Zoogeographic Regions in Canada Based on the Occurrence of Freshwater Molluscs 1 Atlantic Coastal Region 6 Pacific Coastal Region 2 Lake Erie-Lake St. Clair Region 7 Beringian Refugium 3 Great Lakes- St. Lawrence Region 8 Subarctic Region 4 Red River-Assiniboine River Region 9 Arctic Region 5 Western Prairie Region QL tl 3 )W c. ^ The Freshwater Molluscs of Canada A female Pocket-Book mussel ( Lampsilis ventricosa ) with its mantle flap extended and pulsating to simulate a wounded minnow. This activity attracts fish, and increases the opportuni- ties for juvenile mussels (glochidia) to attach themselves to a fish after they are ejected from the parent. A period of attachment to a fish of the proper species is necessary for maturation of most juvenile freshwater mussels. (Photograph courtesy of John H. Welsh, Boothbay, Maine.) The Freshwater Molluscs of Canada Arthur H, Clarke National Museum of Natural Sciences National Museums of Canada r-iATtG ,:; nD HAux OF CANADA D U CANADA © National Museums of Canada 1981 Published by the National Museum of Natural Sciences National Museums of Canada Ottawa, Canada K1A 0M8 Catalogue No, NM95-17/5 Printed in Canada ISBN 0-660-00022-9 Edition franchise Les Mollusques d’eau douce du Canada ISBN 0-660-00023-7 Managing editor: Viviane Appleton Text editor: Lorraine Smith Production: Donald Matheson James MacLeod Design: Eiko Emori Typesetting: The Runge Press Ltd. Printing: D. W. Friesen & Sons Ltd Contents Acknowledgements 9 Introduction 1 1 Why Collect Shells? 11 How to Collect Freshwater Shells 12 Arrangement and Care of the Collection 16 Scientific Names 17 Mollusc Classification and Some Special Features 19 Distribution Patterns in Canada 21 Molluscs as Pollution Indicators 24 The Freshwater Molluscs 27 Key to the Families of Canadian Freshwater Molluscs 29 Class Gastropoda (Snails) 31 Subclass Prosobranchia (Gill-breathing Snails) 33 Order Mesogastropoda 33 I Superfamily Viviparacea 33 Family Viviparidae (Mystery Snails) 33 II Superfamily Valvatacea 41 Family V alvatidae ( Valve Snails) 41 III Superfamily Rissoacea 55 Family Hy dr obiidae ( Spire Snails) 55 Family Truncatellidae (Looping Snails) 73 Family Bithyniidae (Faucet Snails) 11 IV Superfamily Cerithiacea 81 Family Pleuroceridae (Horn Snails) 81 Subclass Pulmonata (Lung-breathing Snails) 89 Order Basommatophora 89 V Superfamily Acroloxacea 89 F amily Acroloxidae (Primitive Freshwater Limpets) 89 VI Superfamily Lymnaeacea 93 Family Lancidae (Limpet-like Lymnaeas) 93 Family Lymnaeidae (Pond Snails) 97 VII Superfamily Physacea 151 Family Physidae ( Tadpole Snails) 151 VIII Superfamily Planorbacea 175 Family Planorbidae (Ramshorn Snails) 175 Family Ancylidae (True Freshwater Limpets) 219 Colour Plates 229 Class Pelecypoda (Clams and Mussels) 245 Order Eulamellibranchia 247 IX Superfamily Unionacea (Freshwater Mussels) 247 Family Margaritiferidae (Pearly River-Mussels) 247 Family Unionidae (Pearly Mussels) 253 Subfamily Ambleminae (Button Shells and Relatives) 254 Subfamily Anodontinae (Floater Mussels) 212 Subfamily Lampsilinae (Lamp Mussels) 312 X Superfamily Sphaeriacea 357 Family Corbiculidae (Little Basket Clams ) 357 Family Sphaeriidae (Fingernail Clams and Pea Clams) 361 Subfamily Sphaeriinae (Fingernail Clams) 362 Subfamily Pisidiinae (Pea Clams or Pill Clams) 386 Glossary 433 References 437 Index to Scientific and Common Names 441 Acknowledgements I am grateful to Arthur R. Clarke, the late Louise R. Clarke, the late Fran^oise Dehenne, F. Wayne Grimm, Brian T. Kidd, Judith J. McDonald and the late Dr. D, G. S. Wright for field assistance; to Walter MacKay Drycott, the late Reverend H. B. Herrington and several other colleagues for contributing some valuable specimens; and to Muriel F. I. Smith and Jane M. Topping for laboratory assistance. Dr. G. L. Mackie gave constructive criticism on the section on Sphaeriidae. I am also indebted to Dr. Aurele LaRocque, who, through energetic application of his expert knowledge of molluscs and of the French language, provided the fine translation for the French edition of this book. The watercolour paintings are by Valerie Fulford (Figures 110, 128, 129, 131, 134-38, 140, 142, and 143), Jacques Blais (Figure 139), and Aleta Karstad Schueler (all others). Photographs are by the Canadian Conservation Institute of the National Museums of Canada (most of the Pisidium , using a scanning electron microscope), the National Museum of Natural Sciences (Unionacea and Corbicula ), and A. M. Frias-Martins (all others). My work was supported by the National Museum of Natural Sciences and by the Arctic Biological Station, Fisheries and Oceans Canada. 9 Introduction Why Collect Shells Canadians are exceedingly fortunate in having an abun- dance of beautiful unspoiled forests, lakes, and rivers. Thousands have found that frequent escape to these open spaces for fresh air, peace, and relaxation is essential for their mental and physical well-being. As with music and art, knowledge enhances the appreciation of nature. Handbooks for the identification of trees, flowers, mushrooms, mammals, birds, fishes, and insects are justifiably popular. Interest in seashells, fresh- water shells and land snails is also widespread. In fact, many people who wish to make natural-history collections find mollusc shells more practical and desirable than anything else. There are many reasons why people collect shells. Shells are beautiful, intriguing, and free for the taking, and collecting them is fun. Shells are easy to find, and unlike plants and other animals require very litde special preparation or preservation. In addition to healthful exercise, shell collecting provides an interesting diversion in unfamiliar regions. Shells make excellent souvenirs because, as faunal samples, they represent the very essence of any exotic region. Shell collecting often brings about good companionship with other collectors. It many also lead to membership in local shell clubs or in national and international organiza- tions. Enthusiastic shell collectors live in all parts of the world, and a great many of them are eager to exchange their exotic native shells for our ordinary ones, which to them are just as exotic. As familiarity with molluscs grows, most collectors discover that living molluscs are fascinating creatures to observe. Original and important contributions to science can be made in this way. Many molluscs are beautiful and colourful, some can ascend and descend through the water apparently at will, others have soft parts that look like and pulsate like an injured minnow (see frontispiece), and all n have interesting feeding and reproductive habits. A great many basic facts about our most common species are still unknown. For example, during which times of the year do they reproduce in different regions? What do they eat? What are their major predators? And what are their limits of distribution? It is still possible, in fact, to discover new species that are entirely unknown to science. A shell collector's interest might originally be aroused by seashells. Later, freshwater shells and land snails might be added to the collection, especially by someone who lives in an inland location. Many collectors then decide to specialize in freshwater or land shells. Several popular handbooks exist for the identification of seashells, but non- technical books on freshwater or land molluscs are very scarce, and comprehensive texts covering all of Canada do not exist. This book is about the freshwater shells of Canada. It attempts to describe and illustrate all the species that live in this country, to provide keys and descriptions for their identification, and to present information about their ecology and their relationship to man. How to Collect Freshwater Shells Freshwater molluscs are abundant animals and are usually not difficult to collect. The successful collector, however, must learn to recognize a likely habitat. In general, well-vegetated portions of unpolluted lakes, ponds, and slow-flowing rivers are the most productive localities for freshwater snails (class Gastropoda), which occur there on submersed vegetation, on rocks, and on the bottom from the water’s edge out to a considerable depth. Freshwater mussels (family Unionidae) are found princi- pally in rivers and lakes, partly buried in the bottom, where the water is about one-third of a metre to two metres deep. The greatest diversity of species occurs in rather fast- flowing portions of hard-water rivers, that is those containing a moderate or high concentration of dissolved limestone, such as the rivers of southern Ontario and southern Manitoba. Fingernail clams and pill clams (family Sphaeriidae) are most abundant in the muddy and fine sandy bottoms of lakes. They burrow just below the bottom in water a few centimetres to many metres deep. 12 Several important exceptions to these general rules exist. Temporary springtime, that is vernal, pools often support thriving colonies of snails, especially Aplexa hypnorum and Gyraulus circumstriatus in the east and Planorbula campes- tris and Stagnicola caperata in the west. Tiny spring-fed pools in the west may contain^. montanensis. Wave-beaten rocky shores of large lakes may harbour the rare limpet Acroloxus coloradensis on the undersurfaces of boulders. Arctic muskeg pools often teem with Physajennessi jennessi and S’, arctica. Brackish-water estuaries may support rich freshwater-mollusc populations in very shallow water above the level of the lower saltwater layer. Deep water in large lakes may harbour Fossaria decampi and species of Valvata and Pisidium. Rocky creeks in the far east may contain the pearly freshwater mussel Mar garitif era margaritifera , and those in the far west the related species M. falcata. Freshwater molluscs can be collected by hand and put in a pocket. But in most cases hand-picking is slow, and pocketed specimens are likely to be crushed. Therefore, although not essential, a certain amount of equipment is very useful. The usual gear used in collecting freshwater molluscs includes 1) a pair of hip-waders or, in warm weather, tennis shoes and a bathing suit 2) a dip net for sweeping underwater plants and scraping the bottom 3) a glass-bottomed box or bucket for observing the bottom (used mainly when collecting freshwater mussels) 4) a supply of suitable jars and vials with leakproof caps 5) 80 per cent ethyl alcohol or 70 per cent isopropyl alcohol (70 per cent ordinary rubbing alcohol and 30 per cent water) for preserving the catch 6) cloth bags with string or cloth-strip closures for fresh- water mussels 7) field labels made of plastic or durable paper (that is, with high rag content) 8) a field notebook 9) pencils, or a pen and waterproof ink 10) forceps 1 1) a flat pan for sorting small specimens 12) detailed maps of the region to be explored. 13 Additional useful gear includes Nembutal or propylene phenoxetol for relaxing and extending specimens, 10 per cent formalin buffered with borax for initial preservation of specimens (but not for long-term storage), rope and a small dredge for collecting in deep water, a rowboat, outboard motor, oars and life-jackets, an underwater face-mask, fins and snorkel, and Scuba gear, A widely used collecting technique is as follows: the collector wades into a river and walks slowly upstream, carefully scanning the bottom through the glass-bottomed bucket. A sunny day is best for visibility, and the lower the water level the better. By working upstream, the collector will find that disturbed mud drifts behind, leaving the water in front clear. Partly buried freshwater mussels will be obvious, and fully buried ones will reveal themselves as white slits in the river-bottom. These are the mantle edges as seen between the slightly gaping valves. The glass- bottomed bucket, which should be tied to the collector’s waist, is a convenient receptacle for mussels. Once the search for mussels has been completed and the specimens have been placed in cloth bags, the glass- bottomed bucket can be set aside. The dip net is now used for collecting snails from vegetation and various small molluscs from the river bottom. Rocks should also be picked up, examined all over for snails, and then replaced in their original position. Restoring the habitat as closely as possible to its original state is an important aspect of responsible and conservation-oriented collecting. Live specimens should be put into jars with enough water to keep them alive. It takes at least 30 minutes to search a productive locality efficiently. Some collectors, in fact, will spend four to six hours at a collecting site to ensure that the rare species, as well as the common ones, have been found. If snails and sphaeriids are to be kept alive, they should be cool and uncrowded, that is in water that is about ten times greater in volume than the specimens themselves and in a jar large enough to provide half that much air volume. Mussels will remain alive for at least a day if placed in cloth bags kept out of the sun and moistened every few hours. They should not be kept crowded in a bucket of water, because they will soon deplete the dissolved oxygen and die. 14 If specimens are to be of any interest to serious collectors or of any value to science, accurate records must be kept. Minimal data should include 1) the name of the water body the specimens were found in 2) the distance and direction from the centre of the nearest city, town, or village 3) the province, or state, and country 4) the date 5) the collector’s name. Accessory valuable data are 1) the depth of the water where the specimens were collected 2) the kind of bottom (mud, sand, boulders, for example) 3) the kind and density of vegetation 4) the size (approximate width or area) of the water body 5) the approximate current speed 6) the water temperature 7) any other relevant observations Collection sites are referred to as stations, and these are best numbered consecutively in a continuous series. The station number and usually the minimal data are written on a field label placed in the container with the specimens. Jars of living snails should also have the station number written on the cap, because the snails may eat the label. The same number and the minimal and accessory data are recorded in a field notebook. On an extended trip, carbon copies of field notes should be mailed home periodically. A lost field-book can ruin a collecting trip. Many collectors will wish to remove and discard the soft parts of their specimens soon after collection, before the animals die and begin to decompose. Freshwater mussels and fingernail clams are usually cleaned by boiling. This causes the valves to gape, and the cooked, firm body of the clam can then be easily removed. The soft parts of large snails can also be loosened by boiling, and then “un- screwed” from their shells. A bent pin is useful for this. Small snails and pill clams can be spread out on a flat pan or a newspaper and simply allowed to dry out. Soaking in preserving fluid prior to drying is helpful, but is not necessary if an open-air drying area is available and if only a few small molluscs are involved. 15 Many collectors might be interested to know that freshwater mussels from unpolluted habitats are edible. They may be steamed, roasted, fried, or made into chowder. The reader is urged to experiment. If the water is clean enough to drink, the mussels are clean enough to eat. A note on conservation is necessary here. Some of our freshwater species are, or are becoming, very rare because of habitat disruption, increased urbanization, pollution, or over-collecting. Certain freshwater mussels, especially Simpsoniconcha ambigua and species oiDysnomia , are particularly threatened. Collectors are urged to be conserva- tion minded — to collect only as many live specimens as they need, and never to collect all available specimens of any species in a particular locality. The responsible collector also avoids disrupting habitats. Live collecting is not always necessary because empty shells often make perfectly good specimens for the collection. Beach-drift specimens or empty shells left by muskrats are often in excellent condition. For more extensive information on collecting see How to Collect and Study Shells , published by the American Malacological Union and available for US $2.50 from the Department of Malacology, Academy of Natural Sciences of Philadelphia, 19th and the Parkway, Philadelphia, Pa. 19103, USA. Another useful publication, available from the same source for US $1.50, is entitled Papers on Rare and Endangered Mollusks of North America , and was originally published in the scientific journal Malacologia (vol. 10, no. 1, 1970). Arrangement and Care of the Collection After they are cleaned or preserved, all the specimens from a particular collecting station should be sorted into vials or boxes by species; that is, each species should have its own container. A slip of paper bearing the station number and the species or subspecies name should accompany each such lot. Each lot is then catalogued as follows: 1) a catalogue number is assigned and written in india ink directly on the shell or on a small label that is placed with the shells inside each closed container 2) that same catalogue number is written on a larger label, along with the name of the species or subspecies and author, 16 all minimal data and, if space permits, any accessory data, and is placed in the shallow cardboard boxes described below 3) the same information is entered in a ledger book (the catalogue). In this way, the data associated with each species lot will be protected from loss, and the lasting value of the collection will be assured. Museums use dustproof cabinets with large, shallow wooden drawers to house mollusc collections. Shallow cardboard boxes of various multiple sizes (say 5 x 3.5 x 2 cm deep, 5x7x2 cm, 10x7x2 cm, etc.) are placed in the drawers, and all lots of the same species are placed together in horizontal or vertical rows. The species are arranged together with other species of the same genus, all genera in the same family being stored together, and so on. These are all arranged in systematic, or phylogenetic, order, that is in their presumed evolutionary sequence, from the most primitive to the most advanced groups. The drawers are also labelled to indicate the genera or species they contain. The arrangement of species in this book follows the phylogenetic order advocated by Taylor and Sohl (1962) and Moore (1969). In practice, many collectors are obliged to use miscel- laneous vials and boxes. Cigarette boxes make good containers for small shells, and may be stored in shoe boxes on shelves. Many kinds of containers will do, but of course uniformity enhances the appearance of the collection. Scientific Names Systematics has been defined as the science of deducing evolution in action. Through classification and the use of names, it seeks to show evolutionary relationships among animals and plants. Living creatures are usually divided into two major groups, the Animal Kingdom and the Plant Kingdom. The major divisions of the Animal Kingdom are called phyla (Chordata, Arthropoda, Mollusca, for example). Phyla are further subdivided into classes, classes into orders, orders into families, families into genera, genera into species, and sometimes species into subspecies. Occasionally, to show 17 relationships more precisely, it is necessary to use additional categories, for example subclass between class and order, and subgenus between genus and species. A species includes all individuals potentially able to breed together to produce similar individuals. Some species have common names, but these may be local and not known to people who live elsewhere or speak another language. The scientific name of an animal is understood internationally and is vastly preferable to a confusing variety of local common names. The scientific name of a species consists of the genus name, with the first letter capitalized; the subgenus name, if applicable, in round brackets, also with the first letter capitalized; and the specific name, uncapitalized. It is usual also to include the name of the author who first described and named the animal and the date of publication. Following approved practice, if the specific name used for the animal in this book is now in a different genus from the one originally proposed, the original author and date are placed in round brackets. An example is Stagnicola (Hinkleyia) montanensis (Baker, 1913). This species was first described and named by F. C. Baker in 1913. However, Baker named it Galba montanensis. A subspecies is a population, or group of populations, that is significantly different from other populations of that species but is still potentially able to breed with those populations. Subspecies of the same species also occupy different areas. If these areas overlap, widespread