Plate 1, figures 3, 3a Nucula colombiana Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, p. 371. — Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 385. Shell small (length 4 to 5 mm.), subsolid, inequilateral, the posterior side short, sharply descending, subtruncate and with the margin pouting a little in the middle of the flattened area. Anterior side longer, its dorsal margin somewhat arched, slightly narrowed and rounded towards the end. Umbone wide. Surface porcellaneous white, shiny, very smooth except for one or more shallow, concentric undulations, the growth lines not visible. Interior of shell pearly and with the ventral margin of the valve smooth. Hinge with about seven teeth in the posterior series and about 14 in the anterior. Length 4.5 mm., height 3 mm., max. diameter 2.2 mm. This is a small, simple species dredged in Panama Bay and off Manta, Ecuador, in waters ranging from 29 to 41 fathoms. It resembles Nucula declivis but its ventral margin is smooth. Dall recorded this species off the coast of Chile in waters as deep as 401 fathoms. Range — From Panama southward. Panama: Panama Bay. Ecuador: off Manta. Genus ACILA H. and A. Adams, 1858 Type species by subsequent designation, Stoliczka, 1871, Nucula divarv- cata Hinds. Like Nucula but often larger (max. length about 50 mm.), the surface sculptured with a characteristic pattern of parallel divaricating and more or less radial riblets which appear as if stacked or packed close together the main line of divarication extending from the umbo across the middle of the shell disk to the ventral margin, the peaks of their inverted V's forming a line of sharp, acute angles pointing towards the beak. A secondary line of reversed divarication may be developed along the posterior rostral side which often forms a shallow sinus ending in a slight bulge or pout at the margin. Acila (Acila) diyaricata burica Olsson Plate 17, figures 9, 9a Acila isthmlca burica Olsson, 1942, Bull. Amer. Paleont, vol. 27, No. 106, pp. 177, 178, pi. 1, figs. 2, 6, 8, 9. Acila has not been reported as living in Panamic waters, however a large species is plentiful as fossil in the Pleistocene-Pliocene beds along the Burica Peninsula of southwestern Panama. Some of the fossils bear a strik- ing resemblance to the figures of A. divaricata submirabths Makiyama (Schenck, 1936, Geol. Soc. America, Special Papers, No. 4, pp. 88, 89, pi. 14, figs. 8, 11) from the upper Pliocene of Sasage, Kazusa, Japan, but also known to be living off Japan and the Celebes. It seems possible that A. divaricata burica may still be living in Panamic waters. 58 AXEL A. OLSSON Family NUCULANII>AE (Ledidae) Shell small or medium-sized, mostly porcellaneous, elongate, the pos- terior side longer, narrower and often rostrate at the end, the anterior side shorter, rounder and convex. Hinge and ligament as in the Nuculidae, the chondrophoral pit usually internal but sometimes migrating upwards to the dorsal margin to become partly external. Pallial line more or less sinuous. Two genera may be recognized. I. Shell with the posterior side much narrowed, often arcuate and pointed at the end, the anterior side higher, rounded at the end and often convex. Posterior-dorsal submargin, subelliptical in shape, flattened or concave (rostrum). Genus Nucidana II. Shell eloneate, lanceolate, depressed, the posterior side not strongly rostrate. Rostrum absent or very narrow. Genus Adrana Genus NUCULANA Link, 1807 Type species by monotypy. Area rostrata Chemnitz (^=Mya pernula Miiller). Recent, seas of Europe. Shell with the posterior side narrowly elongate, arcuate, rostrate; an- terior side shorter, higher and rounder. Rostrum more or less bicarinate, subtruncate at the end which may show a slight gap, beaks small, opistho- gyrate. Escutcheon distinct, elliptical, the lunule indistinct and small. Hinge teeth numerous, arranged in two series, the posterior set almost twice as long as the anterior. Chondrophore small, triangular, inclined backwards; pallial sinus small, shallow. Sculpture of concentric threads, evenly spaced on the umbo, crowded together ventrally. The genus Leda Schumacher, 1817 of the older writers has the same type species. The genus Nuculana has been divided into many subgenera on small differences, characters which cannot be easily expressed in a key. The fol- lowing subgenera have species regional in the Panamic-Pacific Province. Subgenera of Nuculana I. Shell having the posterior side longer than the anterior. The posterior set of hinge teeth nearly twice as long as the anterior. 1. Posterior side with a double keel or bicarinate. Surface marked with growth lines only. Subgenus Nuculana, s.s. 2. Posterior side nodosely bicarinate. Surface with strong concentric sculpture. Subgenus Costelloleda 3. Posterior side much narrowed, attenuated and straight. Shape and sculpture suggestive of a crassatellid. Subgenus Thestyleda II. Shell with the anterior and posterior sides subequal in length, the an- terior side high, inflated and rounded, the posterior side pointed at the end. A. Shells relatively small. 4. Posterior side sharply rostrated, the rostrum concave or flattened, bordered by an angle or ridge. Subgenus Saccella PANAMIC-PACIFIC PELECYPODA 59 5. Shape corbuliform, the rostrum not clearly defined or without a sharp border or rib. Subgenus Jupiteria B. Shell large. 6. Surface polished and marked by concentric and oblique lines on the two sides. Subgenus Politoleda Subgenus SACCELLA Woodring, 1925 {Ledina Sacco, Dec. 1898, not Ledina Dall, April 1898.) Type species by original designation, Area fragilis Chemnitz (T=Leda commutata Philippi). Miocene to Recent, Mediterranean. Shell generally small, the posterior side much narrowed, sharply pointed at the end, the rostrum concave, wide, unicarinate or bordered by a sharp ridge or rib. Hinge with the anterior and posterior set of teeth of nearly equal length. Surface sculptured with fine or coarse concentrics. Posterior end with a small, open gap. Thiele considered Saccella as a synonym of Jupiteria Bellardi 1875, the type species of which [A^, concava (Born)] is a Miocene fossil from Italy, Jupiteria is closely similar to Saccella differing mainly by its more Corbula-\\\it shape and in having the rostrum less well defined, bordered simply by a blunt or weak ridge. Several of our Pacific species could be allocated to either section with equal reason. Key to Panamic-Pacific species of Saccella I, Shell strongly inequilateral, the posterior side much the longer, narrowed and contracted, and produced into a sharply pointed end, A. Mostly quite small species (length 12 mm. or under), the anterior side generally cut into by an impressed ray. a. Sculpture generally fine and uniform. 1. Concentric riblets continuous over the whole surface from the anterior submargins to the edge of the rostral keel. A^. ornata (PI. 2, fig. 3, 3a) 2. Concentric riblets not quite continuous over the whole surface, often partially smooth near the rostral keel. N.acrita{?\.2,i\g.7) b. Sculpture coarser and unequal. 3. Shell rather depressed, the concentric riblets much larger, heavier and more widely spaced in the middle zone. A^. impar (PI. 2, fig. 6) II. Shell higher, the two ends more nearly alike in length, the posterior side appearing short and stubby. B. Shell relatively large, 20 mm. or more in length. 4. Sculpture formed by uniform, rounded, close concentrics between deeply grooved interspaces. An anterior ray is often present. N. fastigata C. Shell smaller, 20 mm. or less in length. c. Concentric riblets are uniformly developed over the whole surface, ca. Concentric riblets low, rounded and appressed, separated by incised lines only. 60 AXEL A. OLSSON 5. Average length about 15 mm. Rostrum is narrowly elliptical in shape. N. eburnea cb. Concentric riblets raised and separated by wider and deeper interspaces, cba. Rostral keel bordered in front or below by a deeply indented ray, thus the posterior end of the shell may appear double-pointed. 6. Shell subelongated, the concentric riblets coarse, separated by inter- spaces, wider than the riblets. N.dranga{V\.2,{\g.S) 7. Shell shorter, higher and stubbier. Concentrics close. Anterior ray lacking or weak. N. elenensis elenensis 8. Anterior and posterior rays are both well developed. N. elenensis crispa ebb. Posterior ray is absent or very weak. 9. Concentric riblets relatively fine. Rostral keel rounded. N. callimene 10. Concentric riblets stronger, the rostrum more sharply defined. N. acapidensis (PI. 2, figs. 8, 8a) 11. Shell quite small, the concentric riblets strong. Anterior slope with an indented ray or fold. A^. hindsii 12. Shell small, concentric riblets strong. Rostrum is deeply concave bord- ered by a coarsely noded keel. Anterior ray is also developed. N. excavata Xucnlana (Saccella) ornata (d'Orbigny) Plate 2, figures 3, 3a Leda ornata d'Orbigny, 1846, Voy. Amer. Merid., vol. S, p. 546, pi. 82, figs. 4, 5, 6; Hanley, 1860, in Sowerby, Thes. Conch., Nuculidae, p. 24, No. 41, pi. 228, figs. 97, 98. Nuculana ornata (d'Orbigny), Hertlein and Strong, 1940, Zoologica, vol. 2S, pt. 4, No. 25, p. 405. Smaller than N. elenensis with a longer, more attenuated posterior side terminating in a sharply pointed end. The anterior slope is crossed by a wide, flat ray extending from the beak to the margin in front of which the surface is sharply raised, its edge often more or less beaded by the concentric sculpture. The sculpture is neat and regular, formed by concen- trics of medium strength and regularly spaced over the whole surface. Pos- terior or rostral keel strong, elevated, the enclosed rostral area wide, finely sculptured with the continuation of the external concentrics of the disk but more closely spaced. Fossil in the Pliocene of Ecuador. Range — Coasts of Peru and Ecuador. Peru: Bayovar, Bay of Sechura. Paita. Ecuador: Manta. Nnculana (Saccella) acrita (Dall) Plate 2, figure 7 Leda (Jupiteria) acrita Dall, 1908, Bull. Mus. Comp. Zoology, vol. 43, No. 6, pp. 374, 375 "Panama Bay". Leda laeviradius Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 106, pi. 17, fig. 7 "Guaymas". Nuculana (Saccella) laeviradius (Pilsbry and Lowe), Hertlein and Strong, 1940, Zoo- logica, vol. 25, pt. 4, pp. 396, 397, pi. 2, figs. 4, 7. Shell small (length 6 to 7 mm.), white or translucent, with a thin, pale straw-colored periostracum, subequilateral, the anterior side swollen, the posterior narrowly rostrate and acute at the end. Anterior dorsal margin PANAMIC-PACIFIC PELECYPODA 61 gently arcuate; the posterior slope straight, the opposed margins of the valves slightly pouting in the middle of a longitudinally striate, depressed rostral area bounded on each side by a rounded angle; these terminate at the slightly gaping end. A shallow, flattened ray of variable strength extends from the beak to the anterior basal margin; the edge in front of this ray is more or less crested by the concentric sculpture. Middle of valve sculptured with strong concentric ripples but which fade out or become obsolete leaving a smooth ray in front of the posterior rostral angle. Fresh specimens have a pale or subtranslucent straw-color and a thin periostracum; such specimens usually show faint radial streaks, seen best on the posterior side. Dead valves are porcellaneous white or yellow and show no radial markings. The anterior ray is strong in most shells. The sculpture is variable, typically with strong, rounded concentric riblets with wide interspaces and this sculpture covers most of the disk except for a narrow band below the rostral carina. As noted by Dall, an occasional speci- men may occur which is smooth over most of the surface. Range — Lower California to Ecuador. Mexico: Lower California; Guay- mas. Costa Rica: Port Parker (Hertlein and Strong). Panama: Bay (Dall). Ecuador: Off Esmeraldas. Nucniana (Saccella) impar (Pilsbry and Lowe) Plate 2, figure 6 Leda impar Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, pp. 106, 107, pi. 17, figs. 3-6 "Guaymas". Nuculana (Saccella) impar (Pilsbry and Lowe), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 396, pi. 2, fig. 6. The shell is of medium size (length about 10 mm.), narrowly elliptical, inequilateral, the beak located a little in front of the middle, the disk weakly convex to depressed. Anterior side higher, somewhat elongated, its margin obliquely rounded; the posterior side is somewhat longer, rostrate, concave above, sharply pointed at the end and with a smaller point below, its mar- gin, therefore, appearing somewhat bicarinate. The posterior-dorsal area is narrowly depressed and strongly sculptured longitudinally, bordered by a strongly noded rostral cord. Below the rostral cord, there is a narrow, de- pressed zone across which the concentric riblets of the sculpture extend with diminished strength. Surface sculpture consists of 10 or more strong, nar- row, concentric riblets between wide, flattened interspaces; these concen- trics are heaviest and most widely spaced over the middle of the disk, closer together on the surface of the umbone and near the ventral margin. Hinge with the anterior and posterior set of teeth of nearly equal length, the resilifer between them quite small; there are 14 teeth in the posterior row, all strong and nearly equal in size, except the first two on the inner side; there are 18 teeth in the anterior row, the first eight at the inner end being much smaller, the others increase rapidly in size towards the front. Pallial line and sinus indistinct. The lunule is a small, narrow, depressed area, transversely marked as if by the images of the teeth below. The rostral carina is flatly noded by the ends of the concentric riblets and where these are far apart, there may be one or two subsidiary nodes. Ventral margin finely crenulate except at the extreme posterior end. Length 10.2 mm., height 5 mm., semidiameter 2mm. (a left valve USNM). Off lower California, sta. 2822 in 21 fathoms U. S. Fish Com. Length 12 mm., height 6.2 mm., diameter 4.6 mm. (Pilsbry and Lowe). 62 AXEL A. OLSSON A well-marked species characterized by its strong sculpture and in having minute crenulations along its inner ventral margin. Range — Lower California to Costa Rica. Mexico: Lower California; Punta Penasco (Lowe); Guaymas (Pilsbry and Lowe). Costa Rica: Port Parker (Hertlein and Strong). Ifuculana (Saecella) fastlgata Keen Plate 2, figures 2, 2a; Plate 3, figure 9 Nucula gibbosa Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198 "Tumbez". — Sowerby, 1833, Conch. Illust., Nuculae, p. 4, pi. IS, fig. 9. Not N. gibbosa of Fleming, 1828. Leda gibbosa Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 120, sp. 28, pi. 228, fig. 79. Nuculana (Saccclla) gibbosa (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 395, 396, pi. 2, figs. 5, 8. Nuculana (Saccella) fastigata Keen, 1958, Bull. Amer. Paleont, vol. 38, No. 172, p. 240, pi. 31, figs. 1, 2. New name for A^. gibbosa Sowerb>/, 1833. Shell often quite large (max. length about 31 mm.), elongate-subovate, convex and rather solid, white, often chalky, under an olive-brown periostra- cum, the anterior side rather long with straight dorsal margin, the posterior side narrowed and rostrated. Sculpture is formed by strong, narrowly rounded concentric riblets, their intervals as wide and flat-bottomed; this sculpture is nearly uniform over the whole surface. Anterior slope has a slightly de- pressed ray which hardly affects the sculpture but may .sinuate the ventral margin to a small degree. Anterior-dorsal area depressed, longitudinally sculptured, the small lunule within smooth. Rostrum is quite large, ellipti- cal, strongly sculptured, the rostral ridge low. Pallial sinus is large. Length 31 mm., height 17 mm., diameter 12.8 mm. Range — Mexico to Peru. Peru: Tumbez; Zorritos. Nacnlana (Saccella) ebarnea (Sowerby) Plate 2, figures 4, 4a; Plate 3, figure 10 Nucula eburnea Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198. — Sowerby, 1833, Conch. Illust., Nuculae, pp. 4, 6, pi. IS, fig. 10. Leda eburnea Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 124, No. 33, PI. 228, fig. 90. — Sowerby, 1871, Reeve, Conch. Icon., vol. 18, Laeda, pi. 5, fig. 29. Nuculana (Saccella) eburnea (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, p. 395, pi. 2, figs. 1, 2, 3. Shell of medium size (length up to about 16 mm.), about twice as long as high, semi-elliptical, the umbones and beaks submedian, convex. Pos- terior side narrowed, attenuate, the dorsal margin concave, the end pointed, the anterior side narrowly rounded. Lunule distinct, elliptical, a trifle more than half the length of the anterior side. Posterior-dorsal or rostral area wide, as long as the posterior side, sculptured with straight, parallel lines and defined by an outer angle. Surface is sculptured with evenly spaced, incised lines forming concentric ribbons, uniformly developed over most of the surface except for a narrow, smooth ray sometimes present just below the posterior angle. The commonest species of Nuculana, easily recognized by its plain sculp- ture of even, smooth concentrics, and well-defined lunule. Range — Gulf of Fonseca, El Salvador southward to northern Peru. Panama: Bucaro. Canal Zone: Venado Beach; Colombia; Isla del Gallo. Ecuador: Santa Elena; Punta Blanca; Galeras. Peru: Zorritos. PANAMIC-PACIFIC PELECYPODA 6S XucQlana (Saccella) dranga, new species Plate 2, figure 5 Shell of medium size (length about 12 mm.), subelliptical, the length about twice the height, the beak and umbone placed nearly in the middle. There is a deeply indented ray along the lower side of the posterior or rostral keel which sharply bends or in some cases slightly dislocates the sculptural lamellae which cross it; the anterior ray is much weaker or wholly absent, the lines of sculpture being merely depressed, or weakly flexed by it. The posterior end is pointed, occasionally with a smaller point below it on the lower side of the indented ray. Sculpture is strong and on most specimens quite uniform; it is formed by strong, triangular, concentric lamellae or riblets, their dorsal side a trifle shorter and steeper, sometimes with a small overhang between deeply grooved or wavelike interspaces of the same width. The concentrics are generally of uniform size across the middle of the disk (20 or more), a little smaller on the surface of the um- bone and somewhat more crowded together near the ventral margin; an occasional one is deeper and marks a rest period. The rostrum is large, set apart by the posterior or rostral angle, which is nodose or serrated by the concentrics; its shape is narrowly elliptical and marked with fine, parallel lamellae. The lunule is small and narrow, flat, with cross sculpture formed by the roots of the hinge teeth. Hinge provided with strong teeth, in an equal series, about 18 teeth in the anterior row and about 16 in the posterior row, the middle ones extremely small. Length 12 mm.; height 6 mm.; diameter 2.3 mm. Esmeraldas, Ecuador. Holotype ANSP 218926. This may be a widely distributed species, often identified with N. elenensis (Sowerby) from which it is separated by its greater length in ratio to its height and sharper sculpture. Relations are also indicated with N. acapulcensis Pilsbry and Lowe. The species is named for the late Mr. Ted Dranga, well-known shell collector and who acco^mpanied the author on his Ecuadorian expedition of 1955. Range — Off Ecuador but probably north to Mexico. Ecuador: Esmeraldas. Nncalana (Saccella) elenensis (Sowerby) Plate 1, figure 9 Nucula elenensis Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198. — Sowerby, 1833, Conch. Illust., Nuculae, p. 4, No. 19, pi. 15, fig. 1+ "Tumbez". Leda elenensis Hanley, in Sowerby, 1860, Thes. Conch., Nuculidae, p. 121, No. 29, figs. 70-72. (Fig. 70 is considered as the typical form). Nuculana (Saccella) elenensis (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 393, pi. 1, figs. 17, 18, 19 (copied from Hanley) ; the others are N. acapulcensis Pilsbry and Lowe. Not A'^. elenensis Maxwell Smith, 1944, Panamic Marine Shells, fig. 626B. The shell is small or medium-sized (length 12-13 mm.), short, stubby, soHd and convex, with nearly central beaks, rounded anterior side and a narrowed, pointed posterior end, deeply concave on the dorsal margin. The sculpture is formed by subequal, coarse, concentric riblets between deeply grooved, sometimes pitted interspaces. There is usually an impressed zone extending from the beak to a point near the anterior-ventral margin causing a slight flattening or flexing of the concentric riblets. On the posterior side, there is a wider and more deeply impressed ray just below the keel which 64 AXEL A, OLSSON may deeply emarginate the posterior-ventral end so that it appears double pointed. There is a small, narrowly linear lunule and a much larger, well-, sculptured rostrum covering the whole length of the posterior area between the dorsal margin and the keel. This species is variable and several subspecies or races could easily be recognized. The typical form of N. elenensis is shown by figure 14 in Sower- by's Conchological Illustrations and by Hanley's figure 70 in his monograph of the Nuculidae. To this shell, Hanley proposed the varietal name of gibbosa and described it as follows: Beaked-ovate, very ventricose, the anterior indented ray not very conspicuous; ribs scarcely so broad as their intervals; front extremity only slightly narrowed; rostrum much recurved, its tip above the middle; ventral margin remarkably arched in front, and much rising behind. This species is relatively rare at most localities, generally small and seldom exceeding 12 mm. in length. Although variable in its convexity, the species is easily distinguished by its rather stubby form, strong sculpture and by its well-marked posterior rib so that the posterior end appears as if double pointed. The anterior ray is weak or strong, and it often forms a slight flexure across the anterior slope. Range — Coast of northern Peru and Ecuador. Ecuador: Esmeraldas; Manta; Santa Elena; Ancon. Peru: Bay of Sechura. ^'ucnlana (Saccella) elenensis crispa (Hinds) Nucula crispa Hinds, 1843, Proc. Zool. Soc. London, p. 100 (Hab. Gulf of Nicoya; from 36 fm.— Hinds, 1844, Zool. Voy. Sulphur, Moll. pt. 3, p. 64, pi. 18, fig. 14. Leda crispa (Hinds), Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 134, sp. 50, pi. 229, figs. 107, 108. Nuculana crispa (Hinds), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 403. Shell small, (length about 6.5 mm.), stubby, coarsely concentrically costellated throughout, the riblets somewhat shelving and about as broad as their intervals which are radiatingly lirated at the posterior end. The posterior end is sharply rostrate, bordered by a deeply indented ray below, the rostrum large, with close concentric lines bordered by a coarsely costellated keel. This form was described as a species by Hinds. It is here considered as a subspecies of N. elenensis in which the anterior indented ray is strongly developed. Range — Panama southward to Ecuador. Ifncnlana (Saccella) callimene (Dall) Plate 1, figures 7, 7a, 7b Leda (Jupiteria) callimene Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, p. 372, pi. 17, figs. 3, 4 "Gulf of Panama, 259 fathoms". Nuculana (Saccella) callimene (Dall), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 393, pi. 1, fig. 13. Shell small (average length, 15 to 16 mm.), solid, plump, white or yellowish brown, equivalve and inequilateral. No escutcheon but the pos- terior-dorsal area is wide, bounded by a rostral angle; there is an elongated, narrow lunule poorly defined by a slight change of sculpture. Sculpture con- sists of numerous, small, concentric riblets between somewhat wider, grooved interspaces, uniformly developed over the whole surface except for a narrow, PANAMIC-PACIFIC PELECYPODA 65 smoothish space along the rostral carina. On the anterior, rounded slope, the concentric riblets are flexed slightly by an impressed ray. Interior of the shell shows its solid build, the adductor scars being deeply impressed, the pallial line also impressed and showing a small, shallow sinus. Hinge plate is relatively large and stout, the hinge teeth strong and with approxi- mately the same number in each set. Length 15.5 mm., height 10.5 mm., diameter 7 mm. This is a deepwater species from the Gulf of Panama. The posterior- dorsal side is nearly straight, the two ends of the shell appearing subequal. Sculpture is fine and close. A similar species (N. chiriquiana Olsson) occurs in the Pliocene of the Burica Peninsula. Range — Panama. Ifuculana (Saccella) acapnlcensis (Pilsbry and Lowe) Plate 2. figures 8, 8a Leda (Saccella) acapnlcensis Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 107, pi. 17, figs. 1, 2 Acapulco, Mexico in 20 fathonas. Nuculana (Saccella) elenensis (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, pp. 393, 394, pi. 1, figs. 12, 14, IS, 16, 22. (Not A^. elenensis Sowerby, 1833.) The shell is rather solid, plump, white under a thin light grayish-olive periostracum. Anterior end rounded but with somewhat uneven outline, posterior end produced, rostrate, tapering to a narrow point, the dorsal slope concave behind, the edges of the valves projecting very little above the posterior keel. Ventral margin strongly arcuate, straight or even slightly concave close to the posterior point. Lunule not sunken, very narrowly lanceolate, transversely costulate; posterior dorsal area broadly lanceolate, bounded by a rounded rib in each valve, a little convex in the middle, con- cave along the ridges, longitudinally costate in continuation of the ex- ternal concentric ridges, which are a little enlarged as they pass over the posterior rounded rib or keel. Sculpture of regular concentric costae about as wide as their intervals. Towards the ventral margin the ridges have abrupt lower margins. The interior is white. Hinge with about 14 well-de- veloped teeth on each side of the broadly triangular resilium, and with a group of about six minute, narrow teeth behind, and about 10 before the resilium. Pallial sinus small, rounded at the end. Length, 13.2 mm., height 7.0 mm., diam. 5.0 mm. Length, 15.3 mm., height 8.3 mm., diam. 6.3 mm. — (Pilsbry and Lowe.) This form was united with N. elenensis by Hertlein and Strong (fol- lowed also by Myra Keen) but it appears to be a distinct species, differing from N. elenensis by its longer form, less convex valves, and by its more regular and sharper sculpture. The anterior slope bears sometimes a weakly indented ray. Range — Mexico to Ecuador. Mexico: Acapulco. Ecuador: Esmeraldas. Ifucniana (Saccella) hindsii (Hanley) Leda hindsii Hanley, 1860, Proc. Zool. Soc. London, p. 440 Nicoya. — Hanley, in Sowerby 1860, Thes. Conch., vol. 3, Nuculidae, p. 135, sp. 51, pi. 229, fig. 102. Nuculana hindsii (Hanley), Hertlein and Strong, 1940, Zoologica, vol. 25, Pt. 4, p. 4D4. Nuculana (Saccella) hindsii (Hanley), Tucker Abbott, 1954, American Seashells, p. 339 Shell small (length about 8 mm.), light yellowish brown, ovate-oblong, inequilateral, more or less vientricose with a conspicuous indented ray on the anterior slope. The sculpture of closely spaced concentric riblets cover 66 AXEL A. OLSSON the external surface except for a smooth space below the rostral keel; these riblets are numerous and regular, scarcely as wide as their intervals. Tucker Abbott reported this Nuculana as common along the west coast of the United States where it has generally been identified in the past as N. acuta Conrad, an Atlantic Coast species. Range — Alaska to Panama. Nuculana excarata (Hinds) Nucula excavata Hinds, 1943, Proc. Zool. Soc. London, p. 100 Panama in 30 fm. — Hinds, 1844, Zool. Voy. Sulphur, Moll., pt. 3, p. 64, pi. 18, fig. 17. Leda excavata (Hinds), Hanley, 1860, Thes. Conch., vol. 3, Nuculidae, pp. 31, 32, sp. 52, pi. 229, figs. 104, 105. Nuculana excavata (Hinds), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 404. Keen, 1958, Bull. Amer. Paleont., vol. 38, No. 172, p. 239.— Keen, 1958, Sea Shells of Tropical West America, p. 20, fig. 19. A small, rather oblique, sharply beaked shell, short ovate, plump. The posterior or rostral ridge is large and scabrously noded by the sculp- ture which consists of numerous, sublamellose concentric riblets, regularly disposed over the whole surface except on the dorsal areas. The beak is in the middle, the anterior end rounded, the posterior with a sharp beak, its tip narrow and curved upward. This species has not been recorded since its discovery and is known only from its original figures and imperfect description. As Myra Keen has recently noted, the name "excavata" is preoccupied (by Goldfuss, 1837) and will need replacement if and when the types or authentically identified specimens are found. Range — Panama. Subgenus POLITOLEDA Hertlein and Strong, 1940 Type species by original designation, Nucula -polita Sowerby. Shell relatively large, elongate subelliptical, the posterior end sharply pointed. Posterior-dorsal area narrow, as long as the posterior side and neatly sculptured with small, parallel incised lines. Surface white, poHshed or glazed, with minute growth lines and sculptured with strong, quite widely spaced incised lines which on the posterior side pass upwards obliquely across the umbonal slope, usually fading out on the surface of the mid-um- bones to appear again more widely spaced on the anterior side. Pallial sinus large, widely rounded and reaching to a line under the beak. Nuculana (Polltoleda) polita (Sowerby) Plate 2, figures 1, la Nucula polita Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198.— Sowerby, 1833, Conch. Illust., Nuculae, p. 4, pi. 15, fig. 11. Leda polita Hanley, in Sowerby, 1860, Thes. Conch., vol. 3, Nuculidae, p. 125, sp. 36, pi. 228, fig. 68.— Sowerby, 1871, Reeve, Conch. Icon., vol. 18, Laeda pi. 3, fig. 16. Nuculana polita (Sowerby), Maxwell Smith, 1944, Panamic Marine Shells, p. 48, figs. 622, 626C. , ^ Nuculana (Politoleda) polita (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt 4, pp. 397, 398, pi. 2, fig. 9. This species is easily recognized by its large size and characteristic sculpture. It is especially common on the beach at Old Panama. Range — Guatemala to Panama. Panama: Old Panama; Panama City; San Carlos. Canal Zone: Palo Seco; Venado Beach. For other records see Hertlein and Strong. PANAMIC-PACIFIC PELECYPODA 67 Subgenus COSTELLOLEDA Hertlein and Strong Type species by original designation, Nucula costeUata Sowerby. Shell elongate with strong concentric sculpture. Nuculana (Costelloleda) costellata (Sowerby) Plate 3, figure 8 Nucula costellata Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198 (Hab. ad Panamam). — Sowerby, 1833, Conch., Illust., Nuculae, p. 4, pi. 15, fig. 8. — ^Reeve, 1841, Conch. Icon., vol. 1, Nucula, pi. 85, fig. 8. Leda costellata Hanley, in Sowerby, 1860, Thes. Conch., vol. 3 Nuculidae, p. HI, sp. 11, pi. 228, fig. 59. Nuculana (Costelloleda) costellata (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 398, 399, pi. 2, fig. 10. Shell elongate, rather thin, compressed, white, under a pale olivaceous or ash-colored epidermis, occasionally iridescent, the surface sculptured with distant, erect concentrics which terminate just below the posterior- umbonal angle formed by two nodose or squamose ridges enclosing between them a flat, smooth area; interval between the concentric lamellae smooth; posterior-dorsal area or rostrum large, smooth, concave, its margins pouting; lunule linear. A more or less subobsolete anterior ray is generally present. Length 22 mm., height 8 mm., diameter (both valves) 4.4 mm. — (Hert- lein and Strong). Generally rare. Range — Lower California to Panama. ]N^uciiIana (Costelloleda) marella Hertlein and Strong Nuculana (Costelloleda) marella Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 399, 400, pi. 2, figs. 12, 13. Much like N, costellata (Sowerby) but is larger, more rostrate, and has finer concentric sculpture. Rare. Range — Gulf of California to Panama. Panama: Gulf of Chiriqui in 35 to 40 fathoms. Subgenus THESTTLEDA Iredale, 1929 Type species by original designation, Leda ramsayi E. A. Smith. New South Wales. Shell small or of medium size, thin, the anterior side wide, rounded, the posterior side nearly twice the length of the anterior, sharply narrowed, attenuated and squarely truncated at the end. Surface sculptured with strong, concentric rugae which turn sharply upward as they cross the pos- terior or rostral ridge. Two radial ridges form keels along the rostrum. Chondrophore large. This subgenus is based on an Australian species, but the following appears to belong to it also. Nuculana (Tliestyleda) lumiata (Carpenter) Leda hamata Carpenter, 1864, Kept. Brit. Assoc. Adv. Sci. for 1863, pp. 612, 644. Santa Barbara, Calif. — Sowerby, 1871, Conch. Icon., vol. 18, Laeda, sp. 56, pi. 9, fig. 56.