interbreed- ing can be expected in that zone. A subspecies name consists of the complete species name followed by the subspecific name. The same rules concerning authors, dates and use of brackets apply. An example is Stagnicola (Stagnicola) catascopium preblei (Dali, 1905). This subspe- cies was described by W. H. Dali in 1905 as the species Lymnaea preblei. The interested reader is referred to Ross (1974) and Mayr (1969), and to the scientific journal Systematic Z oology , for fuller discussion of classification procedure and the formation of scientific names. is Molluscan Classification and Some Special Features Snails, slugs, clams, mussels, scallops, oysters, chitons, tooth shells, squids and octopuses are all molluscs. The features these animals have in common constitute a good definition of what molluscs are. The phylum Mollusca may also be defined as comprising all invertebrate animals that are soft-bodied, non-seg- mented, have a muscular foot for burrowing or crawling, and possess a mantle — an enveloping sheet of tissue that in most species secretes a calcareous shell. With the major exception of pelecypods (bivalves), most molluscs also have a head with tentacles, eyes, mouth, and a radula — a rasping organ in the floor of the mouth. Seven classes of living molluscs are usually recognized: Monoplacophora, Polyplacophora, Aplacophora, Scapho- poda, Pelecypoda, Gastropoda, and Cephalopoda. Only the two largest classes, Pelecypoda and Gastropoda, live in fresh water, and only Gastropoda live on the land. All of the classes, however, are found in the sea. General information on molluscan classes is given in most textbooks on general biology. For detailed information on marine groups, however, consult Abbott (1974) or Bousfield (1960), and on land snails Pilsbry (1939-48) or Burch (1962). Canadian freshwater gastropods belong to two subclasses — Prosobranchia (also called Streptoneura) and Pulmonata (which, together with Opisthobranchia, are also called Euthyneura). Most prosobranchs have an operculum (used to seal the shell aperture), breathe by means of gills, and individuals are either male or female. Pulmonates have no operculum, breathe by means of a pulmonary sac, or lung, and are hermaphroditic. Canada has four superfami- lies of freshwater prosobranchs (divided into six families) and four superfamilies of pulmonates (also containing six families). Most systems of classification do not subdivide the class Pelecypoda into subclasses but only into about five orders. All Canadian freshwater bivalves belong to the order Eulamellibranchia. This group is characterized by 1) a hinge containing a few teeth of diverse shapes and sizes 2) two large adductor muscles of about the same size, one anterior and one posterior 3) a partly closed mantle with well-developed siphons 4) leaf-like gills within the mantle cavity. Two superfamilies are represented in Canada — Sphaeriacea and Unionacea. The major external and internal features of prosobranch and pulmonate snails and of eulamellibranch bivalves are illustrated on the front and back endpapers. Snails have many unique features, but their feeding organ — the radula—is one of the most interesting. This is a tough, elongate, moveable membrane in the mouth that bears many similar transverse rows of tiny sharp teeth. The radula is pressed against the food and pulled back and forth. This action rasps the food into tiny particles and carries it back into the mouth. Scientists have shown that the number and shape of the radular teeth in each transverse row are very useful in classification. All Canadian prosobranch snails, for exam- ple, typically have 7 teeth in each transverse row. The formula for this is usually 2-1-11-2, meaning that each row has 2 marginal teeth, 1 lateral, 1 central, another lateral, and 2 more marginals, in that order. The shape of the teeth and the number of projections on each (the “cusps”) differs from family to family, but is generally similar within families and very similar within genera. Similarly, the pulmonates are characterized by having radular teeth set in rows, with one distinctive central tooth in each row flanked by many teeth on either side. These teeth may or may not be separable into laterals and marginals. Each family of pulmonates has very distinctive radulae. For detailed information on radulae see the fascinating book by Solem (1974). Another uniquely molluscan feature is the glochidium larva of freshwater mussels. These animals retain their young for various lengths of time in modified portions of the gills. The young mussels, the glochidia, are released by the parent when its light-sensitive mantle-spots are stimulated, for example by the shadow of a passing fish. Mussels of the genus Lampsilis and their relatives even possess special mantle structures apparently designed to lure fish into their vicinity. The glochidia of each species of mussel, with a few exceptions, must attach to the gills or fins of a fish belonging to one, or a few, species for further development to take place. Most glochidia never accomplish this, but those that do succeed remain attached for a few weeks and metamorphose into tiny mussels. They then drop to the bottom and take up the normal life of a mussel, that is they crawl around siphoning water for respiration and to obtain phytoplankton as a source of nourishment and growth. Distribution Patterns in Canada Every region of Canada has its own species of freshwater molluscs. For example, that part of southern Ontario which includes Lake Erie and Lake St. Clair and the rivers and streams draining into them harbours twelve species of freshwater mussels and one species of pill clam that occur nowhere else in Canada. Such an area is called a zoo- geographic region. Several such regions exist in Canada (see front endpaper). The most clearly defined regions, that is those in which many species have similar distributional limits, are the Lake Erie-Lake St. Clair Region, the Red River-Assiniboine River Region, and to a lesser extent the Pacific Coastal Region. The other regions have boundaries that are not sharply defined. A general knowledge of the zoogeographi- cal regions of Canada will nevertheless be very useful to a collector. There are many interesting reasons why Canadian species are distributed as they are, and why Canadian zoogeographic regions exist as they do. These reasons involve the glacial and postglacial history of the country, its climate, geology, and geography, and the biology of the species themselves. For more details than those that follow, see Clarke (1973), During four different periods of the Pleistocene epoch, which itself lasted from about one million to about five thousand years ago, most of Canada was covered with glacial ice. For freshwater molluscs the most important non-glaciated regions were a part of the Yukon Territory and Alaska known as the Beringian Refugium, and the large area south of the glacial ice, most of which is in the United States. Within the glaciated region all the freshwater molluscs were wiped out, of course, but each time the ice receded they reinvaded the previously ice-covered region. 21 Many species, especially most of the freshwater mussels and all of the large prosobranch snails (Viviparidae and Pleuroceridae), require continuous waterways for migra- tion. Glochidia of freshwater mussels may be carried over long distances while attached to their fish hosts. The present distributions of freshwater mussels and large operculate snails were therefore brought about largely by postglacial stream confluences, for example the drainage pathways taken by glacial meltwater. Such species are most useful for delimiting zoogeographic regions. On the other hand, most small snails and many small clams (sphaeriids) are probably carried about imbedded in the feathers of water birds or in mud attached to their feet. Sphaeriids may also be transported while clamped to the feet of large aquatic flying insects. Therefore, the present distributions of small molluscs tend to transcend zoogeographic and drainage- system boundaries. The zoogeographic regions based on the occurrence of freshwater molluscs in Canada are as follows: 1 ) The Atlantic Coastal Region This area was populated by freshwater molluscs chiefly from the Atlantic Coastal Plain to the south. Character- istic species and subspecies are Lyogyrus granum , Margaritifera margaritifera,Anodonta cataracta cata - racta, A. implicata , an dLampsilis ochracea. 2) The Lake Erie-Lake St. Clair Region This rich drainage area in south-central Ontario was populated from the Ohio -Mississippi system when glacial meltwater in that region flowed south. It has twelve unionid species not found elsewhere in Canada, including Quadrula pustules a, Cyclonaias tuber culata, Pleurobema coccineum,Ptychobranchus fasciolaris, and Obliquaria reflexa. Some of its species also extend into Region 3 . 3) The Great Lakes -St. Lawrence Region The mollusc fauna of this area was derived from both the Atlantic Coastal Plain and the American Interior Basin. Characteristic species are Valvata perdepressa, Pleurocera acuta , Goniobasis livescens,Acella halde- mani , and Alasmidonta marginata. 22 4) The Red River -Assiniboine River Region This rich area was populated from the upper Mississippi River by migration through glacial meltwater channels and possibly through recent confluence. Characteristic species, many of which are found in Regions 2 and 3 but originate from another source, include Cincinnatia cincinnatiensiSyAmblema plicata,Fusconaia flava , Quadrula quadrula , and Propter a aiata . Some of the species extend into Region 5. 5) The Western Prairie Region This large region in southern Manitoba, Saskatchewan, and Alberta was populated from the American Interior Basin. Its characteristic species and subspecies are Rakerilymnaea bulimoides,Stagnicola caperata, Promenetus exacuous megas , Planorbula campestris, and Helisoma trivolvis subcrenatum. 6) The Pacific Coastal Region This region covers most of British Columbia and was populated from the Pacific coastal area in the United States. Characteristic species ar eFossaria truncatula , Physa columbiana, Margaritif era falcata,Gonidea angu- lata, andAnodonta nuttalliana. As some species occur only in the Columbia River system, that area might be designated as a distinct subregion. 7) The Beringian Refugium In Canada this region covers only the Yukon River system in the Yukon Territory and northern British Columbia and some small river systems in the northwestern Northwest Territories. It was a refuge area during the glacial period for many species, most of which have now spread beyond its borders. Its most distinctive species ar c Lymnaea atkaensis,Stagnicola kennicotti , andAnodonta beringiana. 8) The Subarctic Region The largest faunal zone in Canada, this region extends south of the tree line from Labrador to the mouth of the Mackenzie River. It largely coincides with the Boreal Forest botanical region, and was populated chiefly from adjacent regions to the south. Characteris- tic species and subspecies are Stagnicola catascopium preblei , Anodonta grandis simpsoniana , Sphaerium nitidum , and Pisidium conventus. 23 9) The Arctic Region This area extends north of the tree line to the southern part of the Arctic Archipelago, and its fauna was probably derived chiefly from the Beringian Refugium. No freshwater molluscs occur farther north. Character- istic species and subspecies are Valvata sincera helicoi- dea^Stagnicola arctica , and Physa jennessi jennessi. Thus, a collector travelling from one zoogeographic region to another will encounter different species. The whole molluscan fauna will not change, however, because most species occur in more than one zoogeographic region. For example, the common freshwater mussel Elliptio complanata is found in Regions 1, 3, and 8, the abundant pulmonate snail Stagnicola elodes occurs everywhere except in the Arctic Region, and the ubiquitous pea clam Pisidium casertanum occurs in all regions. Molluscs as Pollution Indicators Mollusc populations are affected by all three kinds of water pollution— thermal, inorganic, and organic. Thermal pollution sometimes occurs where river water is used for industrial cooling. This may heat the water enough to kill molluscs outright or adversely affect their reproduc- tive cycles. If the warming is minor, however, mollusc populations may actually increase. Inorganic pollution is principally industrial. It may poison water to the extent of killing all molluscs. Inorganic pollution that kills some species but not others, however, is difficult to detect biologically; no precise tolerance limits are known for any species of freshwater mollusc exposed to particular inorganic pollutants. Freshwater mussels live for many years, and during each winter form a more or less distinct growth ring on their shells. Chemical analysis of the shells can reveal if water pollution from radioactive materials or heavy metals has occurred, and when. Organic pollution is usually caused by sewage and insecticides. Chemical analysis of the soft parts of molluscs can reveal recent pollution by insecticides. In natural water, sewage is first attacked by bacteria that use oxygen. Because bacteria increase rapidly in the presence of sewage, all the oxygen dissolved in water may be used up. Nevertheless, as the sewage is degraded and if no more sewage is added, a sewage-polluted river will become reoxygenated down- stream, and the water will become clean. In water with little oxygen, pulmonate snails that come to the surface to breathe air have an advantage over other molluscs that must extract dissolved oxygen from water with their gills. Gill-breathing molluscs are therefore the first to be killed by low oxygen concentrations. A few gill- breathers (for example Amblema plicata,Anodonta cata- racta cataracta,A . grandis grandis , Sphaerium transversum , S, striatinum , andCampeloma decisum) appear to be reasonably tolerant of low oxygen concentrations. Pulmo- nates, however, are much more tolerant. Low diversity, and especially the presence of only a single species (usually of the genus Physa), is often indicative of organic pollution. Physa , in fact, may be unusually abundant in mildly polluted water because the species of fish that would normally prey upon it cannot tolerate the polluted environment. As a general rule, the presence of highly diverse communities of freshwater molluscs gives assurance of clean water. No freshwater mussels are found in grossly polluted water. Their absence from mildly polluted habitats may be caused by the absence of their fish hosts, which may be more susceptible to low oxygen than the mussels. The presence of dense mussel beds indicates clean (but not necessarily drinkable) water, partly because the substantial amount of oxygen required over the long term is obviously available and partly because the mussels themselves filter and purify the water. High mussel diversity also indicates high fish diversity, and implies good fishing. The excellent recent volume edited by Hart and Fuller (1974) gives a more detailed picture of the relationship between molluscs and water pollution. 25 The Freshwater Molluscs The following section contains illustrations, range maps, descriptions, and comments about the distribution, ecology, and biology of all the species and subspecies of freshwater molluscs known to inhabit Canada. A few that have not been recorded in Canada but are likely to migrate here are also included. Many species, especially freshwater mussels used in the manufacture of pearl buttons, have long-standing common names. Such names are given here. For species that do not have them, I have proposed common names. In doing so, I tried not simply to translate the scientific names but to suggest names that give useful information about the morphology, ecology or distribution of the species. The structural terms used in the key and in the text are defined on the endpapers and in the glossary. The key that follows is meant to facilitate identification of unknown molluscs by leading the collector directly to the families they belong to. As familiarity with freshwater molluscs grows, the family is identified more readily, but, to begin with, use of the key will be helpful. The next step in identification should be to compare the illustrations of the species in that family and examine the range maps. Finally, by reading the texts on description and habitat, the collector should be able to pinpoint the species the specimen belongs to. The specimens illustrated in the black-and-white plates that face each of the species descriptions are from the collection of the National Museum of Natural Sciences, Ottawa, and were collected over many years in Canada and the northern United States. The caption under each plate indicates either the specimens’ actual measurements or the percentage enlargements. For plates 1 to 90, the captions give the largest dimension of all the specimens illustrated, but in plates 91 through 144 the measurements are those of only the largest of the two pairs depicted. The pea clams illustrated in plates 160 to 179 were photographed through a scanning electron microscope, and only the magnifications are given. 27 The colour plates are reproductions of watercolours painted from actual specimens especially for this book. The specimens appear in taxonomic order on the plates, and are identified by their scientific name and by the number allotted to that species or subspecies in the text. Information on where the specimens were obtained can be found in the corresponding species descriptions, under the captions for the black-and-white plates. The specimens are reproduced 2/3 of actual size, except for No. 136, which is life size. It is helpful to remember that in all likelihood the first species collected will be those most abundant in the region. For example, among the freshwater mussels or clams of eastern Canada Elliptio complanata is dominant, in the prairies Lampsilis radiata siliquoidea is the most common, and in British Columbia Anodonta kennerlyi an dMargariti- ferafalcata are the most abundant. Among the Lymnaeidae, the first species found is usually Stagnicola elodes , and among the pill clams (Pisidium) probably P. casertanum. Also important to remember is that living land snails are sometimes found in shallow water, and that empty shells of terrestrial snails commonly occur in beach drift. If a Canadian “freshwater” snail does not appear in this book, it is probably a land snail. These can be identified by using Pilsbry (1939-48) or Burch (1962). In some parts of Canada, for example in the Ottawa region and in the vicinity of Hudson Bay, Pleistocene fossil marine shells also occur in beach drift. In a few areas, such as the St. Lawrence River estuary, some freshwater-tolerant marine molluscs also live in close association with true freshwater species. Marine molluscs can be identified by using Abbott (1974) or Bousfield (1960). The host fishes for freshwater mussels, where known, are recorded under their standardized common names following the list published by the American Fisheries Society (Bailey etal. 1970). 28 Key to the Families of Canadian Freshwater Molluscs 1 Shell double, i.e. composed of two halves or valves Shell single, i.e, spiral or cap-shaped 2 Shell small, 25 mm long or less (except up to 50 mm in Corbicula ), with small to medium-sized pseudo- cardinal hinge teeth and with lateral hinge teeth both in front of the pseudocardinal teeth and behind them Shell larger, more than 25 mm long in most specimens, and with hinge teeth not as above 3 Shell less than 25 mm long; lateral hinge teeth not serrated Shell up to 50 mm long; lateral hinge teeth finely serrated 4 Shell small, cap-shaped, without hinge teeth and with a clearly defined apex that is not near the margin Shell spiral and not as above 5 Shell more than S mm long; Columbia River system only Shell 8 mm long or less 6 Apex sharply pointed, acute and located posteriorly and to the left; rare Apex blunt and located posteriorly and in the midline or to the right; common 7 Living snail with an operculum Living snail without an operculum 8 Shell medium-sized to large, i.e. more than 12 mm high, and with a horny operculum Shell smaller than 12 mm or with a calcareous operculum Pelecypoda (clams or mussels) 2 Gastropoda (snails) 4 3 Superfamily UNIONACEA* (3 families) (p. 247) Family SPHAERIIDAE (p. 361) Family CORBICULIDAE (p. 357) (freshwater limpets) 5 7 Family LANCIDAE (p. 93) 6 Family ACROLOX1DAE (P- 89) Family ANCYLIDAE (P- 219) 8 13 9 10 *The families of freshwater mussels or clams (super- family Unionacea) are not separable on shell characters alone; therefore, Unionacea is keyed out here as a unit. 29 9 Width more than half the height Width less than half the height 10 Shell more than 9 mm high and with a calcareous operculum; eastern Canada Shell less than 9 mm high or with a horny operculum 1 1 Shell wider than high, with or without strong spiral ridges, and with a nearly circular aperture; operculum multispiral Shell higher than wide, without strong spiral ridges, and with an ovate aperture; operculum paucispiral 12 Shell small, up to 5,5 mm long, slender (width divided by height about 0,55-0.60), with up to 7 whorls, an ovate aperture, and a distinct lip that surrounds the aperture; amphibious; southeastern Canada only Shell relatively wider or with fewer than 7 whorls or without a distinct lip that surrounds the aperture; wholly aquatic; widespread 13 Shell disc-shaped or spire projecting only a little above body whorl; shell width greater than height Spire projecting much above body whorl; shell width less than height 14 Shell dextral or right-handed Shell sinistral or left-handed Family VIVIPARIDAE (P- 33) Family PLEUROCER I DAE CP- 81) Family BITHYNIIDAE (P- 77) 11 Family VALVATIDAE (P- 41) 12 Family TRUNCATELLIDAE following Taylor (1966). DISTRIBUTION Columbia River system from the Kootenay and Wigwam rivers in southern British Columbia south through Idaho, western Wyoming, northern Utah, Washington, and Oregon. Found also in the Olympic Penin- sula of Washington. ECOLOGY In the northwest United States this species lives on and under rocks and among vegetation in large and medium-sized lakes, in rivers, and in creeks. Currents at its river localities may be rapid to slow. 70 17 Lithoglyphus virens a: Creek near Olympia, Wash.; 8.1 mm, b: Siuslaw River, Oreg.; 8.3 mm. 71 FAMILY TRUNCATELLIDAE (Looping Snails) Shells small, dextral, with an elevated spire, more or less cylindrical, umbilicate or non-umbilicate, and smooth or sculptured. Operculum horny and paucispiral. Dioecious. A few species are intermediate hosts for blood flukes, which are parasites of warm-blooded animals, including man. The family is worldwide. Some species live in fresh water, others are amphibious, some live in the litter zone of salt-water beaches, and others are wholly terrestrial. 73 18 Pomatiopsis lapidaria (Say, 1817) River-Bank Looping Snail DESCRIPTION Shell small, up to about 5.5 mm high, slender (W/H ca. 0.55-0.60), rather strong, and with about 7 flatly rounded whorls. Nuclear whorl rounded and projecting slightly above the following whorl. Spire high, acute, subtending an angle of about 45°, and with slightly bulging sides. Whorls flatly rounded and separated by incised sutures. Aperture ovate, barely touching the penultimate whorl. Lip thickened and sur- rounding the aperture. Umbilicus mainly exposed and deep. Periostraeum reddish brown to brown. Sculpture consisting of rather fine but prominent and crowded collabral lines. Similar to Hydrobia nickliniana (Lea, 1839) except that in H. nickliniana the lip is not thickened, the aperture is larger, and the whorls are more convex. Moreover, H. nickliniana is aquatic, not amphibious; it is a doubtful inhabitant of Canada but it may occur in southern Ontario. DISTRIBUTION In Canada, this species has been found at only a few places in southern Ontario, namely the Sydenham River at Alvinston, the Thames River near Chatham, and the Ottawa River near Ottawa. In the United States it occupies a broad area from the East Coast to the midwest and south to Texas. ECOLOGY Amphibious. Lives on wet ground princi- pally along the edges of streams. Eggs are laid in the soil from spring to late summer. It is capable of serving as the intermediate host of the oriental blood fluke, Schistosoma japonicum. Another species of Pomatiopsis, P. cincin- natiensis (Lea, 1840), is recorded from southern Ontario by some authors, but I have seen no specimens from Canada. It is relatively wider than/ 5 , lapidaria and is also amphibious. 74 a IS Pomatiopsis lapidana a: Sydenham R. near Alvin ston, Ont.; 5.5 mm. b: Thames R. near Chatham, Ont.; 5.2 mm. 75 FAMILY BITHYNIIDAE (Faucet Snails) Shell small to small-medium, dextral, slender to broad, with an elevated spire, umbilicate or non-umbilicate, and smooth (in most species) or sculptured. Operculum calcareous and paucispiral or with concentric growth lines. Tentacles long, pointed, and tapering. The radula has 7 teeth in each row (fomula 2- 1-1-1- 2) and each tooth has many cusps. Dioecious. Eggs are laid in groups. The family is world- wide. Previously known as Bulimidae. Bithyniidae and Bithynia are now nomina conservanda. 77 19 Bithynia tentaculata (Linnaeus, 1767) Faucet Snail DESCRIPTION Shell large, up to 13 mm high, moderately inflated (W/H 0.57-0.68), conical, with 5-3/4 whorls, and with a sharply rounded apex. Nuclear whorl smooth, shining, and decurrent. Spire acutely produced. Spire whorls flatly convex and separated by impressed sutures. Aperture less than half the shell height, ovate, but acute above. Lip continuous and somewhat thickened. No umbilicus. Periostracum shining and pale brown. Sculpture consists of growth rests and crowded, fine collabral threads. Opercu- lum white and calcareous. This common species may be recognized by its large size, calcareous operculum, and lack of an umbilicus. It is often cited as Bythinia tentaculata (L) or Bulimus tentaculatus (L). DISTRIBUTION Introduced and now widespread in the lower Great Lakes-St. Lawrence system, also in the mid-Atlantic United States. Native to Europe. ECOLOGY Lives in shallow water in large lakes, large rivers and canals, where it feeds on filamen- tous algae. Very abundant in favourable situations. The breeding season is in July and August, and egg capsules are deposited principally on the shells of other individuals. 78 19 Bithynia tentaculaia a,b: Trent R. near Trenton, Ont.; a 9.6 mm, b 10.1 mm, c: South Nation R. near Plantagenet, Ont.; 1 1.0 mm. 79 IV Superfamily Cerithiacea FAMILY PLEUROCERIDAE (Horn Snails) Shell small to medium-sized, dextral, of medium width, high spired, rather heavy-shelled, non-umbilicate, and smooth to highly sculptured. Operculum horny and paucispiral. Tentacles long, tapering, and very narrow; foot short and wide. The radula has 7 teeth in each row (formula 2- 1-1- 1-2) and each tooth is multicuspid. The animals are dioecious but males lack a penis. Eggs are laid singly or in small groups. Predominantly a North American family, but with a few representatives in eastern Asia. 81 20 Pleurocera acuta Rafinesque, 1831 Flat-sided Horn Snail DESCRIPTION Shell up to about 37 mm high, narrow (W/H ca. 0.35-0.42), attenuated but vari- able, and rather thick and heavy. About 14 flat- sided whorls (earliest whorls ordinarily corroded away). Early whorls with 2 spiral carinae but later whorls smooth and form- ing an even, flat-sided cone. Body whorl angular at the periphery and with or without carinae. Aperture small, about 25% to 30% the height of the shell, with a sigmoid outer lip and a broad canal at the base. No umbilicus. Periostracum blackish, brown- ish, or yellowish brown. Sculpture, in addition to that mentioned, consists of sigmoid collabral lines. Operculum reddish brown, corneous, and paucispiral with 3 whorls, an acentric, sunken nucleus, and well-marked growth lines and fine striae. Larger th&n Goniobasis livescens , with flat-sided rather than flatly curved whorls, no callus on the parietal wall (in G. livescens a callus is present), a twisted instead of smooth columella, and a body whorl that is angular at the periphery rather than rounded. Also the aperture is relatively smaller, more angulate, and with a broad canal below. DISTRIBUTION Great Lakes- St. Lawrence system, upper Ohio-Mississippi drainage, and Erie Canal and contiguous waters in New York State. ECOLOGY Found in quiet areas of large streams and in lakes. A burrowing species that prefers mixed sand and mud bottoms. Eggs are deposited in sand-covered masses from April to June. 82 20 Pleurocera acuta a,b,c: Grand R., Grand Rapids, Mich.; a 26.7 mm, b 24.6 mm, c 27.3 mm. d: L. Erie near St. Williams, One.; 20.2 mm. 83 21 Goniobasis livescens (Menke, 1830) Great Lakes Horn Snail DESCRIPTION Shell up to about 25 mm high, rather narrow (W/H ca. 0.38-0.50), more or less attenuated but highly variable in shape, and of medium thickness. Up to about 10 flat, flatly rounded, or rounded whorls (but earliest whorls ordinarily corroded away). Early whorls with a low but prominent spiral carina just above the suture. Later whorls without a carina and, in many specimens, bearing coarse, collabral wrin- kles. Suture bordered below by a narrow, pale-coloured band. Aperture sharply rounded below, acute above, about 35% to 40% the height of the shell, and in some specimens brownish within. No umbilicus. Sculpture, in addition to carinae and wrin- kles, of fine collabral lines and, in some specimens, also a few low, spiral bands. Colour yellowish, brown or black. Opercu- lum brown, corneous, and paucispiral with 3 whorls, an acentric nucleus and radial striae. Sometimes confused withPleurocera acuta. See that species. DISTRIBUTION Widespread in the Great Lakes-St. Law- rence system. Also in the Erie Canal in New York and in some contiguous water bodies. ECOLOGY Occurs in lakes, rivers, streams of all sizes, and springs. Frequently found crawling on stones in a few centimetres of water in clear, rapid streams, but also lives at several metres depth in lakes. Eggs are laid singly or in small groups from April to August. S4 ATT l a 21 Goniobasis livescens a,b: South Nation R. near Plantagenet, Ont.; a 18.7 mm, b 17,6 mm. c: Salmon R., Hastings Co., Ont.; 17.6 mm. 85 22 Juga plicifera (Lea, 1838) Graceful Keeled Horn Snail DESCRIPTION Shell up to about 35 mm high, narrow (W/H ca. 0.28-0,35), attenuate but variable. About 15 whorls (the early whorls ordinarily corroded away), with about 1 0 to 12 heavy axial plicae on each whorl (in some specimens obsolete on the latest whorls or confined to the upper halves of those whorls), and with numerous spiral cords. Earliest 3 or 4 whorls very convex and more- or-less smooth. Aperture rounded below, acutely angled above, with a sigmoid outer lip, and with a broad canal below the columella. Periostracum blackish or brown. Sculpture (in addition to above) of heavy sigmoid growth rests and fine collabral threads. Operculum ovate, with about 3 whorls, dark brown except paler above, and with nucleus near centre of lower part. This is the only species of Juga living in the State of Washington and therefore the only one from the northwestern United States likely to be found in Canada. 3 . silicula (Gould, 1847) is a synonym. DISTRIBUTION Olympic Peninsula of Washington and south in the Columbia and other drainage systems to California. Doubtfully recorded from Vancouver Island. Possibly in south- ern British Columbia. ECOLOGY Occurs in muddy-sand bottoms of small and medium-sized lakes and slow-flowing streams. Like Pleurocera acuta , it burrows in the substrate. The animal is pale dusky- grey, with dark transverse stripes on the head and tentacles. Distinguished from Pleurocera and Goniobasis on the basis of genitalia and egg-mass formation (see Taylor 1966; Clarke 1976), 86 87 Subclass Pulmonata (Lung-breathing Snails) Order Basommatophora V Superfamily Acroloxacea FAMILY ACROLOXIDAE (Primitive Freshwater Limpets) Shell small, limpet- or cap-shaped, thin, with an ovate aperture, distinct radial sculpturing, and an acute apex located posteriorly and to the left of the midline. The anatomy is dextral whereas in Lancidae and Ancylidae it is sinistral. The radula has many (about 10 to 15) marginal teeth and about 4 to 7 lateral teeth on each side of the central tooth. The egg capsules are transparent, gelatinous, and contain a small number of eggs. The family is predomi- nantly Eurasian; there is but one North American species. 89 23 Acroloxus coloradensis (Henderson, 1939) Pointed Lake Limpet DESCRIPTION Shell up to about 4,6 mm long, 2.9 mm wide and 1.2 mm high, limpet-shaped, thin shelled, elliptical or ovate, and with a prominent, characteristic apex. Apex sharply pointed, pinched, thorn-like, located behind the centre and directed to the left, and radially striate with the striae continu- ing over the surface of the shell to the margin. Anterior, posterior, and lateral surfaces all flattened, or anterior surface slightly convex and/or posterior surface somewhat concave. Anterior and posterior margins rounded and lateral margins flatly convex and, in some specimens, convergent posteriorly, Periostracum of moderate thick- ness, brown, and adherent. Surface sculp- tured with fine radial striae and fine lines of growth. Can be easily distinguished by its sharp, spine-like apex, which is directed poste- riorly and toward the left margin. In other freshwater limpets, the apex is rounded, not pinched, and in the midline or on the right of centre. DISTRIBUTION At the present time is known from only a very few localities in the Rocky Mountains, namely Purden Lake near Prince George, British Columbia, Jasper National Park in Alberta, and Montana and Colorado; in eastern Canada only from Matheson and Arkell, Ontario, and the Chibougamau area of Quebec. ECOLOGY Rare. Characteristic of rocky, exposed por- tions of oligotrophic and mesotrophic lakes, where it occurs in shallow water on the undersides of rocks. It has also been found in a eutrophic pond (near Arkell, Ontario) attached to logs. Egg capsules are pale yellow and contain 2 or 3 eggs. The radula formula is about 7-13-1-13-7. 90 23 Acroloxus color ademis a,b: L. Gabrielle, Chibougamau region, Que. ; 4.7 mm. c,d: Pond northeast of Arkell, Halton Co., Ont.; 4.7 mm. 91 VI Superfamily Lymnaeacea FAMILY LANCIDAE (Limpet-like Lymnaeas) Shell small-medium, limpet- or cap-shaped, rather thin, with an ovate aperture, concentric and radial striae, and a distinct blunt apex located in the midline and subcentral to, or in front of, centre. A ring-shaped muscle scar is visible in the interior. The anatomy, jaw, and radula are similar to Lymnaeidae, not to Acroloxidae or Ancylidae. The egg capsules are sausage-shaped, transparent, gelatinous, and contain only a few eggs. The family consists of only the genus Lanx but there are three subgenera, Lanx y Fisher ola> and Walkerola. It is restricted to Pacific coastal drainages from the Columbia to the Sacramento River system. 93 24 Lanx (Fisher old) nuttalli (Haldeman, 1841) Greater Columbia-River Limpet DESCRIPTION Shell limpet-like, up to about 13 mm long, 10 mm wide, 6 mm high, and with the apex prominent in the midline and placed close to the anterior end. Apex smooth. Anterior and posterior margins more sharply rounded than lateral margins. Anterior slope straight or concave. Posterior slope convex. Interior bluish or purplish in the central portion but whitish around the edge. A subovate muscle scar encircles the inner portion of the shell; this scar is continuous except for a gap on the right side. Periostracum brown to brownish black. External sculpturing consists of concentric growth rests, fine concentric lines, and more or less discern- ible radial striae. The relatively large and heavy shell of this species distinguishes it from all other North American limpets. The anterior apex and the discontinuous ring-like muscle scar will distinguish L. nuttalli from other species of Lanx . ECOLOGY Occurs in the Columbia River upstream horn Richland, Washington, on diatom- covered rocks in the main channel of the river, which is free-flowing in that region. Living specimens are accessible only dur- ing periods of low water in the late summer or early fall. DISTRIBUTION Columbia River and its tributaries in the northwestern United States, Not yet found living in Canada although recently Dr, Leonard Kalas reported finding a bro- ken shell in the Columbia River at Trail, British Columbia. 94 24 Lanx nuttalli a,b: Columbia R, near McNary Dam, Benton Co,, Wash.; 12.2 mm c,d: Another specimen, same locality; 9.4 mm. 95 FAMILY LYMNAEIDAE (Pond Snails) Shell small to large, dextrally coiled, mainly thin-shelled, with an elevated spire, with or without an umbilicus, and without an operculum. Tentacles short, triangular, and flattened. The jaw has 3 plates and the radula has a small central tooth, a few bi- or tricuspid laterals and many bi-, tri- or multicuspid marginals. Monoecious (male and female organs in the same animal) and capable of self- or cross- fertilization. Egg masses are gelatinous, transparent, colour- less, sausage-shaped, and contain from a few to many eggs. The family is worldwide. 97 25 Fossaria decampi (Streng, 1896) Shouldered Northern Fossaria DESCRIPTION Shell up to about 1 1 mm high, 5 mm wide, with 6 shouldered whorls (most specimens are much smaller) and with aperture about 45% to 60% of the shell height, lymnae- iform, dextral, and of medium thickness. Nuclear whorls satiny, brown, and forming a bluntly rounded apex. In many specimens the brown colour extends to the penultimate whorl and contrasts with the whitish body whorl. Whorls abrupdy to roundly shoul- dered, and separated by deep sutures. Aperture narrow, abruptly arched and rounded above, flattened laterally, and broadly rounded below. Inner lip narrowly reflected and, in its lower part, erect. Umbilical chink prominent and bordered by inner lip. Sculpture consisting of growth rests and numerous fine, closely spaced collabral lines and ridges. This small species may be recognized by its shouldered whorls, laterally flattened body whorl, elevated and reflected inner lip, and characteristic aperture that is narrowly arched above and broadly rounded below. DISTRIBUTION Great Lakes-St. Lawrence drainage north to the Hudson Bay lowlands and the Mackenzie River, and west to British Columbia. Its southern limits have not been determined. ECOLOGY A cold-water species occurring only in large lakes in the southern part of its range and in both lakes and rivers in the northern part. It lives among submersed vegetation and on various kinds of bottom. Radula formu- lae of 20-1-19 to 23-1-22 have been found. The first lateral teeth are tricuspid. 98 25 Foss ana decampi a: Halkett L., Prince Albert National Park, Sask.; 11 ,2 mm. b: Edith L. near Jasper, Alta.; 9.4 mm. 99 26 Foss aria exigua (Lea, 1841) Graceful Fossaria DESCRIPTION Shell up to about 9 mm high, 4 mm wide, with 5-1/2 whorls (most specimens are smaller) and with aperture about 45% to 50% of shell height, lymnaeiform, dextral, narrow, attenuated, and thin-shelled. Nu- clear whorls satiny and dome-shaped. Spire extended and subtending an angle of about 40°. Spire whorls as high as wide, or higher than wide, and roundly shouldered. Sutures deeply impressed. Body whorl flattened, subcylindrical and about 2/3 the length of the shell. Aperture ovate, slightly flared at base, outer lip thin, and inner lip slightly reflected with the lower part nearly erect. Umbilicus small and narrowly open, or closed by the reflected lip. Periostracum partly or wholly brown. Sculpture consist- ing of fine collabral lines, irregular growth rests and, in some specimens, poorly de- fined spiral lines. This small snail may be identified by its narrow and attenuate form and its tall and roundly shouldered whorls. Compare with F. modicella andF. parva. DISTRIBUTION Great Lakes-St. Lawrence system north to the Hudson Bay lowlands, west to Manitoba and Minnesota, and south in the Ohio- Mississippi system to Alabama. ECOLOGY Lives among vegetation in protected parts of lakes and ponds, in backwater areas of rivers, in swamps, and in subarctic muskeg pools. Mud is the usual substrate. Radula formulae of 20- 1-21 to 25-1-25 have been recorded. 100 26 Foss aria exigua a: Lower Red L., Minn.; 7.9 mm. b: Attawapiskat R. near Attawapiskat, Ont.; 8.1 mm. c : Winisk R. near Winisk, Ont.; 8.4 mm. 101 27 Fossaria ferruginea (Haldeman, 1841) Fragile Fossaria DESCRIPTION Shell up to about 8 mm high, 4 mm wide, with 5 rounded whorls and with aperture about 50% to 55% of shell height, lymnae- iform, dextral and thin-shelled. Spire ex- tended and subtending an angle of about 45°. Sutures impressed. Aperture ear- shaped, outer lip convex and gently rounded above, inner lip narrow and reflected. Umbilicus closed by inner lip or left open only as a small chink. Periostracum yellow- ish brown or reddish and shining. Sculpture of narrow, clearly defined collabral lines and faint, irregular spiral lines. Differs from F. truncatula in that the whorls are sharply rounded above, the sutures are not deep, the shell is very thin 0 truncatula is strong and solid), and the umbilicus is nearly or completely closed. DISTRIBUTION Fraser River drainage (Hatzic Lake) and Columbia River drainage (Duck Lake near Creston) in British Columbia south to central California. ECOLOGY The scant information available indicates that it lives among dense vegetation in eutrophic lakes. Other habitats, however, may also be occupied. Nothing is known about its reproduction, radula, or soft anatomy. 