— Dall, 1902, Proc. U. S. Nat. Museum, vol. 24, p. 558, pi. 40, fig. 9. Nuculana hamata (Carpenter), Grant and Gale, 1931, Mem. San. Diego Soc. Nat Hist., vol. 1, p. 125, pi. 1, figs. 14, 15. Nuculana (Thestyleda) hamata (Carpenter), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pi. 2, fig. 14.— Tucker Abbott, 1954, American Seashells, p. 339, fig. 26d.— Palmer, 1958, Mem. Geol. Soc America, No. 76, p. 61, pi. 2, figi. 4-6. 68 AXEL A. OLSSON Generally less than 15 mm. in length, compressed, of a dark chestnut- brown color, its shape and sculpture like that of a small crassatellid, the posterior side much longer than the anterior, narrowly attenuated and squarely truncated at the end. This is a common species off the coast of California, often dredged in waters of 20 to 200 fathoms. Hertlein and Strong record the species off the Mexican coast (east of Cedros Island). Dall (1921) gave its range as from Puget Sound to Panama, but the species is probably not a member of the Panamic-Pacific fauna. Genus ADKAIfA H. and A. Adams, 1858 Type species by subsequent designation, Stoliczka, 1871, Nucula (Adrana) lanceolata Lamarck. No locality cited. (See Hertlein and Strong, 1840, p. 406). Shell elongate or narrowly lanceolate, compressed, the dorsal margin nearly straight with small, subcentral beaks, the ventral margin rounded and often sinuate near the ends. No rostral area but a narrow, flattened lunule and escutcheon is usually well developed, bounded by a rounded, often crenate umbonal ridge. Ligament internal and attached to a wide, often weakly bilobed chondrophore placed under the beak and directed anteriorly. Hinge teeth numerous and arranged in an anterior and posterior series. Pallial sinus rounded and of moderate size. Sculpture smooth or composed of threadlike, concentric ridges, sometimes becoming oblique posteriorly. Drift valves of these lovely shells are often common on some sandy beaches. About six valid species are recognized in this review and as shown in the keys belong to two well-marked groups. Key to species of Adrana L The dorsal margin is nearly straight, the lower or ventral margin is commonly sinuated towards the anterior end. A. Shell relatively narrow and slender, the ratio of height to length about 1 to 5. 1 _ ...„ ^ A. sowerhyana B. Shell higher, ratio of height to length about 1 to 4 or less. 2. Length about 38 mm, the beaks placed near the anterior one-third. Gulf of California. PI. 3, fig. 7. A. penascoensis 3. Average length about 60 mm. The beak is placed a little anterior of the middle. A. ctdtrata 4. Shell larger, often exceeding 100 mm. in length. Beaks placed quite close to the middle. A. suprema n. Dorsal margin arched at the beak, concave behind. C. Concentric sculpture developed over the whole surface of shell. 5. Shell length about 35 mm. The lines of sculpture are relatively fine and developed uniformly over the whole disk. A. crenijera 6. Shell smaller, the lines of sculpture heavy and coarse on the anterior side. A tonosiana PANAMIC-PACIFIC PELECYPODA 69 D. Sculpture lines varied, concentric on the anterior side and more or less oblique on the middle and posterior zones. A smooth ray generally borders the posterior carina. 7. » „ A. exoptata Adrana cultrata Keen Plate 3, figures 1, 2 iVucula elongata Sowerby, 1832, Proc. Zool. Soc. London, p. 197 (Xipixapi).— Sowerby, 1833, Conch. Illust., Nuculae, pi. 14, fig. 2.— Reeve, 1841, Conch. Icon., Laeda vol. 1, p. 110, pi. 84, fig. 2. Not A^. elongata Bosc, 1801, or Defrance, 1825. Leda elongata Hanley, in Sowerby, 1860, Thes. Conch., vol. 3, Nuculidae, p. 106, sp. 1, pi. 227, fig. 39. Adrana elongata (Sowerby), Hertlein and Strong 1940, Zoologica, vol. 25, pt. 4, p. 409, pi. 2. fig. 16.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist, vol. 107, art. 2, p. 170. Adrana cultrata Keen, 1958, Bull. Amer. Paleont, vol. 38, No. 172, pp. 240, 241. New name for A'^. elongata Sowerby, preoccupied. Blade-shaped, highest under the beak which is nearly central, the posterior-ventral margin evenly curved, the anterior-ventral margin slightly sinuated. The shell is rather thin, semitransparent, gaping at both ends, white, under an excessively thin, brown or olivaceous periostracum, the surface sculptured with fine, threadlike striae, so fine above as to appear almost wanting, close and regular in the middle, more remotely spaced in front. Average length, 50 mm. Range — Mexico to Ecuador. Adrana snprema (Pllsbry and Olsson) Plate 3, figure 5 Nuculana (Adrana) sufrema Pilsbry and Olsson, 1935, Nautilus, vol. 48, No. 4, p. 117, pi. 6, fig. 1. Adrana suprema (Pilsbry and Olsson), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, p. 411. The shell is long, strongly compressed, subequilateral, with dark olive- brown epidermis (largely or wholly lost in specimens seen); glossy. The dorsal outline is nearly straight, the ventral margin gently convex, straight- ened or slightly concave towards the posterior end, the greatest height being about the anterior third of the length. Anterior end more obtuse than the posterior. Dorsal areas extremely narrow, bounded by inconspicuous angles. Sculpture of weak growth lines and excessively fine and clear-cut longitudinal striae, obliquely crossing the lines of growth posteriorly, mainly curving with them in the anterior half. They are wanting in a band along the dorsal side, but extend nearly to the ends. Interior white, the pallial sinus occupy- ing more than one-third of the total length, truncate at the end. Tooth-row long, occupying 60% of the whole length, anterior and posterior series of about equal length, teeth very small V-shaped. Cartilage pit very shallow, about 10 mm., long in the type. Length 107 mm., height 23.5 mm., semi- diameter 4.6 mm. — [Pilsbry and Olsson, 1935]. This is the largest Adrana and is distinguished by the nearly central beaks, those of A. cultrata are a little more anterior. Range — Panama. Panama: Beach between Port Guanico and the Guanico River, Los Santos Province. Adrana sowerbyana (d'Orbigny) Plate 3, figures, 3, 3a Nucula lanceolata Lamarck, Sowerby, 1833, Conch. Illust., Nuculae, p. 3, pi. 14, fig. 1. 70 AXEL A. OLSSON — Hanley, 1846, Cat. Bivalve Recent Shells, Suppl. pi. 19, fig. 49. (Not Nucula lanceolata Lamarck, 1819.) Leda soiuerbiana d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, p. 544. (New name for N. lanceolata Sovjrerby, 1833, not Lamarck, 1819.) Leda soiverbiana d'Orbigny, Hanley, 1860, in Sowerby, Thes. Conch., vol. 3, Nuculidae, p. 107, No. 2, pi. 227, fig. 33. Adrana sonverbyana (d'Orbigny), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, pp. 410, 411. Shell elongate, compressed, white or translucent, nearly five times as long as high, the beaks flattened and small, placed a little anterior of the middle. The dorsal margin is straight except for a slight upturn at the extreme posterior end. The ventral margin has a uniform gentle curve except for a small sinuation near the anterior end, and a much milder one at the posterior end. Lunule long and narrow, no rostral area, the escutcheon extremely narrow, long and smooth. Sculpture over most of the surface con- sists of fine, close concentric incised lines forming narrow ribbons, occasion- ally smoothing out on the posterior slope, becoming coarser and wider as they bend backwards along the anterior or lunular margin, and strongly sinuated by the bend in the anterior-ventral margin. There is a smooth ray just below the posterior-dorsal margin. Length 60.5 mm , height 12.5 mm., diameter 21 mm. right valve. Isla del Gallo, Colombia, Certain nomenclatural problems connected with this species have been discussed in some detail by Hertlein and Strong. My shell from Isla del Gallo, Colombia, agrees in shape well with that shown by Sowerby (as lanceolata) in his Conchological Illustrations, plate 14, figure 1. Range — Panama to Ecuador. Colombia: Isla del Gallo. Ecuador: Xipixapi (Puerto Callo), (Sowerby), Adrana crenifera (Sowerby) Plate 3, figures 4, 4a, 4b Nucula crenifera Sov^erby, 1833, Proc. Zool. Soc. London for 1832, p. 197. — Sowerby, 1833, Conch. Illust, Nuculae, p. 3, No. 4, pi. 14, fig. 3. Leda crenifera (Sowerby) Hanley, 1860 in Sowerby's Thes. Conch., vol. 3, Nuculidae, p. 110, sp. 8, pi. 227, figs. 37, 38. Laeda arcuata Sowerby, 1871, Reeve, Conch. Icon., vol. 18, Lacda, pi. 4, fig. 20. Nuculana arcuata (Sowerby) Pilsbry and Olsson, 1935, Nautilus, vol. 48, No. 4, p. 118, pi. 6, figs. 2, 3. Adrana crenifera (Sowerby), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No, 25, p, 408. Shell elongate-lanceolate, dull white, slightly convex, the length about four times the height. Beaks small, not quite in the middle, the posterior side being a little longer than the anterior. The dorsal margin is not straight, sloping down slightly on each side of the beak and with the posterior ex- tremity turned up somewhat. The ventral margin is well rounded except near the posterior end which is drawn out and attenuated. Lunule is as long as the anterior side, narrow, bounded externally by a coarse, rounded rib; the escutcheon is similar, its bounding rib finely crenate. Sculpture consists of fine, sharp, concentric threads, evenly developed over the whole surface. There is a distinct, flattened ray below the posterior-umbonal angle. This species is locally plentiful along the coast of Ecuador and Peru. A. arcuata (Sowerby), described without indication of locality, appears PANAMIC-PACIFIC PELECYPODA 71 to be the same species, as confirmed by J. R. Le Brocton Tomlin after examination of the type at the British Museum (Natural History). Range — Coast of Ecuador and northwestern Peru. Peru: Punta Picos; Zorritos; Tumbez. Ecuador: Ancon Point; Santa Elena; Punta Blanca; Canoa. Adrana exoptata (Pilsbry and Lowe) Plate 3, figure 6 Leda (Adrana) exoptata Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 107, pi. 17, figs. 8, 9. Adrana exoptata (Pilsbry and Lowe), Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, pp. 409, 410, pi. 2, fig. H.— Hertlein and Strong, 1955, Bull. Araer. Mus. Nat. Hist., vol. 107, art. 2, pp. 170, 171, pi. 3, figs. 6, 7. Shell small (length usually less than 20 mm.), elongate, compressed, the anterior side somewhat higher and shorter. Dorsal margin is not quite straight. Sculpture is formed by fine, threadlike ridges concentrically ar- ranged on the anterior part, straightening out and sloping towards the ventral margin and crossing the lines of growth obliquely on the middle and posterior sides. A smooth radial band lies below and in front of the posterior carina; this smooth zone may be narrow with the sculpture ending sharply against it or the band may be wider if the sculptural ridges fade out towards it in a more irregular manner. TTiis is a small species seldom exceeding 17 mm. in length and easily recognized by the sculpture becoming oblique on the middle and posterior sides of the disk. The smooth band below the posterior carina is variable in its development and in some shells may be lacking. Range — ^Mexico southward to Ecuador. Mexico: Guaymas; Tangola- Tangola. Panama: Pearl Islands; Pina Bay; (Hertlein and Strong). Colombia: Ardita Bay; Aquacata (Hertlein and Strong). Ecuador: Off Cabo Pasado (Hertlein and Strong); Esmeraldas. Adrana tonosiana (Pilsbry and Olsson) Plate 3, figures 11, 11a Nuculana (Adrana) tonosiana Pilsbry and Olsson, 1935, Nautilus, vol. 48, No. 4, pp. 117, 118, pi. 6, fig. 4.— Hertlein and Strong, 1940, Zoologica, vol. 24, pt. 4, No. 25, p. 412, pi. 2, fig. 15. This species closely resembles A. crenijera (Sowerby), which it seems to replace to the northward of Ecuador. A. tonosiana is much smaller, proportionately shorter and higher, with coarser sculpture on a band below the anterior-dorsal angle, the concentric threads spreading apart, dividing and with an intercalary threadier appearing between them along the um- bonal-lunular angle. Range — Off Mazatlan to Panama. Panama: Biicaro; Gulf of Chiriqui (Hertlein and Strong). For Guatemala, El Salvador, and Nicaragua records see Hertlein and Strong. Family JfTJCINELLIDAE Shells mostly minute, obliquely oblong, subtrigonal or egg-shaped, the anterior side short, porcellaneous. Ligament internal seated in a small resilifer bordered by a few, relatively large subtaxodont teeth. 72 AXEL A. OLSSON Genus KUCOELLA Wood, 1851 Pleurodon Wood, 1840, not of Harlan, 1831 (Mammalia); Nuculina d'Orbigny, 1844, not of "Felippi" Porro, 1837; Cyrillona Iredale, 1829; Neopleurodon Hertlein and Strong, 1940. (See Vokes, 1956, Jour. Paleont., vol. 30, No. 3, pp. 652.) Type species by monotypy, Pleurodon ovalis Wood. The shell is usually small, resembling Nucula but with a non-nacreous structure, its shape oval, subtrigonal to obliquely egg-shaped, the anterior side being shorter and more sharply descending, the posterior side hence longer and often a little expanded. Hinge plate relatively short and wide, somewhat angulated under the beak, in the angle of which lies a small resilifer, bordered on each side by a few, relatively large teeth; the left valve has a prominent, posterior lateral tooth which is received in a de- pression in the opposite valve. Surface smooth or with fine concentrics. There is some uncertainty as to the orientation of the valves of Nucinella (see Vokes, p. 656) which must await fuller knowledge of the internal anatomy and the study of the ligament from fresh specimens. Vokes considered the ligament as external, Dall and some other authors as internal. In the above description, I have considered the ligament as being internal and the shorter side as anterior. Nucinella subdolns (Strong and Hertlein) Plate 17, figure 12 Pleurodon subdolus Strong and Hertlein, 1937, Proc. California Acad. Sci., 4th ser., vol. 22, No. 6, p. 162, pi. 35, figs. 14, 18, 19. About 5 miles west of Mazatlan, Mexico, 12 fra. Cyrilla (Neopleurodon) subdolus (Strong and Hertkin), 1940, Zoologica, vol. 25, pt. 4, p. 420. Nucinella subdolus (Strong and Hertlein), Vokes, 1956, Jour. Paleont, vol. 30, No. 3, p. 666. Shell minute, obliquely ovate, smooth, white, translucent; beaks prominent, hinge line short, straight, forming a small, flaring projection at each end; hinge plate broad, continued as a shelf along more than half of the posterior side of each valve, the inner margin turned up and, in the left valve, ending in a lateral tooth; cardinal teeth small, indistinct, divided into a posterior and anterior series, three or four in each, which meet at an angle, those in the posterior series being larger and wider spaced. The type measures: length 1.85 mm., height 2.5 mm. — [Strong and Hertlein, 1937]. Although known from only a few specimens dredged off Mazatlan, Mexico, this small species may prove to have a wide distribution through the Panamic Province. A few imperfect specimens, probably this species, are known from the Pliocene of Quebrada Camarones, Ecuador, Nucinella adamsi (Dall) from the Florida Straits is a similar species. PANAMIC-PACIFIC PELECYPODA 73 Subclass FILIBRANCHIATA Order EUTAXODONTIDA Superfamily ARCACEA Family ARCIDAE To this great family belong the Ark shells, sometimes conservatively referred to a single genus, Area. For our purpose, the arks are divided into three groups or subfamilies, the Arcinae, Anadarinae, and the Noetinae. The Arcinae comprise the true Arks; they are mostly nestlers living under stones or clustered together in cracks and crevices, the shell anchored by its byssus which passes through a narrow or wide opening between the ventral margins of the valves. The Anadarinae and Noetinae are mostly free without a functional byssus or if a byssus is present, it is usually short, the margins of the valves showing little or no gap and fit together closely. The arcoid hinge is taxodont or composed of many small teeth and sockets arranged in a more or less continuous series along a straight hinge line. The ligament is external, attached to a narrow or high cardinal area, usually of triangular shape. Most species are marine but several are brackish and live habitually buried in the soft mud of mangrove swamps and similar situations or at the mouths of rivers emptying into the sea. Such brackish-water species have a coarse, heavy periostracum as protection against the corrosive action of acid waters. The ligament of the Arcidae is always external. In most genera of the family, the ligament covers most of the cardinal area or the space between the hinge line and the lateral margins of the umbone and the beak. This elastic structure is made up of two distinct layers; the upper or top layer, usually brown in color, is chitinous in composition, usually thin and functionally corresponds to the tensilium of other pelecypods; it is under- lain by a second or heavier layer composed of vertical, closely packed fibers generally showing a gray or silky luster and color. This lower layer represents the resilium although it lies entirely above the axial fulcrum of the hinge. The area covered by the ligament is set apart on each side by a deep groove into which the tensilium dips and is attached directly to the wall of the shell. Often the surface of the ligament and of the cardinal area beneath it may be plain and smooth (Cunearca) but more often it is cut into by deep lines; in most of the Arcinae and Anadarinae, these in- cisions are in the form of transverse grooves forming more or less trigonal or tent-shaped markings; in the Noetinae, these markings are vertically arranged. These grooves serve for the attachment of ribbons of tensilium which like rubber bands are stretched across the space above the hinge line and through their combined action aid greatly in the operational ef- ficiency of the whole ligament. The cardinal area may be fully or but partly covered by the ligament. The extent of the ligamental coverage should be noted as it is often an important character helpful in identification of a specimen in hand. Subfamily ARCDf AE Lamarck, 1809 or Fleming. 1828 Shell generally a nestler, more rarely a rock borer, attached by a byssus 74 AXEL A. OLSSON passing through a gap along the middle of the ventral margin. Valves often distorted and irregular in shape. Sculpture more or less decussated, formed by small or medium-sized radial riblets and concentric threads. Ventral margins of the shell smooth, not crenulated or fluted by the ribbed sculp- ture. Subfamily ANADARINAE Reinhart, 1935 Shell mostly free, the byssus small, the margins of the valves fitting tightly. Beaks are generally prosogyrous. Sculpture typically formed by strong, coarse, radial ribs, smooth or noded which form strong flutings along the ventral margins. Subfamily NOETINAE Stewart, 1930 Shell mostly free, with or without a byssal gap. Beaks opisthogyrous. Cardinal and ligamental area wholly or mostly anterior of the beaks, and generally marked with vertical grooves. Sculpture of fine or strong, often flattened ribs which flute or crenulate the margins. Posterior adductor scar bordered by a flange. Subfamily STRIARCmAE 7 KEY TO THE GENERA OF ARCIDAE IN THE PANAMIC-PAFICIC REGION I. Arcinae. Nestlers and borers, the shape of the shell regular or dis- torted, the ventral margin with a byssal gap placed a little anterior of the middle. Surface sculpture composed mostly of fine radial rib- lets or threads, noded or decussated by concentrics. Inner, ventral margins of the valve smooth, little affected by the external ribbed sculpture. A. The ligament covers the whole of the cardinal area, usually on both sides of the beak. a. The major part of the ligamental coverage lies behind the beaks; the posterior section of the hinge line the longest. 1. Shell rectangular, often expanded or winged posteriorly and with a prominent umbonal angle. Sculpture formed by numerous, somewhat irregular riblets. Cardinal area is relatively high and wide, the ligamental grooves forming tent-shaped incisions, usually few in number and irregular in their development. Color brown, often with zigzagged markings. Genus Area 2. Shell not conspicuously winged or emarginated and the umbonal angle rounded. Sculpture finely ribbed and decussated. Cardinal area elongated, thickly covered by tent-shaped, ligamental grooves. Genus Barbatia b. The major part of the ligament lies in front or anterior of the beaks, the anterior section of the hinge also much longer. ■^ A fourth subfamily, the Striarcinae may be recognized and would include the genus Arcopsis. Most genera of the Striarcinae are fossil. They resemble the Arcinae by their external sculpture and in having a ventral byssus, sometimes resulting in a gap, but they have a vertically striated ligament and the raised or flanged adductor scars of the Noetinae. PANAMIC-PACIFIC PELECYPODA 75 3. Shell narrowly elongated, pholadiform, rounded in cross-section, the anterior side much drawn out and wedged-shaped at the end, the posterior side greatly shortened and carinated. Genus Litharca B. The ligament with the resilium (generally with grooves) does not cover the whole surface of the cardinal area. c. Cardinal area relatively narrow, the ligament with the resilium developed mainly over its posterior portion; the anterior portion short, without transverse grooves, bare or covered by the periostra- cum only. The radial and concentric riblets finely or coarselj'^ beaded by their intersection. ca. The posterior-umbonal slope is strongly angled. 4. Sculpture more or less uniform and similar over the whole surface. Periostracum thin or lacking, white. Genus Acar 5. Radial riblets very unequal in size, those on the posterior-umbonal slope, large, highly elevated and coarse, the others low and flat. Genus Calloarca cb. The posterior-umbonal slope is low and rounded. 6. Shell relatively thin, white, under a coarse, pilose, brown perio- stracum, the radial riblets fine and numerous. Genus Fugleria d. The cardinal area relatively high with the ligament restricted to a small, inverted V-shaped area under the beak; the ligament area is vertically grooved or striated. 7. Shell small, solid, convex, boat-shaped, the sculpture formed by fine beaded, radial riblets. Genus Arcopsis II. Anadarinae. The shell is usually free in the adult stage or if held by a short byssus, the valves show no byssal gap along the ventral margin. The beaks are prosogyrous, facing forward over a cardinal area of variable size. The ligament is mainly developed behind or posterior of the beak, its area smooth or with transverse tent-shaped grooves originating under the tip of the beak. The external sculp- ture is typically formed by strong radial ribs which produce deep flutings along the inner side of the ventral margin. 8. A cardinal area is well developed, often quite high, and generally equally formed on both sides of the beak. Genus Anadara 9. The cardinal area is narrow and almost lacking so that the beaks are closely adjacent to the hinge margin. Ligament largely restricted to the posterior side, the posterior set of teeth hence the longest. Genus Lunarca III. Noetinae. Shell for the most part free. Beaks opisthogyrate or coiled backwards above the cardinal area. Ligament and cardinal area mostly or wholly anterior in position, vertically grooved or striated. Surface sculptured by rounded or flattened ribs, the interspaces often with interstitials. Posterior adductor scar bordered by a strong flange. 76 AXEL A. OLSSON 10. Shell with a solid built, subrhomboidal to subtrigonal shape with prominent umbones often bordered by a sharp, posterior, umbonal angle, the posterior side hence appearing as if sharply truncated. Genus Noetia 11. Shell thinner, modioliform, the posterior side much expanded. Riblets small. Genus Sheldonella Subfamily ARCDfAE Genus ARCA LInn6, 1758 Type species defined by Opinion 189, International Commission on Zoological Nomenclature, Area noae Linne. Shell of moderate size, subelongate, obscurely winged and generally with an umbonal angle and sharp beaks placed above a wide, flattened cardinal area. Middle of disk crossed by a wide depressed zone which more or less emarginates the ventral margin to form an open byssal gap. Sculp- ture radial, formed by alternating and generally irregular ribs. Cardinal area usually large, as long as the greatest length of the shell, wide and covered by the ligament, marked by scattered tent-shaped grooves radiating from the vicinity of the beaks. Hinge long and narrow, the teeth small and numerous, the posterior set the longest. Periostracum usually heavy and coarsely pilose. Area (Area) paciflca (Sowerby) P'late 4, figures 2, 2a-2d; Plate 86. figure 6 Byssoarca pacifica Sowerby, 1833, Proc, Zool. Soc. London, p. 17. Area pacifica (Sowerby), Reeve, 1844, Conch. Icon., Area, pi. 11, fig. 75.— Maury, 1922, Paleont. Amer., vol. 1, No. 4, pi. 4, pi. 1, fig. 15. Area (Area) pacifica (Sowerby) Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 155.— Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, pp. 26, 27, pi. 14, figs. 3, 4. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 179. This species is distinguished from its allied West Indian and Caribbean A. zebra Swainson (A. occidentalis Philippi) by its much wider, flatter cardinal area covered by a dark-brown to black ligament; by its generally more distorted form; wider, more expanded posterior side; by its larger byssal gap and coarser sculpture. Judging from specimens we have from Bocas Island, Panama, A. pacifica is apparently also living along parts of the Caribbean coast of Central America. Full grown specimens are usually heavily encrusted with marine growth. The surface of the shell below the periostracum is colored a rich mahogany brown or marked with zigzag strips of brown on a light-colored or white base. Length 65.4 mm., height 32 mm., diameter 46.3 mm. Punta Patilla, Panama City. Range — Lower California to northern Peru and the Galapagos Islands. Panama: Panama City; Biicaro; Burica Peninsula; Pearl Islands. Ecuador: Esmeraldas; Charapota; Manta; Santa Elena. Peru: Tumbez; Boca Pan; Mancora; Lobitos; Paita. Area (Area) nmtabllls (Sowerby) Plate 4, figures 3-3b; Plate 6, figures 2-2d Byssoarca mutabilis Sowerby, 1833, Proc. Zool. Soc. London, p. 17. PANAMIC-PACIFIC PELECYPODA 77 Area mutahilis (Sowerby) Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 13, fig. 85. — Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 167, pi. 1, fig. 5.— Maxwell Smith, 194»-, Panama Shells, fig. 648, Area (Area)mutabilis (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No, 47, p. 26, pi. 11, figs. 8-10. — Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 154. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 180, pi. 11, figs. 1, 2; text-figs. 79, 80 a-c— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist., vol. 107, art. 2, p, 171. Shell generally small, oblong, subrhomboidal, ventricose, often irregular or distorted, the ventral margin carrying a fairly large byssal gap, Umbones wide, often worn, and ending in slightly inrolled beaks and bordered pos- teriorly by a sharp umbonal ridge. Cardinal area elongate, subrhomboidal, high, concave, colored uniformly brown, with a few triangular or lozenge- shaped ligament grooves on the anterior portion. Sculpture consists of fine, more or less scabrous riblets over the main portion of the surface except on the posterior slope where they are much coarser. The periostracum when well preserved is quite dense, yellowish-brown in color and along the um^ bonal keel forms a high, deeply serrated fringe. This species is similar to Area umbonata Lamarck of the Atlantic and Caribbean but seems smaller, the largest specimen seen having a length of about 40 mm. Range — Gulf of California to Ecuador. Panama: Panama City; Bucaro; Ocones; Burica Peninsula, Ecuador: Puerto Callo; Isla la Plata; Santa Elena. Area (Area) trnncata (Sowerby) Plate 4, figure 1 Byssoarea truneata Sowerby, 1832, Proc. Zool. Soc. London, p. 19. Area truneata (Sowerby), Reeve, 1844, Conch, Icon., vol. 2, Area, pi. 11, fig. 74. — Maury, 1922, Paleont. Amer., vol, 1, No, 4, p, 169, pi. 1, fig. 2. This is a Galapagos Island species, unknown elsewhere. Distinguished from A. pacifica by its longer, more rectangular form, uniform dark-brown color with obscure markings on the sides only, and with a narrower byssal gap. The type lot in the British Museum (Nat. Hist.) consists of three double-valve specimens. Photographs of the type in the British Museum are presented on Plate 4. Range — Galapagos Island. Genus LITHAKCA Gray, 1842 Type species by subsequent designation. Gray, 1847, Byssoarea Hth- odomus Sowerby, A rock borer. The shell in the adult reaches a length of nearly 100 mm,, elongately cuneiform in shape, subequivalve and strongly inequilateral, the anterior side being much longer, appressed and rounded at the end, the posterior side much shorter, with an angled or carinated umbonal ridge. There is a narrow byssal gap along the middle section of the ventral margin, the byssus itself being a narrow, wedge-shaped plug of a greenish-black color by means of which the shell is attached to one wall of its bore. The beaks are probably prosogyrate in the young but in all the specimens seen the umbones are deeply worn. The cardinal area is long, unsym- metrical wedge-shaped, highest under the beak, narrowed anteriorly and 78 AXEL A. OLSSON of a nearly black or purple-black color; it is unequally divided into two sections by an incised line starting at the beak and running obliquely down- ward and in an anterior direction to the hinge line (divisional ligamental line); on the posterior side of this hne, the cardinal surface is striated hori- zontally and smooth, while on its longer anterior side it is crossed by a series (often 14 or more) of evenly spaced oblique slits to which threads of the tensilium are attached. The hinge line is long, narrow and straight, its teeth small and numerous, vertical or inclined, divided into an anterior and posterior set by the incised line mentioned above; in an average speci- men, there are 28 small teeth in the posterior set and about 75 in the anterior set. The sculpture is nearly always destroyed by wear, especially on the umbones and across the mid-surface of the valves but small patches usually remain along the ventral side and on the posterior slope; in the spots where the sculpture is still retained, it is seen to consist of fine, radial riblets crossed by crowded concentric layers producing a pattern of lacelike, scalloped teeth, their interspaces retaining small tufts of a straw-colored periostracum. Interior of shell porcellaneous, the pallial line lying quite close to the ventral margin. Adductor scars distinct, the ventral margin plain. This is a curious genus, represented by a single known species (Litharca lithodomus) ranging from Ecuador northward to Panama and Costa Rica. It was assigned by Frizzell to a separate subfamily the "Litharcinae" but anatomical observations made possible by the discovery of living specimens, show that the genus is closely allied to Area sensu stricto. The elongated form of the shell is merely an adaption to a rock-boring habit in which the anterior end of the shell and not the posterior became drawn out and lengthened. The longer side of the shell is anterior and assumes a flattened, wedge- like form at its end; the much shorter and carinate side is posterior and is often more or less covered with extraneous marine growth. The beaks and umbones are always worn but commencing at a point below the assumed position of the beak, a faintly engraved line (divisional ligament line of Frizzell) passes obliquely across the cardinal area to the hinge line, dividing the area and the line of the hinge teeth into two unequal sections. The dip of this line is usually about 30 degrees or somewhat less depending upon the size of the specimen in hand. In the larger of the specimens figured (length 93 mm.), the hinge has 27 teeth in the posterior set and about 94 in the anterior set. The lengthening of the shell of Litharca, so as to ac- commodate itself to the narrow confines of a straight bore, was accomplished by a flattening of the umbones and a pulling out or lengthening of the axis of the shell mainly along the anterior side. As a consequence of this down- ward squeeze, the umbones and the beaks were pushed backwards thus causing the ligamental line to slant down sharply, its inclination lowering as the elongation of the shell increased. Our smallest specimen has a length of 13 mm. This shell has 12 hinge teeth in the posterior set and 18 in the anterior. The umbone is already so deeply worn that the shape of the beak has been destroyed. Litharca Uthodomus (Sowerby) Plate 5, figures 1, la-It Byifarca lithodomus Sowerby, 1833, Proc. Zool. Soc. London, p. 16. PANAMIC-PACIFIC PELECYPODA 79 Area lithodomus (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 12, fig. 76. Area (Litharea) lithodomus (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 169, 170. — Rcinhart, 1935, Mus. royal d'Histoire nat. Belgique, Bull., tome 11, No. 13, p. 18. Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 27, pi. 11, figs. 1, 2, 3. Litharea lithodomus (Sowerby), Frizzell, 1946, Jour. Paleont., vol. 20, No. 1, pp. 45-50, pi. 10, figs. 1-5; text figures 2, 6. There are four double-valve specimens in the British Museum (Nat. Hist.) of which three have been placed apart in the type lot. These speci- mens have the locality label of Monte Christi (the name of a town inland from Manta). These specimens were apparently collected alive. The largest specimen in the type lot measures 86.6 mm. Litharea lithodomus is fairly common at Manta, and loose valves can generally be found along the beach to the west of the city. It appears to be fairly well known to some of the fishermen who gather it along with the larger Lithophagae, Chamas, and other mollusks for food and bait. Litharea lithodomus is a true rock borer, the opening of its bore showing on the sur- face of rocky ledges as a deep, rounded, or lens-shaped hole, often an inch to an inch and a half across. At Manta, these bores are found princi- pally on the under surface of projecting ledges of massive sandstones, avoid- ing the softer layers. In cross-section, the bore is usually lenticular rather than circular, its sides polished and tapering to a flat wedge at the end, the mollusks being attached by its narrow, green byssus to one wall but loose enough so that considerable movement backward and forward along the bore is still possible. When feeding, the ark lies with its short posterior end close to the open end of the bore but it pulls back quickly when disturbed, its flattened, anterior end fitting snugly against the walls of the bore but a narrow space above the umbones is open, often occupied by a nestling Acar. This sliding movement along the bore results in heavy wear of the sides and umbones of the shell which is thus often reduced to a paper thinness, only small patches of the original bristly periostracum being re- tained along the posterior side and along the ventral margin. Range — Panama southward to Santa Elena, Ecuador. Panama: Bucaro; Burica Peninsula. Ecuador: Esmeraldas; Bahia; Manta; Manglaralto; Santa Elena. Genus BARBATU Gray, 1847 Type species by original designation and tautonomy. Area barbata Linne, Recent, Mediterranean Sea. The shell is subquadrate to subelliptical in shape, subequivalve and in- equilateral, the ventral margin straight or with a wide, open byssal gap or notch, the posterior-umbonal slope rounded or angled. The cardinal area is low or high, longer on the posterior side, covered by the ligament and with obliquely transverse, sometimes tent-shaped grooves which begin under the beak; the ligamental grooves may be developed on both sides of the beak or only on the posterior portion; in the latter case, the anterior section of the cardinal area is bare or covered only by an extension of the perio- stracum. The sculpture is formed principally by small, close-set radial rib- 80 AXEL A. OLSSON lets, noded or cancellated by the concentrics. The periostracum is profuse, pilose and dark-colored, the color of the shell underneath being white or brownish. Hinge line long and straight, with numerous small teeth, the posterior set being much the longer, the distal members enlarged and set obliquely. Two subgenera are regional. I. The shell is fairly regular in shape, the color of the surface below the periostracum brownish. Sculpture is formed by small, radial, threadlike riblets, the smaller spaced between larger ones so that the pattern appears rayed. Cardinal area is low and narrow, the ligamental grooves few in number. Subgenus Barbatia, s.s. II. Shell generally much distorted, the ventral margin deeply sinuated by a large, open, byssal gap. Color of shell beneath the periostracum is white. Sculpture formed by rather coarse, beaded, radial riblets, not in rayed pattern. Cardinal area is generally quite high and closely covered with tent-shaped ligamental grooves. Subgenus Cucullaearca Barbatia (Barbatia) lurida (Sowerby) Plate 6, figure 4 Byssoarca lurida Sowerby, 1833, Proc. Zool. Soc. London, p. 19 Santa Elena, Ecuador. Area lurida Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 14, fig. 95. Barbatia (Barbatia) lurida (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. i74._Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 182-184, pi. 11, figs. 3 a-b; text figs. 81 a-c. Byssoarca vespertilio Carpenter, 1856, Cat. Mazatlan Shells, Brit. Mus. p. 140. No. 192, Mazatlan, Mexico. Barbatia (Barbatia) vespertilio (Carpenter), Maury, 1922, op. cit., pp. 174, 175. Shell small or of medium size, obliquely oblong, convexly humped, highest along the posterior-umbonal slope, the anterior side somewhat narrower than the posterior. Umbones are wide and full, sometimes slightly sulcated. The sculpture is similar to that of B. barbata, being composed of small, threadlike radials, the posterior set interspersed with larger or deeper ones so as to give a banded or rayed appearance. Color dark-brown on the posterior half and a lighter brown on the anterior. The hinge line is shorter than the full length of the shell, the teeth small in the middle zone, the distal members much larger. Interior white in the anterior section, brown in the posterior, the anterior-ventral margin sinuated by the byssal gap- Although B. lurida and B. vespertilio are here placed together as a single species, fresh specimens with the periostracum intact may show them to be distinct. Worn beach specimens of B. lurida from Santa Elena, Ecuador, and northwestern Peru, have a slightly distorted shell with the beaks placed a little in front of the middle and the posterior-umbonal slope is higher and more convex. The cardinal area is like that of B. barbata of Europe and generally covered completely with strong ligamental grooves on both sides of the beaks. The sculpture is rayed. The type of B. vespertilio examined at the British Museum is a perfect specimen, covered with perio- stracum, and the two valves spread open and glued onto a glass plate; its dimensions are: length 33.5 mm., height 16 mm. PANAMIC-PACIFIC PELECYPODA 81 B. cancellaria (Lamarck), 1819 (PI. 6, fig. 5) from the Caribbean and western Atlantic is not closely related to either B. lurida or B. barbata, al- though it was generally identified with the European species by past authors (Dall, Sheldon, Maxwell Smith). The Caribbean shell has lower, more anterior beaks, and the ligament covers only the posterior part of the cardinal area, the short anterior portion remaining bare except for a thin extension of the periostracum over it. Range — Coast of Mexico southward to northern Peru. Panama: Rio Ocones beach. Colombia: Isla del Gallo. Ecuador: Peurto Callo; Isia la Plata; Santa Elena. Peru: Zorritos; Caleto Sal. Subgenus CUCULLAEABCA Conrad, 1865 Type species by subsequent designation, Stoliczka, 1871, Byssoarca lima Conrad, 1847=C. cucvlloides Conrad, 1833. Eocene and Oligocene of the Gulf States of United States. Shell elongate to obliquely subquadrate, subequivalve but usually dis- torted, white under a copious, heavy periostracum. Basal margin sinuated by a wide, byssal gap. Sculpture is formed by fine to coarse, more or less sharply beaded riblets. Hinge long, straight, the teeth in a continuous series in the young but sometimes interrupted later, the distal members larger and oblique. Cardinal area large, high, elongate and subtrigonal, densely covered by wavy or tent-shaped grooves, and completely covered by the ligament on both sides of the beaks. Barbatla (Cucnllaearca) reereana (d'Orbigny) Plate 4, figures 4, 4a, 4b Area helblingii Bruguiere, Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 14, fig. 90. (Not Area helblingii Bruguiere, 1789). Area reeveana d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, pt. 3, Mollusques, pp. ^o< ^^ > r^ f . < > ,: V. „ , c y ^1 Shell subequivalve, convex, thin, white under a black or brown sub- pilose or foliated periostracum. Cardinal area like that of Acar with the ligament narrow and developed principally on the posterior side, the anterior section bare. Hinge that of Barbatia, the posterior set of teeth well developed or subobsolete. The sculpture is formed by small, threadlike riblets, weakly cancellated by concentrics. The Recent species of this subgenus have a thin, white shell under a black or brown, subpilose or foliated periostracum, generally thinly de- veloped over the umbones, more profusely so around the ventral margin where it may form into thin, loose, leaflike ribbons, finely serrated at the ends. Fulgeria illota (Sowerby) Plate 6, figures 1, la, lb Byssoarca illota Sowerby, 1933, Proc. Zool. Soc. London, p. 18 Gulf of Nicoya. Area illota (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 12, fig. 78. Area (Byssoarea) Tabogensis C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol, 5, pp. 486, 545, No. 424. — Turner, 1956, Occas. Papers on Mollusks, Mus. Comp. Zool., vol. 2, No. 2D, p. 90, pi. 19, figs. 7, 8. Barbatia (Acar) illota (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 182, 183, pi. 2, figs. 8, 14. Barbatia (Fulgeria) illota (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc, America, No. 47, p. 37. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 187, 188, pi. 11, figs. 6-8; text-figs a-c. The shell is small or of medium size (length 37 mm,), subquadrate to trapezoidal, generally thin, convex, with a shallow sulcus across the middle to the ventral margin. Color of shell beneath the brownish periostracum is white. Ribs are small, threadlike, finely cancellated by the concentrics. The periostracum is quite copious, covering the whole disk, except the umbones which are sometimes bare, and consists of broad, thin, leaflike fila- ments, finely serrated at the end, and most heavily developed along the ventral margin. Length 32.3 mm., height 22 mm., diameter 14 mm. Palo Seco, Canal Zone. 84 AXEL A. OLSSON This is a common species at Panama living under stones, B. tenera (C. B. Adams), a Recent West Indian species and B. millifilia Dall, a Pliocene fossil from Florida are both similar to the Pacific form. Range — Gulf of California to northern Peru. Panama: Bucaro; Panama City. Canal Zone: Palo Seco; Venado. Ecuador: Isia la Plata, Manta; Puerto Callo; Santa Elena. Peru: Caleto Sal; Lobitos. Genus CALLOARCA Gray, 1857 Type species by monotypy, Byssoarca alternate Sowerby. Recent, Panama. Shell elongately subquadrate, relatively thin, with a strong, umbonal angulation. Cardinal area as in Acar, the ligament nearly or wholly pos- terior of the beak. Umbones and the middle of the valves with a shallow sulcation. Sculpture is formed by fine, flattened riblets in raylike groups on the anterior and middle surface but become much enlarged along the umbonal angulation. Calloarea alteraata (Sowerby) Plate 4, figures 5, 5a Byssoarca alternata Sowerby, 1833, Proc. Zool. Soc. London, p. 17. Area alternata (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 13, fig. 88. Barbatia (Cucullarca) alternata (Sowerby), Maury, 1922, Paleont. Araer., vol. 1, No. 4, p. 184, pi. 30, fig. 11. Barbatia (Calloarea) alternata (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 30, pi. 11, figs. 5-7. — Durham, 1950, Mem. Geol. Soc America, No. 43, p. 55, pi. 1, fig. 14. — ^Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 186. Area (Calloarea) alternata (Sowerby). Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, No. 19, p. 159. This is an elegant species with the characters given above for the subgenus. It is relatively common at Panama, particularly at Palo Seco, Canal Zone, elsewhere it appears to be rare. Cuming's specimens were dredged in 12 fathoms of water, attached to stones. West Colombia. Hert^ lein and Strong recorded it from localities in Costa Rica, Nicaragua, and the Gulf of California. It occurs as a Pleistocene fossil in Lower California. The periostracum appears to have been thin, brown, membraneous, with short, frondlike filaments, expanded at the end, set along the interspaces. Length 46.6 mm., height 24 mm., diameter 22 mm. Palo Seco, Canal Zone. Range — Gulf of California to Ecuador. Canal Zone: Palo Seco; Fort Amador. Panama: San Carlos; Guanico. Ecuador: West Colombia (Cum- ing). Genus ARCOPSIS von Koenen, 1885 Type species by subsequent designation, Reinhart, 1935, Area limopsis von Koenen. The type species is from the Paleocene of Denmark. (Fossularca Cossmann, 1887). The shell is generally small, solid, plump, byssiferous, oblong to sub- quadrate, subequilateral with high, full, subcentral umbones and prosogyrate beaks, and nearly square, blunt ends. Hinge taxodont, the teeth interrupted PANAMIC-PACIFIC PELECYPODA 85 in the middle, the posterior set longer, the sides of the teeth finely grooved. Cardinal area longer than high, the ligament, vertically grooved, and re- stricted to a triangular area under the beak. Adductor scars large, subequal', bordered on the inner side by a raised edge or flange. Sculpture consists of numerous, fine, threadlike riblets between wider interspaces, generally decussated by concentrics. Surface covered by a hairy or bristly perio- stracum. Valve margin smooth or nearly so. Arcopsis solida (Sowerby) Plate 6, figures 3, 3a, 3b Byssoarca solida Sowerby, 1833, Proc. Zool. Soc. London, p. 18 "Paytam Peruviae". Area solida (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 16, fig. 106. Barbatia (Fossularea) solida (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 21, 22, pi. 2, figs. 7, 12. Area (Areopsis) solida (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 158. ArcoPsis solida (Sowerby), Rest, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 192, 193, pi. 12, fig. 10. Shell small (length to about 20 mm.), white or cream-colored and generally encrusted with marine growth. Sculpture is formed by small, radial threads or riblets, finely or coarsely beaded, the surface often worn smooth. Arcopsis adamsi (E. A. Smith) from the Caribbean is a closely similar species but is generally smaller, thinner, and less convex. Range — Lower California to northern Peru, and the Galapagos. Pan- ama: Bucaro; Panama City. Colombia: Isla del Gallo. Ecuador: Esmeraldas; Manta; Puerto Callo; Santa Elena. Peru: Zorritos; Mancora; Lobitos; Paita; Yasila; Chimbote. Subfamily ANADARIKAE Genus ANADARA Gray, 1847 Type species by original designation. Area antiqvMa Linn^ (Area scapha Meuschen {^maculosa Reeve). Recent, Red Sea. Shell of medium or large size, obliquely subovate to elongate, moder- ately solid. Valves convex between tightly closed margins, subequal in size and sculpture. Umbones wide and prominent, terminating m small, proso- gyrate beaks placed over a rather wide, unsymmetrical cardinal area. Cardinal area smooth or nearly so, covered completely by the ligament. The sculpture is nearly similar in both valves and consists of numerous (about 34), close-set ribs, simple, smooth at first but often dividing and becoming bi- or quadruplicate at the ends. Hinge with the teeth arranged in a continuous series, small and vertical in the middle zone, enlarged and divergent at the ends. The above description is based on the type specimen of Area antiquata preserved at the Linnean Society of London, supplemented by a few other shells at the British Museum (Nat. Hist.) believed to represent the same species. As indicated by Hanley, the original of Linne's antiquata is a small, somewhat worn left valve which bears the number 144 corresponding to the numeration in the 10th and 12th edition of the Systema Naturae. An external view shown natural size was illustrated by Hanley, plate 3, figure 4. Photographs of the same specimen were also furnished Woodring by the Linnean Society and were reproduced by that author in his Bowden mono- graph. A second, larger, unworn specimen with both valves was also found 86 AXEL A. OLSSON by Hanley in the same tray as the type. This second specimen was thought by Hanley to have been subsequently added by Sir J. Smith, the pur- chaser of the Linnean collection in order to further elucidate the species. Cuming identified this specimen as Area maculosa Reeve. It is the opinion of this author, that this second specimen represents Linnaeus species and proves antiquata a Red Sea or Indian Ocean species. A broader definition of the genus is as follows: Shell small or large, solid or of medium texture, porcellaneous, rhombic to elongated, with equal valves or if unequal, the left valve is larger, its margin overlapping the other, and the sculpture of the two valves may be somewhat discrepant. Umbones prominent, anterior of the middle, with the small, prosogyrate beaks pointing inward or inrolled over a cardinal area of variable height, low or high trigonal in shape and extending on both sides of the beaks. The surface of the ligamental and cardinal area may be smooth or grooved by tent-shaped, or more rarely, by straight longi- tudinal lines. Hinge line straight, with numerous teeth in a graduated series, small or minute in the middle, larger and divergent at the extremities. Sur- face sculptured by strong ribs which are plain, noded, or divided, the in- terspaces deeply grooved. Sculpture of the two valves similar or more or less discrepant. Key to the subgenera of Anadara I. Cardinal area covered completely by the ligament. A. Cardinal area is elongate and rather narrow, smooth or grooved with tent-shaped lines. Shell ovate to elongated, equivalve as to shape, convexity, and sculpture. 1. Cardinal area smooth or vertically striated, the ligamental grooves generally absent or of erratic development. Ribs bi-or quadriplicate in the adult. Subgenus Anadara, sensu stricto Red Sea and Indo-Pacific. 2. Cardinal area covered by tent-shaped ligamental grooves. 2a. Posterior side not depressed, winged, or emarginated. Subgenus Diluvarca 2b. Posterior side more or less impressed, emarginated. Subgenus Rasia B. Cardinal area high, trigonal, set-off by deep, marginal grooves. 3. Shell solid, equivalve. Internal margins strongly fluted. 3a. Ribs relatively few and wide. Beaks large, strongly coiled, Cardita-like. Periostracum coarse, black. Subgenus Senilia African 3b. Ribs quite numerous, noded, the beaks normal. Subgenus Larkinia 3c. Ribs less numerous, mostly smooth. Subgenus Gtandiarca, new subgenus PANAMIC-PACIFIC PELECYPODA 87 4. Shell thinner, inequivalve, with discrepant sculpture. Cardinal area smooth or with the ligamental groove sparingly developed. Subgenus Cunearca II. Cardinal area usually not fully covered by the ligament, the anterior portion wholly or partly bare (in some species, the ligamental grooves encroach more widely in large, gerontic specimens). C. Cardinal area elongate or narrowly subtrigonal, much longer than high. Shell elongated or subelliptical in shape. 5. Posterior side not winged or deeply emarginated. 5a. Shell inequivalve, thin, fluted within, the ribs simple, smooth or weakly noded. Subgenus Scapharca Not regional. 5b. Shell equivalve, solid, the ribs generally mesially grooved in the adult. Subgenus Sectiarca, new subgenus 6. Posterior side winged or deeply emarginated, the ribs plain or noded. Subgenus Caloosarca, new subgenus D. Cardinal area subtrigonal, high. Shell subovate, elevated, inflated and often quite thin. Ribs plain or noded, separated by flat interspaces. Subgenus Esmerarca, new subgenus Subgenus DILUYARCA Woodring, 1925 Type species by original designation, Area diluvii Lamarck. Miocene, Europe. Shell subequivalved, the margins closed, moderately solid. Cardinal area long and relatively narrow, covered by the ligament on both sides of the beak and deeply engraved with crowded transverse or chevron- shaped grooves. Sculpture more or less similar in the two valves and formed by numerous rounded smooth or coarsely noded ribs. Periostracum coarse and of a dark color. Diluvarca was proposed by Woodring in 1925 as a subgenus of Barhatia and believed to differ from Anadara in having a closed ventral margin. The weakly sinuated margin shown by Linnean type of Anadara antiquata is probably due to wear and not a natural byssal gap. Nevertheless, typical Anadara as defined in the key does not seem to occur in our American Tertiary and Recent faunas. For the American species, most clearly related to Anadara, sensu stricto, the name "Diluvarca" will be used. 4nadara (Diluvarca) tuberculosa (Sowerby) Plate 7, figures 3, 3a Area tuberculosa Sowerby, 1833, Proc. Zool. Soc. London, p. 19 Real Llejos, Nicaragua; mangrove roots. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 3, fig. 18. Area (Seapharca) tubereulosa Sowerby, Dall, 1910, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 154, 253, pi. 27, fig. 4. Scapharca (Scapharca) tuberculosa (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 26, 27, pi. 1, fig. 12. Anadara (Anadara) tuberculosa (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 63. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, no. 2, p. 195, pi. 13, figs. 17 a-b. Shell obliquely ovate, rather solid, broadly convex, slightly more so along the posterior-umbonal slope, equivalve. When living, the shell is it AXEL A. OLSSON covered by a heavy, brown to black, strongly wrinkled periostracum, the umbones often corroded and showing the white shell. Ribs are numerous, (33 to 37 in number), relatively large, rounded, close set and separated merely by a groove or narrowly lined interspaces, usually with a scattering of nodes or tubercles along their summits. Umbones wide and prominent, often weakly sulcated. Cardinal area is narrow in the shape of a depressed or flattened triangle and engraved with three or more tent-shaped grooves, the whole area covered by the ligament. Length 54.6 mm., height 39.6 mm., diameter 32.4 mm. Guayaquil, Ecuador (market). This is a common and widely distributed species, living buried in the soft mud amongst the roots of mangrove trees. "As reported by Coker (Dall, 1909, p. 154), among the first phenomena to catch one's attention on entering the mangrove swamps is a sound heard repeatedly on every side, as of nuts falling into the water or soft mud. Tracing the sound with some care, it is found to come from the watery hollows in the mud occupied by the concha prieta, and is presumably made by the sudden closing or opening of its valves under water by the mollusks". The common name of this ark is "Concha Prieta", in allusion to its black color. It is a common article of shell food, and on sale in market places throughout its range. Range — Lower California to Peru. Numerous records. Peru: Tumbez, (its most southerly occurrence). inadara (Dilnvarca) simills (C. B. Adams) Plate 7, figures 2, 2a Area stmilts C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol. 5, pp. 485, 486, 545, No. 422 Panama. — Turner, 1956, Occas. Papers on Mollusks, Mus. Comp. Zool., vol. 2, No. 20, pp. 85, 86, pi. 20, figs. 1, 2. Area (Anadara) similis C. B. Adams, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 157, pi. 1, figs. 2, 5. The shell is ellipsoidal, slightly oblique posteriorly, relatively thin. Surface covered by a brown or black, wrinkled periostracum, often scaley and when worn away showing a white-colored shell beneath. Ribs numerous (40 to 44), small, narrow, separated by rather wide interspaces, the ribs more or less strongly tuberculated, especially near the ventral margin. Hinge is narrow and straight, the teeth small and numerous, arranged in an uninterrupted series. Length 51 mm., height 33.5 mm., diameter 27.8 mm. Limones, Ecuador. Similar in shape to the common A. tuberculosa but with a more elliptical shape, more numerous ribs, and thinner shell. Range — Nicaragua to the Gulf of Guayaquil. Costa Rica: Punta Arenas (Hertlein and Strong). Panama: vicinity of Panama City. Ecuador: Limones; Guayaquil (market). Anadara (Dllnyarca) cepoides (Reeve) Plate 9, figures 7, 7a Area eepotdes Reeve, 1844, Proc. Zool. Soc. London, p. 47. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 10, fig. 66. Scapharea (Scapharea) cepoides (Reeve), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 193, pi. 3, fig. 6. Area (Seapharea) eepotdes Reeve, Hertlein and Strong, 1943, Zoologica, vol. 28, pt 3, No. 19, p. 162. PANAMIC-PACIFIC PfiLECYPODA 89 Shell large, broadly subovate or roundly quadrate, ventricose, the umbones being full, wide and placed a little anterior of the middle, the terminating beaks weakly sulcated. The valves are slightly unequal, the ventral margin of the left valve overlapping that of the right but the rounded convexity of each valve is almost the same. The substance of the shell is so light and so thin that the furrows of the external ribs show into the interior almost throughout. Ribs number 33 to 34, of which 8 are found on the posterior slope; these ribs are square or rectangular in section, smooth and flat-topped, almost alike in each valve, their interspaces flat and somewhat narrower. The cardinal area is broadly, obhquely subtrigonal in shape, and of medium height; it is covered completely by the ligament and cut into by three or four transverse grooves. The periostracum is dark in color, usually brown, and a little scaly. Hinge narrow, straight, the teeth small and arranged in a continuous series. Length 90 mm., height 85 mm., diameter 77.3 mm. South America. Dr. T. B. Wilson, ANSP 4292. Length 70 mm., height 60 mm., diameter 46 mm. Panama, Amer. Museum, specimen measured by Maury, 1922. There are several specimens of this large species in the collection of the Academy of Natural Sciences in Philadelphia labelled simply South America, Dr. T. B. Wilson. Reeve cited San Miguel, Panama, which is probably the San Miguel, Rey Island of the Pearl Island group. Hertlein and Strong recorded this species from Ceralbo Island, Gulf of California. Range — Gulf of California to Panama. Mexico: Ceralbo Island, Gulf of California. Panama: San Miguel, Rey Island, Pearl Islands. Anadara (Dllinarca) obesa (Sowerby) Plate 8, figures 8, 8a Area obesa Sowerby, 1833, Proc. Zool. Soc. London, p. 21 (Atacames).— Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 1. fig. 3- Area (Seapharca) obesa Sowerby, Hertlein and Strong, 1843, Zoologica, vol. 28, pt. 3, p. 163. Seapharca (Scapharea) obesa (Sowerby), Maury, 1922, Paleont. Amer. vol. 1, No. 4, pp. 189, 190, pi. 3, figs. 4, 5 Anadara (Seapharca) obesa (Sowerby), Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 205, pi. 16, figs. 28 a-b; text-figs. 90 a-c. Shell of medium size (length up to about 40 mm.), subequivalve, ovate, with wide, convex, and nearly central umbones. Cardinal area narrow, much longer than high, nearly covered by the ligaments and marked with wide, tent-shaped grooves. Ribs numerous (42 to 44), narrow, rectangular, between flat-bottomed interspaces, their summits smooth or weakly noded. Anterior side obliquely rounded, the posterior slope subtruncate, the um- bonal slope weakly angled, its margin straight, cuneate at its ventral corner. Length 39 mm., height 28.7 mm., diameter 25.6 mm. Tumbez, Peru. This is a relatively common species in northern Peru and along the coast of Ecuador. As noted by Maury, there are no allied species in the Hving Caribbean fauna but several fossil forms are known from the East Coast Miocene. Range— Mtxxco to northern Peru. Panama: Bucaro; San Carlos. Ecuador: Sua; Galeras; Charapota; Manta; Punta Blanca; Santa Elena. Peru: Tumbez; Zorritos; Boca Pan; Mancora. 90 AXEL A. OLSSON Anadara (Dilnrarca) adamsi, new species Plate 6, figures 7, 7a, 7b The shell is relatively small (length 23 mm. or less), subrectangular, with wide umbones ending in small, slightly sulcated beaks placed near the anterior one-fourth, this line is also the zone of greatest height and con- vexity; posteriorly the height narrows as the ventral margin advances slightly upward, its posterior-ventral comer being slightly produced and angular. The hinge line is straight, about half the length of the shell and bears a continuous series of small teeth, numbering about 15 in the anterior set and about 20 in the longer posterior set; the teeth are finely striated on the sides. Cardinal area is of medium height, almost wholly covered by the ligament which generally carries a single, transverse groove on the posterior side. The surface is sculptured with small ribs, about 30 in number, and similar over the whole disk; on some specimens, the ribs are strongly noded, especially over the anterior side; in others, the ribs are weakly noded to smooth. The umbones are slightly sulcated. Color white, the periostracum thin and showing generally only as crossthreads in the interspaces of the ribs. Length 23 mm., height 16 mm., diameter 14.6 mm. Palo Seco, Canal Zone. Mr. Lee R. Beil Coll. Holotype, ANSP 218916. This is a small species, fairly common at Palo Seco, Canal Zone. The posterior-ventral side is slightly impressed. Range — Panama. Panama Canal Zone: Palo Seco. Anadara (Dilnvarca) lablosa (Sowerby) Plate 84, figures 10, 10a Area labiosa Sowerby, 1833, Proc. Zool. Soc. London, p. 21 Turabez, Peru. — ^Reeve, 1844, Conch. Icon, vol. 2, Area, pi. 10, fig. 67. Seapharea (Seapharca) labiosa (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 192, 193, pi. 31, figs. 1, 3. Anadara (Seapharca) labiosa (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 74. — Keen, 1958, Sea Shells of the Tropical West America, p. 38, fig. 63. The shell is broadly rectangular, with wide, low umbones, the valves slightly unequal, that of the left being a trifle larger so that the posterior- ventral margin overlaps and slightly embraces the other. The posterior margin is obliquely truncate, its dorsal corner set at an angle about 120 degrees. Ribs numerous, about 39 in number, relatively narrow and flat- topped, the periostracum thin and of a brown color. Length 56.4 mm.; height 35.9 mm.; diameter 26.9 mm. Holotype, British Museum (Natural History). In the type lot at the British Museum there are three complete speci- mens and one small valve. The above description is based largely on the type material. This is apparently a rare species and has been collected only on a few occasions. Range — Lower California to northern Peru. Mexico: Gulf of California and Acapulco. Peru: Tumbez. Subgenus RASL4 Gray, 1857 Type species by subsequent designation, Stewart, 1930, Area formosa Sowerby. (Cara Gray, 1857, type species by subsequent designation, Stewart, 1930, Area avieuloides Reeve, 1844 (young of Area formosa Sowerby). PANAMIC-PACIFIC PELECYPODA 91 Shell elongate-subrectangular, flat or moderately convex, generally with the dorsal-posterior side somewhat depressed, often more or less aviculoid or emarginate, especially in the young. Umbones wide, full, passing over gradually into the normal inflation of the valves, the beaks small, and prosogryrate. The cardinal area is long and narrow, covered entirely by the ligament, and marked with numerous V-shaped or chevron-like grooves. Sculpture formed by numerous, flattened ribs between narrower inter- spaces, the anterior set of ribs noded or divided mesially. Hinge formed by numerous, small teeth continuous along the entire hinge line. Cara Gray, 1857 is considered to be a synonym of Rasia since its type species, the Area aviculoides of Reeve is but the young form of Area formosa Sowerby. Anadara (RasIa) forniosa (Sowerby) Plate 7, figure 4 Area formosa Sowerby, 1833, Proc. Zool. Soc. London, p. 20 Gulf of Tehuantepec. — Reeve, 1844, Conch. Icon., vol. 2, Area pi. 2, fig. 10. Area (Anadara) formosa Sowerby, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 156. Seapharca (Seapharea) formosa (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 28, 29, pi. 2, fig. 11. Anadara (Anadara) formosa (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 62, pi. IS, figs. 4-6. Area aviculoides Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 10 fig. 63. Seapharca (Seapharea) aviculoides (Reeve), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 24, 25, pi. 2, fig. 2. Shell large, oblong, rectangular, the hinge line and ventral margin straight but not quite parallel, divergent slightly on the posterior side. Color white but fresh specimens are covered with a dense, pilose, brown periostracum. Ribs strong, numerous, generally about 33 in number, the anterior set narrow and with a medial groove, the posterior ones wider and simple. Length 102 mm., height 58 mm., diameter 52.7 mm. Pearl Islands. This is a widely distributed species, seldom common at any locality. Young shells are more strongly auriculated than the adult; a specimen of this kind from Santa Elena was named avieuloides by Reeve. Range — Lower California to northern Peru. Panama: Pearl Islands; Bucaro. Ecuador: Manta; Isla la Plata; Santa Elena. Peru: Zorritos; Mancora; Yasila near Paita. Anadara (Rasia) emarginata (Sowerby) Plate 8, figures 6, 6a Area emarginata Sowerby, 1833, Proc. Zool. Soc. London, P. 20. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 4, fig. 26. Seapharea (Seapharea) emarginata (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 23, pi. 2, fig. 5. Area (Cara) emarginata (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 159. Anadara (Seapharea) emarginata (Sowerby), Rost, 1955, Allan Hancock Pacific Ex- peditions, vol. 20, No. 2, pp. 203, 204, pi. 14, fig. 22; text-figs. 89 a-c. Shell of medium size (up to 50 mm.), thin, often irregular, subequi- valve, elongate, subquadrate, the dorsal and ventral sides straight, sub- parallel, the anterior end slightly narrower. Anterior side short, rounded, the posterior side much longer, emarginate or with a deep notch below the 92 AXEL A. OLSSON hinge line. Beaks small, placed at the anterior one-third and usually with a small black stain, weakly sulcated across the umbones. Ribs 28 to about 30, flat between squarish interspaces, wider posteriorly, the anterior ribs usually finely noded. Cardinal area long and narrow, completely covered by the ligament. Length 38.6 mm., height 17.5 mm., diameter 15.2 mm. Zorritos, Peru. Range — Lower California to northern Peru. Panama: Panama City, Bucaro. Ecuador: Mompiche; Sua; Santa Elena. Peru: Tumbez; Zorritos; Lobitos; Paita. Subgenus LABKINIA Reinhart, 1935 Type species by original designation, Anadara larkinii (Nelson). Shell subtrigonal, nearly as high as long, solid and heav-y, with high, prominent umbones and small prosogyrate beaks. Posterior side subtruncate, flattened to deeply impressed, generally with the umbonal angle prominent. Cardinal area high, subtrigonal, covered by the ligament, and marked off by a deep groove on each side, its surface smooth or covered with trans- verse, ligamental grooves. Ribs numerous, narrow, between square- or steep- walled interspaces, the summit of the ribs beaded with coarse or scabrous nodes. Hinge teeth numerous, continuous, vertical in the middle, oblique, and divergent at the ends. Atiadara larkinii is a fossil species from the upper Miocene and Pliocene of Peru and Ecuador. It has a coarse, solid shell with high central umbones and small beaks placed above a high cardinal area, which is at first smooth, later becoming marked with crowded, transverse grooves. The subgenus is well represented by numerous fossil species in the Caribbean Miocene (A. chiriquiensis Gabb). Anadara (Larkinla) multlcostata (Sowerby) Plate 7, figure 5; Plate 9, figure 6 Area multlcostata Sowerby, 1833, Proc. Zool. Soc. London, p. 21 Gulf of Tehuantepec. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 4, fig. 23. Seapharea (Seapharea) multieostata (Sowerby), Maury, 1922. Paleont. Amer., vol. 1, No. 4, p. 195. Area (Larkinia) multieostata Sowerby, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 162. Anadara (Larkinia) multieostata (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 66, pi. 8, figs. 9-11.— Durham, 1950, Mem. Geol. Soc. America, No. 43, p. 54, pi. 1, figs. 15, 16, 17.— Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 196, text-figs. 84 a-d. Shell large, subquadrate or squarish, solid, with wide, prominent and nearly median umbones terminating in small, prosogyrate beaks above a medium-height cardinal area. Posterior umbonal slope subangular, the pos- terior margin straight as if truncated. Anterior side short, rounded at the margin and somewhat shortened at the hinge as if slightly auriculate. Cardinal area fully covered by the ligament and carved with one or more chevron-shaped grooves. Valves are nearly alike, convex, the beaks not sulcated, the ventral marginal overlap almost lacking. Ribs numerous (about 33), narrowly rounded, and of about the same width as their interspaces, smooth except along the anterior umbonal slope where they are finely and sharply noded. Periostracum brown, rather copious and neatly con- PANAMIC-PACIFIC PELECYPODA 93 centrlcally marked, its concentric rings bearing small, spinelike denticula- tions, the points of which are directed dorsally, both over the summit of the ribs and in the depths of the interspaces. This is quite a different species from Anadara grandis, distinguished easily by its more rhombic form, more numerous ribs and by the peculiar markings of its periostracal layer. The range of the species as given by Hertlein and Strong is from California to Panama, but I have not seen specimens south of Mexico. Range — Newport Bay, California, south to Panama, and the Galapagos Islands. Subgenus GRAJfDIARCA new subgenus Type species Area grandis Broderip and Sowerby. Shell large, high trigonal, equivalve, solid, often becoming heavy and ponderous in the adult. Umbones wide and prominent, central, and usually feeble sulcate, bordered posteriorly b}'^ the umbonal ridge at first relatively sharp or angled, later becoming lower and rounded. Beaks small, curved in over a wide, triangular cardinal area. Ligament coarse and heavy, covering the cardinal area completely, the surface of the cardinal area striated with faint, vertical hnes and marked with few to many deep, triangular to lozenge-shaped ligamental grooves. Ribs strong, rectangular in section between deeply grooved interspaces, the summit of the ribs smooth or concentrically wrinkled except on the most anterior ones which are crudely noded. Interior of shell widely and deeply fluted by the ribs around the ventral margin. Hinge teeth small, vertical, in a continuous series. Surface of shell pro- tected by a thick, smooth, black periostracum. Like Larkinia but differing by its less truncated posterior side and fewer, plainer ribs. Anadara (Grandiarca) grandis (Broderip and Sowerby) Plate 7, figures 1, la-lc Area grandis Broderip and Sowerby, 1829, Zool. Jour., vol. 4, p. 365. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 1, fig. 4. Area (Anadara) grandis Broderip and Sowerby, Dall, 1910, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 154, 253, pi. 25, figs. 9, 10. Seapharea (Scapharca) grandis (Broderip and Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 194, pi. 3, fig. 13. Anadara (Larkinia) grandis (Broderip and Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, pp. 65, 66, pi. 13, figs. 4-6. — Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, pp. 161, 162.— Frizzell, 1946, lour. Paleont, vol. 20, No. 1, pp. 41-44.— Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 195, 196. Shell with the characters described for the subgenus. Ribs about 26 or 27, typically square in section, elevated, mostly smooth except on the anterior slope where they are crudely noded, their interspaces deep and flat and of the same width as the ribs. Living specimens have a thick black periostracum as protection against acid waters. An average specimen measures: length 105 mm., height 85 mm., diameter 85 mm. Tumbez, Peru. This is a common, widely distributed species and often used as food in parts of northern Peru, Ecuador, and Panama, where it is known to the fishermen as "Pato de Buro". Although drift shells may occasionally be 94 AXEL A. OLSSON picked up on some open beaches, its usual habitat is lying deeply buried in soft mud banks which border mangrove swamps; hence, its distribution coincides closely with that of the mangrove. The southern limit^ of both living Anadara grandis and of the mangrove is at the mouth of the Tumbez River in northwestern Peru although fresh-looking shells of this ark washed out of Pleistocene tablazo deposits occur as far south as Sechura Bay near the northern border of the Peruvian faunal province, C. B. Adams, who collected so extensively in Panama and carefully noted the ecological con- ditions under which each species lived, recorded that this ark was found liv- ing half buried in the mud and algae under trees a Httle above half tide level. As fossil, Anadara grandis extends back into the Miocene at which time, it spread into the Caribbean, generally occurring in beds with other brack- ish-water species, often associated with lignites. Range — Lower California to Tumbez, Peru. Panama: San Miguel Bay; mouth of the Rio Chepo. Canal Zone: Farfan Beach. Colombia: Buena- ventura; Tumaco. Ecuador: Limones; Cojimenes; Manglaralto; mouth of the Guayas River and adjacent shoreline southward to the Peruvian border. Peru: Tumbez. Subgenus CUNEABCA Ball, 1898 Type species by subsequent designation, Gardner, 1926, Area incongrua Say. Shell trigonal, inflated, with full umbones and small, submedial and slightly prosogyrate beaks over a high, triangular cardinal area covered completely by the ligament. The cardinal area bared of the ligament is smooth or marked obscurely with normal or longitudinal lines, the area outlined by deep, side grooves to which the edges of the tensilium were once attached. Hinge with numerous taxodont teeth in a continuous series, small in the middle zone, larger at the ends. Valves slightly unequal, the left valve being larger, its ventral margin overlapping, the external sculpture discrepant, the ribs of the left valve larger, and more coarsely noded. Valve margins strongly fluted. Anadara (Cunearca) bifrons (Carpenter) Plate 9, figures 3, 3a, 3b Area cardiiformis Sowerby, 1833, Proc. Zool. Soc. London, p. 22 San Bias, Gulf of California. — d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, p. 634. Not A, cardiiformis Basterot, 1825. Area bifrons Carpenter, 1856, Cat. Mazatlan Shells, Brit. Mus., p. 134, No. 184. Scapharca (Cunearca) bifrons (Carpenter), Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 197-199, pi. 3, fig. 12. Anadara (Cunearca) bifrons (Carpenter), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 70. Area (Cunearca) bifrons (Carpenter), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 160. Area (Scapharca) corculum Morch, 1861, Malak. Blatter, bd. 7, p. 205. New name for Area cardiiformis Sowerby. Area brasiliana Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 3, fig. 17. Not of Lamarck. The shell figured is apparently A. cardiiformis from San Bias, Bay of California, and not the West Atlantic form. 8 Anadara grandis was reported as living in Sechura Bay by Frizzell. This record (s based either on fossil specimens washed out of tablazo beds such as found at Bayovar or Recent specimens brought from the north by fishermen. PANAMIC-PACIFIC PELECYPODA 95 The shell is generally large (up to 55 mm.), convex, subquadrate, in- equivalve, with full, nearly medial umbones and usually quite thin. The posterior submargin is strongly flattened as if truncated almost at right angles. The left valve has 28 to 30, large ribs, flat, smooth and separated only by lined interspaces on the middle and posterior surfaces, strongly noded and with wider interspaces on the anterior portion; the ribs on the umbone are finely beaded throughout. Right valve is similar but the ribbed interspaces are wider. Cardinal area is longer than high, smooth. Carpenter's type of A. bifrons in the British Museum (Nat. Hist.) is herein figured; its dimensions are as follows: length 37.9 mm., height 30.8 mm. diameter of the closed valves 27.5 mm. A. bifrons is a larger species than A. aequatorialis, and of a more rhombic form, the posterior side so strongly impressed or flattened so as to appear as if cutoff sharply, the ven- tral and anterior margins meeting to form a right angle. Allied closely to A. brasiliana Lamarck (incongrua Say) of the western Atlantic, the Pacific shell is generally smaller, more rhombic in shape, and the sculpture is smoother. Range — ^Gulf of California to northern Peru. Panama: Guanico; Bucaro. Colombia: Isla del Gallo. Ecuador: Galeras; Mompiche. Peru: Tumbez; Zorritos; Paita (D'Orbigny). Anadara (Cunearca) aequatorialis (d'Orbigny) Plate 9, figures 4, 4a, 5, 5a Area ovata Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 8, fig. 49. Santa Elena, Ecuador. Not A. ovata Gmelin, 1791. Area aequatorialis d'Orbigny, 1846, Vol. Amer. Merid., vol. 5, p. 636. New name for A. ovata Reeve, not of Gmelin, 1791. Seapharca (Cunearea) aequatorialis d'Orbigny, Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 34, pi. 3, figs. 2, 9. — Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 160. Anadara (Cunearea) aequatorialis (d'Orbigny), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, pp. 69, 70. — Rost, 1955, Allan Hancock Pacific Expedi- tions, vol. 20, No. 2, pp. 206, 207, pi. 15, figs, a-c; text-figs. 92 a-c. Area subelongata Nyst, 1848, Mem. Acad. Royale Sci., Lettres, Beaux-Arts Belgique, t. 221, p. 70. The shell is of medium size, relatively thin to slightly thickened, sub- ovate and slightly inequivalve, the anterior side rounded and somewhat produced, the posterior side flattened, its margin appearing obliquely truncated, its end somewhat pointed. Umbones wide and prominent with a slight depression extending along the front of the umbonal angle towards the ventral margin. Ribs on the left valve number 30, the anterior set of 10 are rather coarsely noded throughout, the rest finely noded or smooth. The ribs on the right valve are narrower and separated by wider inter- spaces, the anterior ones noded, the rest plain. The shell is relatively thin at first becoming heavier with age. Our largest specimen, a shell from Sua, Ecuador, has a length of nearly 44 mm. and is heavy. This species with bifrons seem to form an intergradational series and at times specimens are difficult to separate. A. aequatorialis seems to be more common south of Panama. Range — Panama southward to Peru, perhaps northward to the Gulf of CaHfornia. Panama: Bucaro. Ecuador: Sua; Mompiche; Limones; Manta; Santa Elena. Peru: Tumbez; Zorritos; Boca Pan. 96 AXEL A. OLSSON Anadara (Cuiiearca) perlablata (Grant and Gale) Plate 9, figures 2, 2a Area labiata Sowerby, 1833, Proc. Zool. Soc. London, p. 21. — Reeve, 1843, Conch, Icon., vol. 2, Area, pi. 1, fig. 7. Not A. labiata Solander, 1786 "Hab. ad Real Llejos et ad Tumbez." Area (Area) perlabiata Grant and Gale, 1931, Mem. San Diego Soc. Nat. Hist., p. 141. New name for A. labiata Sowerby. Area (Cunearea) perlabiata Grant and Gale, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 161. Anadara (Cunearea) perlabiata (Grant and Gale), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 70, pi. 14, figs. 1, 2, 6. Shell small or of medium size (up to about 36 mm.), nearly equivalve (the left valve a trifle larger than the right), subquadrate, the anterior- ventral side convex and rounded, the posterior-ventral margin slightly inflexed because of a weak surface depression extending downward from the beak to the ventral margin. Umbones prominent and nearly central terminating above in small, narrow, pointed beaks curved over a high, triangular, ungrooved, cardinal area. Sculpture discrepant on the two valves, the ribs of the left valve being neatly beaded over the umbone and anterior umbonal slope, later becoming smooth ventrally, the ribs of the right valve being narrower and smooth from the first, only a few of the ribs on the anterior slope below the beak being noded. The ribs number between 26 to 28, of which 9 are placed on the posterior slope. Surface white under a thin, black periostracum which scales off easily and on beach shells is pre- served only in patches; when well preserved the periostracum shows cross scales in the intervals on both valves. Hinge line shorter than the length of the shell, the teeth small and in a continuous uninterrupted series. Length 33.2 mm., height 33.1 mm., diameter 32 mm. Puerto Pizarro, Tumbez, Peru. Length 36 mm., height 36.4 mm., diameter of a left valve 16 mm. Tumaco, Colombia. This is a mud-flat species, often found in the mouth of rivers where it occurs with Anadara grandis. Chione (Iliocliione) subrugosa, Dosinia dunkeri and Diplodonta. It is especially common at Tumaco, Colombia, and at Puerto Pizarro in the mouth of the Tumbez River, Peru. Range — Lower California to northern Peru. Panama: San Miquel, Pearl Islands. Colombia: Tumaco. Ecuador: Manta; Puerto Palmito, Santa Elena. Peru: Puerto Pizarro, Tumbez River. Anadara (Cunearea) nux (Sowerby) Plate 9, figures 8, 8a Area nux Sowerby, 1833, Proc. Zool. Soc. London, p. 19 Xipixapi. — Reeve, 1843, Conch. Icon., vol. 2, Area, pi. 1, fig. 1. Seapharea (Cunearea) nux (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 196, pi. 3, figs. 7, 8. Area (Cunearea) nux Sowerby, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 161.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist., vol. 107, art. 2, p. 173. Anadara (Cunearea) nux (Sowerby), Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 205, 206, pi. 16, figs. 20 a-c; text-figs. 91 a-c. Shell small, cordate, convex, subequivalve, the umbones wide and ter- minating in small, incurved beaks placed at the anterior one-third and separated by a fairly high, cardinal area longer than wide. The sculpture of the two valves is somewhat discrepant, the ribs on the left valve being PANAMIC-PACIFIC PELECYPODA 97 noded for the most part while those of the right valve have nodes only on the anterior seventh or eighth, the others are smooth. Ribs number about 22 or 23, are rectangular in section, somewhat wider than their interspaces which are often strongly cross-threaded. Periostracum thin, deciduous, light brown or straw-colored with a row of strong, coarse bristles in the inter- spaces. Length 20 mm., height 17.7 mm., diameter 15.1 mm. Common. This species resembles A. chemnitzi (Philippi) of the Carib- bean but is generally smaller and with narrower and more oblong umbones. Range — Gulf of California to northern Peru. Panama: San Carlos. Ecuador: Mompiche; Limones; Galeras; Manta; Montanita; Santa Elena. Peru: Tumbez; Zorritos; Mancora; Lobitos; Negritos. Subgenus SCAPHARCA Gray, 1847 Type species by original designation, Area inaequivalvis Bruguiere. Recent. Coast of southeastern India. Shell of medium size, oblong to subrectangular, relatively thin, moder- ately convex with a rounded umbonal slope, the umbones placed at the anterior one-third, flattened or slightly sulcate. The valves are slightly unequal, the left valve being a trifle larger, its margin overlapping that of the right. Sculpture is similar in each valve and consists of smooth ribs, rectangular in section and separated by flattened interspaces of the same width, the interspaces interlaced by strong cross threads. The cardinal area is elongate, narrow, marked with one or two ligamental grooves; ligament covers the area except for a narrow marginal zone on the anterior side. Teeth numerous, arranged in a continuous series, divergent at the ends. In the type species, the shell is relatively thin so that the ribs show through into the interior as strong flutings. Sculpture is similar on both valves. The ribs are smooth and separated by flattened interspaces. Subgenus SECTIARCA new subgenus Type species, Anadara floridana Conrad (^4. secticostata Reeve of some American authors). Plate 8, figure 2. Shell elongately subrectangular, subequivalve, moderately convex and heavy. Umbones wide, the beaks small, prosogyrous. Cardinal area elongate, much longer than wide, the ligamental grooves mainly developed over the posterior portion, the anterior portion wholly or partially bare. Ribs nu- merous, narrower than their flat interspaces, typically lined or grooved in each valve. Hinge long, narrow with small, numerous teeth in a continuous series. Posterior side oblique but not winged or emarginated. Sectiarca is similar in shape to Scapharca but has a heavier shell and the valves are alike, without an overlapping margin. Ribs are typically grooved in each valve. Coverage of the cardinal area is variable. In A. floridana, the anterior portion of the cardinal area is often completely bare (PI. 8, fig. 2) in some specimens, partly covered in others. The Pliocene A. lienosa (Say) has strong groovings over the whole area, except for a small bare space along the dorsal margin. 98 AXEL A. OLSSON Anadaia (Sectlarca) conclnna (Sowerby) Plate 8, figures 1, la Area concinna Sowerby, 1833, Proc. Zool. Soc. London, p. 20. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 6, fig. 34. Area (Seapharea) concinna Sowerby, Hertlein and Strong, 1943, Zoologica, vol, 28, pt. 3, pp. 162, 163.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist, vol. 107, art. 2, p. 172, pi. 2, fig. 20. Seapharea (Seapharea) concinna (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 25, pi. 1, fig. 10. Area cumingiana Nyst, 1948, Mem. Acad. Roy. Sc. Lett Beaux-Arts, vol. 22, p. 22. (New name'for concinna Sowerby, non concinna Phillips 1829, as Cueullaea). Shell of medium size, elongately ovate, somewhat cylindrical and evenly convex, the ratio of height to length about 1 to 2, the dorsal and ventral margins straight and nearly parallel, the two ends olsliquely rounded. Sculpture consists of about 28 to 31 ribs, the anterior divided by a medial groove and strongly noded, their interspaces laced by finer cross concentrics; the other ribs are simple and smooth. The anterior section of the cardinal area is smooth, the posterior section traversed by 1 to 3 oblique grooves. Length 33.5 mm., height 19 mm., diameter 15.6 mm. Fort Amador Beach, Balboa, Canal Zone. This species appears to be locally common in waters of 10 fathoms or more but is rarely found on the beach. It is especially common in the mud dredged from the entrance of the Panama Canal at Balboa and Palo Seco. This species is similar to several fossil forms from the Miocene such as A. inaequilateralis Guppy from Jamaica and Santo Domingo and A. daiiensis Brown and Pilsbry from Panama. It occurs as a Pliocene fossil in Ecuador. Range — Gulf of California to Ecuador. Costa Rica: Gulf of Nicoya. Panama: Bucaro; Burica Peninsula; Canal Zone: Palo Seco; Fort Amador. Ecuador: Off Esmeraldas; Off Cabo Pasados; Charapota; Punta Blanca. Subgenus CALOOSARCA, new subgenus Type species, Anadara rustica (Tuomey and Holmes). Pliocene of South Carolina and Florida. Shell broadly elongate, moderately heavy, equivalve, convex. Cardinal area elongate, rather low or narrow, not covered fully by the ligament, the small portion anterior to the beaks usually bare. Posterior side deeply im- pressed, often winged or emarginated. Ribs simple, plain or heavily noded and often differing considerably in size, the anterior set sometimes mesially grooved. Hinge teeth small, numerous and in a continuous series. In the average specimen of A. rustica, the cardinal area in front of the beak is bare, but in gerontic specimens the anterior area may be partly covered or furrowed with ligamental grooves. In A. notabilis of the Caribbean, the cardinal area has essentially the same characters as in .4. rustica (see Plate 8, fig. 3). Anadara (Caloosarca) blangrulata (Sowerby) Plate 8. figures 5. 5a, 5b Area biangulata Sowerby, 1833, Proc. Zool. Soc. London, p. 21. (Atacames). PANAMIC-PACIFIC PELECYPODA 99 Area Soiverbyi d'Orbigny, 1846, Voy. Ara^r. Merid., vol. 5, pt. 3. Mollusques, p. 637. (Name changed because of A. biangulata Lamarck, not A. Soiuerbyi Sowerby, 1840.) Area (Scaphareaf) biangulata (Sowerby), Maury, 1922, Paleont. Amer., vol. 1 No. 4, pp. 191, 192. Area (Anadara) biangulata Sowerby, Hertlein and Strong, 1843, Zoologica, vol. 28, pt. 3, No. 19, pp. 155, 156, pi. 1, fig. 3. Anadara (Seapharea) biangulata (Sowerby), Rost, 1955, Allan Hancock Pacific Expedi- tions, vol. 20, No. 2, p. 201, text figs. 86, 87 a-c. Area gordita Lowe, 1935, Trans. San Diego Soc. Nat. Hist., vol. 8, No. 6, p. 16, pi. 1, fig. 1. The shell is short, oblong, ventrlcose with full, wide umbos, the maxi- mum inflation of the valves placed in the anterior-middle half of the shell, the posterior side narrowed and subacuminate. Cardinal area of medium height, wholly covered by the ligament on the posterior side and partly so on the anterior side. Ribs, about 30 in number, are relatively narrow and of the same width as their interspaces. The ribs are smooth or finely beaded and connected by strong cross threads in the interspaces. Sowerby 's biangulata was not figured by its author and the types were not located at the British Museum. The species was described from a single specimen dredged by Cuming at Atacames, Ecuador. Several dead valves were dredged off Esmeraldas by Olsson and Dranga in 1955. A small, left valve was dredged by Dr. G. Petersen off Zorritos in northern Peru. D'Orbigny's specimen of biangulata (name changed to Sowerbyi) was ob- tained by M. Fontaine in the Guayaquil area. This specimen is presented in the D'Orbigny Collection at the British Museum. It is a large, double- valved shell and measures 67.5 mm. in length. Range — Lower California to northern Peru and the Galapagos Islands. Mexico: Gulf of California. Ecuador: Esmeraldas; Atacames (Cuming). Peru: Off Zorritos and in the Gulf of Guayaquil. Galapagos: Galapagos (Hertlein and Strong). Subgenus ESMERAKCA new subgenus Type species, Anadara reinharti (Lowe). Shell with slightly unequal, convex valves and somewhat discrepant sculpture. Cardinal area is high, trigonal, flat or nearly so, largely covered by the ligament except for a narrow space along the anterior side, and cut into by two or more tentlike incisions. Periostracum thin, with a row of bristles along the ribbed interspaces. The type species Anadara reinharti has been refern;d by most authors to Seapharea although often with much uncertainty. Rost noted a resem- blance to species of Cunearea and to Larkinia. The approach of Esmerarea to Cunearea is quite marked, especially by its somewhat unequal valves and slightly discrepant sculpture, the greatest difference is in the characters of the cardinal and ligamental areas. In Cunearea, the cardinal area is usually quite high and trigonal, smooth and the ligamental coverage is complete as well as lacking the tentlike incisions. 100 AXEL A, OLSSON Anadara (Esmerarca) reinharti (Lowe) Plate 8, figure 4; Plate 9, figure 1; Plate 10, figures 4-4d Area (Anadara) reinharti Lowe, 1935, Trans. San Diego Soc. Nat. Hist, vol. 8, No. 6, p. 16, pi. 1, figs. 3a, 3b, 3c "Guaymas". — Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 157. Anadara (Scapharca) reinharti (Lowe), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 74. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 198-200, pi. 13, figs. 18 a-c, 19 a-b; pi. 14, figs. 20 a-c; text-figs. 85 a-d. The shell is large, rhomboid, whitish, with full, convex umbones ending in small, prosogyrate beaks, anterior of the middle and inrolled a little over a rather wide, obliquely triangular cardinal area. Usually, the valves are moderately thin so that the ribs show on the inside as shallow furrows which end as deeper, sharp-edged flutes at the margin. The valves are slightly unequal in size, the margin of the right valve extending beyond the other a trifle and the external sculpture is likewise somewhat discrepant as in Cunearca. Ribs number about 25, there are 17 ribs in front of an ill- defined posterior umbonal angle and 7 or 8 smaller, less well-defined ribs behind. The ribs of the left valve are a little stronger, subrectangular in section, and more or less transversely noded, especially anteriorly, their interspaces narrower and flattened; in the right valve, the ribs are narrower and as wide as their interspaces, the latter with some distant cross threading. Periostracum thin, deciduous, with bristles set in the inter- spaces. An average specimen measures: length 56.1 mm., height 51.3 mm., diameter 44.5 mm. This species was described by Lowe from a small shell with a length of only 27.7 mm and of solid texture. When full-grown, the shell reaches a size more than twice as large and the valves are generally quite light in weight. The young shell has been compared with that of A. multicostata but none of our specimens show much resemblance to that species. Its slightly discrepant sculpture and size of the umbones of the valves re- calls species of Cunearca but the noding of the right valve is not so pro- nounced. It is best distinguished by the characters of the ligament and cardinal area as described above for Esmerarca. Apparently a common species locally, although seldom or ever obtained on the beach. According to Mr. Harry Johnson, it is the commonest shell obtained by the shrimpers off the coast of Panama. Range — Gulf of California to Ecuador. Genus LUIfARCA Gray, 1857 (Argina Gray, 1842, not Argina Huebner, 1918, in Lepidoptera) (Arginarca McLean, 1951 type Area (Arginarca) campechiensis Gmelin) Type species by monotypy. Area costata Gray, 1857 (believed to be a deformed specimen of A. pexata Say)=:i4. campechiensis Gmelin. Shell medium-sized to large, ovate-oblong, subequivalve, inflated, the umbones and beaks placed at the anterior one-quarter. The cardinal area is long and narrow, placed entirely behind the beaks and covered completely PANAMIC-PACIFIC PELECYPODA 101 by the ligament. Hinge teeth divided into two series, the anterior set being short and irregular, the posterior set much longer, regular. Tip of the beak often stained with black. Lnnarca brerifrons (Sowerby) Plate 8, figures 7, 7a-7c Area brevifrons Sowerby, 1833, Proc. Zool. Soc. London, p. 22. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 1, fig. 6. Scapharea (Argina) brevifrons (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, pt. 4, p. 200. Argina brevifrons variety buearuana Sheldon and Maury, 1922, op. eit., pp. 200, 201, pi. 2, fig. 16; pi. 3, fig. 10. Lunarca brevifrons subsp. brevifrons (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 75. Lunarca brevifrons subsp. buearuana (Sheldon and Maury), Reinhart, 1943, op. cit., p. 75, pi. 7, figs. 5-7. Area (Argina) vespertina Morch, 1861, Malak. Blatter, vol. 7, p. 204. Lunarea vespertina (Morch), Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 209, 210, pi. 15, figs. 24 a-b; text-figs. 93 a-c. The count of 22 or 23 ribs as given by Reeve for this species is incorrect as the type examined in the British Museum has 35 ribs in the left valve. All our specimens of L. brevifrons from Peru have 30 or more ribs. Area (Argina) vespertina Morch and Area (Barbatia?) melanoderma Pilsbry and Lowe are forms of L. brevifrons. The beak is commonly stained with a black streak. Range — Lower California to northern Peru. Panama: Old Panama; San Carlos; Biicaro. Ecuador: Mompiche; Galeras; Manta; Santa Elena. Peru: Tumbez; Zorritos; Punta Picos; Mancora; Negritos. Subfamily NOETDfAE Genus NOETIA Gray, 1857 Type species by monotypy, Noetia triangularis Gray = N. reversa (Sowerby). Recent, Panama-Pacific province. Shell subrhomboidal to subtrigonal, its posterior side flattened or im- pressed, its end pointed or produced. Beaks opisthogyrate, varying in posi- tion from nearly central to strongly posterior. Cardinal area high or narrow, covered by the ligament, and vertically grooved or striated, the ligament largely or wholly confined to the anterior side. Adductor scars large and distinct, the posterior one usually with a raised edge or flange below. Surface covered with a dense, scaly to pilose periostracum. Noetia (Noetia) reversa (Sowerby) Plate 10, figures 1, la, lb Area reversa Sowerby, 1833, Proc. Zool. Soc. London, p. 20. Tumbez, Peru.— Reeve, 1843, Conch. Icon., vol. 2, Area, pi. 1, fig. 5 Noetia reversa (Gray), Sowerby, Maury, 1922, Paleont. Amer., vol. 1, No. 4, p. 171, pi. 1, figs. 7, 11. Noetia reversa (Sowerby), H. and A. Adams, MacNeil, 1938, Prof. Paper 189-A, U. S. Geol. Survey, pp. 38, 39, pi. 6, figs. 7, 22, 23. Noetia (Noetia) reversa (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 77, pi. 14, figs. 5, 7, 8.— Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 163.— Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, p. 211, text-figs. 94 a-c. Area Hemicardium Koch in Philippi, 1843, Abbild. und Beschreib. Conchylien, vol. 1, p. 43, Area, Tafel 1, fig. 1. Noetia triangularis Gray, 1857, Annals Mag. Nat. Hist, 2d ser., vol. 19. p. 371. Shell of medium size (largest about 50 mm.), convex and solid. Pos- terior side short, sharply truncated, usually flat, its margin straight, occa- 102 AXEL A. OLSSON sionally flexed, its end produced and pointed. Anterior side longer, rounded to subquadrate in shape. Ribs, which number usually about 25, are flat and rather broad, close-set and wider anteriorly, narrower and more widely spaced posteriorly. The ligament lies wholly anterior of the beaks. Perio- stracum coarse and heavy, concentrically scaly, pilose, and of a velvety, dark-brown color. Several names have been given to fossil forms of Noetia from the late Tertiary beds of the Pacific and Caribbean coastal lands of Central America and northern South America, many of which are so similar to N. reversa that they could well be considered as subspecies of the Recent shell. Some fossil Noetias attain a much larger size (up to 85 mm.), than the Recent shell. Most specimens of N. reversa are quite regular in shape but some shells from Sua, Ecuador, are strongly produced posteriorly and resemble the Miocene N. macdonaldi Dall from the northeast coast of Costa Rica. Range — Lower California to northwestern Peru. Panama: San Carlos; Bucaro; Chepo. Colombia: Isla del Gallo; Choco. Ecuador: Galeras; Sua; Manta; Isla la Plata; Santa Elena. Peru: Tumbez; Zorritos; Boca Pan; Mancora. Subgenus EONTIA MacNeil, 1938 Type species by original designation, Area ponderosa Say. Recent, East Coast of the United States, Massachusetts to northern South America. Ligament not wholly restricted to the anterior side, a small segment not vertically grooved, present on the posterior side. Ribs less flattened and divided by wider interspaces. An East American group but with one species on the Pacific Coast. Noetia (Eontia) olssoiii Sheldon and Maury Plate 10, figures 2, 2a Noetia olssoni Sheldon and Maury, 1922, Paleont. Amer., vol. 1, No. 4, pp. 10, 11, pi. 1, fig. 9. Eontia olssoni (Sheldon and Maury), MacNeil, 1939, Prof. Paper 189-A, U. S. Geol. Survey, p. 13, pi. 1, fig. 19, 20. Noetia {Eontia) olssoni Sheldon and Maury, Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, p. 77, pi. 2, figs. 13, 14. Shell small, (the largest seen, about 27 mm.), elongate-subtrigonal, the umbones high, convex, nearly central, ending in a small, narrow, curved, pointed beak seated above the cardinal area. The umbonal angle is strong and sharp, extending to a pointed posterior end. Anterior side is long, narrowed, rounded at end. Sculpture consists of numerous, small, narrow beaded riblets separated by interspaces carrying an interstitial thread. Cardinal area an unequal-sided triangle, the short side posteriorly, the longer anterior portion vertically grooved. Ligament completely covers the cardinal area, the larger part on the anterior side. Surface covered by a thin periostracum, generally worn off in beach shells. Ventral margin sinuous, toothed on the anterior and posterior sides. Beaks usually colored pink. This species is closely related to N. centrota (Guppy) from the south- ern Caribbean but has smaller, narrower umbones and a more compressed posterior side. Both the Caribbean and Pacific species have the umbones colored pink. Range — Panama southward to Peru. Panama: Burica Peninsula; PANAMIC-PACIFIC PELECYPODA 103 Bucaro. Colombia: Isla del Gallo. Ecuador: Esmeraldas; Sua; Cabo Pasados; Manta; Manglaralto; Santa Elena; Ancon. Peru: Zorritos; Punta Picos; Mancora; Negritos. Genus SHELDONELLA Maury, 1917 Type species by monotypy, Noetia (Sheldonella) maotca Maury. Mio- cene of Santo Domingo. Shell small, modioliform, thin or subsolid, the posterior side widely expanded. Posterior-umbonal slope is strongly convex or vaulted, the ventral side below it usually impressed. Beaks small, nearer the anterior end, slightly opisthogyrate. Cardinal area is an elongate, flat zone of moder- ate width distributed along the hinge line; the ligament itself being re- stricted to a triangular area under the beak almost equally divided between the anterior and posterior sides, the extreme posterior half of the cardinal area being bare. The area of the ligament is vertically grooved. Sculpture is formed of numerous, small ribs, their interspaces with a smaller inter- stitial riblet. Ventral margins closed, without a byssal gap. The smaller species of Eonotia such as A^. olssoni and N. centrota bear resemblance to Sheldonella in their hinge characteristics and sculpture but they differ notably in shape and in possessing a strong, umbonal angle. Sheldonella delgata (Lowe) Plate 10, figures 3, 3a Area delgada Lowe, 1935, Trans. San Diego Sec. Nat. Hist., vol. 8, No. 6, p. 16, pi. 1, fig. 2. Noetia (Sheldonella) delgada (Lowe), Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, pp. 77, 78, pi. 12, figs. 3-5.— Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 163. Rare and local. This species is similar to S. maoica Maury from the Miocene of Santo Domingo. The Panama specimens were obtained from shell drift collected along the east shore of the Burica Peninsula. Range— Mexico southward to Panama. Mexico: Manzanillo (Lowe), also Hertlein and Strong. Panama: near Punta Piedra south of Puerto Armuelles. Family OLYCYMEKIDAE Shell usually solid, porcellaneous, equivalve, with subcentral umbones and small prosogyrous or opisthogyrous beaks above a well-defined cardinal area, the valves generally quite convex, subcircular, subovate to subtrigonal in shape, generally slightly inequilateral, the anterior side is usually more evenly rounded while the posterior side is often somewhat narrowed and angulated, the valve margins closing tightly. The hinge plate is arched and bears numerous chevron-shaped taxodont teeth on each side, the teeth smaller in the middle zone and often partly or completely obliterated there by the downward spread of the cardinal area. The cardinal area may be narrow or high, subtriangular in shape, usually more or less equally de- veloped on each side of the beak, or the posterior side may be much longer, its surface deeply engraved by tent-shaped grooves, the whole covered by a dark-brown ligament. Adductor scars usually well marked, subequal, often elevated and connected by an entire pallial line lying just withm the ventral margin. Surface smooth or radially sculptured, the ventral margin smooth but more often furrowed. Periostracum thin or almost absent or heavy and densely pilose. 104 AXEL A. OLSSON Recent species appear to belong to three generic groups distinguished as follows: I. Shell subovate, subcircular or slightly subelliptical, nearly equilateral, the anterior side more evenly rounded, the posterior often somewhat narrower and angulated at the end. Beaks nearly medial above the cardinal area and but slightly opisthogyrous. A. Surface with relatively weak sculpture, the riblets low, often indistinct, smoothish, or if radial riblets are present, they are usually overrun by fine longitudinal threads or striations. Periostracum coarse and heavy, dark in color and densely pilose. Genus Glycymeris B. Sculpture more strongly emphasized, the ribs well formed, smooth or concentrically wrinkled but without superimposed radial threads or striations. Periostracum weakly developed or v/anting. Genus Tuceton^ II. Shell decidedly inequilateral, the anterior side being the longer, well rounded, the posterior side flattened or impressed. Beaks strongly opisthogryrous, placed near the anterior end of the cardinal area. Genus Axinactis General Key to Panamic and Peruvian species I. Surface with relatively weak sculpture formed by low, inconspicuous ribs, generally overrun by threadlike subsidiaries or the surface may be nearly smooth. Glycymeris A. Shell small or of medium size (seldom above 45 mm.), ovate-sub- circular in shape. Cardinal area small, short, triangular. 1. Shell ovate in shape, the height often appearing slightly greater, sur- face generally appearing almost smooth except for underlying sub- obsolete radial ribs, the coloration brownish or cream, plain or lightly rayed, the interior white. Peruvian. G. ovata B. The shell larger and the sculpture generally more pronounced. Panamic. Ba. Shell relatively large, subcircular in shape, nearly equilateral, the pos- terior side differing only slightly in shape from the anterior. 2. Shell large (up to about 100 mm.), the surface beneath the coarse periostracum finely marked with transverse wavy or zigzag lines, especially over the umbones. Gulf of California. G. gigantea 3. Shell smaller, the surface marked more densely with brown spots or streaks. G. macidata Bb. Shell of medium size, subelliptical in shape, inequilateral, the posterior side somewhat longer and produced. 4. Surface finely sculptured by low ribs overrun by linen-like subsidiaries. Color more uniformly brown or cream; spots if developed are more sparingly distributed. G. lintea PANAMIC-PACIFIC PELECYPODA 105 II. Surface ribbing strongly emphasized. Tucetona C. Ribs rounded, simple, separated by wide or merely narrowly lined in- terspaces. Subsidiaries lacking or consisting of concentric wrinkles only. Ca. Shape subcircular, the submargins not strongly impressed or flattened. Ribs numerous (35-40). 5. Average size about 38 mm., with high convex umbones and beaks. General color white, lightly or heavily maculated with brown. T. multicostata Cb. Shape subtrigonal with the anterior and posterior submargins impressed and flattened, the cardinal area narrower. Ribs fewer, not over 30. 6. Average size about 30 mm. T. sirigilata 7. Average size larger with broader and flatter ribs. T. strigUata canoa D. Ribs relatively few, large, and covered by strong, cordlike subsidiaries. Shell decidely inequilateral, the beaks opisthogyrous. Genus Axinactis 8. Ribs about 6 in number. A. inaequalis 9. Ribs 10 to 12 in number. A. delessertii Genus GLTCYSIERIS Da Costa, 1778 Type species by tautonomy, Glycymeris orbicularis Da Costa, 1778 {=zArca glycymeris Linne 1758). Europe. Shell usually solid, suborbicular to subcircular, equilateral or nearly so, equivalve, closed, with prominent central umbones ending in small, approximate beaks. Ligament external, covering the cardinal area which may be amphidectic (along both sides of the beak) or entirely anterior, the beaks then becoming opisthogyrate, the cardinal area usually heavily marked with chevron-shaped ligamental grooves. Hinge plate arched, the teeth arranged in a continuous series or the middle zone obliterated by the downward migration of the cardinal area, the lateral teeth always largest. Sculpture principally radial, formed by fine threads, sometimes almost obsolete, the surface then approaching smoothness, or with large, strong ribs. An umbonal ridge running from the beak and angulating the posterior margin is sometimes faintly indicated. Muscle scars distinct, situ- ated high in the valves. Ventral margins of the valve fluted. When fresh, the surface is covered with a dark-colored, soft, velvety periostracum. Glycymeris (Glycymeris) OTata (Broderip) Plate 11, figures 6, 6a Pectunculus ovatus Broderip, 1832, Proc. Zool. Soc. London, p. 126 Hab. ad insulam Lobos. — Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 1, fig. 2. Pectunculus intermedius Broderip, 1832, Proc. Zool. Soc. London, p. 126 Hab. ad Iquiqui. — Reeve, 1843, op. cit., pi. 1, fig. 1. Shell of medium size (length about 44 mm.), obliquely subovate, solid. Surface beneath the brown epidermis white and when well preserved minutely decussate but without the usual fine riblets. Epidermis ashy to dark brown. 106 AXEL A. QLSSON This is a species of the Peruvian faunal province not ranging north of Paita. It is often a common fossil in the Peruvian tablazos. Beach speci- mens are usually worn smooth. The typical form of ovata is rounded sub- ovate, the more elongate elliptical form is that named intermedia and if fairly constant may perhaps be separated as a subspecies. Range — Paita southward to Chile. Peru: Paita Peninsula; Bay of Sechura; Lobos Islands; Callao, Glycymeris (Glycymeris) macniata (Broderip) Plate 11, figures 2, 5 Pectunculus maculata Broderip, 1832, Proc. Zool. Soc, p. 126.— Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 1, fig. 4. Glycymeris (Glycymeris) maculata (Broderip), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 150. The shell is often large (length 80 mm.), convex, heavy, nearly cir- cular, the posterior side with a low, obscure angulation. Surface smoothish but when fresh showing a submicroscopic sculpture of low, rounded riblets on the umbones crossed by small, equidistant concentrics becoming grad- ually replaced ventrally by fine, raised radial threadlets which are evenly distributed and not bunched together in riblike groups. Hinge plate solid, the teeth relatively few, the laterals large, the middle series continuous or broken. Ground color white, thinly or thickly speckled with brown streaks, more or less arranged in a zigzagged pattern. Interior of shell white, the umbonal cavity and the beaks tinged with violet or brown. Length 69.5 mm.; height 70.2 mm.; diameter 46.4 mm. Punta Blanca, Ecuador. Range — Lower California to northern Peru. Panama: Pearl Islands; Guanico. Ecuador: Sua; Isla la Plata; Manta. Peru: Zorritos. Glycymeris (Glycymeris) gigrantea (Reeve) Plate 11, figure 1 Pectunculus giganteus Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 1, figs. 3a, 3b Guaynaas. Glycymeris (Glycymeris) gigantea (Reeve), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 150. Glycymeris gigantea (Reeve), Durham, 1950, Mem. Geol. Soc. America, No. 43, p. 56, pi. 2, figs. 1, 8. Similar to G. maculata but larger (max. about 1(K) mm.), and more distinctly marked with waved or zigzagged brown bands. Periostracum coarse and dark-brown in color. This large glycymerid seems to be restricted in its distribution to the Gulf of Cahfornia. It differs principally from G. maculata by its larger size and color markings, the brown spots arranging themselves in a more definite zigzag pattern, and perhaps it should be accorded only a subspecific standing. Range — Gulf of California. Mexico. Guaymas. Glycymeris (Glycjinerls) lintea, new species Plate 11, figures 4, 4a Shell of medium size (length to about 60 mm.), broadly subelliptical, longer than high, the posterior side is longer, somewhat produced and pointed at the end. The sculpture is fine, formed over the middle of the valve by numerous, low, rounded riblets, the whole closely overrun by fine, threadlike longitudinals producing a subsidiary sculpture like that of fine linen; this fine sculpture covers the whole surface evenly but the PANAMIC-PACIFIC PELECYPODA 107 larger ribs fade-out over the anterior and posterior submargins. Color light- cream or whitish, plain or lightly maculated with brown, the tip of the beak and the adductor scars more darkly colored. Hinge plate long and narrow, the teeth usually in an unbroken series. Inner margin finely furrowed. Length 57.7 mm., height 48.2 mm., semidiameter 16.5 mm., Holotype, Coast between Punta Blanca and Puerto Callo, Ecuador. ANSP 218915. Distinguished from G. maculata by its more elliptical form and produced posterior side, generally lighter and more uniform coloration and fine sculpture. This species seems related to G. spectralis Nicol of the Caribbean but is much larger. Range — Panama to northern Peru. Panama: Guanico, Pearl Islands. Ecuador: Punta Blanca, Punta Carnero near Santa Elena. Peru: Zorritos. Genus TUCETONA Iredale, 1931 Type species by original designation, Pectunculus jlabeUatus Tenison- Woods. Surface sculptured with strongly emphasized radial ribs between shal- low or deep interspaces, the ribs simple or divided terminally and crossed by concentric wrinkles or striations. Periostracum thin or wanting. Tocetona multicostata (Sowerby) Pectunculus multicostata Sowerby, 1833, Proc. Zool. Soc. London, p. 195. — Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. S, figs. 2, 6. Glycymeris (Tuceta) multicostata (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 151. Shell of medium size (length 40 mm.), subcircular, a trifle higher than long, convex, solid, the umbones wide, oblique, subcarditiform. Ribs between 35 to 40, narrow, rectangular, between deep square grooves of nearly the same size, uniform through the middle, smaller on the sides, the ribs and interspaces coarsely cross-threaded. Hinge teeth relatively few and large, the cardinal area subamphidectic, the anterior side longest. Color white, maculated with brown, the interior white or with a brown stain over the posterior portion. Range — Coast of Mexico to Ecuador. Ecuador: Isla la Plata, Manta. Colombia: Gorgona Island. Panama: Pearl Islands, Bahia Honda (Hertlein and Strong). Tucetona strigilata (Sowerby) Plate 11, figure 3 Pectunculus strigilatus Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 196. "Hab. ad Sanctam Elenam". — Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 6, fig. 31. Glycymeris (Tuceta) tessellata strigilata (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, pp. 152, 153. Glycymeris tessellata strigilata (Sowerby), Hertlein and Strong, 1955, Bull. Amcr. Mus. Nat. Hist., vol. 107, art. 2, p. 175, pi. 3, figs. 25-28. Pectunculus tessellatus Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 196 "Monte Christe and in the Bay of Xipixapi". 108 AXEL A. OLSSON Glycytneris (Tuceta) tessellata (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, pp. 151, 152. Pectunculus minor d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, pt. 3, Mollusqucs, p. 62S, No. 709. (Not P. minor I. Lea 1833) Glycymeris chemnitzii Dall, 1909, Proc. U. S. Nat. Museum, vol. 37, No. 1704, p. 253. New name for P. minor d'Orbigny. Shell orbicular, triangular, rounded or expanded ventrally, narrowed inward dorsally, the submargins somewhat appressed, straight, the anterior margin rounded, the posterior more produced and angled at the end, especi- ally if viewed from within. Surface sculptured with 22 to 25 ribs, generally square or rectangular in section separated by flattened interspaces, the ribs larger along the middle, smaller and crowded on the sides, both ribs and interspaces crossed by fine, raised concentric threads. Cardinal area small, triangular surmonted by the small beaks placed slightly posterior of the mid-point. Internal margin coarsely furrowed in the middle zone, the marginal furrows small or absent. Coloration white, irregularly splotched with brown, or entirely ashy white with a brownish cast. Length 29.4 mm., height 30 mm., semidiameter 9 mm. Left valve, Zorritos. T. tessellata and T. strigilata were described by Sowerby at the same time and on the same page, the former placed first; both seem to represent variations of each other, T, strigilata is the commonest and most typical form, for that reason I have given it precedence over the other. T. strigilata appears closely related to T. arata Conrad from the Miocene of North Carolina. Pectunculus pectenoides Deshayes from Panama is perhaps equiv- alent. Range — Lower California to northern Peru. Ecuador: Manta, Santa Elena. Peru: Zorritos. Tucetona strigilata canoa (Pilsbry and Olsson) Glycymeris canoa Pilsbry and Olsson, 1941, Proc. Acad. Nat. Sci. Philadelphia, vol. 93, p. 54, pi. 13, figs. 2, 2a Pliocene, Punta Blanca, Ecuador. Glycymeris (Tuceta) tessellata canoa Pilsbry and Olsson, Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 152. This form was first described as a fossil from the Pliocene of Ecuador. It has been reported from the Recent fauna by Hertlein and Strong who considered it as a giant form or subspecies of T. tessellata. According to these authors, it differs from T. tessellata (strigilata) by its much larger size, extremely broad ribs, and in that the color markings are arranged in concentric zigzag lines rather than in the shape of large spots. Range — Gulf of California and perhaps southward to Ecuador. Known living only at Arena Bank, in the southern end of the Gulf of California (Hertlein and Strong). Subgenus AXOACTLS Morch, 1861 Type species by subsequent designation, Hertlein and Strong, 1943, Axinaea (Axinactis) inaequalis (Sowerby). Shell solid, rounded to obliquely subtrigonal or cardiform, the umbones PANAMIC-PACIFIC PELECYPODA 109 and beaks with a strong posterior curve, opisthogyrate, with the larger portion of the cardinal area lying on the anterior side. Ribs through the middle zone of the disk are large and relatively few in number (6 to 10) fading out on the appressed submargins into cord or threadlike radials. Two species. Key to species Axinactis I. Ribs relatively few (about 6), large in the middle, the valves convex with appressed submargins. G. inaequalis II. Ribs more numerous (about 10), valves rounder. G. delessertii Axinactis inaequalis (Sowerby) Plate 11, figures 8, 8a, 8b Pectunculus inaequalis Sowerby, 1832, Proc. Zool. Soc. London, p. 196. — Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 4, fig. 16 Bay of Panama and Real Llejos. Pectunculus assimilis Sowerby, 1832, Proc. Zool. Soc. London, p. 196 dredged in sandy mud and gravel, in from eight to twelve fathoms at Puerto Portrero and in the Bay of Guayaquil. — Reeve, 1843, op. cit., pi. 4, fig. 15. Glycymeris inaequalis (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 153. Shell coarse, obliquely trigonal to flatly cardiform, the umbones strongly curved posteriorly. Beaks small, opisthogyrate, with the cardinal area lying almost wholly on the anterior side of the beaks. Ribs in the middle zone of the valve large, few (six or seven) becoming small on the submargins or replaced there by the strong longitudinal threads which overrun them. Hinge teeth in an arch, large and relatively few in number. Color sometimes nearly white but generally with a pattern of transverse, zigzag brown bands, closely or widely spaced. Length 40.3 mm., height 44.4 mm., diameter 30 mm. Punta Mambri, Ecuador. Range — Gulf of California to northern Peru. Panama: Panama City; Pearl Islands; Burica Peninsula. Canal Zone: Venado Beach. Ecuador: Esmeraldas; Limones; Manta; Isla la Plata; Santa Elena; Punta Mambri. Peru: Zorritos; Mancora; Sechura. Axinactis delessertii (Reeve) Plate 11, figures 7, 7a Pectunculus delessertii Reeve, 1843, Conch. Icon., vol. 1, Pectunculus, pi. 9, fig. 52. Hab — / Reeve, 1843, Proc. Zool. Soc. London, p. 190. Glycymeris (Axinactis) delessertii (Reeve), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, p. 153. Shell like A. inaequalis but larger, rounded, the ribs more numerous. Interior white stained with brown on the posterior side. Range — Mexico to Panama. Mexico: Tres Marias Is. (ANSP 160732. H. N. Lowe). Panama: Panama. (ANSP 7953. T. B. Wilson). Family LIMOPSIDAE The shell is small or of medium size, glycymerid in shape, sometimes nearly symetrically rounded or trigonal, or strongly obliquely suborbicular, the anterior side then shorter than the other, equivalve. Umbones are sub- central with the beaks rising a Httle above the hinge and cardinal area. no AXEL A. OLSSON Cardinal area as in Glycymeris is generally low, triangular but with the ligament restricted to a small, central pit under the beak of triangular shape. Surface sculpture is varied, sometimes smooth or with concentric markings only, or with radial costae and threads in different strength, the whole covered by a brown-colored periostracum generally tufted. Hinge as in the Glycymeridae consists of a series of obliquely set taxodont teeth on both sides of the beak usually in a curved or arched form. Genus LIMOPSIS Sacco, 1827 Type species by monotypy. Area aurita Brocchi. Miocene and Pliocene of Italy. With the general characters of the family. The genus Limopsis has been divided into several smaller groups on basis of sculpture and whether the ventral margins are smooth or cren- ulated, characters poorly expressed in some species, intergradational in others. Most species of Limopsis live in deep water or in cold, northern seas. Limopsis zonalis Dall Plate 1, figure 8 Limopsis zonalis Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, pp. 393, 394, pi. 7, figs. 6, 9. Shell relatively large for the genus, obliquely ovate, slightly convex or compressed, white or cream-colored under a brown, villous periostracum, the tufts of long hair arranged in neat radial rows. Height 25 mm., length 27 mm., diameter 10 mm. Gulf of Panama in deep water. This is a deep-water shell dredged by the steamer Albatross at depths ranging from 555 to 782 fathoms in the Gulf of Panama. It has been in- cluded here for the sake of completeness and in the expectation, that since it is a fairly common species in the proper depth environment, it may yet be obtained by shrimp and fish trawlers operating off the coast of Panama. This species or an allied form is common as fossil in the upper Miocene of northern Ecuador. Range — Panama. Panama: Gulf of Panama. USNM. Order DYSODONTIDA (Anisomyarla) Superfamily MTTILACEA Family MTTILIDAE Shell elongately ovate, bullet to wedge-shaped, often with an oblique axis, the valves equal. Beaks small, prosogyrate, placed usually near the anterior end, the umbonal slope posteriorly, often prominent and vaulted. Hinge line posterior of the beaks usually straight, plain or with a crenulated margin in harmony with a ribbed external sculpture, edentulous, or with small dysodont teeth on the anterior lunular margin below the beaks. Ligament subinternal, attached to an elongated calcified resilifer, usually- white in color, compact or with a pitted or cellular basal foundation. Typi- cally bimyarian, the anterior adductor scar is always much smaller than PANAMIC-PACIFIC PELECYPODA HI the other and sometimes wholly eliminated in the adult, hence the posterior adductor scar is large and sometimes confluent with that of the posterior retractor. Surface smooth or with radial riblets; the sculpture is usually- much stronger on the posterior-dorsal side, finer on the ventral side of the umbonal slope. Inner layer of the shell is ordinarily nacreous, the outer layer thinner, darker, and covered by a thin or heavy, yellow, brown, green or black periostracum, hairy or bristly, often peeling off from dead valves. Marine, brackish to fresh water. Most species live in colonies, the shell anchored by its byssus to rocks, piling or to sea-weeds. Some species form nests of byssus in which they lie buried. Some species are rock borers such as the Lithophagas and Adula. Earlier authors distributed the species of this family amongst two key genera, Mytilus and Modiolus, principally from the position of the beaks, whether entirely terminal, the anterior end of the shell therefore more or less pointed, or with the beaks more remote, the anterior margin projecting a space in front of them. All transitional forms occur between these two types and many species have, at different times and by the same author, been referred to both genera. The reader is referred to the recent important paper of Tron Soot-Ryen, 1955, A Report on the Family Mytilidae: Allan Hancock Pacific Expedi- tions, vol. 20, No. 1 for much additional information on this family. Key to Panamic-Pacific genera I. Resilifer lined with a chalky white layer, its basal part cellular, hence showing as a line of pores or pits on its exposed edge. 1. Shell mytiliform, the beaks strictly terminal, pointed. Anterior or lunular side below the beaks with a few, short, riblike folds terminating in strong teeth within the margin. Mostly cold water and northern. Genus Mytilus 2. Shell modioliform, the beaks a little removed from the end, the anterior margin projecting beyond them. No folds or teeth on the anterior side and margin. Genus Mytella II. Resilial layer white, compact and showing no pores or pits on the side. A. Surface smooth or marked with concentric growth lines (except Aulacomya, which has variable ribs on umbones), the margin of the valves plain or smooth. a. Individuals free or nestlers, not boring into rock, coral or shell. aa. Shell mytiliform, the beaks terminal and pointed. 