102 27 Fossaria ferruginea a: Duck L. near Creston, B.C.; 10.0 mm (spire broken). b,c: Shuswap L. near Salmon Arm, B.C.; b 7.9 mm, c 8.2 mm. 103 28 Fossaria modicella (Say, 1825) Modest Fossaria DESCRIPTION Shell up to about 9,5 mm high, 5 mm wide, with 5-1/2 whorls and with aperture about 45% to 55% of shell height, lymnaeiform, dextral, elongated, and moderately thin- shelled. Nuclear whorls satin-like and bluntly dome-shaped. Spire moderately at- tenuate and spire angle about 40° to 45°. Whorls flatly rounded, without shoulders, and not as high as wide. Sutures well marked but not deep. Aperture subelliptical. Outer lip thin and convex; inner lip slightly thickened, narrow, somewhat reflected or turned up, and straight or bent just above the umbilicus. Umbilicus small and open. Periostracum light brown or yellowish brown. Sculpture consisting of fine colla- bral lines and ridges, irregularly spaced growth rests and, in some specimens, numerous fine spiral lines. Differentiated fromf. exigua by the absence of whorl shouldering and by the relative height of the whorls (height less than width in modicella , equal or greater than width in exigua ). Differs from F. parva , in that the whorls are more flatly rounded, the sutures are not deep, the aperture is elliptical rather than rounded, and the umbilicus is not partly obscured by the inner lip. DISTRIBUTION North America south of the tree line, except not recorded from the southeastern United States or Mexico. ECOLOGY Occurs in perennial lakes, ponds, and streams, and in vernal pools and ditches. Also occurs on moist sandy or muddy beaches. Vegetation is normally present, and the most commonly observed substrate is mud. The radula formula is reported as 25-1-25 but no doubt some variation exists. For a discussion of the problematic Fossaria modicella morph rustica see Clarke (1973) and references cited there. 104 28 Fossaria modicella a: Kakisa L. near Great Slave L., N.W.T.; 7,2 mm. b: L. Manitoba, Man.; 7.1 mm. 105 29 Fossariaparva (Lea, 1841) Amphibious Fossaria DESCRIPTION Shell up to about 8 mm high, 4 mm wide, with 5-1/2 whorls and with aperture about 40% to 50% of shell height, lymnaeiform, dextral, and of moderate thickness. Nuclear whorls satiny, about 1-1/4 in number and forming a rounded apex. Spire angle about 45°. Whorls very convex and rounded with deep sutures. Aperture medium-sized, uni- formly ovate or, in many specimens, with inner lip centrally indented and continuous. Outer lip thin and convex; inner lip wide and reflected. Umbilicus clearly defined, deep, and partly covered by the inner lip. Periostracum yellowish brown to brown. Sculpture is of crowded, fine collabral lines, irregular growth rests, and obscure spiral lines. Distinguished by its roundly convex whorls, incised sutures, rounded aperture, reflected inner lip, and open umbilicus. Its amphibious habits are also distinctive. Compare with F. modicella, Bakerilymnaea bulimoides morph perplexa, and B. dalli. DISTRIBUTION Occurs throughout most of North America north of 36° latitude and south of the tree line, except that it is absent from both eastern and western coastal drainage sys- tems, In the Rocky Mountains it extends south to Arizona and New Mexico. ECOLOGY Amphibious. Lives on wet mud flats, lake shores and river banks near the water’s edge, and in marshes. Also occurs among vegeta- tion submerged in shallow water but is more prone than any other lymnaeid to leave the water. Radula formulae of 16-1-16 to 24 1-24 have been recorded. 106 29 Fossaria parva a: Wain wright Park, Wainwright, Alta.; 7.3 mm. b,c: Pond near Whitemud Creek, west of Edmonton, Alta. ; b 4.4 mm, c 5.0 mm. 107 30 Fossaria truncatula (Muller, 1774) Liver-Fluke Fossaria DESCRIPTION Shell up to about 1 1 mm high, 6 mm wide, with 5-1/2 rounded whorls (most specimens are smaller) and with aperture about 40% to 50% of shell height, lymnaeiform, dex- tral, and fairly solid. Nuclear whorls 1-1/4 in number, with the first whorl very small and the next much larger. Spire extended and turreted; spire angle about 45°. Sutures deeply impressed. Aperture ovate; outer lip thin, convex, and abruptly rounded above; inner lip folded back. Umbilicus open and partly covered by the broad reflexed inner lip. Periostracum pale yellow- ish brown or greyish brown and shining. Sculpture consisting of fine collabral lines and fine, irregularly spaced spiral lines. The strongly rounded whorls (shouldered in many specimens), solid shell, deep and partly obscured umbilicus, and general appearance are such distinctive features that identification of this species, once seen, can confidently be made. Compare with F. ferruginea. DISTRIBUTION Columbia River drainage in British Colum- bia (Osoyoos Lake, stream near Bridesville, Christina Lake, and Duck Lake near Creston), and Yukon River drainage in the Yukon Territory and Alaska. The species is widespread in Europe and in central Asia. It is also reported in Iceland and in scattered localiues in Africa. ECOLOGY Occurs among vegetation in permanent lakes, ponds, streams, and marshes. Usual substrate is mud. The species is an interme- diate host for the sheep-liver fluke. Fasciola hepatica . The first lateral radula teeth are tricuspid. 108 30 Fossaria truncatula a: Osoyoos L., B.C.; 10.0 mm. b: Stream near Bridesville, B.C.; 10.7 mm. 109 31 Bakerilymnaea bulimoides (Lea, 1841) Prairie Pond Snail DESCRIPTION Shell up to about 1 1 mm high, 7 mm wide, with 5-1/2 whorls and with aperture length about 40% to 63 % of the shell height, lymnaeiform, dextral, and highly variable in shape- The spire may be acutely pointed and pinched (morph techella), acute but not pinched (morphs alberta, perplexa , and Vancouver ensis), subacute and somewhat bulbous (morph bulimoides s. str.), or broad, rounded, and obtuse (morph cockerelli). Nuclear whorl smooth, satiny, and brown. Sutures impressed. Body whorl inflated and dominant, especially in morph cockerelli. Aperture subovate. Outer lip with a thick- ened internal varix (reddish-brown in many specimens) behind the edge. Inner lip broad and extending over the umbilicus but not obscuring it. Periostracum brown to greyish brown. Sculpture consisting of fine colla- bral lines and, in some specimens, also of finer spiral striae. Irregular dark-brown and whitish collabral streaks may also be present. This highly variable species is best distinguished by its characteristic shell forms (in morphs techella, bulimoides s. str . and cockerelli , see figures) and by its expanded columella. Morphs alberta and perplexa (which appear to be synonymous) are similar to Fossaria parva but differ in having slightly thicker shells and broader reflected inner lips. Morph vancouverensis , a giant form (18 mm) from southern Vancouver Island, is intermediate between morphs techella and bulimoides s. str. in shell form and may be a distinct subspecies. Examination of the radula may be necessary for positive identification. Species of Fos- saria have tricuspid first lateral teeth, while those of Bakerilymnaea are bicuspid. DISTRIBUTION Southern Manitoba to southeastern British Columbia and southern Vancouver Island. In the United States the region west of the vicinity of the Mississippi River. ECOLOGY Lives in perennial-water habitats (lakes, ponds, and slow-moving streams) and vernal habitats (roadside ditches, temporary pools). Ordinarily occurs among dense vegetation that is growing on a mud bottom. Radula formulae of 20-1-19 to 23-1-23 have been recorded. 110 31 Bakerilymnaea bulimoides a: Morph cockerelli : pool near Taber, Alta.; 5.5 mm. b: Morph bulimoides s. str . : pool near Aldersyde, Alta.; 11.4 mm. c: Morph techella: pool near Cayley, Alta.; 10.5 mm. d: Morph perphxa : ditch near Eisenhower Junction, Alta.; 4.7 mm. Ill 32 Bakerilymnaea dalli (Baker, 1907) Small Pond-Snail DESCRIPTION Shell up to 6 mm high, 3.3 mm wide, with 5 whorls and with aperture about 45% to 55% of shell height, lymnaeiform, and dextral. Whorls convex, roundly shouldered and 5 in number. Nuclear whorl small, flatly rounded, brownish and satiny. Sutures very deep. Spire angle about 50°. Aperture ovate and lip continuous in many speci- mens. Outer lip evenly rounded. Inner lip flatly reflected over the umbilicus, which is small but clearly defined. Sculpture consist- ing of fine collabral threads and finer but somewhat obscure spiral striae. Recognized by the large number of whorls in relation to its very small size, by its incised sutures, and by its roundly shouldered whorls. Compare with Fossaria parva. DISTIBUTION Southern Ontario and Ohio west and north to the Prairie Provinces and eastern British Columbia, and south to Arizona. Details of its southern distribution have not been worked out, ECOLOGY Lakes, ponds, small rivers, and marshes are all suitable habitats for this small species. Vegetation is present and bottom deposits are of diverse types. Does not normally occur out of the water and thereby differs from Fossaria parva. Radula formulae of 22-1-21 and 21-1-21 have been recorded. The first lateral teeth are bicuspid. 112 32 Bakerilymnaea dalli a: Creek near Edson, Alta.; 5.4 mm. b: Wigwam R., B.C.; 4.7 mm. 113 33 Radix auricularia (Linnaeus, 1758) European Ear Snail DESCRIPTION Shell up to about 30 mm high, 25 mm wide (most specimens are half this size), with 5 whorls, swollen lymnaeiform, dextral, thin, and fragile. Spire short, acute, and pinched in many specimens. Body whorl greatly swollen, enlarged, and constituting more than 90% of the volume of the shell. Aperture ear-shaped, patulous, dilated, and even extending above the spire apex in some specimens. Periostracum thin and pale brown or golden. Sculpture consists of crowded collabral lines, microscopic spiral lines and often irregular malleations or flattened spiral bands. The bulbous body whorl and small, sharply pointed spire of this large species distinguish it from all others. Compare with Lymnaea stagnalis sanctaemariae. DISTRIBUTION Native to Eurasia but has been widely introduced in North America, especially, but not exclusively, in the vicinity of major cities. Known to occur in western Canada at Banff, Alberta, and in British Columbia in Kootenay Lake, the Okanagan River system, and North Vancouver. ECOLOGY Occurs in lakes, ponds, and slow-moving rivers. Mud is a frequent substrate. The radula formula is approximately 50-1-50, with the first lateral tooth tetracuspid. 114 33 Radix auricularia a: Pond, Warm Spring, Park Co., Colo.; 25.0 mm. b: Lava L,, Deschutes Co., Oreg,; 18.8 mm. 115 34 Radix peregra (Muller, 1774) Wandering Snail DESCRIPTION Shell up to about 7 mm high, 5 mm wide, with 3-1/2 whorls and with aperture height about 75 % of shell height, obese lymnae- iform, dextral, and thin-shelled. Whorls flatly rounded. Nuclear whorl rounded, shining and finely punctate. Spire short, broad, and with spire angle exceeding 90°. Body whorl ovate, dominant, and about 90% as long as the shell. Aperture ovate, wide and long, and with thin, broadly curved outer lip and flattened inner lip that bears a thin callus. Umbilicus closed by the re- flected inner lip. Periostracum brownish. Surface shining and sculptured by distinct, fine, collabral lines and ridges and obscure spiral lines. Resembles Radix auricularia but North American specimens are much smaller and their apertures are less expanded. In addition, the first lateral radular teeth are tricuspid, not tetracuspid as ini?, auricu- laria. Compare also with Pseudosuccinea columella. DISTRIBUTION This is a common Eurasian and North African species. It also occurs in Iceland. In North America it is known only from a few localities in southern Newfoundland. ECOLOGY Lives in ponds, other quiet waters, and stagnant habitats. In this book it is placed in Radix rather than Lymnaea because of its close relationship toi?. auricularia. 116 117 35 Pseudosuccinea columella (Say, 1817) American Ear Snail DESCRIPTION Shell up to about 21 mm high, 12 mm wide, with 4 whorls and with aperture height about 65% to 75% of shell height, succine- iform, dextral, thin, fragile and with a capacious body whorl. Protoconch dark brown, small, and about 1-1/4 whorls. Spire sharply conic, rather short and narrow, and with sutures consticted and well impressed; spire angle about 50°. Whorls rounded and enlarging rapidly. Aperture large, ovate, and expanded ba sally. Outer lip thin and broadly curved; inner lip arched and closely ap- pressed to the parietal wall so only a narrow slit is left open. In some specimens the inside of the empty shell is visible through the aperture almost to the apex. Columella plait spirally twisted. Periostracum light greenish brown to yellowish brown. Sculp- ture consists of coliabral lines and streaks and spiral lines. This medium-sized species may be recog- nized by its large ovate aperture and thin shell. It resembles the terrestrial snail Succinea ovalis but differs from that species in the possession of a distinct protoconch and a twisted columella. In living speci- mens the tentacles are broad and triangular and the eyes are on swellings near their bases, whereas in S. ovalis the eyes are at the ends of long peduncles and the tentacles arc small protuberances near the bases of the eye stalks. The head-foot region is also smooth, while that of S. ovalis appears to be covered with scales. Fundamental inter- nal anatomical differences also exist. DISTRIBUTION Occurs from southern Manitoba and the Great Lakes- St. Lawrence River system south throughout North America east of the vicinity of 100° longitude. Also occurs in Central and South America. Has been introduced into the western United States, Europe, Australia, and South Africa. ECOLOGY Lives in lakes, ponds, and sluggish streams among lily pads and reeds, and at the edges of these water bodies on sticks and on mud. The radula formula is approximately 35-1-35 and the lateral teeth are tricuspid. U8 35 Pseudosuccinea columella a: Meach L. near Hull, Que.; 8.8 mm. b,c: Rideau R. near Ottawa, Ont,; b 11.1 mm, c 12.7 mm. 119 36 Acella haldemani (Binney, 1867) Slender Pond Snail DESCRIPTION Shell up to about 25 mm high, 5 mm wide, with 5-1/2 whorls and with aperture length about 39% to 42% of shell length, slender lymnaeiform, dextral, thin, and fragile. Nuclear whorl long and ovate. Spire very narrow and long; spire angle about 20°. Whorls flat-sided, oblique, descending rap- idly, and with impressed sutures that lie at 45° relative to the shell axis. Aperture long and narrow, not laterally expanded, acute above, and flared below. Outer lip thin and more or less broadly curved, and inner lip erect, straight, long, and touching (in most specimens) but not appressed to the parietal wall. Umbilicus a slender chink behind inner lip. Periostracum yellowish white to brown. Sculpture consisting of fine collabral lines and wrinkles. The long and slender, almost needle-like shell of this species cannot be mistaken. It has a superficial resemblance to the young of Lymnaea stagnalis but it is much narrower and the spire sides are nearly straight, rather than concave. DISTRIBUTION Great Lakes- St. Lawrence drainage and vicinity in southern Ontario, southern Que- bec, northern Vermont, New York, Ohio, Illinois, Wisconsin, and Minnesota. ECOLOGY Rare. Occurs in widely separated localities and is found only sporadically. Favourable habitats are among reeds in eutrophic lakes and ponds at a depth of about 0.3 to 1.0 metre. The radula formula is about 21-1-21 and the lateral teeth are bicuspid. 120 36 Acella haldemani a,b: “New York”; 20.7 mm. c: Georgian Bay, L. Huron, Ont.; 10.2 mm. 121 37 Bulimnea megasoma (Say, 1824) Showy Pond Snail DESCRIPTION Shell up to about 47 mm high, 30 mm wide, with 6 whorls and with aperture height about 55% to 65% of shell height, swollen lymnaeiform, dextral, and fairly thick and solid. Nuclear whorls number 1-1/4, and are satiny and yellowish to dark brown. Spire rather short, with straight or convex sides, conical with evenly rounded whorls and impressed sutures. Body whorl dominant, large, broadly rounded, inflated but not bulbous, and comprising most of the shell volume. Aperture large, acutely angled above, flatly rounded laterally, rather sharply rounded below, and chestnut-brown to purplish within. Parietal wall flattened, with a spirally twisted columella plait, and a prominent callus that obscures the umbili- cus. Periostracum glossy, brownish or greenish and with or without collabral streaks of muted green, orange, yellow- brown, or purple. Sculpture principally of coarse collabral lines and ridges. This large, rotund, colourful species is quite different from any other. Compare with S ’ tagni cola catascopium. DISTRIBUTION Upper Albany, Winnipeg and Nelson River drainages in the Canadian Interior Basin; Great Lakes -St. Lawrence system east to Lake Champlain; and upper tributaries of the Ohio -Mississippi River system. ECOLOGY Occurs in large and small lakes, in slow- moving rivers, and in pond areas of creeks. Vegetation is of variable abundance and the usual bottom is mud. Radula formulae of 48-1-47 to 49-1-49 have been observed. The lateral teeth are tricuspid. 122 37 Bulimnea megasoma a: Marchington R. near Drayton, Ont.; 45.0 mm. b: Wildgoose L. near Longlac, Ont.; 37.3 mm. 123 38 Lymnaea stagnalis jugularis (Say, 1817) Great Pond Snail DESCRIPTION Shell up to about 56 mm high, 27 mm wide, with 7-1/2 whorls and with aperture height about 48% to 58% of shell height, lymnae- iform, dextral, and thin. Nuclear whorls smooth, shiny, satiny, forming a pointed apex and numbering about 1-1/2. Spire tall, narrow, with concave sides (in many speci- mens), with spire angle about 40° but variable, and with flatly-rounded whorls and impressed sutures. Body whorl capacious, inflated, shouldered in some specimens, roundly convex, and in volume constituting most of the shell. Aperture ovate except angled above; outer lip thin and fragile; inner lip with a thin but prominent callus. Columella twisted and forming a heavy, oblique spiral plait. Periostracum light tan to dark brown. Surface relatively smooth except malleated in some specimens, with prominent collabral lines, growth rests, and fine spiral lines. This large, thin-shelled species is recog- nized by its long, narrow spire that has concave sides and by its bulbous body whorl. Compare it withL. stagnalis sanctae- mariae. L.s. appressa (Say, 1818) is a synonym. Say’s first (1817) description of jugularis is recognizable, but that publication (Nicholson’s Encyclopedia) is very rare. In later, more common editions the description was altered and became equivocal. DISTRIBUTION Throughout Canada south of the tree line, but absent from the region east of northern James Bay and Hudson Bay and also from the Atlantic Provinces. In the United States it occurs throughout the Great Lakes- St. Lawrence system, in the upper Mississippi River system in Ohio and Illinois, and in the Rocky Mountains south to Colorado. ECOLOGY Occurs in all perennial-water habitats. Vegetation is always present and bottom sediments are of diverse types; it is often found among cattails ( Typha ). Radula for- mulae of 37-1-36 to 46-1-46 have been recorded, and the first lateral teeth are bicuspid or tricuspid. The nominal subspecies wasatchensis Hemphill, recorded from western Canada and United States, exhibits a relatively longer spire, more rounded aperture, and more inflated body whorl than typical L. s . jugularis. These interrelated characters are too irregularly expressed, however, to merit separate taxonomic recognition for those populations. 124 38 Lymnaea stagnates jugularis a: Montreal R. near Montreal L., Sask.; 50.8 mm. b: Rideau R., Ottawa, Ont.; 61.1 mm. c: Lake near High River, Alta.; 51.5 mm. 125 39 Lymnaea stagnalis sanctae- mariae Walker, 1892 Walker's Pond Snail DESCRIPTION Shell similar to that of Lymnaea stagnalis jugularis but differing principally in relative proportions. Aperture height is about 65% to 70% of the height of the whole shell, while inL. s. jugularis that ratio is less than 60% in nearly all specimens. Also the aperture is very wide and patulous, and the body whorl is capacious and almost globu- lar. The spire is short, less acute, and has only about 4 whorls, whereas in L. s. jugu- laris it has 5 to 6 whorls. The last part of the body whorl in many L. s. sanctaemariae is also malleated or otherwise irregular. DISTRIBUTION Lake Superior watershed and adjacent parts of the Lake Huron, Winnipeg River and Wisconsin River watershed. Intergrades withL. s. jugularis occur in adjacent pans of the Nipigon, Attawapiskat, Severn, Hayes and Nelson River systems in Canada. ECOLOGY Characteristic of large and medium-sized lakes. Frequently found attached to large rocks exposed to wave action, but is also found in more protected habitats. Egg masses are reported as thicker and more solidly formed than inL. s. jugularis. The radula, however, is similar in both sub- species. 126 39 Lymnaea stagnalis sanctaemariae a: Knee L., Man.; 51.7 mm. b: Sandbar L. near Ignace, Ont.; 48.2 mm, c: Ozhiski L,, Ont.; 39,8 mm. 127 40 Lymnaea atkaensis Dali, 1885 Alaskan Pond Snail DESCRIPTION Shell up to about 42 mm high, 30 mm wide, with almost 6 whorls and with aperture height about 50% to 65% of shell height, lymnaeiform, dextral, rather thin, moder- ately fragile, but variable in all characterise tics. Nuclear whorls rough, shining, about 1-1/2 to 2 in number, and forming a pointed apex. Spire short to long, moderately broad to narrow with an angle of 30° to 60°, scalariform, and with shouldered and strongly convex whorls. Sutures constricted and deeply impressed. Body whorl large, irregular, malleated, and shouldered in many specimens. Aperture large and ear- shaped with thin and convex outer lip and erect, continuous, reflected inner lip. Um- bilicus moderately wide, deep, and revealing earlier whorls except in specimens in which it is partly obstructed by the reflected inner lip. Periostracum straw-coloured or yellow- ish brown. Sculpture consisting of fine collabral striae, dark-brown growth rests, spiral lines and bands, and irregular malleations. Differs conspicuously from all other species within its geographical range except Stagnicola catascopium> which extends close to its range in British Columbia. That species has flatly rounded whorls, sutures that are well marked but not constricted and deep, and (in most specimens) a lower spire. The radulae and anatomy of the species are also different. DISTRIBUTION Lakes in Alaska (including the Aleutian Islands), the Yukon Territory, the North- west Territories east to the vicinity of Darnley Bay (about 69°50'N, 122°E), and northern British Columbia in the Macken- zie River system (Peace and Liard River drainages) and presumably in the Yukon River system. This is a Beringian relict species. ECOLOGY Occurs in northern British Columbia in clear, cold, oligotrophic lakes on rocks and among sparse submersed aquatic vegetation at depths of 0.3 to 5 metres. The radula has both bicuspid and tricuspid lateral teeth, and gross formulae of 4 1-1 -39 and 43-1-41 have been observed. 128 40 Lymnaea atkaemis a,b: Lake near Paulatuk, N.W.T. (69°24'N, 124°33' W); a 30.1 mm, b 35.4 mm. 129 41 Stagnicola ( Hinkleyia ) caperata (Say, 1829) Blade-ridged Stagnicola DESCRIPTION Shell up to about 16 mm high, 7 mm wide, with 6-1/2 whorls and with aperture height about 45% to 60% of shell length, lymnae- iform, and dextral. Nuclear whorls brown or reddish-brown, satiny, about 1-1/3 in number, and forming a pointed apex. Spire conoid, with flat or convex sides, with spire angle about 60°, and with whorls flatly rounded. Sutures impressed. Body whorl inflated. Aperture ovate; outer lip thin and reinforced by a varix which may be purple; inner lip broad and expanded over the umbilicus. Umbilical chink partly or wholly open. Periostracum variable, yellowish brown to blackish, and closely adherent. Most unabraded specimens (when viewed at 25 X or 50 x magnification) exhibit fine, low, compressed, blade-like spiral ridges standing erect in spiral grooves that are impressed in the underlying shell surface. Recognized by its unique, microscopic, spiral, blade-like periostracal ridges. Com- pare with 5. montanensis and S. elodes. DISTRIBUTION Typically a prairie species. Positively re- corded from southern Manitoba to southern and central Alberta, and south in the United States to Nevada and Utah. Also reported from eastern Canada and the United States, and even from the Yukon Territory, Alaska and California, but these records are proba- bly erroneous. ECOLOGY Found most frequently in temporary- water habitats (ditches, shallow pools, vernal ponds) or in spring-flooded margins of permanent-water habitats. Also occurs rarely in large permanent lakes, rivers, and swamps. Radula formulae of 28-1-28 to 35-1-32 have been observed. The lateral teeth are bicuspid. 130 41 Stagnicola caperata a: Ditch near Cayley, Alta.; 10.0 mm. b: Creek near Carstairs, Alta.; 1 1.0 mm. 131 42 Stagnicola ( Hinkleyia ) montanensis (Baker, 1913) Mountain-Spring Stagnicola DESCRIPTION Shell up to about 1 5 mm high, 7 mm wide, with 6-1/2 whorls and with aperture height about 38% to 50% of shell height, lymnae- iform, dextral, and of moderate thickness. Nuclear whorls brown to reddish-brown, about 1-1/3 in number, and forming a blunt apex. Spire angle about 60°; spire sides straight or bulging. Aperture relatively small, and long ovate; outer lip curved; inner lip rather straight, oblique, and sometimes angled where it is appressed to the previous whorl. Inner lip broadly re- flected, sub-triangular, and exposing a small distinct umbilicus. Periostracum brownish and shiny. Under 25 X magnification the sculpture is seen to consist of numerous spiral rows of tiny crescents (on most specimens) whose ends point away from the aperture, and numerous irregularly-spaced collabral lines. Resembles S. caperata but differs con- spicuously in its microsculpture. Compare the two species. DISTRIBUTION Recorded in the Rocky Mountain region from southwestern Alberta south to Nevada and Utah. May also occur in British Columbia. ECOLOGY Characteristic of clear, cold mountain streams and small spring-fed pools. Has also been found in a roadside ditch. A radula formula of 28- 1 -32 has been reported. 132 133 43 Stagnicola (Stagnicola) arctica (Lea, 1864) Muskeg Stagnicola DESCRIPTION Shell up to about 22 mm high, 1 1 mm wide, with 6-1/2 whorls and with aperture length about 45% to 58% of shell length, lymnae- iform, dextral, and unusually variable in all features, but normally of moderate thickness and with heavy columella devel- opment. Nuclear whorls rounded, shiny, yellowish-to-reddish brown, and about 1-1/2 in number. Spire angle about 50°; spire of medium length and with impressed sutures and convex whorls that are wider than high. Body whorl convex but not inflated. Aper- ture subovate and purplish brown within (in many specimens). Outer lip convex, with or without an internal varix; inner lip broad, thick, and expanded over the umbilicus, obscuring it in many specimens. Columella plait heavy, moderate, or absent. Perios- traeum variable, pale brown to blackish. Sculpture variable and composed of colla- bral lines and spiral ridges, bands, or malleations. Resembles the widespread Stagnicola elodes but is smaller, with a proportionately larger body whorl and much heavier colu- mella development. DISTRIBUTION An arctic and subarctic species. Occurs across northern Canada from Labrador to the Yukon Territory and beyond into Alaska. ECOLOGY Occurs in lakes, ponds, rivers, streams, ditches, and muskeg pools. Vegetation abundance and bottom sediments are vari- able. Radula formulae from 29- 1 -27 to 31-1-30 have been reported, and the lateral teeth are bicuspid. Stagnicola yukonensis Baker is a synonym. 134 43 Stagnicola arctica a: Moose R., Moose Factory, Ont,; 15.5 mm. b: Hannah Bay, James Bay, Ont.; 15.7 mm. 135 44 Stagnicola ( Stagnicola ) catascopium catascopium (Say, 1817) Lake Stagnicola DESCRIPTION Individual populations of this species may differ widely from each other. In some populations shells may reach 33 mm in height and 23 mm in width, but in other populations these dimensions are halved. Adult specimens have 5 to 6 whorls, and the aperture length is between 50% and 70% of shell length. Specimens may be with or without a columella plait, an open umbilicus, and strong surface sculpturing. Whorls may be rounded to nearly globose, shouldered or unshouldered, and with a flattened to pyramidal spire. The aperture is ovate to subquadrate, large to very large, and variable in degree of flare. The varix present behind the outer lip in many specimens may be brown. The inner lip is broad and partially or completely reflected over the umbilicus. Sculpturing is strong to weak, and may be composed of spiral lines, ridges and flat bands, collabral lines of growth, white varices, or any combination of these characters. Typically a rather large and heavy shell with low spire, broad aperture, inflated whorls, deep sutures, and thickened inner lip. The only subspecies recognized as distinct are those which occur as multiple, contiguous populations and which can be differentiated by more than a single charac- ter, such as S. catascopium nasoni and S’, catascopium preblei] these are discussed in the following pages. DISTRIBUTION Generally extends across North America below the tree line and south in the United States to about 40°N. Within these limits the only large area where the species is absent is northern British Columbia, the Yukon Territory and Alaska, that is the area occupied by Lymnaea atkaensis. ECOLOGY Characteristic of large lakes and large rivers although also found in smaller bodies of water. Its most frequent habitat is on rocks exposed to waves and currents. Radula formulae of 31-1-30 to 35-1-35 have been reported. The lateral teeth are bicuspid. 136 44 Stagnicola catascopium catascopium a: Winisk R,, Ont.; 18.7 mm. b: Mistassin L., Ont.*, 15.0 mm. c: St. Lawrence R., Que.; 13.7 mm. 137 45 Stagnicola ( Stagnicola ) cata- scopium nasoni (Baker, 1906) Miniature Lake-Stagnicola DESCRIPTION Shell up to about 12 mm high, 8 mm wide, with 4 whorls and with aperture height about 60% to 75% the height of the shell, broad lymnaeiform, rotund, solid, and with expanded aperture and broad flaring lip* Nuclear whorls dark brown, satiny, and about 1-3/4 turns. Whorls rounded but not inflated. Spire broad but acute and with impressed sutures. Body whorl subglobose and dominant. Aperture ovate, expanded, and white or brownish within; outer lip sharp but internally thickened; inner lip broad, thickened, and reflected. Umbilicus obscured by inner lip. Periostracum yellow- ish or purplish brown. Sculpture consisting of impressed spiral lines and fine, crowded collabral ridges. Distinguished from S', c, catascopium by its unusually small size, solid appearance, and wide, flaring aperture. DISTRIBUTION The Great Lakes from Lake Superior to western Lake Ontario; Lake Geneva, Wisconsin; Rainy River system and Lake of the Woods. ECOLOGY In Lake of the Woods occurs on wave- exposed black shale rocks at, and just below, the water surface. Here the dark shells are well camouflaged and resemble air bubbles. Egg masses are about 5 to 6 mm long, crescent-shaped, and contain from 8 to 20 pale-yellow eggs. The snails move rap- idly, that is lik ePhysa gyrirta. 138 45 Stagnicola catascopium nasoni a: L. Nipigon, Om,; 15.4 mm. b: Batchawana Bay, L. Superior, Ont.; 13.6 mm. 139 46 Stagnicola ( Stagnicola ) cata- scopium preblei (Dali, 1905) Subarctic Lake-Stagnicola DESCRIPTION Shell up to 42 mm high, 28 mm wide, with almost 7 whorls and with aperture height about 55% to 65% of shell height, broad lymnaeiform, dextral, variable in shape, and with swollen whorls. Nuclear whorls brown, about 1-1/2 in number, relatively large, and forming an acute apex. Spire short but acute with deeply impressed to channelled sutures and inflated, shouldered whorls. Aperture large, ovate to subquad- rate; outer lip thin and irregularly curved, with or without a reddish-brown internal varix; inner lip broad, appressed to the body whorl above and reflected over the umbili- cus below but not obscuring it. Umbilicus open and deep. Periostracum pale brown. Sculpture coarse, of spiral ridges and bands, collabral lines and ridges, and irregular malleations. Differs from S\ catascopium s. str. in that the shell is larger, the umbilicus is entirely open rather than closed or partly open, the whorls are more uniformly shouldered, and the aperture is relatively smaller. DISTRIBUTION Northern Saskatchewan and northern Man- itoba in the Hayes, Nelson and Churchill River systems. ECOLOGY Known only from large oligotrophic sub- arctic lakes. One specimen had a radula formula of 39-1-39 and bicuspid lateral teeth. Details of its ecology are unknown. 140 46 Stagnicola catascopium preblei a,b,c: Limestone L., northeastern Man,; a 37.6 mm, b 33.5 mm, c 40.0 mm. 141 47 Stagnicola ( Stagnicola ) elodes (Say, 1821) Common Stagnicola DESCRIPTION Shell up to about 32 mm high, 14 mm wide, with 7 whorls and with aperture height about 45% to 55% of shell height, lymnae- iform, dextral, variable in shape, and elon- gate. Nuclear whorls rounded, shining, and finely punctate. Spire rather long, average spire angle about 45° but variable, whorls rounded, and sutures impressed. Body whorl convex, somewhat inflated, and con- stituting about 2/3 the length of the shell. Aperture subovate and more or less ex- panded; outer lip thin, with or without an internal varix, and with a brownish-purple band within; inner lip broad and with a prominent callus. Columella plait promi- nent, heavy, and spiral. Umbilicus narrowly open or closed. Periostracum yellowish brown to blackish brown. Sculpturing is of numerous coarse collabral and spiral lines, a few growth rests, and (in many specimens) with spiral bands or malleations or both. The most abundant species of its genus. In some populations specimens approach S. proxima or S. reflexa in appearance. Compare with those species. DISTRIBUTION Occurs throughout Canada below the tree line, and south in the United States to about 38°N. In the Rocky Mountains it extends farther south, that is to about 33°N. ECOLOGY Ubiquitous. Found in all kinds of aquatic habitats. Especially numerous in thick vegetation and on muddy substrates. Radula formulae of 27-1-26 to 34-1-33 have been observed. Until recently, this species was known as Stagnicola (or Lymnaea) palustris (Muller), 142 47 Stagnicola elodes a; Pond, Quamichan, Vancouver Is., B.C.; 23.2 mm. b: Pond, False R., Ungava Bay, Que.; 20.9 mm. 143 48 Stagnicola ( Stagnicola ) kennicotti Baker, 1933 Western Arctic Stagnicola DESCRIPTION Shell up to about 21 mm high, 10 mm wide, with 7 whorls and with aperture height about 35% to 45 % of shell height, lymnae- iform, dextral, and solid. Nuclear whorls satiny, 1-1/2 to 2 in number, and forming a high, domed apex. Spire angle about 45°; spire rather long, with straight sides and rounded whorls. Sutures constricted, im- pressed and, in many specimens, incised. Aperture, roundly ovate; outer lip thin, convex, and without an internal varix; inner lip flattened, wide, reflected over the umbili- cus and curved or angulate. Umbilicus visible only as a small narrow chink. Periostracum pale brown. Sculpturing is of irregular collabral lines, low spiral ridges, and spiral rows of tiny crescents between the ridges. Related to 5. arctica but differs in that the aperture is smaller (height less than 45% of shell height), the spire is longer, and no columella plait is present. DISTRIBUTION Occurs in the Northwest Territories on the mainland arctic coast of Canada from near Bathurst Inlet to Liverpool Bay, as well as on southern Victoria Island. ECOLOGY An arctic species. Found in large lakes, small lakes, pools, and streams. Radula formulae range from 29-1-29 to 33-1-32. The lateral teeth are bicuspid. 144 48 Stagnicola kenmcotti a; Creek, Bernard Harbour, N.W.T.; 15.1 mm (para- type). b,c: Lake near Bathurst Inlet, N.W.T.; b 12.9 mm, c 13.6 mm. 145 49 Stagnicola ( Stagnicola ) proxima (Lea, 1856) Rocky Mountain Stagnicola DESCRIPTION Shell up to about 22 mm high, 1 1 mm wide, with 6-1/2 whorls and with aperture height about 45% to 55% of shell height, lymnae- iform, and dextral. Nuclear whorls brown, satiny, 1-1/2 to 2 in number, and rounded. Spire sharply acute, pyramidal, pinched in many specimens, and with spire angle about 30° to 45°. Whorls flatly rounded and sutures impressed or incised. Body whorl large, well rounded to rotund. Aperture medium-sized, ovate, and (in many speci- mens) with a continuous lip; outer lip thin and convex; inner lip broad, reflected over the umbilicus, curved or straight, and typically without a columella plait. Umbili- cus narrow but distinct in most specimens. Periostracum light brown to black. Sculp- ture consisting of coarse collabral lines and growth rests and less distinct spiral lines. Resembles S', elodes but may be distin- guished by its more rotund body whorl, rounder aperture, more sharply acute and pinched spire, and more rapidly enlarging whorls. The two taxa are closely related, however, and may be only subspecifically distinct. DISTRIBUTION In the Rocky Mountains from British Columbia and Alberta south to California. ECOLOGY A montane species. Occurs in lakes, ponds, streams, and roadside ditches. Lives on various substrates. The radula formula is 31-1-30 to 36-1-35 and the lateral teeth are bicuspid. The nominate subspecies rowelli appears not to be valid. 146 49 Stagnicola proximo. a: Maligne L., Jasper National Park, Alta.; 9.7 mm. b: Pond, Banff, Alta.; 15.2 mm. c: Pond, Banff, Alta.; 11.2 mm. 50 Stagnicola ( Stagnicola ) reflexa (Say, 1821) Striped Stagnicola DESCRIPTION Shell up to about 35 mm high, 12 mm wide, with 7 whorls and with aperture height of most specimens about 44% to 50% of shell height, lymnaeiform, dextral, slender, and with flat-sided whorls. Nuclear whorls about 1-1/2 in number, turreted and satiny. Spire long, with slightly convex sides; spire angle about 25° to 30°. Sutures impressed. Last 2 or 3 whorls much elongated. Aperture long; outer lip sharp and thin but thickened internally by a brownish or reddish varix; inner lip narrow and reflected over the umbilicus and obscuring it com- pletely or leaving only a small chink. Columella oblique and in adult specimens with a spiral plait. Surface light to dark brown, with (typically) or without alternat- ing zebra-like dark and light collabral bands, and with numerous collabral ridges and spiral grooves. Resembles S. elodes but may be distin- guished by its narrower form, more-elongate later whorls, and in many populations by its zebra-like dark and light bands. DISTRIBUTION Scattered areas in the southern and south- western parts of the Canadian Interior Basin, the Great Lakes- St. Lawrence system throughout, and the upper Ohio- Mississippi drainage area south to about 37°N. ECOLOGY Occurs among vegetation in a variety of perennial-water and vernal habitats, namely lakes, ponds, sheltered areas of streams, swamps, and ditches. The usual substrate is mud. The radula has about 40 lateral plus marginal teeth on each side of each central tooth. Stagnicola reflexa is considered by some authors as a morphological variant of 5. elodes (Say). 148 50 Stagnicola reflexa a: L, Superieur near Grand-Metis, Que.; 34.5 mm. b: Pond near Starr L., Whiteshell Provincial Park, Man,; 23.0 mm. c: Chippawa, Welland Co., Ont.; 19.7 mm. 149 VII Superfamily Physacea FAMILY PHYSIDAE (Tadpole Snails) Shell small to medium-sized, sinistral (coiled to the left), mainly thin-shelled, with an elevated spire, with or without an umbilicus and without an operculum. Tentacles slender and cylindrical, and foot narrow. The mantle in Physa has numerous finger-like extensions that project from the aperture over both sides of the shell. Jaw single, and radula with teeth arranged in V-shaped rows. Many multicuspid lateral and marginal teeth are on each side of the wide, multicuspid central tooth. Monoecious and capable of cross- or self-fertilization. Egg masses gelatinous, transparent, whitish, and crescent-shaped. The family is worldwide. 151 51 Physa gyrina gyrina Say, 1821 Tadpole Snail DESCRIPTION Shell up to about 24 mm high, 16 mm wide, with 5-1/2 whorls (most specimens are much smaller) and with aperture 60% to 80% of shell height, sinistral, variable in form, thin to slightly thickened, and more or less transparent. Spire acute and of medium length. Nuclear whorl small, rounded, finely punctate, and generally red to reddish brown. Whorls gendy rounded and loosely coiled, that is overlapping the previous whorl only to a line that is below, or at the periphery of, that whorl. Sutures impressed and bordered below by a narrow pale band. Body whorl large and well rounded but not strongly inflated. Aperture loop-shaped, mainly basal, acute above, flady rounded laterally, and rounded ba sally. Outer lip thin to slighdy thickened, and bordered inside by a prominent red or reddish collabral band. Columella oblique, thin to slightly thickened, and with an extensive wash of callus on the parietal wall. Narrowly umbili- cate or non-umbilicate. Periostracum pale yellowish brown to greyish brown and with a dull surface. Sculpture consists of numer- ous coarse lines of growth; in some speci- mens, one or more internal varices are visible externally as whitish collabral bands; and, in most populations, crowded, im- pressed spiral lines cross the growth lines. Well characterized by its small, acute, and reddish apex; inflated whorls; and medium- sized, rather thin shell. In Canada its closest relatives are P. heterostropha and P. john- soni ; compare with these. P. vinosa Gould, 1847, from Lake Superior appears to be a thick-shelled ecologically induced variant of P. gyrina . DISTRIBUTION Quebec west within the tree line to the northwestern Northwest Territories, Alaska and British Columbia. South in the central and western United States to the Gulf of Mexico and California. ECOLOGY Abundant. Occurs in almost all perennial- water habitats and in temporarily flooded pools and swamps. Often abundant in mildly polluted water bodies; in fact, where it occurs alone and in abundance, it is indicative of organic pollution. Egg deposi- tion occurs principally in the spring. The animal moves quite rapidly. 