3. Often large, externally like Mytilus, the anterior adductor scar obsolete and the hinge teeth reduced to a single, riblike tooth. Genus Choromytilus 4. Similar but with a persistant anterior adductor scar and generally with a series of low, radial ribs or streaks on the umbones. Peruvian. Genus AulacoTnya 112 AXEL A. OLSSON ab. Shell partly modioliform, the beaks not quite terminal. Anterior side very short, externally outlined by a faint lunular line, its inner margin smooth or weakly toothed. 5. Shell elongately wedge-shaped, dark brown to black, glossy and with a satiny sheen, internally white or vinaceous. Genus Semimytilus ac. Shell modioliform, the anterior margin short, projecting but without a lunular line, no hinge teeth. 6. Shell elongate to hatchet-shaped, the ventral side often deeply im- pressed. Periostracum smooth, scaly or bearing bristles. Genus Modiolus b. Borers in rock, coral or shell. 7. Surface smooth or with concentric lines of growth, the periostracum dark brown to black, and without secondary lime incrustation. Genus Botula 8. Surface incrusted with a secondary coating of lime (except Lithophaga, sensu stricto). Shell typically elongated, cylindrical or bullet-shaped. Genus Lithophaga several subgenera B. Surface sculptured with radial riblets, strong or partly obsolete, the inner margins crenulated by the external ribbing at least in some groups. Dysodont teeth present in most cases. c. Shell ovate to obliquely subcircular, the longer axis nearly vertical. Sculpture with small divaricating riblets. 9. Shell small, subnacreous, the hinge teeth strong. Genus Crenella d. Shell elongate, mytiliform to modioliform. da. Individual, free or nestlers. daa. Cavity of the beak bearing a small, shelflike platform or septum on which the anterior adductor scar is placed. 10. Shell generally small, mytiliform, with ribbed sculpture, often with lines of bristles. Genus Septijer dab. Cavity of the beak without a septum, the anterior adductor scar placed on the shell wall itself. daba. Ligament relatively short, only about half the length of the hinge line. 11. Margins of the shell strongly crenulated all around. Dysodont teeth strong along the anterior margin. Genus Brachidontes dabb. Ligament as long as the hinge line or nearly so. dabba. Ligament extending forward to the tip of the beak. PANAMIC-PACIFIC PELECYPODA U3 12. Anterior end of shell full, its margin well rounded, and with small normal crenulations only. The posterior adductor scar is quite large, confined to the dorsal side. Genus Hormomya 13. Anterior end of shell narrowed and pinched, its dysodont teeth large and coarse. Posterior adductor scar circling the posterior end of the valve on the inside. Genus ScolimytUus dabbb. Anterior margin turned in dorsally so as to lie closely under the beaks and ends in a sharp, cutlike break, the ligament does not extend forward of this point. 14. Shell full, convex, fan-shaped, coarsely ribbed but with the surface usually eroded. Color deep purple or black. Genus PerumytUus db. Borers in rock or coral growth. 15. Shell cylindrical, bullet-shape, the beaks terminal. Surface smooth or encrusted but not corroded. Genus Lithophaga 16. Shell elongated, irregular, the beaks near the middle, the umbones and midzone often deeply corroded. Genus Adula 17. Shell modioliform, sculpture with fine radials except in the midzone which is smooth, the periostracum covered with bristles. Genus Gregariella Genus MTTILUS Linn6, 1758 Type species by subsequent designation, Anton, 1839, Mytilus edulis Linne. North Atlantic. Shell mytiliform or ovate- oblong, usually with a strong, oblique axis. Beaks placed at the extreme anterior end are small, the posterior side wide and rounded, convexly vaulted along the umbonal arch extending from the beak to the posterior-ventral corner. Hinge with a series (about four to six), small, dysodont teeth on the anterior margin or narrow plate below the beak. Ligament subinternal, narrowly hnear in shape, within the dorsal margin, and attached to a whitish chalky resilifer, the basal founda- tion of which is finely pitted. Anterior adductor scar small, lying in the cavity of the beak and connected with the pallial line which lies as a gradu- ally widening band within and parallel to the ventral margin; posterior adductor and retractor scar united and forming an irregular pipe-shaped impression. Cold water. M. edulis is typically a North Atlantic species but various closely re- lated forms or subspecies have been named from the Southern Hemisphere. M. edulis Linne, Plate 12, figure 6. Mytilus arciformls (Ball) Plate 12, figures 4-4b Modiolus arciformis Dall, 1909, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 152, 258, pi. 28, fig. 2 Huaquilla, Ecuador. Volsella (Volsella) arciformis (Dall), Hertkin and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 72, pi. 1, fig. 5 Monypenny, Nicaragua. 114 AXEL A. OLSSON Shell narrowly elongated, decidely arcuate, the base being strongly in- flected and the dorsal margin arched. The ventral side is flattened, thereby emphasizing the angled edge of the umbonal slope. Color an olive-brown, the periostracum thin, smooth, often worn-off in spots, the surface beneath with strong concentrics. The small beaks are almost terminal, the short anterior margin below folded so as to form 3 or more weak teeth and shallow pits. Resilifer is nearly as long as the arched dorsal margin, narrowly hnear, white, its basal edge strongly pitted. Posterior adductor scar pipe-shaped, the upper arm long and narrow, confluent with the retractor scar at its end. The anterior adductor scar present. This recognizable species was referred to Mytella and placed in the synonym of M. falcata (d'Orbigny) by Soot-Ryen but its relations lie closely with Mytilus. It is apparently a mud-flat species, especially common along the mangrove-fringed shores of the Gulf of Guayaquil. Range — Salvador to the Gulf of Guayaquil. Salvador: Gulf of Fonseca (Hertlein and Strong). Nicaragua; Monypenny Point (Hertlein and Strong). Ecuador: Huaquilla (Dall); Posorja; Puna Island; Santa Elena. Genus SEMIMYTILUS Soot-Ryen, 1955 Type species by original designation, Mytilus algosus Gould, 1850. Shell small or of medium size, mytiliform, the beaks almost terminal, the dorsal margin almost straight with the ligament along it narrow and linear. Anterior end short, reflexed below the beak, and extended forward forming a short, slightly pouting extremity, its rolled over margin smooth or rarely weakly denticulated, its external surface forming a small lunule circumscribed by a line. Anterior adductor scar very small, continued into the irregular pallial line which follows the ventral margin closely, the pos- terior adductor and retractor joined forming an irregular, pipe-shaped scar. Surface smooth or with undulated concentrics, the periostracum thin, brown or black, shiny or with a silky sheen. Two species. Key to species of Semimytilus 1. Length about 45 mm; anterior end quite narrow, the posterior narrow to medium well rounded; pallial and muscle impression usually distinct. Peruvian faunal zone. S. algosus 2. Shell smaller and more stubby, the posterior end more widely rounded; pallial and muscle impression weakly marked. Paita Buffer Zone. S. nonuranus SemlmjiJlus algosns (Gould) Plate 14, figure 8 Mytilus algosus Gould, 1950, Proc Boston Soc. Nat. History, vol. 3, p. 344.— Gould, 1852, United States Exploring Expedition, vol. 12, p. 450, atlas, 1856, pi. 41, figs. 566, 566a. Semimytilus algosus (Gould), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 25, 26, pi. 4, fig. 17; text-figures 8, 9, 14, 15, 16. Mytilus dactyliformis Hup6, 1854, Gay, Hist. Chile, Zool., vol. 8, p. 310, pi. 5, fig. 6. PANAMIC-PACIFIC PELECYPODA 115 The type locality as given by Gould is the Fiji Islands which is prob- ably incorrect, Valparaiso, Chile, was selected as type locality by Soot-Ryen. This species, as here understood, is probably confined largely to the South American coast washed by the Humboldt Current. It is extremely abundant to the south of Lima, at Paracas, and the Bahia de la Inde- pendencia. Semlmytilus nonuranus (Pilsbry and Olsson) Plate 17, figure 10 Modiolus (Modiolus) nonuranus Pilsbry and Olsson, 1935, Nautilus, vol. 49, No. 1, p. 16, pi. 1, fig. 3. Shell small (generally less than 40 mm.), the small beaks terminal, the short anterior margins hardly passing beyond them. Valves strongly convex, the umbonal slope straight, the ventral margins but little impressed. The periostracum is thin, smoothish, colored brown on the ventral side and a rich black or green-black on the posterior slope, often with a satiny luster. Interior cream-white with a ray of vinaceous of varying intensity under the umbonal slope. Length 39.00 mm., height 19.50 mm., diameter 16.50 mm. This seems to be a good species, smaller than S. algosus, of a different shape, the posterior side much wider and more rounded, and its range more northerly. It is a common species between Sechura Bay and Lobitos, usually attached to rocks, swept by strong surf waves, which it thickly covers. Range — Coast of northwestern Peru. Peru: Nonura Bay and Punta Aguja at the southwestern end of Sechura Bay; Punta Capullana between Talara and Lobitos. Genus CHOEOMTTILUS Soot-Ryen, 1952 Type species by original designation, Mytilus chorus Molina. Coasts of Chile and southern Peru. Often large, strongly obliquely ovate-oblong, of a deep blue or purple- black color, the surface smooth and covered by a coarse, black periostracum. Interior white except for the margins which are dark. Choromytilus chorus (Molina) Plate 12, figure 10 Mytilus chorus Molina, 1782, Saggio suUa Storia Naturale del Chile, p. 202.— Reev«, 1857, Conch. Icon., vol. 10, Mytilus, pi. 2, fig. 4.— Dall, 1909, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 151, 257, pi. 25, fig. 1. Choromytilus chorus (Molina), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 31, pi. 2, figs. 7, 8; text-fig. 5. With general characters of the genus. According to Dall (1909), this is the largest of the mussels along the Chilian and southern Peruvian coast and generally regarded as the best of the edible shell fish. It is known as Choro de Concepcion after Conception Bay in Chile where it abounds. Range — Coast of Peru and Chile from Pacasmayo to Tierra del Fuego. Choromytilns pallioponctatns (Carpenter) Plate 12, figures 7, 7a Mytilus Palliopunctatus Dunker in Carpenter, 1855, Cat. Mazatlan Shells, Brit. Mus., p. 118, No. 167 Mazatlan, Mexico. — Reeve, 1857, Conch. Icon., vol. 10, Mytilus, pi. 19, fig. 5. Mytilus (Chloromya) palliopunctatus (Dunker), Hertlein and Strong, 1946, Zoologica, vol. 31, No. 2, p. 70. Choromytilus palliopunctatus (Carpenter), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No, 1, pp. 31, 32, pi. 1, fig. 5; text-figs. 4, 13. 116 AXEL A. OLSSON Shell long, swollen, rather straight, pointed, almost always rubbed at various angles, but when perfect exhibiting fine radiating stria and some^ times much stronger concentric lines of growth. Shell reddish purple in color, often white gray on the surface. Interior of a lustrous dark purple, white near the byssal gap and often finely punctate. The beak is terminal, with the anterior margin deeply impressed below to produce a folded hinge structure above it. The posterior adductor is relatively large, pipe-shaped, the retractor scar placed under the resilifer about half way towards the beak. No anterior adductor scar. Range — Lower California to Panama. Mexico: Mazatlan; Acapulco. Nicaragua: Corintho (Hertlein and Strong). Genus Aulacomya Morch, 1853 Type species by subsequent designation, Von Ihering, 1900, Mytilus magellanicus Chemnitz, 1785 (= Mytilus ater Molina, 1782). Straits of Magellan and northward to middle Peru. Shell large, mytiliform and often coarse, the surface marked with strong, radiating striae over most of its disk or confined to the umbonal slope. Beaks small and terminal. The hinge which is placed below and behind the beak is formed by a plate continued in from an obscure lunule and consists of a strong rib or fold in the right valve and a flattened furrow in the left valve. The resilifer is long, narrow, chalky, and compact or with an unpitted foundation. Anterior adductor scar eliminated in the adult. Cold waters of the Southern Hemisphere. Aulacomya ater (Molina) Plate 14, figure 9 Mytilus magellanicus Chemnitz, 1785, in Martini and Ciiemnitz, Neues Syst. Conchyl.- Cabinet, vol. 8, p. 162, t. 83, fig. 742.— Lamarcic, 1819, Anira. s. Vert, vol. 6, pt. 1, p. 119.— Lamarcic, Encyclop. Meth., pi. 217, fig. 2.— Dall, 1909, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 151, 258, pi. 25, fig. 4. Mytilus decussatus Lamarck, 1819, Anim. s. Vert., vol. 6, pt. 1, p. 120. — Hidalgo, 1879, Moluscos del Viaj« al Pacifico, p. 52, pi. 3, fig. 4. Mytilus americanus d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, Mollusques, p. 648. Mytilus ater Molina, 1782, Saggio sulla Storia Naturale del Chili, p. 202. Aulacomya ater (Molina), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 33, 34, pi. 1, fig. 6; text-figs. 17-18. Along the Peruvian coast, this species has been reported as far north as Callao. It appears to be plentiful at Paracas and southward. Fresh shells have a dark-brown, polished periostracum which in old shells peels off, revealing a purplish-white surface streaked with radial lines of purple over the whole disk or confined to the umbonal slope; interior pearly white. Range — Southern half of the South American continent on both coasts, and on the Pacific side as far north as Callao. Genus PERUMTTILUS new genus Type species Modiola purpurata Lamarck. Shell of medium size, with obliquely elongated, convex valves, the beaks nearly terminal. Sculpture produced by relatively large, crude radial PANAMIC-PACIFIC PELECYPODA 117 ribs, usually corroded, producing rather coarse crenulation around the posterior margin, finer ones along the ventral margin and often becoming obsolete there. Surface color usually purplish over the posterior surface and white on the anterior-ventral side. Dorsal margin above the hgament not crenulated. The anterior margin below the beak is turned backwards along the hinge and terminates in a sharp stump as if cut off abruptly; it marks the forward end of the ligament. The rounded end of the anterior margin in front of the beak has several small teeth or crenulations. Posterior adductor scar rounded, joined with the narrow, linear retractor scar, together forming a pipe-shaped impression. The type species has been referred to Brachidontes but it differs by important hinge characters as well as in other features. PerumytilDS purpuratus (Lamarck) Plate 12, figure 1; Plate 14, figures 1-lb Modiola purpurata Lamarck, 1819, Anim. s. Vert., vol. 6, p. 113. Mytilus ovalis Lamarck, 1819, idem., p. 121. — Encylop. Meth., pi. 219, figs. 3a, 3b. — d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, p. 648. Modiolus purpuratus (Lamarck), Dall, 1910, Proc. U. S. Nat. Museum, vol. 37, No. 1704, pp. 153, 258. Brachidontes Purpuratus (Lamarck), Soot-Ryen, 1955, Allan Hancock Expeditions, vol. 20, No. 1, p. 45, pi. 4, fig. 18, text-fig. 30. Shell small or of medium size (length up to about 40 mm.), elongately ovate, convex, narrowed and sometimes deeply compressed along the an- terior-ventral side. The sculpture is formed by coarsely wrinkled radial riblets, rather large on the rounded posterior slope, finer on the ventral side. Color is a dark purple to nearly black over the posterior surface, often white on the anterior part. The umbonal slope is often worn nearly smooth by exposure to the heavy surf waves. This is a common species of the cooler Peruvian coastal fauna from Callao southward; northward it seems to be much rarer as well as smaller in size. A few specimens were collected on the island of Lobos de Tierra and at Yasila near Paita. Dall has recorded the species from Estero Zarumilla on the Ecuadorian border near Capon but we have never seen specimens from so far north. Range — Gulf of Guayaquil southward to Chile. Ecuador: Estero Zarumilla (Dall). Peru: Yasila near Paita; Lobos de Tierra; Callao and southward (common). Genus BRACHIDONTES Swainson, 1840 Type species by monotypy, Modiola sulcata Lamarck, 1819 (Encyclop. Meth., pi. 220, figs. 2a, 2b). Shell small or of medium size, mytiliform, with the small beaks not quite terminal and from which there extends posteriorly an umbonal in- flation and along which lies the long axis of the shell. Posterior-dorsal or hinge margin straight or weakly curved, usually ending distally in a small angle, and more or less strongly crenulated along its whole length. Hinge margin on the short anterior side has two or more, small, dysodont teeth. Ligament subinternal, its resilifer forming a narrow scar about half the length of the posterior-dorsal margin. The adductor scars are distinct, the 118 AXEL A. OLSSON anterior one small and rounded, the posterior longer, pipe-shaped connected with the retractor scar. The pallial line not enlarged. Surface with ribbed sculpture. There is some question as to the identification of Lamarck's M. sulcatus and whether it represents an Atlantic or Indo-Pacific species. The above description is based largely on M. citrinus Roeding from Florida. (See Olsson and Harbison, 1953, Mon. No. 8, Acad. Nat. Sci. Philadelphia, pp. 61, 62.) Brachidontes citrinus (Roeding) {:=zArca modiolus Linne, 1767), Plate 12, figure 3. Genus HORMOMTA Morch, 1853 Type species by subsequent designation, Jukes-Brown, 1905, Mytilus exustus Linne. Shell small or medium-sized, mytiliform, with the small beaks near but not quite terminal, the valves vaulted, convex or angulated along the long, umbonal axis, often deeply impressed on the ventral side. Dorsal margin straight or slightly convex, curving into the posterior margin, the ligament and its scar narrow and lying along nearly its whole length. Posterior and vientral margins strongly crenulated by the external sculpture, the short, anterior margin with similar small crenulations and not the larger and stronger dysodont teeth. Anterior adductor scar relatively large, ovate, the pallial line distinct, the posterior adductor scar, large, pipe-shaped and often covering a large part of the inner posterior surface. External surface ribbed, sometimes much reduced or subobsolete over the impressed ventral portion. Like Brachidontes, but differs by its longer ligament which extends along most of the dorsal margin; the dorsal margin not normally crenulated above the ligament; also by the larger posterior adductor scar. Honnomya exustns (Llnn6) Plate 12, figure 2 Genus SCOLDtYTILUS, new genus Type species Modiolus (Brachydontes) playasensis Pilsbry and Olsson. Shell small, mytiliform or modioliform, the beaks plated almost termin- al, the valves elongated with the longer, oblique axis lying along the con- vex or sharply arched umbonal slope, the ventral side commonly flattened or deeply impressed. The surface sculpture is formed by radial riblets which may be weak or coarse. The posterior adductor scar is fused with that of the retractor and with a part of the pallial impression forming a single, large, lobate-shaped or ribbon-like band within the posterior margin. Liga- ment, as in Hormomya, is nearly as long as the posterior-dorsal margin. Hinge with one to three, fairly large, strong, dysodont teeth under the beak. The valve margin is crenulated throughout except for a short space along the impressed ventral side where the fluting of the riblets is weak or obsolete. A group of small species combining some of the characters of Brachi- dontes and Hormomya but sufficiently distinct to warrant generic separa- tion. Two subgenera may be recognized. PANAMIC-PACIFIC PELECYPODA 119 Key to subgenera Scolimytilus I. Umbonal slope convex or rounded, the surface ribbing rather fine and fairly uniform. Posterior adductor and pallial line impression, fused and lobate in shape. Subgenus Scolimytilus s.s. II. Umbonal slope often strongly arched, the ribbed sculpture divided, coarse on the dorsal side. Adductor and pallial impression narrow and ribbon-like. Subgenus AeidimytUus Scolimytilns (Scolimytilus) playaseusis (Pllsbry and Olsson) Plate 13, figures 2-2c Modiolus (Brachydontes) playasensis Pilsbry and Olsson, 1935, Nautilus, vol. 49, No. 1, p. 17, pi. 1, fig. 4 Playas, Ecuador. Shell with an average length of about 20 mm., medium-elongate, obliquely wedge-shaped, with nearly terminal beaks and a straight dor- sal margin, forming with the posterior margin a corner angle of about 120 degrees. The ventral side is flattened or impressed, rounding above into a fairly pronounced umbonal slope, highest in the middle zone and from there sloping downward to form a rounded posterior end. Ligamental scar linear, narrow, straight, as long as the dorsal margin, the small beak at its anterior end, with one or more medium-sized teeth below it and a few small crenulations on the anterior margin which project a little beyond it. Sculpture is produced by low, smoothish, radial riblets of nearly uniform strength over the whole surface except along the middle part of the um- bonal slope which may be smooth. Inner margins of valves crenulate con- forming to the outside ribbed sculpture. Periostracum of a rich brown color, glossy and where peeled off, the color underneath is a purple-brown. In- terior of shell of a pale brown, the pallial and muscle impressions distinct, and generally as figured. The type measures: length 20.7 mm., height 9 mm., diameter 8.7 mm., ANSP 164617. This is a local species, probably restricted to the inner shores of the Gulf of Guayaquil. From other species of the genus, it will be separated by the rich brown color of its glossy periostracum, its lower riblets, nearly uniformly developed over the whole disk, and by its wider, wedge shape, its ventral margin straight or but little impressed. Pallial and adductor impressions are generally well marked. Range — Shores of the Gulf of Guayaquil, Ecuador and Peru. Ecuador: Playas; Posorja. Scolimytllns (Scollmytllns) esmeraldensis, new species Plate 13. figures 1-lb Shell of medium size (length from 14 to 17 mm.), elongate, mytiliform, the beaks anterior and placed nearly at the end, the anterior end itself being short, narrowed, and pinched. The dorsal or ligamental margin is long, usually a little bowed in the middle, the scar of the ligament below it white, enameled and extending nearly its whole length. Beyond the dor- sal or ligamental margin, the posterior side descends obliquely and is broad, appearing as if narrowly rounded or subtruncated at the end. The ventral side is usually flattened or impressed in the middle, sometimes strongly 120 AXEL A. OLSSON SO. In fresh shells, the periostracum is thin, vernicose and dark olive- brown to nearly black in color with some lighter streaks showing through. Beneath the periostracum, the color of the shell is variable, in some speci- mens, it is white or grayish white; others are grayish purple flecked and rayed with lighter patches. Sculpture consists of numerous, small, radial riblets, developed uniformly over the surface except in the middle ventral zone which is smoothish. Inner margin of the valves crenulated all around except for a small space along the ventral side which is smooth; the ligamental margin is always strongly crenulated. Extreme anterior or lunular side has a few, small, strong riblets forming crenulations at the margin. Impression of the adductor and retractor muscles as described for the genus. Length 14.1 mm.; height 9.6 mm.; diameter 5.6 mm. Esmeraldas, Ecuador. Holotype ANSP 218929. Length 17 mm.; height 11 mm.; diameter 7.4 mm. Esmeraldas, Ecuador. Paratype ANSP 218930. Range — Ecuador. Ecuador: Esmeraldas. ScoUmytilns (Scolimytilns) aeqnatorlalis, new species Plate 12, figures 9-9b The shell is small (length about 10 mm.), obliquely elongated, with anterior, almost terminal beaks. The posterior-umbonal axis is slightly curved, convex and high along the middle zone; the ventral side is flattened or moderately impressed, the shape of the shell therefore somewhat arcuate. Hinge line straight and about half the length of the shell, the ligament nearly as long; beyond the end of the ligament or its scar, the posterior margin turns downward at an angle of 150 degrees, continues straight for a distance and then curves evenly forming a rounded end, or it may bend more sharply so that the end of the shell appears truncated. The periostracum is thin, vernicose, and imparts to the surface a glossy, varnished appearance. External color of the shell is two-toned, dark purplish- brown to nearly black on the dorsal side of the umbonal ridge and a lighter olive-yellow on the ventral side, these two zones of color showing through into the interior. Beneath the periostracum, the sculpture is plain or smooth except for some weak riblets generally present on the posterior- dorsal surface. The inner margins of the valve is smooth except for crenu- lations present above the ligament. Hinge teeth small, confined to the space below the beaks supplemented by weak crenulations along the short, an- terior margin. Posterior adductor scar of medium size, pioe-shaped. Length 10.1 mm.; height 6.8 mm.; diameter 6 mm. Punta Centinella, Santa Elena Peninsula, Ecuador. Holotype, ANSP 21927; paratype, ANSP 21928. Range — Coast of Ecuador and northwestern Peru. Ecuador: Punta Centinella, Santa Elena, on rocks at medium tide level. Peru: Paita. Subgenus AEIDIMTTILUS, new subgenus Type species Mytilus adamsiana Dunker. Shell small, mytiliform with ribbed sculpture, usually divided, the ribs on the posterior-dorsal side of the umbonal ridge much coarser. Ventral side usually strongly impressed resulting in a high, angular umbonal ridge and often a distorted appearance to the whole shell. Adductor and pallial impressions united, but smaller and narrower than in Scolimytilns . PANAMIC-PACIFIC PELECYPODA 121 Scolimytilns (Aeidlmytilns) adamslanus (Dunker) Plate 12. figure 5; Plate 13, figures 4, 4a, 6 Mytilus adamsiana Dunker, 1856, Proc. Zool. Soc. London, vol. 24, p. 360. (issued May, 8, 1857). Panama.— Reeve, 1858, Conch. Icon., vol. 10, Mytilus, pi. XI, fig. 55. Brachidonies (Hormomya) adamsianus (Dunker), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, pp. 70, 71. Hormomya adamsiana (Dunker), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 37-40, pi. 3, fig. 11, text-figs. 22, 25, 31. The shell is small (length to about 16.5 mm.), generally narrow and elongate, the umbonal ridge high, angled and vaulted, the ventral side flattened or impressed. The beaks are small and nearly terminal in position. The dorsal side of the umbonal ridge is coarsely sculptured with large radial ribs, few in number near the beak but increase by forking or addition distally and on the successive growth disks, each setoff by a shelf or a deep resting mark; ribs on the ventral side much smaller. Color of surface is some shade of purple on the dorsal side and white on the ventral side. Dorsal or hinge margin crenulated above the scar of the liga- ment. Length 15.6 mm.; height 9.3 mm.; diameter 6.6 mm. Punta Banda, Lower California, Mexico. Mr. T. Burch. Length 15.2 mm.; height 8 mm.; diameter 8 mm. Jipijapa (Puerto Callo), Ecuador. Range — Lower California to Ecuador. Panama: Panama (Dunker). Ecuador: Santa Elena; Puerto Callo (this is the port of Jipijapa, the Xipijapa of Cuming). Scolimytilns (Aeidimytilus) puntarenensis (Pilsbry and Lowe) Plate 13, figures 5, 5a Mytilus (Hormomya) puntarenensis Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 104, pi. 10, fig. 6 Puntarenas, Costa Rica (Lowe). Brachidontes Puntarenensis (Pilsbry and Lowe), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 46, 47, pi. 3, fig. 14; text-fig. 29. Shell small (length from 10 to about 18 mm.), generally broadly modoliform, high or wide posteriorly, narrower anteriorly, the small beaks much pinched and placed at the extreme end, and when perfect, the umbonal region bearing several nepionic caps, of which the first is extremely small and smooth, the others with ribbed sculpture. The ventral side is flattened to deeply impressed, the umbonal slope running prominently from the beaks to the posterior-ventral corner and rises as a high, rounded or subangu- lated ridge; some specimens are almost as long as high. The sculpture is costate, formed by small, radial riblets divided generally into two sets by the umbonal ridge, those on the dorsal side being larger, neatly granulated and quite uniform, the others below the umbonal ridge much finer and smoother. Anterior margin below the beak has a large external rib or ridge which passes into the hinge and forms there a large, knoblike tooth. Ex- ternal color a uniform dark-brown or deep purple, heaviest over the pos- terior-dorsal slope grading into a lighter shade or white on the ventral side. Length 17 mm.; height 8 mm.; diameter 8.7 mm. (Type, Puntarenas, Costa Rica, ANSP 155629). Length 11.7 mm.; height 9 mm.; diameter 8 mm. Punta Carnero, Santa Elena, Ecuador. 