152 51 Physa gyrina gyrina a: Montreal R. near Montreal L., Sask.; 18,7 mm. b: Pond near Nevis, Alta.; 19.7 mm. c: L. de Montigny near Val-d f Or, Que,; 1 1.7 mm. d: Macamic L. near La Sarre, Que.; 13.0 mm. 153 52 Physa gyrina latchfordi (Baker, 1928) Gatineau Tadpole Snail DESCRIPTION Shell up to about 26 mm high, 20 mm wide, with 6-1/2 whorls and with aperture about 74% to 82% of shell height, sinistral, variable in form, slightly thickened, trans- lucent, and shouldered. Spire obtuse, short, and with concave sides. Nuclear whorl small, reddish, and forming a sharp apex. Spire whorls flatly rounded and separated by lightly impressed sutures. Body whorl roundly but conspicuously shouldered, tab- ulate above, and flatly rounded below. Aperture ovate-quadrate and wider below but also rather wide above. Outer lip thin and fragile. Columella vertical, somewhat thickened, and straight or somewhat curved. No umbilicus. Periostracum yellowish brown to brown and with a shiny surface. Sculpture consists of fine collabral threads and ridges and finer spiral rows of punctae. Distinguished by its large, wide, and strikingly shouldered shell. Intergrades oc- cur with P. g . gyrina ; compare with that subspecies. DISTRIBUTION Has been found in Meach Lake (the type locality) and Pink Lake in the Gatineau River system of western Quebec. Inter- grades with P. g. gyrina occur in Lac Lapeche and Lac Philippe, two other lakes in the same river system. ECOLOGY Lives on gravel bottoms in wave -exposed areas of large lakes. Its radula is similar to that ofP. g. gyrina except that the central tooth appears to have about 2 additional cusps. Nothing else is known about its biology or anatomy. 154 155 53 Physa heterostropha (Say, 1816) Eastern Physa DESCRIPTION Shell up to about 21 mm high, 18 mm wide, with 6 whorls (most specimens are much smaller) and with aperture about 67% to 82% of shell height, sinistral, variable in form, thin to slightly thickened, and translu- cent to opaque. Spire obtuse and short. Apex decollated in most specimens, but when visible the nuclear whorl is small, rounded, finely punctate, and generally red to reddish brown. Whorls rounded or shouldered and tightly coiled, that is over- lapping the previous whorl to a line that is above the periphery of that whorl. Sutures impressed and bordered below by a narrow pale band. Body whorl large and well rounded and roundly shouldered in many specimens. Aperture loop-shaped, mainly basal, acute above, rounded laterally, and sharply rounded ba sally. Outer lip thin to slightly thickened, and bordered inside by a prominent red or reddish collabral band. Columella somewhat oblique, thin to slightly thickened, and with an extensive callus on the parietal wall. No umbilicus. Periostracum pale yellowish brown to grey- ish brown, and with a shiny surface. Sculpture consists of numerous coarse lines of growth and in a few populations also of crowded, impressed spiral lines crossing the growth lines. Similar toP. gyrina and, in fact, both names may turn out to apply to the same species. Typical P. heterostropha differs from P. gyrina in being more tightly coiled and in having a lower spire, a somewhat shouldered body whorl, weaker (or absent) spiral sculpturing, and shiny periostracum. DISTRIBUTION Atlantic Provinces of Canada south at least to New Jersey and Pennsylvania, and perhaps farther south. Its taxonomic rela- tionships need to be clarified. ECOLOGY Very common. LikeP. gyrina , occurs in all kinds of perennial-water and temporarily flooded habitats, usually among vegetation. 156 53 Physa heterostropha a,b: Caribou Stream, Aroostook Co., Maine; a 13.6 mm, b 12.1 mm. 157 54 Physa integra Haldeman, 1841 Solid Lake Physa DESCRIPTION Shell up to about 1 5 mm high, 9 mm wide, with 5 whorls (most specimens are smaller) and with aperture about 57% to 73% of shell height, sinistral, variable in form, noticeably thickened, and opaque. Spire acute and rather short. Nuclear whorl small, rounded, finely punctate, and brown. Whorls gently rounded and loosely coiled, each overlap- ping the preceding whorl up to a line that is at, or below, the periphery. Sutures im- pressed. Body whorl large, well rounded, and somewhat shouldered in some speci- mens. Aperture ear-shaped, acute above, gently rounded laterally, and becoming sharply rounded basally. Outer lip thickened within by a heavy white callus (also clearly visible externally) and bordered inside by a brownish collabral band. Several whitish bands representing previous growth stages may be visible through the shell. Columella thickened and reflected over the umbilical region or forming a wide, flat expansion. No umbilicus. Periostracum yellowish brown to white, and with a dull to somewhat shiny surface. Sculpture consists of coarse lines of growth, whitish collabral bands, and (in some specimens) fine spiral lines. Shells ofP. integra are thicker and heavier than shells of other species; they have prominent white collabral bands and a thick, flattened inner lip. DISTRIBUTION Throughout the Great Lakes- St. Lawrence and Ohio -Mississippi systems. ECOLOGY Found in rather shallow water in lakes (but deeper thanP. gyrina) in either exposed or protected situations, and on clay, mud, sand, or rocky bottoms. The male genitalia are distinctive (see Te 1975). The radula formula is approximately 130-1-130. 158 54 Physa Integra a: St. Lawrence R., Cornwall, Ont.; 1 1.6 mm. b: Mohawk, N.Y.; 14.3 mm. 159 55 Physa jennessi jennessi Dali, 1919 Blunt Arctic Physa DESCRIPTION Shell up to about 9 min high, 5 mm wide, with 5 whorls (most specimens are some- what smaller) and with aperture 60% to 75% of shell height, sinistral, thin, and transpar- ent. Spire acute and short with a rounded apex. Nuclear whorl large, rounded, and of the same colour as later whorls. Whorls gently rounded, the early whorls partly enveloping the preceding whorl up to a line located above the periphery, later whorls enveloping to the periphery. Spire whorls not misshapen or pulled up. Sutures shal- lowly impressed and bordered below by a narrow pale band. Body whorl dominant, disproportionately enlarged, roundly shoul- dered above, flattened laterally, sharply rounded basally, and constituting about 5/6 to 7/8 of the shell length. Aperture ear- shaped, mainly basal, acute above, flatly rounded laterally, and rounded basally. Outer lip thin and with or without a brownish collabral band within the aper- ture. In some specimens, broad white collabral streaks mark previous growth rests. Parietal wall covered by a rather prominent and extensive but thin callus. No umbilicus. Periostracum pale yellowish brown to greyish brown and with a shiny surface. Sculpture consists principally of collabral striae and prominent growth rests. Differs from P. j, skinneri principally in that the penultimate and/or first pre-penulti- mate whorl is not disproportionately pulled up, while in P. j. skinneri that character is pronounced. The parietal callus in P. j, jennessi is also thicker and more prominent. DISTRIBUTION Known from localities close to Hudson Bay and James Bay and throughout the area between Hudson Bay and the northern Yukon Territory. Probably also occurs in Alaska. ECOLOGY An arctic species. Found in small lakes, ponds, woodland pools, muskeg pools, small pools on top of flat boulders, and slow-flowing streams. Vegetation present in some habitats but absent in others; sub- strates are rocks or mud. Its reproduction has not been investigated. The radula is similar to that of P.j. skinneri. 160 55 Physa jennessi jennessi a,b: Creek, Bernard Harbour, N.W.T.; a 8.0 mm, b 7.0 mm (paratypes). c: Pool, Churchill, Man.; 8.4 mm. 161 56 Physa jennessi atheami Clarke, 1973 Blunt Albino Physa DESCRIPTION Shell up to about 7 mm high, 5 mm wide, with 4 whorls and with aperture 71% to 94% of shell height, sinistral, variable in form, subglobose, thin, and transparent. Nuclear whorl large, rounded, about 0.7 mm wide, elevated well above second whorl, and of the same colour as later whorls. Spire short, about 1/6 the length of the shell, acute to slightly obtuse, with the first 3 whorls enlarging evenly, flatly rounded, and sepa- rated by impressed sutures. Sutures bor- dered below by a narrow paler band. Body whorl capacious, inflated, dominant, roundly shouldered above, and flattened centrally, giving the shell a characteristic but misshapen appearance. Aperture large, pendulous, acute above, flattened laterally, and broadly rounded below. Columella sigmoid (broadly S-shaped) and parietal callus narrow above and broader below. Umbilicus entirely absent or indicated by a tiny slit. Periostracum pale yellowish white and with a shiny surface. Sculpture consist- ing of fine crowded collabral lines and wrinkles and, on some specimens, a single whitish narrow growth rest on the body whorl. Impressed, microscopic spiral lines that cross and interrupt the collabral wrin- kles also occur on some specimens. Differs from both/ 5 ,/, jennessi and P. j. skinneri in its broader, more capacious body whorl and the whitish colour of its shell and soft parts. Also differs from P. j. skinneri in its shorter, more regular spire and the fewer and smaller finger-like projections on the mantle. DISTRIBUTION Small lakes in the Banff- Jasper region of the Rocky Mountains and in the upper Athabasca River system downstream from Jasper. ECOLOGY Has been recorded only from medium-sized and small lakes, and in marshes with open water. Bottom deposits are rock and gravel. The soft parts of all specimens are predomi- nantly or wholly whitish. The radulae of specimens 6.5 mm long are about 1.5 mm in length; they have 67 to 75 rows of teeth with about 230 to 330 teeth in each row. 162 56 Physa jennessi a the arm a,b: Horseshoe L, near Jasper, Alta.; a 7.8 mm, b 5.8 mm (paratypes). c: Marsh near Rochester, Alta.; 5.2 mm. 163 57 Physa jennessi skinneri Taylor, 1953 Blunt Prairie Physa DESCRIPTION Shell up to about 12 mm high, 6.5 mm wide, with 5-1/3 whorls (most specimens are somewhat smaller) and with aperture about 61% to 78% of shell height, sinistral, thin, and translucent. Nuclear whorl large, rounded, finely punctate, and brown. Spire rounded and unusual, appearing peculiarly pinched and pulled-up, with the penulti- mate whorl, or the next preceding whorl, or both, markedly attenuate, that is much less enveloped by the succeeding whorl than are the earlier whorls and therefore more exposed. Body whorl dominant, dispropor- tionately enlarged, shouldered above, flat- tened laterally, rather sharply rounded be- low, and constituting about 5/6 of the shell length. Aperture ear-shaped and mainly basal. Outer lip broadly curved laterally and characteristically arched centrally when viewed from the outer side. Suture weakly impressed. Parietal wall covered with a thin callus. No umbilicus. Periostracum pale yellowish brown to greyish brown and with a moderately shiny surface. Sculpture consists of collabral and spiral striae and well-marked growth rests. The large nuclear whorl, blunt apex, and flattened body whorl distinguish P. jennessi and its subspecies from theP, gyrina- P . heterostropha complex. The elevated penultimate or first pre-penultimate whorl will differentiate P. j. skinneri from the arctic P. j. jennessi, with which it should be compared. DISTRIBUTION Southern Canada and northern United States from Ontario northwest to the vicin- ity of Great Slave Lake, west to British Columbia, and south to Utah. ECOLOGY Occurs in lakes, ponds, marshes, and slow- moving streams of all widths. Both vernal or perennial habitats are utilized. Found prin- cipally on muddy bottoms among thick or moderately thick aquatic vegetation. Recorded from depths of less than 1 m to nearly 5 m. The radula of a specimen 1 1.3 mm tall is 2.2 mm long and bears 71 rows of teeth with up to about 230 teeth in each row. 164 b 57 Physa jennessi skinneri a: Lake near Banff, Alta.; 8.4 mm. b: Dease L., northern B.C.; 9.7 mm. c: Lake near Calgary, Alta.; 8,1 mm. d: Lydia L. near Longlac, Ont.; 3.7 mm (juvenile). 165 58 Physa johnsoni Clench, 1926 Banff Springs Physa DESCRIPTION Shell up to about 9 mm high, 5 mm wide, with 4.8 whorls (most specimens are smaller) and with aperture 63% to 72% of shell height, sinistral, variable in form, thin, globose, and nearly opaque. Spire short and acute. Nuclear whorl small, rounded, and dark reddish brown. Whorls gently rounded and loosely coiled, each partly enveloping the preceding whorl to a line located at, or below, the periphery. Sutures well impressed and bordered below by a narrow pale band. Body whorl dominant, well rounded, and roundly shouldered. Aperture ear-shaped, mainly basal, acute above, flatly rounded laterally, and rounded and flared basally. Outer lip thin and without an internal dark band. Columella oblique, slightly thickened, and not termi- nating abruptly but continuing into the outer lip. Parietal callus very thin and not extensive. No umbilicus. Periostracum pale yellowish brown to reddish brown and with a shining surface. Sculpture consists of numerous collabral lines and in abraded specimens of irregular white collabral and spiral bands. Differs from P. gyrina by its small size, lack of fine spiral striae on unabraded specimens, prominent white spiral streaks on abraded specimens, and general appear- ance. Quite distinct from P. j. skinneri as indicated by characters of the nuclear whorl, spire, and body whorl. DISTRIBUTION Known only from several localities in Banff National Park, Alberta. ECOLOGY Occurs in warm 33°C (92°F) and cold springs. Substrates are rocks and gravel with algae and moss. The radulae of two spec- imens, 7.6 and 6.2 mm high, were both 1.7 mm long; respectively they bore 61 and 60 rows of teeth, with about 2 10 and 205 teeth in each full row. 166 167 59-64 Supplementary Western Physa Species Six additional species of Physa have recently been identified from our British Columbia material by Mr. George Te at the University of Michigan; he is preparing a detailed revision of the Physidae. These species are differentiated and grouped principally on anatomical features, but useful shell charac- ters also exist. 59. Physa columbiana Hemphill, 1890 (Columbia River Physa), is medium-sized, up to 15 mm high, 8 mm wide, thin to moder- ately heavy, with a well-marked parietal callus, flatly rounded whorls and a shiny surface. Distribution restricted to the Columbia River system. Its penial complex is similar to that of two other nominate western species, P. hordacea Lea andP. lordi Baird. 60. Physa concolor Haldeman, 1843 (Halde- man’s Physa), is typically rather small, 7 mm high, 4.5 mm wide, 4-1/2 whorls, thin-shelled, with an extended spire, rounded whorls, and shiny surface. Has been collected near Cres- ton, British Columbia, and in Washington and Oregon. Similar to P. Integra Haldeman in shell characters and penial anatomy. 61. Physa hordacea Lea, 1864 (Vancouver Island Physa), is small, about 8 mm high, 4.5 mm wide, 4-1/4 whorls, subcylindrical, with a large nuclear whorl, blunt apex, flatly rounded spire whorls, rather narrow aperture, and shiny surface. Has been included in Aplexa by previous authors, but exhibits a few columellar mantle digitations, a character that is in accordance with placement in Physa rather than Aplexa. Apparendy endemic to Vancouver Island. 62. Physa lordi Baird, 1863 (Giant Western Physa), is large, 26 mm high, 19 mm wide, thin-shelled, roundly inflated, with a pointed low spire with concave sides, an unshouldered body whorl, and a large aperture that is wider below but still rather wide above. Resembles P. gyrina latchfordi except that subspecies has a rather heavy shell and strongly shouldered whorls. Found from northern British Colum- bia (Peace River system) south to the west- central United States. P. virginea Gould is tentatively considered a synonym. 168 59 Physa columbiana Christina L. near Grand Forks, B.C.; 6.6 mm. 60 Physa concolor Moses L., Grant Co., Wash.; 8,2 mm. 61 Physa hordacea Long L., Nanaimo, B.C.; 5.8 mm. 62 Physa Iordi a: Typical lordi : Vaseux L. near Okanagan Falls, B.C.; 1 1.9 mm. b: Morph virginea : Anderson L., Jefferson Co,, Wash,; 18.4 mm. 169 63. Physa nuttalli Lea, 1864 (Nuttall’s Physa), is medium-sized, 12 mm high, 7 mm wide, 4-1/2 whorls, rather thin-shelled, with a large nuclear whorl, a medium-length taper- ing spire, flatly rounded whorls, an aperture that is wide below and narrow above, a heavy parietal callus, and with or without a brown- ish band within the outer lip. Occurs in ponds and ditches from southern British Columbia (near the Columbia River) to California. The penial complexes ofP. nuttalli andP. pro- pinqua are similar. 64. Physa propinqua Tryon, 1865 (Western Lake Physa), is rather large, 19 mm high, 1 3 mm wide, 5- 1 /2 whorls, thin-shelled, with a medium-length tapering spire, flatly rounded whorls, well-marked growth rests, a narrow and thin parietal callus, an aperture of medium width that is wider below, and with a brown band within the outer lip. Principally a lake species. Occurs on Vancouver Island and throughout central and southern British Columbia south to California. 170 63 Physa nuttalli a,b: Pond near Randle, Lewis Co., Wash.; a 10.6 mm, b 10.4 mm. 64 Physa propinqua Upper Klamath L., Oreg.; 1 1.3 mm. 171 65 Aplexa hypnorum (Linnaeus, 1758) Polished Tadpole Snail DESCRIPTION Shell up to about 18 mm high, 7.5 mm wide, with 7 whorls and with aperture 50% to 60% of shell height, sinistral, elongate, thin, and transparent Nuclear whorl rounded, finely punctate, and amber-col- oured. Whorls flatly rounded and relatively tall, each partly enveloping the preceding whorl up to a line located at the periphery of that whorl. Spire elongate and constituting about 1 /3 of the shell length. Sutures impressed and bordered below by a narrow white band. Body whorl flatly rounded and sub-cylindrical. Aperture acute above, rounded laterally, and flatly rounded below. Outer lip thin, flatly rounded, and only slightly thickened within. Columella oblique, narrow, slightly twisted, and with a very thin callus on the parietal wall. No umbilicus. Periostracum polished, thin, brownish (appearing blackish when con- taining the soft parts), and often exhibiting a greenish glint. Sculpture consists of fine lines of growth and (in some specimens, especially from arctic localities) fine spiral lines. The long, narrow, sinistral form, polished and blackish surface (when alive), and lack of mantle digitations are characters that serve to identify this species positively. DISTRIBUTION New England to the District of Columbia; north to the Gulf of St. Lawrence and James Bay and across the subarctic to Victoria Island, Banks Island and arctic Alaska; and west to the Cascade Mountains. Also occurs in Europe and northern Asia. ECOLOGY Lives principally in vernal habitats, i.e. water bodies that dry up during parts of the year. Often very abundant in temporary shallow pools during the spring. Also found, but rarely, in large permanent rivers and lakes. Most occupied habitats have thick vegetation and a mud bottom. Adult specimens have about 350 teeth in each full radula row. Unlike Physa, there are no finger-like projections on the edge of the mantle. 