122 AXEL A. OLSSON Specimens from Ecuador agree well with the figure of S. puntarenensis given by Soot-Ryen, based on a paratype in the San Diego Museum (Chace Coll.), My shells show much variation in shape and in coarseness of sculp- ture and in some cases approach S. adamsianus quite closely. S. houstonius Bartsch and Rehder, 1939 from Galapagos Islands is also similar. Range — Costa Rica to Ecuador and northern Peru. Ecuador: Jipijapa (Puerto Callo). Peru: Yasila, Paita. ScoUmytilus (Aeldlmytilns) mnltiformis (Carpenter) Plate 17, figure 11 Myiilus multiformis Carpenter, 1855, Cat. Mazatlan Shells, Brit. Mus., pp. 118-120, No. 168 Mazatlan. — Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 70 dis- cussion with adamsianus. Brachidontes multiformis (Carpenter), Soot-Ryen, 1955, Allan Hancock Pacific Expedi- tions, pp. 44, 45, pi. 3, fig. 13; text-fig. 28. Because S. mtdtiformis was not figured by Carpenter, its identification is not entirely certain. In his remarks on the species, Carpenter emphasized the extreme variability of the shell both in shape and sculpture. His un- published manuscript drawings at the U. S. National Museum comprise about 11 sketches, all of which are based on small or immature specimens. These drawings show a small, short, fan-shaped shell with a large, smooth, nepionic area followed by two or more sculptured areas setoff sharply from each other and the nepionic disk by resting lines; the umbonal ridge is low, rounded, not angular, and the ventral side is not noticeably impressed; the scar of the ligament is only about half the length of the dorsal margin which is strongly crenulated. The largest specimen measured by Carpenter has a length of .45 inches or 11.4 mm.; this is probably the specimen num- bered 551 and is here selected as the lectotype; a new figure based on Carpenter's drawing is here given. A few of the Ecuadorian shells are tentatively identified with Car- penter's species but they differ by the smaller nepionic area, which in some cases can be seen only on high magnification. General color black or dark-brown, not green. Range — Lower California to northern Peru. Mexico: Mazatlan (Car- penter). Ecuador: Punta Callo; Santa Elena. Peru: Yasila. Genus SEPTIFER Recluz, 1848 Type species by subsequent designation, Stoliczka, 1871, S. bilocidaris Linne. Shell generally short, modioliform, with a high umbonal angle, the external surface sculptured with small radial riblets, often with bristles. Hinge and posterior margins strongly crenulated, the short anterior side with small dysodont teeth as in Brachidontes and with a small deck or platform placed like a shelf in the umbonal cavity below the beaks. Septlfer zetekl Hertlein and Strong Plate 13. figures 7. 7a Septifer cumingii Recluz. As cited by authors from West America localities but not the true S. cumingii described from the island of Annaa. PANAMIC-PACIFIC PELECYPODA 123 Septifer zeteki Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, No. 5, p. 71, pi. 1, figs. 1, 2. (Holotype from Taboga Island, Panama). Shells quite small, modloliform, widely expanded on the posterior side, impressed along the ventral side and narrowed anteriorly, the valves there- fore having an oblique trigonal form. Sculpture is formed by small radial ribs which may branch at the ends, finely noded by concentrics, much finer on the ventral slope. Color green, mottled with brown, the umbonal angle carrying a row of large bristles. Margins continuously crenulate all around, the beak with a small septum or decklike floor in the tip of the umbonal cavity. Length 6.8 mm., greatest height 4.1 mm., diameter 3.5 mm. (Hertlein and Strong). Range — Gulf of California to Peru and the Galapagos Islands. Ecuador: Puerto Callo. Santa Elena. Panama: Taboga Island. (Hertlein and Strong). Lagartillo. Peru: Bayovar, Sechura Bay. Genus MTTELLA Soot-Ryen, 1955 Type species by original designation, Modiola guyanensis Lamarck. Shell elongate, modioliform, often thin, the beaks and umbones placed near the anterior end. Posterior-dorsal margin straight, curved, or angu- lated at the end, the ligament and its scar nearly as long. Resilifer long and narrow, white, with a narrow pitted foundation. Anterior end relatively short, its margin smooth. Anterior adductor scar distinct, small and of an oblong, irregular outline, the posterior adductor confluent with the retractor and forming a club or pipe-shaped impression. Valves convex or vaulted along the umbonal slope, the dorsal-posterior side usually of a darker color, often with a greenish shade. Periostracum thin, the umbones of the shell commonly corroded. Three species. I. Shell broadly wedge-shaped, the ventral side often deeply impressed. Ratio of length to height, about 7 to 4. M. guyanensis II. Shell longer, often razor-shaped and very thin. 1. Shell exceedingly long, Solen-Vike and very thin. Length to height about 4 to 1. M. speciosa M. tumbezensis 2. Shell shorter, the length to height about 2.4 to 1. Mytella guyanensis (Lamarck) Plate 12, figures 8, 8a Modiola guyanensis Lamarck, 1819, Anim. s. Vert., vol. 6, p. 112.— Delessert, 1841, Rec. Coq. decrites par Lamarck, pi. 13, fig. 9. Modiolus guyanensis (Lamarck), Maxwell Smith, 1944, Panamic Marine Shells, p. S3, fig. 692H. Modiola brasiliensis Reeve, 1857, Conch. Icon., vol. 10, Modiola, pi. 4, fig. 17 Guayaquil; pi. 6, fig. 31 Brazil. 124 AXEL A. OLSSON Volsella (Volsella) guyanensis (Lamarck), Hertlein and Strong 1946, Zoologica, vol. 31, pt. 2, pp. 72, 73. Mytella guyanensis (Lamarck), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 53-55, pi. 5, figs. 22, 23; text-figs. 36, 41-44, The shell is oblong, obliquely wedge-shaped, relatively thin, the hinge margin is straight, more than half the total length, the basal margin descends straight or is deeply impressed. The sculpture is produced by well-developed, raised, regular concentrics along the posterior slope and finer, smoother growth lines on the ventral side. The periostracum is thin, its coloration divided into two contrasting zones; on the posterior portion, the color is a dull or satiny greenish black, generally with a fine pattern of zigzagged or divaricating lines of green showing through; on the ventral slope the color is typically a glossy brown. There is often a ray of brown along the lower side of the umbonal slope which because of its dull luster contrasts sharply with the polished brown surface behind it. The umbones are usually eroded. Length 70 mm.; height 44 mm.; diameter 32.8 mm. Guayaquil, Ecuador, market. Shells from Ecuador and northern Peru have the ventral side flattened or deeply impressed and the umbones are so badly eroded as to expose the pearly inner layer over a wide area; the habitat of this mussel is along the mud flats in front of mangrove swamps or in the adjacent estuaries and esteros. In Ecuador, this mussel is highly esteemed as food and appears in the markets and is served regularly in hotels and restaurants. Range — Lower California to northern Peru; also along the Caribbean coasts of Venezuela southward to Brazil. Panama: Pearl Islands; Garachine. Canal Zone: Venado Beach. Ecuador: Esmeraldas; Cojimenes; Guayaquil. Peru: Tumbez. Mytella speciosa (Reeve) Plate 14, figure 6 Modiola speciosa Dunker in Reeve, 1857, Conch. Icon., vol. 10, Modiola, pi. 7, fig. 35 Tumbez. Modiolus speciosus (Dunker), Maxwell Smith, 1944, Panamic Marine Shells, p. 53, fig. 698. Volsella (Amygdalum) speciosa (Dunker), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 73. Shell elongate and slender, very thin, smooth, the dorsal and ventral margins straight, not quite parallel but diverging at an angle of about 9 degrees. Beaks very small, not quite terminal, the widely rounded anterior end extending beyond them shortly. Posterior margin oblique, sloping down- ward, its dorsal junction widely rounded, more narrowly rounded or atten- uate at the ventral end. Periostracum is very thin, overlying a dull-white surface. The posterior slope is generally colored in various shades of green or green-brown, often concentrically banded or minutely flecked with brown, the long, ventral slope is brown. Interior nacreous, iridescent. Remarkable for its slender, thin shell and beautiful coloration. Generally rare. Very young shells (length 36 mm.) have the same shape as the adult. Large specimens may attain a length of over 100 mm. Range — Lower California to northern Peru. Mexico: Magdalena Bay, PANAMIC-PACIFIC PELECYPODA 125 Lower California (Hertlein and Strong). Nicaragua: Bay of Fonseca. Ecuador: Canoa; Atacames; Santa Elena. Peru: Tumbez; Zorritos; Punta Picos; Negritos. 3Iytella tnmbezensig (Pilsbry and Olsson) Plate 14, figure 7 Modiolus (Modiolus) tumbezensis Pilsbry and Olsson, 1935, Nautilus, vol. 49, No. 1, pp. 16, 17, pi. 1, fig. 5. Mytella speciosa Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 52, S3, pi. 5, fig. 25; text-fig. 37 (not of Reev«, 1857). Shell about 40 to 45 mm. long, thin and much compressed. The beaks are small. In a specimen 43 mm. long, the beak is about 6 mm. from the end which is obliquely rounded. The posterior side is somewhat expanded, its margin straight, rounded into the dorsal and ventral ones. The surface is marked with small, regularly incised growth lines on the ventral slope, much smoother on the posterior-dorsal side. Color of the shell is brown or tan on the anterior-ventral side becoming green or olive minutely flecked with chocolate on the posterior side. Length 41 to 44.5 mm.; height 18.5 to 21.5 mm.; diameter of a single valve 4.25 to 4.5 mm. Tumbez, Peru. This is a small, thin, delicate species common along the tidal mud flats of the river Tumbez in northern Peru. It is distinguished from M. speciosa by its shorter and smaller shell. Range — Lower California to northern Peru. Mexico: Bahia de Magade- lena (Soot-Ryen). Peru: Tumbez. Genus MODIOLUS Lamarck, 1799 Nomen conservandum. Opinion 325, International Com. Zool, Nomen. Type species by monotypy, Mytilus modiolus Linne. Recent, North Atlantic. The name "Volsella" Scopoli, 1777, which has been in general use in late years for this genus, has been suspended by a ruling of the International Commission of Zoological Nomenclature (Opinion 325, dated Jan. 7th, 1955). Shell variable in size, ovate, oblong or obliquely elongated, the small beaks adjacent and almost terminal, convex, the surface covered by a thin or heavy, green, brown to nearly black periostracum, smooth or coarsely pilose and often peeling off from dead shells. Surface under the perio- stracum usually smooth except for growth lines. Dorsal margin curved, the hinge edentulous except for a small projection near the anterior end of ligament. Ligament subinternal, attached to a rather long, broad, curved, inset resilifer. Interior of valves white to purple, the ventral margin with a small byssal gap. Some species build a nest of pebbles and fragments of shell held together by the threads of the byssus. Key to Panamic Modiolus I. Surface of shell is covered with a coarse, peeling periostracum, dark- brown in color and carrying over its posterior portion a dense growth of coarse bristles, the individual bristles being compound or serrated 126 AXEL A. OLSSON along their sides. Axis of shell is oblique, hatchet-shaped, its ventral mar- gin deeply impressed. Color beneath the periostracum is pink or rose-red. M. capax II. Periostracum smooth or if provided with bristles, these are more sparingly developed; the individual bristles simple, flattened but not serrated along their sides. Axis of shell not so strongly inclined. a. Dorsal and ventral margins are nearly straight and parallel, the pos- terior end attenuated and narrowly rounded. Color on the posterior slope is a reddish purple, the anterior-ventral slope white. M. eiseni b. Shell obliquely ovate to subtriangular, the anterior side short and quite high, rounded. Color brown with a lighter ray across the middle. Periostracum thin, like patches of flattened seaweed. M. -pseudotuUpus c. Shell larger, narrower and more elongated. Color dark-brown or black, the surface beneath white. Periostracum smooth. Anterior end short and narrowly rounded. M, pacijicus Modiolus capax (Conrad) Plate 14, figures 4, 4a Modiola capax Conrad, 1837, Jour. Acad. Nat. Sci. Philadelphia, vol. 7, p. 242 San Diego, California.— Reeve, 1857, Conch. Icon., vol. 10, Modiola, pi. 3, fig. 11. Volsella (Volsella) capax (Conrad), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 72. Modiolus capax Conrad, Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 60-62, pi. 6, fig. 30; text-figs. SO, 53a-b, 54, 55. Shell of medium or large size (height 85 mm.), heavy, generally obhque, hatchet-shaped, the height often exceeding the length. Dorsal margin straight, merging smoothly into the posterior margin, the two set at angles of 90 to 120 degrees, the posterior-ventral margin rounded to subtruncated. Anterior-ventral side is usually deeply impressed, more markedly so in southern shells. Fresh specimens have a chestnut-colored periostracum, the posterior portion of which is densely covered with long serrated hairs. Dead shells from which the periostracum has exfoliated, are usually colored a bright rose-red over the posterior surface, white on the impressed ventral side. The resilifer is a wide, deeply excavated pit bordered on the lower side by a strong ridge. This is a widely distributed species easily distinguished by its high, arcuate form, and coarsely pilose periostracum overlying a red or pink- colored shell. Dead shells have usually lost most of the periostracum, or it is retained only over the posterior portion. Range — California southward to Peru and the Galapagos Islands. Panama: Bucaro; Tobago. Canal Zone: Venado Beach. Ecuador: Sua; Manta; Manglaralto; Isla la Plata; Santa Elena. Peru: Tumbez; Paita; Yasila; Sechura Bay. Modlolns eiseni Strong and Hertlein Plate 14, figures 5. 5a Modiolus eiseni Strong and Hertlein, 1937, Proc. California Acad. Sci., ser. 4, vol. 22, p. 160, pi. 34, figs. 11, 14-16 off Mazatlan, Mexico.— Hertlein and Strong, 1955, PANAMIC-PACIFIC PELECYPODA 127 Bull. Amer. Mus. Nat. Hist, vol. 107, art. 2, pp 178, 179, pi. 2, figs. 9, 11.— Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 64, pi. 6, fig. 29. Shell of medium size (length about 50 mm.), relatively thin, elongate. Dorsal and ventral sides straight and subparallel, the posterior side long, inclined towards the base about 30 degrees, forming a produced and nar- rowly rounded end. The anterior side extends a short way beyond the tip of the beak and is obtusely pointed at the tip, A narrowly rounded umbonal slope begins at the beak and extends obliquely backwards to the posterior end, the surface in front and below it a little depressed. Surface smooth except for fine growth lines. Color is pearly white on the anterior one-half and a violet-pink on the posterior side, the division line between the two areas of color lying just below the umbonal angle. In- terior pearly white with the darker color of the posterior surface showing through shghtly. Length 50.5 mm., height 19.5 mm., semidiameter 9.3 mm. Manta, Ecuador. This is a rare species. No trace of a periostracum is shown on any of our specimens. Range — Gulf of California to Ecuador. Mexico: Off Mazatlan (Hert- lein and Strong). Ecuador: Off Cabo Pasados (Hertlein and Strong); Manta. Modiolus pseudotalipus, new species Plate 14, figures 2, 2a Modiolus americanus Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, pp. 67, 68, pi. 6, figs. 27, 28; text-figs. 56. (Not of Leach, Ul5=Modiola tulipa Lamarck, 1819.) Shell oblong, of medium-weight, the umbonal slope full and convex, extending obliquely along the longer axis of the valves from the beaks to the rounded posterior end, the posterior-dorsal and ventral slopes slightly impressed. Anterior side extends a short way in front of the beaks, rather widely rounded at the end. The posterior-dorsal and hinge margins are of nearly equal length, both are straight and set at an angle of about 120 degrees to each other. General surface color is a rich brown, deepest on the anterior-ventral surface and on the posterior-dorsal slope with a zone of lighter color extending from the beaks to the middle of the ventral margin. Interior a pearly white tinged with vinaceous. Length 64.5 mm.; height 38 mm.; diameter of one valve 13.6 mm. Punta Blanca, Ecuador. Holotype ANSP 218956. This species resembles the Atlantic Coast M. americanus (Leach), but the posterior side is longer, narrower, the color banding not so sharply de- fined. From M. pacificus, the species differs at all growth stages by its shorter and higher shell and by its more widely rounded anterior end. Range — Gulf of Cahfornia southward to Peru. Mexico: Magdalena Bay, Lower California, Mazatlan. Ecuador: Isla la Plata. Punta Blanca. Peru: Negritos; Paita; Yasila. Modiolus pacificns, new species Plate 14, figures 3, 3a Shell rather large, elongate modioliform, covered with a black brown periostracum which worn off in patches reveals a nearly white shell un- 128 AXEL A. OLSSON derneath. Umbones low with the small, adjacent beaks placed a short dis- tance behind the anterior end. Anterior side is short, not auriculate, its margins thickened. Dorsal margin carrying the ligament scar is straight, the more posterior portion of the dorsal margin longer, descending at an angle of about 30 degrees. Umbonal slope well rounded, its axis straight and nearly as long as the length of the shell itself, the posterior end narrowly rounded. There is a slight inflexion from the beak to the ventral margin. Interior of valves nacreous and of a dull lead-white color. Length 93 mm., height 53 mm., semidiameter IS mm. (a right valve). Resembles Modiolus rectus (Conrad) of the California Coast but has a straighter shell and a shorter, nonauriculate anterior side. Range — Northern Peru. Peru: Salinas on the Bay of Sechura to the northeast of Bayovar. Paita. Genus MUSCULUS Roeding, 1798 {Modiolaria Beck, 1838; Lanistes (Humph.), Swainson, 1840). Type species by subsequent designation, Iredale, 1915, Mytilus discors Linne. Musculus Roeding has been considered preoccupied by MuscuLus Martyn, 1787 but Martyn's names are unavailable. Shells comparatively small, rhomboidal, modioliform, inflated, moder- ately thin and with a pearly interior. Umbones prominent with the small beaks not quite terminal. Sculpture of surface divided into three areas, the anterior and posterior portions are marked with small radial threadlets, the middle zone smooth. Ligament subinternal and attached to a narrow, inset area under the hinge margin. Hinge edentulous. Subgenus GEEGARIELLA Monterosato, 1884 (Botulina Dall, 1889; Trichomus cuius Iredale, 1924: Tibialectus Ire- dale, 1939). Type species by subsequent designation, Crosse, 1885, Modiolus sulcatus Risso, 1826 (not of Lamarck, 1805, 1819) = Modiolus barbatellus Can- traine, 1835 = Modiolus opifex Say, 1825. Shell modioliform, straight, convex, the beaks almost terminal, the an- terior margin below not passing beyond them or but slightly. Posterior side long, often somewhat attenuated at the end, the umbonal slope narrowly vaulted to subangulated, with the radial riblets divaricating along it. Sur- face marked with fine, radial riblets (decussated on the dorsal side) over the whole posterior and mid-posterior slopes, also the anterior slope but with the anterior-middle-ventral zone smooth; the whole covered by a brown, skinlike periostracum, bearing a mat of hairs mixed with grains of sand along the posterior-umbonal slope, often terminating in a tuft at the end. Inner margins of valves finely crenuated by the ends of the radial riblets, except along the anterior-middle portion. Resilifer narrow and linear, a trifle less than half the length of the dorsal margin and at the forward end passing between the reflexed end of the anterior margin and the beaks. PANAMIC-PACIFIC PELECYPODA 129 Anterior reflex margin ends rather sharply a short distance behind the beaks, usually with a few small dysodont teeth along it and which grade into the normal crenulations forward. Anterior adductor scar large, ovate, the posterior indistinct in my specimens. Borers. Mnscnlus (Gregariella) coarctatus (Carpenter) Plate 16, figures 4-4d Crenella coarctata Dunker, Carpenter, 1855, Cat. Mazatlan Shells, Brit. Mus. p. 123, No. 172. Lithodomus coarctata Dunker, Reeve, 1857, Conch. Icon., vol. 10, Lithodomus, pi. 3, fig. 14. Lithophaga coarctata Dunker, 1883, Conch. Cab., 2d ed., pp. 28, 29, pi. 5, figs. 2, 3. Modiolaria (Gregariella) coarctata (Dunker), Lamy, 1937, Jour, de Conchyl., vol. 81, p. 42. Gregariella coarctata (Carpenter), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 77, 78, pi. 9, fig. 48 ; text-fig. 64. Average size about 27 mm., elongately modioliform, with a wide um- bone weakly sulcated across the middle. The small coiled beak is placed near the anterior end, the posterior end of the valve narrowly rounded to pointed, tufted with periostracal hairs and flexed slightly towards the right. Periostracum thin, brown over a thin pearly layer. Surface sculpture is formed by fine threadlets radiating from the beak and divaricated along the keeled umbonal slope, except on the anterior-middle zone which is smooth. Inner margins of the valve minutely crenulate except in the mid-zone. Hairs of the periostracum rather sparse and confined to the umbonal keel, forming a tuft at the end. Length 28 mm.; height 11 mm.; diameter 10.8 mm. Manta, Ecuador. This is a true rock borer forming smooth-walled, bullet-like holes. It is fairly common at Manta associated with Lithophagas. Resembles M. coralliophaga Gmelin of the West Indies but is more slender and less pointed at the posterior end. Range — Lower California to Ecuador. Panama: Taboga Island (Soot- Ryen). Ecuador: Manta. Mnscnlus (Gregariella) ehenal (Recluz) Mytilus chenui Recluz, 1842, Revue Zool., vol. 5, p. 306. Gregariella opifex Dall, 1921, Bull. 112, U. S. Nat. Museum, p. 22. (Probably not of Say, 1825 fidi Soot-Ryen). Gregariella chenui (Recluz), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 78, pi. 8, fig. 40 ; text-fig. 65. This is typically an East American species but has been recorded from the Pacific Coast by Dall and Soot-Ryen. I have seen no specimens from the Panamic zone. According to Soot-Ryen, the Hancock collections contain many samples of dead specimens taken in depth ranging from 16 to 50 fathoms. Range — Southern California to the Bahia de la Independencia, Peru. (Soot-Ryen). Genus CBENELLA Brown, 1827 Type species by monotypy, Mytilus decussatus Montagu. Recent, North Atlantic. 130 AXEL A. OLSSON Shell small, often minute, obliquely ovate, convex, with small, incurved, prosogyrate beaks. Prodissoconch often well preserved, smooth. Interior pearly, the outer surface covered when fresh by a thin, closely adhering periostracum. Hinge mytiloid, with small toothhke knobs on the anterior margin bordered on the posterior side by a deep, furrow-like pit for the attachment of the ligament which is wholly internal. Surface sculpture composed of fine radials crossed and decussated by concentrics, often divaricated along the middle line of the umbonal slope. Inner margin finely crenulated by the ends of the external riblets all around, sometimes ex- tending into the hinge itself to produce a pseudotaxodont pattern there. Three species appear regional. Key to species of Panamic-Peruvian species of Crenella I. Shell large, height 25 mm. Crenella megas. Panama Bay in 33 fathoms. II. Shell small, minute, height not over 4 mm. 1. Valves nearly oval in shape, the dorsal and ventral sides nearly alike. Crenella ecuadoriana 2. Shell subcircular to rhombic, the dorsal and ventral sides unlike. Pos- terior-dorsal margin straight. Crenella caudiva, new species. Crenella ecuadoriana Pilsbry and Olsson Plate 17, figures 7, 7a Crenella ecuadoriana Pilsbry and Olsson, 1941, Proc. Acad. Nat. Sci. Piiiladelphia, vol. 93, pp. 55, 56, pi. 18, figs. 2, 3. Crenella divaricata d'Orbigny, Hertkin and Strong, 194-6, Zoolcgica, vol. 31, pi. 2, No. 5, pp. 75, 76, pi. 1, figs. 12, 13 (in whole or part). Shell small, the average length about 3.25 mm., plump, elongately oval, nearly symmetrical, a line through the middle of the umbonal slope divides the surface into nearly equal halves. Surface sculpture consists of small, weakly decussated nblets which increase along the umbonal slope and near the ventral margin by occasionally forking and by the addition of intercalaries between their branches. In addition, the sculpture is divided into three contrasting areas by straight lines extending from the beaks to the margins and against which the small, simple (not forking) riblets abut sharply. This small species is locally plentiful in beach drift at Santa Elena. As fossil, it occurs in the Pliocene of Panama and Ecuador. Some authors have considered this small Crenella as the same as C. divaricata d'Orbigny described from Cuba. The Caribbean-West Indian Crenellas have not been thoroughly worked over but a comparison of C. ecuadoriana with the speci- mens from Bocas del Toro, Panama, show that the Caribbean shell is thinner, less symmetrical in shape, usually with a larger, more conspicuous prodissoconch and with weaker sculpture. Range — Lower California to northern Peru. Crenella eaudlTa, new species Plate 17, figure 2 The shell is small, moderately convex but not plump, unsymmetrical, the shape is irregularly subrhomboidal, the posterior side higher than the PANAMIC-PACIFIC PELECYPODA 131 anterior, hence, the dorsal and ventral margins appear to slant in towards each other anteriorly. Beaks almost terminal, and from which the umbonal axial slope extends full and convex to the posterior-ventral corner of the valves. The posterior-dorsal margin is long and straight, the posterior margin widely rounded, the ventral margin narrow and nearly straight. Surface sculpture consists of small riblets separated by narrow, cancellate interspaces, the riblets divaricating along the umbonal axis, simple on the anterior-umbonal slope; there is in addition a line of demarcation separ- ating the central zone of sculpture from that on the anterior-ventral side and another line of separation from the posterior-dorsal zone. Length 2.2 mm., height 2.3 mm. Distinguished easily from C. ecuadoriana by its unsymmetrical valves and subrhombic shape. Range — Ecuador. Ecuador: Santa Elena. Genus BOTULA Morch, 1853 Type species by subsequent designation, Dall, Bartsch and Rehder, 1938. Mytilus juscus Gmelin. Caribbean. The shell is small or of medium size, oblong, subrhomboidal, arcuate, modioliform, convex, the surface covered by a glossy brown periostracum. The umbones are prominent and full, ending in small, coiled beaks re- moved sHghtly from the anterior margin and projecting beyond them. Surface sculpture is formed principally by weak concentric growth lines or their derivatives, interrupted by deeper resting marks, and occasionally iby a few obscure radials over the middle ventral zone. Hinge line straight, edentulous, the resilifer internal and showing as a long scar nearly the length of the hinge line. Interior bluish nacreous. Adductor scars subequal in size, rounded or gourd-shaped, placed low within the shell and near the margins. Botnla fiisca (Gmelin) Plate 16, figures 5-5c Mytilus fuscus Gmelin, 1791, Systema Naturae, ed. 12, p. 3359. Lithophagus cinnamomeus (Chemnitz), Carpenter, 1857, Cat. Mazatlan Shells, Brit. Mus., p. 129 Mazatlan, Mexico. Not of Lamarck, 1819. Botula cinnamomeus (Chemnitz), Strong and Hanna, 1930, Proc. California Acad. Sciences, sen 4, vol. 19, No. 3, p. IS Tres Marias Islands, Mexico. Lithophaga (Botula) fusca (Gmelin), McLean, 1951, Scien. Survey of Porto Rica and the Virgin Islands, New York Acad. Sciences, vol. 17, pt. 1, p. 43, pi. 8, fig. 3. Botula fusca (Gmelin), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 86, pi. 9, fig. 52; text-figs. 70-72. Shell as described for the genus. A single specimen was obtained at Manta where it was found in a rock burrow and like Musculus coarctata, is possibly a true rock borer. The two species live in the same environment. My specimen agrees well with typical B. fusca from the Caribbean. It agrees also with the figure of B. hazvaiensis Dall, Bartsch, and Rehder as illustrated in their Hawaiian paper. The color of the surface is a dark brown to nearly black. Length 22.5 mm.; height 10.5 mm.; diameter 9.6 mm. Manta, Ecuador. Range — Mostly West Indies and the Caribbean; on the Pacific Coast from Mexico to Ecuador (rare). Ecuador: Manta. 132 AXEL A. OLSSON Genus ADULA H. and A. Adams, 1857 Type species by original designation, Mytilus soleniformis d'Orbigny. Rock borers. Shell elongated with closed valves, subcylindrical but generally curved, the ventral margin being broadly impressed along the midzone. The beaks small, flattened and placed slightly in front of the middle and usually so deeply corroded that the pearly inner layer is ex- posed. Posterior end of valves a little wider, with an umbonal angulation generally covered by a thick crust of agglutinated grains of sand form- ing a plug or subtruncated stump. Small shells have the shape of a straight Modiolus with a sharply angled umbonal ridge more than half the length of the shell and the surface sculptured with fine, radial riblets; the perio- stracum thin and of a brown or golden-yellow color. Hinge edentulous, the ligament narrowly linear and subinternal. Inner margins of the valves finely crenulated except along a part of the ventral side. Inner layer of shell pearly, the outer layer thin, and covered by a brown periostracum which is usually retained only along the ventral side and under the cover of agglutinated sand grains at the posterior end. The typical species of Adula are rock borers. A large colony of A. soleniformis panamensis was found near Las Tablas, Panama, boring into a volcanic, tuffaceous agglomerate, mostly along the softer layers. The bores are small, deep shafts in which the small clam fits snugly when re- tracted, closing off the entrance by its bilobed stump of agglutinated sand grains covering the posterior end. The umbones of these shells are deeply worn. Adnia soleniformis (d'Orbigny) Plate 16, figure 3b Mytilus soleniformis d'Orbigny, 1846, Voy, Am^r. M6tid., vol. 5, p. 649, pi. 85, figs. 17, 18 Paita, Peru. Adula soleniformis (d'Orbigny), Dunker, 1882, Syst. Conch, Cab., vol. 8, p. 24, tab. 6, figs. 4, 5. — Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 90. Typical specimens of A. soleniformis from northern Peru and Ecuador are longer and narrower than Panama examples and also attain a larger size (Manta, length 39.5 mm.). The largest Panama shell has a length of 28 mm., and the valves are shorter and higher posteriorly; these Panama shells are separated as a subspecies -panamensis. (PI. 16, figs. 3, 3a) Small shells of A. -panamensis resemble a small Musculus and have a strong umbonal ridge, the ventral side is deeply impressed and the whole surface is covered with fine radial riblets. The posterior ridge bears several long algal-like bristles, but its surface is soon covered with a mass of agglutinated grains of sand which cannot be removed without damage to the shell under- neath. The bores of A. panamensis consist of small shafts, usually closely crowded together, smaller at the lower end, often appearing more or less bilobate at the entrance which is closed off by the stumplike mass of agglutinated sand grains covering the posterior end of the valves. Adula is evidently not rare at localities favorable to its growth. Range — Panama to northern Peru. Panama: Lagartillo near Las Tablas; Guanico. Ecuador: Manta. Peru: Mancora; Paita. PANAMIC-PACIFIC PELECYPODA 133 Genus LITHOPHAGA Roeding, 1798 Type species by monotypy, L. mytuloides Roeding (^Mytilus litho- phagus Gmelin). Borers into rock or thick-walled mollusks, corals, and the like, the shell elongate, subcylindrical, rounded in front, the posterior end often tapered, the beaks strongly anterior. Surface smooth except for lines of growth and sometimes vertical or transverse striations. Hinge narrow, edentulous, the ligament marginal, internal. Inner layer of shell nacreous. Periostracum light brown or chestnut-colored, naked or covered with a calcareous deposit, often becoming much thickened and produced beyond the posterior end of the valves as spurs or blades. Margin of valves closed in the adult. Like other members of the family, the young Lithophaga is fixed by its byssus but it soon begins to bore into the substratum and developing within the rock or a thick-walled shell, a large, often spacious, bullet-shaped chamber, small at the top, the exit to the exterior forming a rounded or key-hole shaped opening. In Leiosolenus, there is also an accessory, flattened, calcareous tube which rises 2 to 5 mm., above the surface, its general ap- pearance that of the elevated end of a Vermetus or worm-tube. Except in Lithophaga, s.s., the surface of the valves is covered by a calcareous en- crustation which often becomes much thickened along the posterior slope, sometimes developing a plumose pattern there, and which may be pro- longed beyond the ends of the valves in the form of thickened wedge-shaped blades or solid, rounded spurs. These calcareous extensions serve to close off the entrance to the burrow when the shell is pulled back. In Rupiphaga, the upper end of the rock chamber is lined with a secondary, thick-walled, cemented tube as do some of the rock-boring Pholades such as Hastasia. Excavation of the lithophagoid burrow is accomplished ap- parently by juices secreted by the animal, the softened debris removed by water currents. The surface of the valves shows generally no abrasive wear as do so many other rock-boring clams. Key to subgenera of Lithophaga Surface of the valves, smooth, clean and polished, without a coating of lime, the periostracum visible throughout. Subgenus Lithophaga, s.s. Surface of valves covered by a secondary deposit of lime. I. Calcareous encrustation on the surface of the valves only, not pro- longed beyond the posterior ends. Orifice of the burrow continued above the surface as an elevated, accessory, calcareous tube, its open- ing bilobate. Subgenus Leiosolenus II. Calcareous coating prolonged beyond the posterior end of the valves as thickened blades or spurs. Orifice of burrow without an accessory tube. 134 AXEL A. OLSSON A. Calcareous extension at the posterior end of one valve only. Rock burrow lined by an inner, thickened, cemented tube. Subgenus Rupiphaga B. Calcareous extensions at the posterior end of each valve. 1. Posterior calcareous extension in the shape of alternate, overlapping or twisted blades. Orifice bilobate. Subgenus Myojorceps 2. Calcareous extensions, straight, equal, not twisted or alternate. a. Calcareous extensions rectangular or wedge-shaped. Encrustation along the posterior slope, smoothish or merely granulose. Subgenus Labis b. Calcareous encrustation along the posterior slope thick and heavy and with a plumose surface pattern. Subgenus Diberus Subgenus LITHOPHAGA, s.s. Surface of valves without a calcareous encrustation. No known species in the Panamic-Pacific faunal area. Subgenus LABIS Dall. 1916 Type species by monotypy, Lithophaga attenuata Deshayes. Surface covered by a thin, calcareous incrustation, thickened at the posterior end and prolonged beyond the valve margin into a short, rec- tangular wedge or blade. Lithophagra (Labis) atti*nuata (Deshayes) Plate 15, figures 3-3c, 4 Modiola attenuata Deshayes, 1S36, in Lamarck's Anim. s. Vert., vol. 7, p. 28. "Habite au Perou, au Chile, dans les pierres." — Sovverby, 1824, Gen. Shells, Lithodomus, fig. 3. Lithodomus attenuatus (Deshayes), Chenu, 1862, Manuel de Conchyliologie, vol. 2, bivalves, p. 156, fig. 767. Lithophaga (Labis) attenuata (Deshayes), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, No. 5, pp. 74, 75. — Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, pp. 99, 100, pi. 10, fig. 57; text-fig. 77. Shell narrowly elongate, subcylindrical, evenly convex over most of its length. Dorsal and ventral margins straight for the most part and parallel except for the posterior half where the dorsal margin descends to form a long-drawn out posterior end tipped by a thick, calcareous wedge or flattened blade. The posterior-umbonal slope is slightly flattened, bordered on the ventral slope and sometimes above by an impressed line, the lines of growth across it showing in a rectangular pattern. Perio- stracum thin, brownish colored and covered by a calcareous encrustation which is much heavier on the posterior slope, prolonged beyond it, as a heavy flattened blade. Length 95 mm.; height 19.2 mm.; diameter 18 mm. Manta, Ecuador. This is a common rock borer at many places and at Manta, Ecuador, it is gathered as a sea-food but is said to have a strong, peppery flavor. The calcareous blades at the posterior end of the valves are coarse and thick, and these protuding slightly at the orifice of the burrow indicate the presence of the clam within; these blades on being touched lightly induce the clam to pull in at once. PANAMIC-PACIFIC PELECYPODA 135 Range — Lower California to Chile. Mexico: San Ignacio Lagoon (Hert- lein and Strong). Costa Rica: Port Parker (Hertlein and Strong). Panama: Guanico. Ecuador: Palmar near Colonche; Manta; Jaramijo. Lithophaga (Labis) peruTiana (d'Orbigny) Plate 15, figures 2-2a Lithodomus peruvianus d'Orbigny 1846, Voy. Amer. Merid., vol. S, pt. 3, MoUusques, p. 651. Modiola atteriuata Philippi, 1847, Abbild. und Beschreib, Conchylien, bd. 2, p. 148, pi. 1 (Modiola), fig. 6 not of Deshayes. Lithodomus cumingianus Dunker, 1857, in Reeve, Conch. Icon., vol. Lithodomus, pi. 21, figs. 8a-b. — Dunker, 1882, Syst. Conch, Cabinet. Lithophaga, p. 5, pi. 2, figs. 9, 10. — Chenu, 1862, Manuel de Conchyliologie, vol. 2, bivalves, p. 156, fig. 769. Shell often quite large, thin, subcylindrical, the ventral margin and the anterior half of the dorsal margin straight and parallel, the posterior section of the dorsal margin descends strongly towards the end. Whole surface is covered by a thin encrustation which thickens near the posterior end, often forming there a short, wedge-shaped point. Length 84 mm.; height 22.3 mm.; diameter 23 mm. Paracas Peninsula, Peru. Since D'Orbigny gave no illustration of this species, some misunder- standing has existed as to its identification. A photograph of a specimen in the type lot at the British Museum (Nat. Hist.) is given here. It differs from atteniiata by its shorter, higher shell, and less attenuated posterior end. It appears to be common along the Peruvian coast south of Lima, where it is often found boring into the massive heads of a colonial polychaete worm (Gunnarea). Range — Coast of Peru. Peru: Callao; Paracas Peninsula. Lithophaga (Labis) inca (d'Orbigny) Plate 15, figure 1 Lithodomus inca d'Orbigny, 1846, Voy. Amer. Merid., vol. 5, pt. 3, MoUusques, p. 651 Paita. The type specimen in the British Museum (Nat. Hist.) is a large shell about 83 mm. in length, thin, with the umbones near the anterior end, convex and full, the anterior margin itself rounded. The posterior side is much elongated, evenly tapering to the end, the urnbonal slope bearing a wide band formed between two shallow lines or sulci, that on the dorsal side simple, that on the ventral side double. The whole surface is covered by a thin calcareous encrustation, smoothish or faintly granulose, thickening at the end to form a flattened beak which projects beyond the valve margins. According to D'Orbigny, this species differs from L. peruviana by its more elongate form, more even taper behind, and in having two radiating sulci along its posterior side. The posterior sulci are usually faint but can be found on close examination. The form is questionably distinct from L. attenuata but may perhaps differ by its less cylindrical and more evenly tapering outline as well as having a somewhat higher and more rounded anterior end. Range — Paita (Fontaine, D'Orbigny). 136 AXEL A. OLSSON Subgenus LEIOSOLEJfUS Carpenter, 1856 Type species by monotypy, Leiosolenus spatiosus Carpenter. Shell as in Lithophaga, s.s., but the surface covered with a thin, cal- careous incrustation, not produced beyond the posterior end of the valves. Burrow bullet-shaped, capacious, excavated in thick-shelled mollusks (Spon- dylus, Chama) narrowly contracted towards a small orifice at the top and often prolonged above the surface by a flattened, calcareous tube. This group was proposed by Carpenter largely on the character of the burrow provided with an elevated, external accessory tube and noted that if the animal, when examined, proved to have long, excurrent siphons, it must take generic rank perhaps in the neighborhood of MytUimeria Conrad. Elongated siphons seem, however, common to most species of Lithophaga. The thin, fairly uniform encrustation covering the shell without posterior appendages together with the elevated, bilobate accessory tube may be accepted as characters distinguishing this subgenus. Lithophaga (Leiosolenus) spatiosa (Carpenter) Plate 15, figure 7 Leiosolenus spatiosus Carpenter, 1856 (as a subgenus of Lithophaga) , Cat. Mazatlan Shells, Brit. Mus., pp. 178, 179. appendix, p. 550. (Mazatlan, in shells of Spondylus). Lithophaga {Leisolenus) spatiosa (Carpenter), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 102, pi. 10, fig. 59. Lithophaga abbotti Lowe, 1935, Trans. San Diego Soc. Nat. Hist., vol. 8, No. 6, p. 17, pi. 1, fig. 5 Kino Bay, Sonora. A specimen assumed to be this species was extracted from the lower valve of a large Chama buddiana, which when detached from the rock on which it was fixed, revealed the chamber of the Lithophaga with its shell enclosed. The lower part of the lithophagid bore had penetrated the vol- canic matrix on which the Chama was perched. The opening of the bore at the surface of the chamid shell is relatively small and is continued into a short accessory calcareous tube. There are several other of these small pipes on the same Chama rising from 3.5 to 5 mm. above its surface. The litho- phagid shell has a length of about 28 mm., thin, obliquely and broadly elongated, the proportion of height to length about 1 to 2.7. The beaks are small, almost terminal, the dorsal margin straight, then descending at the posterior one-third to form a bluntly rounded end. The ventral margin is slightly curved, narrowed somewhat at the obliquely rounded anterior end. The valves are moderately convex, their surface covered completely by a thin, calcareous coating but which does not extend beyond the posterior end. Beneath the encrustation, the periostracum is brownish, molded over the concentric lines of growth. Interior brilliantly pearly, the pallial and adductor impressions showing but faintly. This shell measures as follows: Length 28 mm., height 10.7 mm., diameter S.S mm. (right valve). The type of L. spatiosa has not been figured but there seems little doubt that this identification is correct. The type of L. abbotti has a length of 62.5 mm. which would indicate that this species may attain a large size. Range— GuU of California southward to Panama and possibly Ecuador. Panama: Lagartillo near Las Tablas (boring into Chama buddiana). PANAMIC-PACIFIC PELECYPODA 137 Subgenus MYOFORCEPS Fischer, 1886 Type species by original designation, Lithodomus caudigerus Lamarck = L. aristatus (Dillwyn). Surface of shell with a coating of lime which posteriorly is much thickened and produced beyond the ends of the valves so as to form a pair of twisted, alternating or crossed blades (like the blades of a pair of scissors) and which serve to close-off the bilobate orifice of the burrow excavated in rock or thick-walled shell. Llthopha&a (Myoforceps) aristata (Dillwyn) Plate 16, figures 2-2c Le Ropan, Adanson, 1757, Hist. Nat. Sin^gal Coquillag«s, p. 267, pi. 19, fig. 2. Mytilus aristatus (Solander MS.), Dillwyn, 1817, Cat. Recent Shells., I, p. 303. Modiola caudigera Lamarck, 1819, Anim. s. Vert., 6, p. 116 (after Encyclop. Meth., p. 221, figs. 8a, 8b) — Philippi, 1846, Abbild. und Beschreib. Conchylien, bd. 2, p. 149, pi. 1, Modiola fig. 5. Lithodomus caudigerus (Lamarck), Sowerby, 1824, Genera Shells, Lithodomus, fig. 4. — Reeve, 1857, Conch. Icon., vol. 10, Lithodomus, pi. 3, fig. 16 Lithophaga (Myoforceps) aristata (Dillwyn), Dall, 1898, Trans. Wagner Free Inst. Sci. Philadelphia, vol. 3, pt. 4, p. 800.— Dall, 1909, Proc. U. S. Nat. Museum, vol. 37, No. 1704, p. 153. — Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, No. 5, p. 74. — Soot-Ryen, 1955, Allan Hancock Pacific Expedition, vol. 20, No. 1, p. 98, pi. 10, figs. 53, 54. Lithophagus calyculatus Carpenter, 1857, Cat. Mazatlan Shells, Brit. Mus., pp. 124, 125, No. 174. MS. drawing in U. S. National Museum. Shell small or of medium size (average length about 32 mm.), thin, subcylindrical, modioliform, the beaks nearly terminal, the hinge line about half the length of shell, the posterior half of the dorsal side descending, the ventral margin straight or concave. Periostracum thin, light brown or chestnut, covered by a thin, calcareous incrustation much thickened pos- teriorly and produced beyond the end of the valves in the shape of two, flattened blades which are straight or twisted so as to pass each other alternately and resemble the blades of a pair of scissors. Length 36.7 mm.; height 10.5 mm.; diameter 9.5 mm. Manta, Ecuador, A borer into soft rock or into the thick wall of shells such as Chama, Spondylus, and Ostrea. The opening of the burrow usually shows on the surface as a small, bilobate slit which expands below into a large, bullet- shaped cavity. Range — California to Peru. Also throughout the West Indies and along the southeast coast of the United States; also West Africa. Panama: Guanico; Pearl Islands. Canal Zone: Fort Amador. Ecuador: Esmeraldas; Manta; Palmar; Santa Elena. Peru: Sechura (Dall). Subgenus DIBERUS Dall, 1898 Type species by original designation, Lithophaga plumula Hanley. Shell with one or more radial sulci extending along the posterior um- bonal slope with the calcareous encrustation covering the space between them coarse and heavy, and generally developing a divaricate, plumelike pattern. The calcareous prolongations at the end of each valve has the shape of short wedges. 138 AXEL A. OLSSON Lithophaga (Diberns) plnmnla (Hanley) Plate 16, figures 1-lb Lithodomus plumula Hanley, 1844-, Proc. Zool. Soc. London, p. 17. Panama in Spondyli.-— Reeve, 1857, Conch. Icon., vol. 10, Lithodomus, pi. 4, fig. 23. Modiola (Lithodomus) plumula Hanley, 1856, Cat. Recent Bivalve shells, pp. 239, 387, pi. 24, fig. 23 Philippines. Lithophaga (Diberus) plumula (Hanley), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 75, pi. 1, fig. 10.— Soot-Ryen, 1955, Allan Hancock Pacific Expedi- tions, vol. 20, No. 1, p. 96, pi. 10, fig. 55. Shell of medium size, appearing rather stout and highest near the pos- terior end of hinge, then tapering towards a bluntly rounded end. The whole surface is covered by a calcareous coating which on the posterior slope between the radiating sulci is much heavier, spongy or cellular, usually with its sides incised by deep cuts diverging from the central axis to form a crude plumose pattern likened by Hanley to that of a ruffled flower. The thinner coating of lime on the ventral and anterior side is granulose and wrinkled. The largest specimen measures: length 49.7 mm., height IS mm., diameter 12.3 mm. Manta, Ecuador. Range — Lower California to Peru. Panama: in Spondyli (Hanley); Burica Peninsula. Colombia: Gorgona Island (Hertlein and Strong). Ecua- dor: Manta. Lithophaga (Dibenis) of. snbula (Reeve) Plate 15, figure 6 ? Lithodomus subula Reeve, 1857, Conch. Icon., vol, 10, Lithodomus, pi. 4, fig. 26, Loc— ? Lithophaga plumula kelseyi, Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 75, pi, 1, figs. 8, 9 San Diego, California. Lithophaga (Diberus) subula (Reeve), Soot-Ryen, 1955, Allan Hancock Pacific Expedi- tions, vol. 20, No. 1, p. 97, pi. 10, fig. 56. There is doubt as to the name which should be applied to my shells from Ecuador. They resemble L. plumula but are more delicate and the posterior rib of encrustation is thinner and only slightly furrowed, not developing the coarse plumose pattern of that species. They differ from typical /.. kelseyi from California in the much deeper radial sulci or broad furrow along the dorsal side of the central posterior zone of heavy encrusta- tion, and the calcareous blades at the end of the valves are longer and heavier. A specimen measures: length 39.3 mm., height 10.4 mm., diameter 11.4 mm. Manta, Ecuador, Range — Alaska to California and southward to Peru, Ecuador: Manta. Subgenus RUPIPHAGA, new subgenus Type species Lithophaga hastasia, new species. The shell, as in Lithophaga, s.s., is elongate modioliform, thin, and with a light brown to nearly black periostracum, largely concealed under a calcareous encrustation, thin and light on the anterior portion, thickened along the posterior side so as to form a central rib bordered by furrows and prolonged beyond the end of one valve only (usually that of the right) in a coarse, spikelike prong or blade. Upper portion of bore, PANAMIC-PACIFIC PELECYPODA 139 usually in rock, lined with a tapered, auxilliary calcareous tube as in some of the pholads. Lithophaga (Rupiphagra) hastasia, new species Plate 15, figures 5-5f The shell is narrowly elongate, bullet-shaped or modioliform, thin, subcylindrical, evenly convex over most of the length, the anterior end obliquely rounded with the small, low beak placed a short space behind, the dorsal and ventral margins parallel for the most part, the posterior-dor- sal half descending to form a tapered end. The greater part of the surface is encrusted with a deposit of hme, relatively thin and filmlike on the an- terior portion, coarse and heavy on the posterior side so as to form a thick- ened rib along its middle bordered on each side by a furrow and prolonged considerably beyond the end of one valve (usually the right) forming a stout, solid spikelike plug. Periostracum is largely concealed by lime de- posit but where exposed has a clear brown to dark-brown, nearly black color. Interior is nacreous white. Length 24.5 mm., height 5.8 mm., diameter 6.6 mm. Holotype, Esmeraldas, Ecuador, ANSP 218931. Length 38.3 mm., height 9 mm., diameter 4.3 mm. (right valve). Paratype, Esmeraldas, Ecuador. In this species, the calcareous surface encrustation forms along the posterior side a thickened rib which in one valve (usually the right) is prolonged some distance beyond its end in the shape of a stout, spikelike blade, often two-pronged at the tip; on the surface of the valve, this rib is generally bordered on each side by a deep furrow or groove. The upper part of the bore, usually in an argillaceous rock is internally lined with a heavy, pipehke tube, wider below, much heavier and tapered at the top with a small circular orifice. My observations on this structure are limited to the bore and its internal tube. The fragile Lithophaga shell within is seldom secured intact when the enclosing rock is broken into. Range — Panama to Ecuador. Panama: Guanico. Ecuador. Esmeraldas. Subgenus STU3IPIELLA Soot-Ryen, 1955 Type species by original designation, Lithophagus calyculatus Carpenter. This subgenus is probably a synonym of Myoforceps. An unpublished figure of Lithophagus calyculatus, prepared by Carpenter from the type, is that of a shell closely similar to L. aristata if not identical with it. The shells figured by Soot-Ryen as L. calyculata from the Mexican coast, probably represent another species. Family DREISSENIDAE This family is represented in America by the genus Mytilopsis, a group of fresh- or brackish-water species, both fossil and Recent, and often en- countered in beach drift at localities situated near the mouths of fresh- v/ater streams. They are properly speaking, not a part of the marine Panamic-Pacific fauna. A species is common in some rivers of southwestern Colombia and northwestern Ecuador, usually in the swifter portion of the streams, attached in clusters to boulders and pebbles in the bed or living in 140 AXEL A. OLSSON small holes or pits in rock walls. These clams have the shape of a small Mytilus, with pointed, terminal beaks, a small septum in the beak like Septifer and a smooth or concentrically wrinkled surface covered by a dark- colored periostracum. They are gathered by the Cayapas Indians of Ecua- dor for food. Mytilopsis adamsi Morrison® was described from a lagoon at the mouth of Musselshell Creek on San Jose Island, Pearl Islands, Pan- ama. The same species may also occur on the mainland. Shell mytiloid, the anterior adductor attached to a shelflike platform or thickened septum in the apical section, sometimes with a small, tooth- like lamina or apopthysis below the septum for the attachment of the byssal muscle. Habitat, fresh- or brackish-water. Genus MYTILOPSIS Conrad, 1857 {Praxis H. and A. Adams, Dec. 1857) Type species by monotypy, M. leucophaeatus Conrad, 1831. Recent, southeastern coast of the United States. Shell mytiloid, non-nacreous, with sharply pointed beaks at the extreme anterior end. Hinge line with a furrow for the attachment of the ligament along and within the dorsal margin for most of its length. Adductors two, the posterior one elongate or club-shape, the anterior seated on a flat shelf or septum in the beak roofing over the umbonal cavity which extends well under it. There is a small lamina under the septum for the support of the byssal muscle. Externally the shell is covered with a coarse periostracum, the surface below, smooth or concentrically striated. Mytilopsis trautwineana (Tryon) Plate 84, figure 8 Septifer Trauiivineana Tryon, 1866, Am«r. Jour. Conch., vol. 2, p. 302, pi. 20, fig. 8 Rio San Juan (lat. 4° North) ; New Granada (Colombia). Praxis Milleri Clessin, Miller, 1879, Malak. Blatter, tonne 26, pp. 179, 180, tav. 15, fig. 7 Rio Verde, Esmeraldas, Ecuador. Praxis Ecuadoriana Clessin, Miller, 1879, op. cit., pp. 180, 181, tav. 15, fig. 8 Rio Cayapas, Esmeraldas, Ecuador. Shell narrowly or broadly mytiliform with the general axis inclined about 45 degrees with the hinge line placed horizontally. Hinge line a little shorter than the length of the shell, its posterior margin straight or rounded towards the end, the anterior side weakly impressed so that the umbonal slope appears arched or crudely angular. Internal septum in the beak rather large, excavated, the byssal muscle scar showing plainly on the end of the apophysis below. Periostracum dark-brown to nearly black in color, coarsely, concentrically wrinkled. Interior glossy, bluish-white in color, blotched or streaked with white or black. Length 16 mm.; height 24.4 mm.; diameter 9.6 mm. Rio Cayapas, Esmeraldas, Ecuador. This is a fresh-water species. It was observed on several occasions by the author living in parts of the Rio Cayapas River system in Ecuador, and •Morrison, J. P. E., 1946, Smith. Misc. Coll., vol. 106, No. 6, pp. 46, 47, pi. 1, figs. PANAMIC-PACIFIC PELECYPODA 141 in the Rio Guapi in southwestern Colombia; it usually occurs where the river water is clear and flows over a rocky bottom, the mussel attached in clusters to small boulders, submerged trunks of trees or nestling in holes along the bank if the wall is rock. The associated mollusks are a small Neritina and Lithococcus (Hydrobiidae). Range — Rivers of western Colombia and northwestern Ecuador. Colom- bia: Rio San Juan; Rio Guapi. Ecuador: Rio Verdi; Rio Cayapas, Mytilopslg adamsl Morrison and M. zeteki Hertlein and Hanna Plate 84, figures 9, 9a Two Other species of MytUopsis have been described from the Panamic region but because of the lack of representative material, the status of these two species cannot be analysed at this time. M. adamsi Morrison, 1946, (Smith. Misc. Coll., vol. 106, No. 6, pp. 46, 47, pi. 1, fig. 4) was described from the uppermost end of a fresh-water lagoon on San Jose Island, a member of the Pearl Island group in Panama Bay. Its figure shows an elongated shell, twice as long as high, with a relatively large septum and eroded, deformed beak. Morrison related the species with the Atlantic Coast M. leucophaetus of Conrad. Another species of the genus was described by Hertlein and Hanna, as M. zeteki from the Miraflores Locks (Hertlein and Hanna, 1949, Bull. 7, Cahf. Acad. Sciences, vol. 48, pt. 1, pp. 13-18, pi. 1). In a note from Morrison, he stated that he considered M. zeteki close to M. adamsi if not a growth-form of that species. A few specimens of a small MytUopsis have been collected from shell drift from Venado Beach, Panama Canal Zone. These specimens are small, hatchet-shaped, the height about equal to their length, the interior with a small septum, and the surface white or lightly shaded with gray or pale black. In their present form, the Venado shells agree well with young specimens of M. sallei from Colon, and may indicate a Pacific invasion of that Caribbean species. The two West Atlantic MytUopsis are sometimes difficult to separate; M. sallei is generally higher and more hatchet-shaped and the internal apophyses under the septum is smaller, closer to the dorsal wall, whilst M. leucophaetus is narrowly elongated, its apophyses larger, often closer to the middle and hence more prominent. Family JULIIDAE (Opistobranchia Sacoglossa) Small or minute, bivalved mollusks, greenish in color and living amongst green algae. In the genus Julia, the shell is roughly aviculoid in shape, both valves equal and strongly convex with large, full umbones terminating in small beaks. The higher, longer side is the anterior with a well-rounded end; the shorter side is posterior, pointed at the end with a deep, rounded inden- tation below the beaks resembling a large, sunken lunule. The hinge is heavy, with a large, stout tooth in each valve and which fits into a corresponding socket in the opposite valve. There is a single, large adductor scar in each valve, more or less medially placed and with one or more, smaller accessory 142 AXEL A. OLSSON scars in adjacent position. The valves were probably united by a ligament attached to a linear scar along the dorsal margin just in front of the beaks. Although Julia is now known to belong to the sacoglossate O'pisto- branchs, it is mentioned here because of its long association with the Pelecypoda. Single valves of Julia have a decidely Tectibranch-like aspect as some authors have previously noted. For a discussion of these curious, bivalved snails, the reader should consult the following: S. Kawaguti and K. Baba, 1959, A preliminary note on a tivo-'val'ved sacoglossan gasteropod, Tamanovalva Umax. Japan. Biological Journal, Okayama University, vol. S, Nos. 3-4, pp. 177-184; Kawaguti, S., Formation of the bivalve shell is a gastropod, Tamanovala Umax. Proc. Japan Academy, vol. 35, No. 10, pp. 607-611, 5 figs.; A. Myra Keen, 1960, The riddle of the bivalved gastropods, The Veliger, vol. 3, No. 1, pp. 28-30; J. P. E. Morrison, 1960, Notes on the bivalved univalves; W. J. Clench, The bivalve gastropod and the Opisthobranchs. (Last two read before American Malocological Union, 1960.) Genus JULIA Gould, 1862 Type species by monotypy, Julia exquisita Gould. Recent, Hawaiian Islands. With characters of the family. Julia theeaphora (Carpenter) Plate 17, figure 5 Smaragdinella theeaphora (Nutt.), Carpenter, 1875, Cat. Mazatlan Shells, Brit. Mus., p. 533, No. 692. Julia equatorialis Pilsbry and Olsson, 1944, Nautilus, vol. 57, No. 3, pp. 86, 87, pi. 9, figs. 10, 11. — Arthur Day Howard, 1951, Nautilus, vol. 64, No. 3, pp. 84-86. The shell is small or minute, usually between 2 and 3.8 mm. in length. When fresh, the color of the shell is green or greenish yellow, often with brown stripes, but on weathering it soon becomes white. The valves are moderately convex, subquadrate, the short, posterior side pointed at the end. The texture of the valves is heavy, subtranslucent so that the markings of the exterior often show plainly in the interior. The greatest inflation of the valves is placed in front and below the beaks. Although rare in collections, this species is now known to have a general distribution throughout the Panamic-Pacific faunal province. Be- cause of its small size and often worn appearance it is generally overlooked in picking of shell drift. A manuscript drawing of Snuiragdinella theeaphora, after the type specimen by Carpenter in the library of the Department of Mollusks, U. S. National Museum, shows that species to belong to the genus Julia. It seems likely, therefore, that J. equatorialis represents the same form. Range — Lower California to northern Peru. Mexico: Mazatlan (Car- penter); Socorro Island and Cape San Lucas (Howard). Panama: Bucaro. Colombia: Isla del Gallo. Ecuador: Puerto Callo; Punta Centinella on Santa Elena Peninsula. Peru: Caleto Sal (types of 7. equatorialis). PANAMIC-PACIFIC PELECYPODA 143 Order ISODONTIDA Superfamily FTERIACEA Family PINNtDAE The adult shell has a narrow, pointed anterior end, while the posterior side may be elongated, expanded or fan-shaped, its margin normally open. The shell is composed of two layers of different composition; an outer, pris- matic, more or less flexible, perishable layer, and an inner, nacreous and more durable layer, not formed along the growing ventral margin, conse- quently, the ventral part of the valves is more or less flexible, and the margins of the valves, normally gaping, can be closed tightly by the pull of the mantle and of the posterior adductor muscle. These clams are sedentary, generally found buried in mud, sand or gravel, the anterior end downward and anchored in a vertical position by the byssus, the posterior margin of the valves level with the surface or projecting slightly above it. Hinge is long, narrowly linear, extending along a straight, dorsal margin, the ligament produced to the end of the inner layer only. Some species of Pinna such as rugosa attain a length of nearly two feet. The young Pinna is said to have a normal, equilateral shell. Two genera separated by the presence or absence of a longitudinal keel. Key to the genera of Pinnidae I. Shell narrowly triangular, the dorsal and ventral margins nearly straight, the anterior portion carrying a longitudinal carina formed in the outer layer and dividing the inner layer into two lobes. Genus Pinna II. Shell fan-shaped, the posterior portion expanded. Valves not medially sulcated. Genus Atrina Genus PONA Linn6, 1758 Type species by absolute tautonomy, Concha -pinna Hasselquist (=:Pin- na muricata Linne; or by subsequent designation, Children, 1823, or by Gray, 1847, Pinna rudis Linne). With the general chaiacters of the family. Surface of valves with a longitudinal ridge due to a deep sulcus dividing the inner or nacreous layer. The selection of the type species of this Linnean genus is controversial; for the most recent opinion and a discussion of the subject, the reader is referred to Turner and Rosewater, 1958, "The family Pinnidae in the western Atlantic" (Johnsonia, vol. 3, No. 38, pp. 302, 303). Pinna rugosa Sowerby Plate 18, figure 1 Pinna rugosa Sowerby, 1835, Proc. Zool. Soc. London, p. 84. Hab. in Sinum Panamensis (Isle of Rey). — Reeve, 1858, Conch. Icon., vol. 11, A