172 65 Aplexa hypnorum a,b: Gatineau R., Pointe-Gatineau, Que,;a 16,0 mm, b 15.0 mm. c: Pond near Rocky Mountain House, Alta.; 1 1.0 mm. 173 VIII Superfamily Planorbacea FAMILY PLANORBIDAE (Ramshorn Snails) Shells small to moderately large, dextral or sinistral, flatly coiled in most species and with a very low spire in a few, umbilicus present, and operculum absent. Tentacles long, slender, and cylindrical. An accessory breathing organ, the pseudobranch, is present and functions as a gill when atmospheric air is not available. Jaw in 3 or many segments, and radula with teeth arranged in nearly horizontal rows. About 10 to 40 tricuspid to multicuspid lateral plus marginal teeth are on either side of the small bi-, tri-, or tetracuspid central tooth. Monoecious and able to cross- or self-fertilize. Egg masses gelatinous, transparent, colourless, sausage-shaped, and with numerous yellow eggs. The family is worldwide and some tropical species are intermedi- ate hosts for blood parasites of mammals, including man. 175 66 Gyraulus circumstriatus (Tryon, 1866) Flatly Coiled Gyraulus DESCRIPTION Shell up to about 5 mm wide, 1.5 mm high, with 4 whorls, planospiral, dextral, semi- transparent, and showing the soft parts within. All whorls are visible in both apical and umbilical views, and, except for the tipped-down (prosocline) aperture and colla- bral sculpturing, the apical and umbilical views are very similar. Whorls laterally rounded, increasing in size slowly and with outermost edge near centre. Aperture ovate, with a thin outer lip and lacking a parietal callus. Periostracum pale brown or whitish, smooth, and shiny. Sculpture consisting of fine spiral striae (in most specimens, especially on the base), collabral striae, and lines of growth. Distinguished by being planospiral and semi-transparent and in having slowly in- creasing whorls and (typically) spiral striae. Compare with G. parvus. DISTRIBUTION Prince Edward Island to New England, west in the Great Lakes- St. Lawrence system, northwest to northern Alberta and British Columbia, and south in the Rocky Mountains to New Mexico. ECOLOGY Characteristic of small vernal habitats such as woodland pools, marshes, roadside ditches, prairie ponds, and intermittent streams. Vegetation is ordinarily thick, and substrates are commonly mud. Radula formulae of 14-1-13 to 16-1-16 have been recorded. 176 66 Gyraulus circumstriatus a,b,c: Pond near North Portal, Sask.; 3.7 mm. d,e,f: Another specimen, same locality; 3. 1 mm. 177 67 Gyraulus deflectus (Say, 1824) Irregular Gyraulus DESCRIPTION Shell up to about 8 mm wide, 3 mm high, with 4-1/2 slowly enlarging whorls, planor- boid, dextral, highly variable in form and sculpturing, and with any combination of hairy periostracum, a peripheral keel, or surface malleations. In specimens without such surface sculpturing the outer edge of the body whorl is below' the midline. Apical whorls submersed. Aperture suboval, angled above, expanded at the outer edge in keeled specimens, and inclined down- ward. Inner lip with a thin callus. In many specimens the body whorl is also deflected downward near the aperture. Umbilicus wide, deep, and showing all whorls. Perios- tracum pale to dark brown and usually hirsute, that is covered with hair-like projec- tions arranged in spiral rows parallel to the sutures. Non-hirsute specimens are spirally striate. This small species may be distinguished from other species of Gyraulus by its size (it is the largest species of the genus, especially east of the Rocky Mountains), its keeled, malleated, or hirsute surface (or, if these features are absent, by the relatively low placement of the outermost edge), and by the contrasting appearance of its upper and lower surfaces. Compare with other species of Gyraulus. DISTRIBUTION Occurs throughout mainland Canada north to the central arctic, throughout Alaska, and south in the United States to Virginia and Nebraska. ECOLOGY Occurs in all kinds of permanent-water, eutrophic habitats. The usual substrate is mud. Commonly lives on vegetation but is occasionally found on the bottom. Egg capsules are small, gelatinous, and often contain 2 to 5 eggs. Observed radula formulae are between 15-1-15 and 19-1-18. Locomotion is rather rapid. 178 67 Gyraulus deflectus a,b,c: Neddy Harbour Pond, Bonne Bay, Nfld,; 4.0 mm. d,e,f: Ennadai L., N.W.T.; 6.3 mm. g,h,i: Long L., Longlac, Ont.; 5.5 mm. 179 68 Gyraulus parvus (Say, 1817) Modest Gyraulus DESCRIPTION Shell up to about 5 mm wide, 2 mm high, with 4 whorls, dextral, depressed but not entirely flat, and with rounded, rapidly increasing whorls. Body whorl rounded and periphery near centre. Spire flattened and first 2 whorls immersed. Aperture proso- cline, ovate, in the same plane as the body whorl or somewhat below it, and with a thin rounded outer lip and a thin parietal callus. Umbilicus wide, shallow, and exhibiting all whorls. Periostracum smooth and glossy, pale brown to dark brown, and not hairy. Sculpture not prominent but limited to fine collabral striae and growth rests. This small species may be recognized chiefly by the absence of characters that would assign it to other species, that is to G. circumstriatus or G, deflectus. It is not flatly coiled and semi-transparent, and the upper and lower aspects are clearly different. It also lacks a keel, malleations, or hirsute periostracum, and the outermost edge is near the centre of the body whorl. DISTRIBUTION Occurs throughout Canada and the United States south of the tree line. Also reported from Cuba and (questionably) from northern Eurasia. ECOLOGY An abundant species. Lives on submersed aquatic vegetation in all kinds of permanent or temporary water-filled habitats that sup- port vegetation. Bottom most frequently muddy. Radula formulae vary from 13-1-13 to 17-1-17. ISO 68 Gyraulus parvus a,b,c: Peace R. near Point Providence, Alta.; 4. 1 mm. d,e,f: Herben L. near Lake Louise, Alta.; 4.7 mm. 181 69 Gyraulus vermicularis (Gould, 1847) Pacific Coast Gyraulus DESCRIPTION Shell up to about 7 mm wide, 2.5 mm high, with about 4 slowly enlarging whorls, planorboid, dextral, and with nearly cylin- drical whorls. The outermost edge of the body whorl is at the midline. Apical whorls submersed. Near the aperture the body whorl is deflected downward. Aperture elliptical and strongly slanted downward; inner lip with a thin callus. Umbilicus wide, shallow, and showing all whorls. Perios- tracum smooth and pale brown. Sculpture consists of low spiral threads and cords, fine crowded collabral lines, and a few irregu- larly spaced growth rests. Resembles G. deflectus , but differs in having more cylindrical whorls and in lacking heavy malleations, a peripheral keel, or hairy periostracum. The upper and lower views are also more similar to each other than in G. deflectus. DISTRIBUTION Occurs in the Pacific coastal drainage from Alaska to California. ECOLOGY Lives in various kinds of perennial and vernal eutrophic habitats (lakes, ponds, sloughs, ditches, rivers, and creeks). Occurs most frequently among vegetation. Nothing has been published regarding its anatomy or life history. 182 69 Gyraulus vermicularis a,b,c: Upper Columbia L., B.C.; 6.9 mm. d,e,f: Another specimen, same locality; 7.0 mm. 183 70 Armiger crista (Linnaeus, 1758) Tiny Nautilus Snail DESCRIPTION Shell minute, up to about 3 mm wide, 1 mm high, with 2-1/2 whorls, dextral, thin, depressed, with a complete lip, and (in most specimens) with many prominent triangular blade-like ridges. Ridges especially elevated at the shoulder of each whorl, inclined forward, oriented parallel to lines of growth, and numbering about 12 to 18 on the body whorl. Spire flattened and sutures im- pressed. Whorls increasing rapidly in diam- eter, flattened above, rounded below, and sharply rounded at the outermost edge, which is located at the shoulder. Umbilicus wide, deep, and exhibiting all the whorls. Periostracum pale brown. In fossil speci- mens the periostracum is absent, and only nodular projections of the shell material are visible. Sculpture, in addition to the ridges, consisting of very fine spiral lines. Loose and partly detached coiling occurs in some specimens. This tiny species is easily recognized by its prominent ridges, characteristic shape, and lip that surrounds the aperture. DISTRIBUTION Holarctic. Recorded from scattered locali- ties in Canada from southern Ontario to Alberta and the Northwest Territories, and in the United States from Maine to Minne- sota and Alaska. Also occurs in Europe, northern Asia, and North Africa. ECOLOGY Lives among dense vegetation in eutrophic ponds and slow-moving streams. The egg capsules are about 1.5 mm in diameter and contain 3 to 6 eggs. Radula formulae of 11-1-11 to 16-1-16 have been reported. 184 70 Armiger crista a,b,c; Rideau R., Ottawa, Ont.; 1.5 mm. d,e,f: L, Manitoba, Man.; 1.8 mm. g,h,i: Marean L., northeast of Little Quill L., Sask.; 1.9 mm. 185 71 Promenetus exacuous exacuous (Say, 1821) Keeled Promenetus DESCRIPTION Shell up to 7 mm wide (most specimens are 6 mm wide or less), 2 mm high, with almost 4 whorls, planorbiform, biconvex, dextral, and with the outermost edge of the body whorl centrally located and prominently keeled. In most specimens the keel is sharp but in some it is rounded. Whorls expanding rapidly, broadly convex above and below, angled on the outer edge, and wider than high. Spire low, convex, or flattened. Base of aperture s trongly slanted inward, almost triangular or ovate, and expanded at the outer edge. Outer lip thin to slightly thickened and inner lip with a thin callus. Umbilicus rather narrow, extending to the apex, and exhibiting all the whorls, Perios- tracum pale to dark brown. Collabral sculpture consisting of crowded threads and widely spaced growth rests. Easily distinguishable from other species by its biconvex, flattened form, its promi- nent peripheral keel, its wide and strongly prosocline aperture, and its rapidly expand- ing whorls. Compare with/ 3 , e. megas. DISTRIBUTION Occurs throughout Canada south of the tree line except in Newfoundland, Labrador and subarctic Quebec. Also found in Alaska and in other parts of the United States east of the Rocky Mountains but its precise limits there are unknown. In the western prairies of Canada, it is replaced in most (but not in all) localities by P. e, megas. ECOLOGY A common species. Lives in various kinds of temporary-water and permanent-water habitats, that is large and small lakes, ponds, streams of various widths, roadside ditches, and swamps. Submersed vegetation is al- ways present and the usual substrate is mud. Radula formulae of 16-1-16 to 18-1-18 have been recorded. 186 187 72 Promenetus exacuous megas (Dali, 1905) Broad Promenetus DESCRIPTION Similar to P. exacuous exacuous but its shell is larger (6-9 mm wide), heavier, and has a more prominent, pinched peripheral keel. In fresh or alcohol-preserved specimens the periostracum extends beyond the keel in a blade-like lamina. Spiral sculpture is also more apparent inP. e. megas, and (in many specimens) the periphery is low, causing the upper surface to be domelike and the lower to be nearly flat. The most reliable distin- guishing character, however, is gigantism. DISTRIBUTION Typically a western prairie subspecies. Occurs from eastern Manitoba to British Columbia and in adjacent parts of the United States, Its southern limits have not been determined. ECOLOGY Found in lakes, ponds, streams of various widths, roadside ditches, and swamps. Most abundant where vegetation is thick and the substrate is mud. The radula formula of an Alberta specimen, 5.6 mm wide, is 17-1-17. 1S8 72 Promenetus exacuous megas a,b,c: Leith R. near Whitelaw, Alta,; 8,2 mm. d,e,f; Another specimen, same locality; 7.0 mm. 189 73 Promenetus umbilicatellus (Cockerell, 1887) Umbilicate Promenetus DESCRIPTION Shell up to about 5 mm wide, 2 mm high, with 4 whorls, planorbiform, depressed, and dextral. Spire flattened or with the first 2 whorls slightly immersed. Whorls increas- ing with moderate rapidity and with regular- ity but somewhat expanded near the aper- ture. Sutures impressed. Base of body whorl flatly rounded. Aperture prosocline and roundly convex except at the inner wall, where it is abruptly concave and has a thin callus. Umbilicus prominent, wide, deep, and exhibiting all whorls. Sculpture con- sisting of fine collabral lines and fine revolving striae. Distinguished by its small size, rounded whorls, and prominent, deep umbilicus. Compare with Planorbula campestris. DISTRIBUTION A western species, collected in prairie localities from southern Manitoba to central Alberta and southern British Columbia, In the United States it ranges south in the American Interior Basin to New Mexico. ECOLOGY Rather uncommon. Occurs in vernal ponds, marshes, and springtime flooded margins of intermittent streams. Associated with dense vegetation and mud bottoms. Radula formulae of 17-1-17 and 18-1-18 have been seen. 190 73 Promenetus umbilicatellus a,b>c: Lake near Galahad, Alta.; 4.0 mm. d,e,f: Another specimen, same locality; 5,6 mm. 191 74 Menetus cooperi Baker, 1945 British Columbia Menetus DESCRIPTION Shell small, up to about 8 mm wide, 3 mm high, with 4 whorls, dextral, flattened apically, convex basally, and with a carina or keel at the shoulder of the body whorl. Apical whorls somewhat immersed. Whorls expanding rapidly and separated by shallow sutures. Body whorl with a rounded angula- tion at the shoulder or with a carina at the shoulder that, in different populations, may be either poorly developed or prominent. Aperture prosocline, wider than high, with a thin lip and a callus deposit on the inner wall. Umbilicus broad, with a rounded angulation bounding it and exhibiting all of the whorls. Periostracum pale to dark brown, and dull to somewhat glossy. Fine sculpturing consists of crowded delicate collabral lines. Resembles Promenetus exacuous , but in that species the carina is located medially on the side of the whorl, or lower, not at the shoulder. Several subspecies of M. cooperi and other closely related “species” have been described but require evaluation. Al- berta specimens are strongly carinate, while those from coastal British Columbia locali- ties are roundly carinate. DISTRIBUTION Occurs from northern California to south- ern Alaska and east to central Alberta. In the northern part of its range it is restricted to localities near the coast. ECOLOGY Found among submersed vegetation in perennial-water lakes, ponds, and slow- moving portions of rivers and streams. The radula formula is about 20-1-20. 192 193 75 Planorbula armigera (Say, 1821) Say’s Toothed Planorbid DESCRIPTION Shell up to about 8 mm wide, 3 mm high, with 5 whorls, planorbiform, dextral, and ordinarily with 1 set of 6 tooth-like pro- cesses deep within the aperture. Spire con- cave. Whorls rounded except obscurely carinate above and below and slowly ex- panding. Last part of body whorl expanded and abruptly deflected downward. Aperture ovate and inclined backward toward the base. Denticles located within the aperture about 1/4 whorl back and visible through the aperture and, in cleaned shells, through the shell wall. Rarely, a second set of 6 den- ticles is located behind the first. Umbilicus wide, deep, funnel-shaped, and showing all whorls. Periostracum pale brown to blackish. Sculpture consisting of fine lines of growth and microscopic spiral striae. This medium-sized species (larger than most Gyraulus andPromenetus but smaller than Helisoma) may be easily identified by the presence of at least 1 set of 6 well- developed denticles deep within the aper- ture. In the western species Planorbula campestris, only juvenile specimens bear denticles and each set has 5 processes; the adult is also much larger. DISTRIBUTION In Canada this species occurs from New Brunswick to southeastern Ontario and thence northwest to the vicinity of western James Bay and beyond, within the tree line, to the north-central part of the Mackenzie River system. Also occurs in the Prairies and south in the eastern and central United States to Georgia and Louisiana. P,jenksii (Carpenter, 1871) is a synonym. ECOLOGY Lives among vegetation in most kinds of perennial-water habitats, especially stag- nant, heavily-vegetated water bodies. The usual substrate is mud. It is particularly abundant in subarctic muskeg but is ordi- narily rather uncommon elsewhere. Radula formulae are 18-1-18 to 24-1-24. The animal is blackish and quite active. 194 75 Planorbula armigera a,bjC: Severn L., northern Ont.; 6.3 mm. d,e,f: Kenogamisis L. near Geraldton, Ont.; 4.7 mm (denticles visible through shell walls). 195 76 Planorbula campestris (Dawson, 1875) Prairie Toothed Planorbid DESCRIPTION Shell up to about 12 mm wide, 4 mm high, with 6 whorls, planorboid, dextral, and in most juveniles with 1 to 4 sets of 5 denticles arranged one behind the other within the aperture. Spire flat or centrally concave. Whorls rounded, without carinae, and in- creasing in size slowly. Last part of body whorl very slightly expanded and in the same plane as, or slightly lower than, the penultimate whorl. Aperture ovate except concave at inner lip. Denticles visible through the shell wall and present in most juveniles less than 4.5 mm in diameter and in some specimens up to 9 mm. In full- grown specimens denticles are absent. Umbilicus wide, deep, funnel-shaped, and exhibiting all whorls. Periostracum pale to dark brown. Sculpture consisting of fine, close collabral lines and sharp spiral lines that together produce a satin-like texture. Juvenile specimens resemble Promenetus umbilicatellus except that their early whorls are much darker than the body whorl (not the case in P. umbilicatellus ), the whorls enlarge more slowly, and in many speci- mens denticles are visible through the shell wall. Adults differ from Planorbula armi- gera in attaining a much larger maximum size, in having a body whorl that is not sharply deflected downward and, if denticles are present, in having 5 rather than 6 den- ticles in each set. DISTRIBUTION Principally in the western prairies but also on Vancouver Island and in southwestern Yukon Territory. Extends south in the United States to Utah and New Mexico. ECOLOGY Characteristic of vernal ponds, swamps, and spring-time flooded portions of permanent water bodies. Aquatic vegetation is ordi- narily dense and substrates are mud. The radula of a Saskatchewan specimen 7.6 mm wide had 23 teeth on each side of the central tooth. 196 76 Planorbula campestris a,b ? c: Pond, Lintlaw, Sask.; 11,3 mm. d,ed: Pond near Elk Point, Alta.; 1 1.3 mm. 197 77 Helisoma (Helisoma) anceps anceps (Menke., 1830) Two-ridged Ramshorn DESCRIPTION Shell up to about 20 mm wide, 12 mm high, with 4-1/2 whorls (most specimens are much smaller), planorbiform, dextral, mod- erately strong, and (in most populations) with a prominent carina on the upper surface of the body whorl and another around the umbilicus. Spire immersed to a variable extent but ordinarily deeply re- cessed. Aperture ear-shaped, expanded mar- ginally, somewhat thickened, with a reddish band internally, and with a callus deposit on the inner wall. Carinae (where present) rounded, sharp, or corded; the upper carina located near the centre of the whorl or toward (but not on) the shoulder. Umbilicus deep and rather narrow. Periostracum pale to blackish brown. Spiral striae present on many specimens, Collabral threads fine and closely spaced. Distinguished by its dextral coiling, medium size, and (on most specimens) prominent carinae on the upper and lower surfaces. For subspecies discrimination compare with H. anceps royalense . DISTRIBUTION Occurs throughout most of southern Can- ada south of the tree line. Also extends south to Georgia and northwestern Mexico, but the distributions of its subspecies in the United States have not been worked out. It has been introduced into Italy. ECOLOGY Lives in lakes, ponds, rivers and streams among vegetation and on various substrates. Absent from temporary-water habitats. Radulae from 2 specimens of about 10 mm diameter have 22 to 24 teeth on each side of the central tooth; in larger specimens more teeth occur. The soft parts are sinistrally oriented and the shell is therefore referred to as ultra-dextral. 198 77 Helisoma anceps anceps a,b,c: Meach L. near Hull, Que.; 20.4 mm. d,e,f: Montreal R. near Montreal L., Sask.; 13.8 mm. 199 78 Helisoma {Helisoma) anceps royalense (Walker, 1909) Lake Superior Ramshorn DESCRIPTION Shell up to about 17 mm wide, 10 mm high, with 4-1/2 whorls, planorbiform, dextral, moderately strong, and with a prominent carina on the shoulder of the body whorl and another around the umbilicus. Spire flat to slightly immersed. Aperture ear-shaped, marginally inflated, edged on the outside with a dark-brown band, and with an internal callus deposit on the inner wall. Upper carina sharp or rounded and forming a prominent shoulder. Body whorl laterally flattened toward the base and all whorls flattened on the upper surface. Umbilicus deep and wide. Periostracum pale brown. Collabral sculpturing typically coarse, and in many specimens one or more dark incremental growth rests are visible. Differs from/f. anceps anceps by having a prominent upper carina at the shoulder of the body whorl, flatter upper and basal lateral surfaces, a wider umbilicus, and (in most populations) by coarser collabral sculpturing. DISTRIBUTION Occurs in Lake Superior, Georgian Bay and their drainage systems, and in adjacent portions of the Albany, Attawapiskat and Winnipeg River systems in northwestern Ontario. Beyond this region a few other populations (for example, those in the Gatineau River system in Quebec) resemble this subspecies, but its principal area of occurrence is as defined above. ECOLOGY A distinctive subspecies. Has been collected only from lakes and large rivers. Substrates were chiefly sand or rocks; submersed vegetation was moderately dense to dense. The radula is similar to that of H. a. anceps. 200 78 Helisoma anceps royalense a,b,c: Bamaji L. } Ont.; 13.8 ram. d,e,f: Kenogamisis L. near Geraldton, Ont.; 15.0 mm. 201 79 Helisoma (Planorbella) campanulatum campanulatum (Say, 1821) Bell-mouthed Ramshorn DESCRIPTION Shell up to about 15 mm wide, 6 mm high, with up to 7 whorls, planorbiform, sinistral, and variable in shape. Spire flattened. Whorls more or less flattened. Early whorls on upper side all visible and slightly immersed. Penultimate whorl on upper side below, or level with, body whorl, or project- ing a little above it. Lower side commonly exhibiting only the ultimate and penulti- mate whorls. Aperture bell-shaped in pro- file, abruptly expanded, inverted ear-shaped in cross-section, directed slightly upward, and with a callus on the inner wall. Umbilicus narrow and deep, extending to the apex of the shell, Periostracum brown- ish. Spiral sculpture obscure or very fine. Collabral sculpture consisting of coarse closely spaced threads. In many specimens coiling is irregular. The medium size, sinistral coiling, com- pressed whorls, flattened apex, and bell- shaped aperture of H. campanulatum will distinguish it from all other Canadian species. For comparison with//, c. collinsi see that subspecies. DISTRIBUTION In Canada distributed from Newfoundland to southern Quebec and west to central Saskatchewan. Two old records from the lower Fraser River in British Columbia are probably incorrect. In the United States it is found from Maine and Massachusetts to Illinois and Minnesota. ECOLOGY Common. Occurs in lakes and ponds of all sizes and in slow-moving or backwater portions of rivers. Vegetation is usually present and bottoms are of all types. Radula formulae are about 20-1-20 to 23-1-23. The living animal is reddish brown or blackish and is slow moving. 202 79 Helisoma campanulatum campanulatum a,b,c: Constance Bay, Ottawa, R. near Ottawa, Ont.; 13.2 mm. d,e,f: L. Gauvreau near Masham, Que.; 16.8 mm. 203 80 Helisoma ( Planorbella ) campan- ulatum collinsi Baker, 1939 Low-spired Ramshorn DESCRIPTION Similar to H. c. campanulatum except that a clearly developed spire is present. Popula- tions of individuals in which earlier whorls project above the body whorl an average of 10% or more of the height of the body whorl are considered to beH. c. collinsi. DISTRIBUTION Lake Superior, its drainage system, and in headwaters of the Albany, Winnipeg and Severn River systems. A related form, called H. multivolvis (Case), occurs near Lake Superior in northern Michigan and is probably only an extreme morph of H. c. collinsi. ECOLOGY Has been collected in lakes and in medium- sized rivers. Substrates are sand or sand and gravel; vegetation is present but varies in abundance. The radula formula of a specimen 12 mm wide was 22-1-21. 204 205 81 Helisoma (Pieros oma) corpu- lentum corpulentum (Say, 1824) Capacious Manitoba Ramshorn DESCRIPTION Shell up to 32 mm wide, 16 mm high, with 4-1/2 whorls, planorboid, sinistral, and with a carina located near the outer edge of each whorl both above and below. Upper side flat centrally or slightly concave except for the body whorl, which protrudes above earlier whorls. Carinae on upper surfaces of whorls sharp and forming a 90° angle at the shoulder of early whorls but becoming rounded and more centrally located on the body whorl of mature specimens. Umbilical carina forming an acute angle on the outer edge of early whorls but also becoming rounded and central on the body whorl. Body whorl flattened and in some speci- mens bent upward near the aperture. Aper- ture large, dilated, higher than wide, and extending above, or above and below, the body whorl. Umbilicus wide, deep, and extending to the apex. Periostracum light to dark brown. Fine sculpture consisting of prominent, crowded, strongly elevated colla- bral riblets and microscopic collabral and spiral striae. Distinguished by its large and high form, sharp carinae on the shoulders, laterally flattened whorls, and coarse sculpturing. Compare with//, c. whiteavesi,H. pilsbryi infracarinatum, and H. trivolvis trivolvis. DISTRIBUTION Northwest and west of Lake Superior in the Winnipeg, upper Albany and upper Severn River systems, and in the upper Mississippi River system in northern Minnesota. ECOLOGY Lives in large and small lakes and in rivers, and often in exposed habitats. Vegetation may be sparse to thick, and substrates are of all kinds. Diverse radula formulae between 27-1-26 and 45-1-45 have been recorded. 206 81 Helisoma corpulentum corpulentum a>b,c: L. Seul, northwestern Ont.; 25.8 mm. d,e,f: L. la Croix, Rainy River Dist., Ont.; 23.6 mm. 207 82 Helisoma ( Pierosoma ) corpu- lentum whiteavesi Baker, 1932 Whiteaves’s Capacious Ramshorn DESCRIPTION Similar to if. c. corpulentum except that it is relatively higher (the holotype is 24 mm in diameter and 19 mm high), the upper side is flatter, and the whorls are more tightly coiled. The large ear-shaped aperture gives the shell a Physa -like appearance. DISTRIBUTION Known only from Lac des Mille Lacs (the type locality) and Greenwater Lake, both northwest of Lake Superior in the Winnipeg River system in northwestern Ontario. ECOLOGY This problematic and rare subspecies appar- ently occurs in open-water habitats in lakes. The radula formula is reported as 36- 1-36 to 42-1-42. Another subspecies, H. c. vermilionense Baker, 1929, is recorded from the Rainy River system in northern Minnesota and may occur in Canada, See Clarke (1973) for additional details regarding both of these subspecies. 208 82 Helisoma corpulenium whiteavesi a,b,c: Greenwater L. west of L. Superior, Thunder Bay Dist., Ont.; 23.5 mm. Helisoma corpulentum vermilionense d,e/: Vermilion L,, St. Louis Co., Minn.; 12.2 mm (juvenile, paratype). 209 83 Helisoma (Pierosoma) pilsbryi infracarinatum Baker, 1932 Greater Carinate Ramshorn DESCRIPTION Shell up to 32 mm wide, 18 mm high, with 4-3/4 whorls, planorbiform, sinistral, and with sharp or rounded carinae above and below. These carinae are more or less centrally located but each may be rounded and obsolete on the body whorl. Body whorl overlapping the penultimate whorl, and in many specimens the upper side of the shell is smoothly concave and bowl-like. Body whorl rounded on its outer side but with the outermost edge below the centre. Aperture ovate ear-shaped, higher than wide, and flaring. Umbilicus wide and exhibiting 2 to 3 whorls. Periostracum yellowish to brown- ish. ColJabral sculpture consisting of fine riblets (2 to 4 per mm) and, in some specimens, of one or more growth rests. Differs from//, trivolvis in the possession of a basal carina and in greater axial height. May be distinguished from the//, corpulen- tum group by its bowl-like (not flattened) spire, by the carinae that are more or less centrally located (not near the outer edges of the whorls), and by the more sharply convex lateral area of the body whorl. DISTRIBUTION In the boreal forest from southwestern Quebec to east-central Alberta (Lac la Biche) and farther south in the Rideau and St. Lawrence rivers; in Georgian Bay; and in the Qu’Appelle River system in Saskatchewan. ECOLOGY Ordinarily occurs in lakes, ponds, or quiet backwaters of streams, among vegetation, and on various substrates. The radula formula is approximately 30-1-30 to 37-1-37. 210 83 Helisoma pilsbryi infra canna mm a,b,c: Rapids on Basswood R. west of L. Superior, Ont.; 23.0 mm (paratype). d,e,f; Knee L. at outlet, northern Man.; 28.0 mm. 84 Helisoma (Pierosoma) trivolvis trivolvis (Say, 1816) Larger Eastern Ramshorn DESCRIPTION Shell up to about 32 mm wide, 16 mm high, with 5 whorls, planorbiform, and sinistral. Spire submersed and dished. Whorls more or less carinate centrally or rounded above, rounded below, and rounded on the outer side. Apical depression wide, of moderate depth, and exhibiting all whorls. Umbilical region sunken and revealing 3 to 3-1/2 whorls. Aperture expanded, dilated at the margin, ovate ear-shaped, with width equal to or greater than height, with a callus deposit on the inner wall, and typically with a reddish-brown or purplish band within the aperture. Umbilicus broad and deep. Periostracum yellowish brown to brown. Sculpture moderate and consisting of colla- bral riblets (about 2 to 4 per mm), irregularly spaced growth rests, and in many specimens a more or less apparent spiral carina above. This is the most abundant of the large eastern helisomas. The close-to-centre posi- tion of the upper carina will distinguish it from the H. corpulentum group, in which the carina is at the shoulder. The lack of a lower carina will differentiate it from H. pilsbryi infracarinatum , which has a well-developed lower carina. Its substantial axial height (more than 1 2 mm) will separate it from the western H. trivolvis subcrenatum and from the other species of the genus. Compare//, t. binneyi. DISTRIBUTION In Canada occurs throughout the boreal and deciduous forest regions from eastern Que- bec and Nova Scotia to southeastern Mani- toba and within a small area in central Saskatchewan. Also extends throughout the northeastern United States and farther south, where it intersects other subspecies, whose precise distributional limits have not been established. ECOLOGY Characteristic of well-vegetated perennial- water lakes, ponds, and slow-moving streams. Mud is the usual substrate. Radu- lae from Ontario specimens 25 mm in diameter have about 3 1 to 34 teeth on each side of the central tooth. 212 84 Helisoma trivolvis trivolvis a,b,c: Montreal R. near Montreal L., Sask.; 26.8 mm. d,e,f: Lake on Green R., N.B.; 23.7 mm. 213 85 Helisoma {Piero soma) trivolvis binneyi (Tryon, 1867) Binney’s Stout Ramshorn DESCRIPTION Resembles//, t. trivolvis except for the following: (1) it is relatively higher, that is within population samples the average ratio of height to diameter, excluding the lip, exceeds 0.57, whereas in H. t. trivolvis it seldom exceeds 0.52; (2) a more or less well- defined carina occurs on the undersides of the whorls but not in H. r. trivolvis ; (3) the body whorl is more expansive, causing the apex and the umbilicus to be more deeply immersed; and (4) the aperture is more broadly expanded above and below. DISTRIBUTION Principally in the Pacific drainage from southern British Columbia to California but also in a few lakes in western Alberta. In Lake Wabamun, Alberta, inter grades com- pletely with//, t. subcrenatum. Populations intermediate between H. t. binneyi and H. t. subcrenatum — corresponding to “//. binneyi randolphi” Baker, 1945, and “//. columbiense ” Baker, 1945 — also occur in British Columbia. Herein, H. t. binneyi is used only for the extreme morph described above. Intermediate populations are best referred to as H. trivolvis Say, without any subspecies name. ECOLOGY Occurs in eutrophic, well-vegetated lakes. No detailed information is available regard- ing its specific ecology or anatomy. 214 85 Helisoma trivolvis binneyi a,b,c: Dragon L. near Quesnel, B.C.; 20,5 mm. d,e,f: East end of Sylvan L., Alta.; 22.7 mm. 215 86 Helisoma (Pieros oma) trivolvis subcrenatum (Carpenter, 1856) Larger Prairie Ramshorn DESCRIPTION Similar to H . t. trivolvis except that its height does not exceed 10 mm whereas the height of adult//, t. trivolvis almost always exceeds 10 mm and in most specimens exceeds 12 mm; also its coiling is looser and sutures deeper. Some populations exhibit spiral, pale-coloured streaks or irregular coiling. The two subspecies occupy distinct zoogeo graphical regions. DISTRIBUTION Western North America from California and Utah to Yukon Territory and Manitoba. ECOLOGY Occurs in nearly all perennial-water habi- tats that support significant rooted vegeta- tion. Mud is the most frequent substrate. Specimens from Alberta about 20 mm wide have radulae with 28 to 30 teeth on each side of the central tooth. 216 86 Helisoma trivolvis subcrenatum a,b,c: Loch Haven, Cypress Hills Provincial Park, Sask.; 20.8 ram. d,e,f: Third Vermilion L., west of Banff, Alta.; 26.8 mm. 217 FAMILY ANCYLIDAE (True Freshwater Limpets) Shell small to small-medium, not spiral but shaped like a broad, low cone, mainly thin-shelled, with rounded or ovate aperture, radial and concentric sculpturing, and a blunt apex located either centrally or behind the centre and either in the midline or to the right. The soft parts are sinistrally organized, with a pseudobranch (false gill) on the left side. The radula has about 8 to 37 bicuspid to multicuspid lateral plus marginal teeth on each side of the bi- to tetracuspid central tooth. The egg masses are small, ovate, gelatinous, transparent and have a few whitish eggs. The family is worldwide. 87 Laevapex fuscus (CJB. Adams, 1841) Dusky Lily-Pad Limpet DESCRIPTION Shell up to about 8 mm long, 5 mm wide, 3 mm high (most specimens are much smaller), broad cone-shaped, thin-shelled, more-or-less elliptical at the base and rather low. Apex elevated, sharply rounded, located to the right of the midline and posterior of centre, and without microscopic radial lines. Anterior slope slightly convex, posterior slope concave, and lateral slopes more or less straight. Aperture elliptical or with sides a little flattened and conver- gent posteriorly. Concentric lines of growth very fine. Radial lines also seen on the sides of some specimens below the apex. Perios- tracum very thin, closely adherent, and pale brown. Distinguished from Ferrissia species by having a smooth rather than radially striate apex and by characters of the soft parts, which are visible through the shell, that is the presence of a dark pigment band across the middle of the mantle and the presence of epithelial attachment areas between the anterior muscle scars and between the posterior and the right anterior muscle scars. These characters are best seen on specimens that are well cleaned and have had the periostracum removed by soaking in a weak solution of laundry bleach in water. DISTRIBUTION Southern Ontario and Quebec to Massachu- setts, south to Florida and Louisiana, and west to Oklahoma, Kansas, and Iowa. Also in the upper Albany River system in northwestern Ontario. ECOLOGY Occurs in heavily vegetated permanent- water habitats on the undersides of lily pads and on other emergent vegetation. The radula is similar to that of Ferrissia species but the genitalia are distinctive, that is the penis is large and without a flagellum; in Ferrissia the penis, when present, is small and has a club-shaped flagellum. 220 221 88 F errissia fragilis (Try on, 1863) Oval Lake-Limpet DESCRIPTION Shell up to about 5.5 mm long, 3.2 mm wide, 1.6 mm high (most specimens are much smaller), broad cone-shaped, thin, subovate, wider anteriorly than posteriorly, low, and highly variable in form. Apex elevated, rounded, located in the midline (or a little to the right) behind the centre, and sculptured with numerous very fine radial striae that are visible at about 50 x magnifi- cation. Anterior slope convex, posterior slope concave, and lateral slopes straight. Aperture suboval in one plane, abruptly rounded anteriorly and posteriorly, and flatly convex laterally. Lateral margins converging posteriorly in many specimens, causing the posterior margin to be more sharply curved than the anterior. Perios- tracum very thin, closely adherent, and pale brown. Concentric lines of growth very fine, and radial sculpture poorly marked. Distinguished by its small size (less than 4 mm long in most specimens), thin shell, rather straight sides that typically converge posteriorly (in western Canadian speci- mens), and its predominantly still-water habitat. See Basch (1963) for a discussion of the variation in this limpet. DISTRIBUTION Common in southwestern British Columbia and in southern Ontario and Quebec. Widely distributed in the United States. ECOLOGY Occurs principally in lakes, ponds, and ditches. Often found on the stems of cattails (Typha)^ near their bases. Also lives in slow- flowing streams. The radula is similar to that of other species of F errissia. A septate morph resembling the marine genus Crepi- dula (slipper limpets) exists in some locali- ties in the United States, Basch (1963) considers the morph occur- ring from British Columbia to Oregon to be distinctive, and has called it “form” isabellae. It is larger than typical F, fragilis, and approaches F. parallela in shell ap- pearance. 222 223 89 Ferrissia parallela (Haldeman, 1841) Flat-sided Lake Limpet DESCRIPTION Shell up to about 7.6 mm long, 3.2 mm wide, 2.7 mm high, limpet-shaped, thin- shelled, long, narrow, and with aperture sides straight and parallel or somewhat convergent anteriorly. Apex elevated, ob- tuse, located in the midline slightly behind the centre and covered with very fine radial striae, visible at 50 x and preserved princi- pally on young specimens. Left and right lateral surfaces flattened, posterior slightly concave, and anterior a little convex. Aper- ture long, ovate, and with lip all in the same plane or slightly saddle-shaped, i.e. concave at the ends and convex at the sides. Periostracum very thin, closely adherent, and yellowish brown. Lines of growth mostly fine and well marked. Radial striae on body of shell obscure but generally distributed. Easily distinguished by its long, narrow shell, its straight, more or less parallel sides, and its habitat. DISTRIBUTION Occurs in southern Canada from New- foundland and Prince Edward Island to southern Manitoba. According to the litera- ture (Basch 1963), it is also found across the northern United States. ECOLOGY Lives in lakes, swamps, and slow-flowing rivers among thick or moderately thick vegetation. Often found on stems of cattails ( Typha) and sedges (Scirpus) or on the undersides of lily pads. Egg capsules are white and most contain 1 to 3 eggs. The central tooth of the radula has 2 large central cusps and 2 small marginal ones; the lateral and marginal teeth are multicuspid. 224 225 90 Ferrissia rivularis (Say, 1817) Sturdy River Limpet DESCRIPTION Shell up to about 7 mm long, 4 mm wide, 3 mm high, limpet-shaped, thin to notice- ably thickened, ovate, high or low spired, and variable in form. Apex elevated, rounded, located in the midline (or a little to the right) behind the centre, and covered with very fine radial striae. Striae preserved best on young specimens and visible at 50 x * Anterior slope convex, posterior concave, and lateral slopes more or less straight. Aperture oval with all margins convex and in the same flat plane. Periostracum thin, closely adherent, and pale brown. Lines of growth mostly fine and irregular, radial sculpturing obscure and principally anterior. Distinguished by its oval and often thickened shell, by its relatively large size, and by its habitat. DISTRIBUTION Eastern Canada from New Brunswick to Saskatchewan. In the United States at least from Maine to North Dakota, and North Carolina to Wyoming. ECOLOGY Lives attached to rocks and mussel shells in rivers and creeks, or attached to rocks in exposed habitats in lakes. The radula formula is 19-1-19 to 21-1-21, and the cusps are the same as inF. parallela. 226 90 Ferrissia rivularis a,b: Carp R. near Carp, Ont.; 4.8 mm. c,d: Whitesand R. near Sheho, Sask.; 2.8 mm. 227 91 Margaritifera margaritifera 92 Margaritifera f ale ata 229 94 Amblema plicata 230 231 99 Elliptio complanata 101 Pleurobema coccineum 100 Elliptio dilatata 102 Alasmidonta viridis 232 104 Alasmidonta marginata 106 Alasmidonta varicosa 233 234 109 Lasmigona costata 111 Anodontoides ferussacianus 235 236 115 Anodonta grandis grandis 1 16 Anodonta grandis simpsoniana 237 119 Anodonta kennerlyi 120a Anodonta nuttalliana 238 120b Anodonta nuttalliana 121 Strophitus undulatus 122 Piychobranchus fasciolaris 124 Truncilla donaciformis 123 Obliquaria reflexa 239 125 T runcilla truncata 127 Carunculina parva 128 Obovaria olivaria 240 241 242 137 Lampsilis radiaia radiaia 138 Lampsilis radiata siliquoidea 135 Lampsilis fasciola 136 Lampsilis ochracea 243 141 Villosa iris 142 Dysnomia lorulosa rangiana 9 143 Dysnomia triquetra 9 244 Class Pelecypoda (Clams and Mussels) Order Eulamellibranchia IX Superfamily Unionacea Freshwater Mussels FAMILY MARGARITIFERIDAE (Pearly River-Mussels) Shell large, bivalved, of medium thickness, with pearly nacre, pseudocardinal hinge teeth well developed, and lateral hinge teeth- only partly developed or absent. All 4 demibranchs (gills) are marsupial (have brood chambers for glochidia), but the marsupial microstructure is less complex and presumably more primitive than in Unionidae. The glochidia are hookless but have irregular small teeth at the ventral margin of the valves. The mantle is not united posteriorly and does not form separate siphonal openings. The family occurs only in North America and Eurasia. 247 91 Margaritifera margaritifera (Linnaeus, 1758) Eastern-River Pearl Mussel DESCRIPTION Shell up to 150 mm long, 65 mm high, 40 mm wide, and with shell wall 10 mm thick at mid-anterior; long-oval, and with straight or concave lower margin. Except for closely spaced concentric lines the surface is mainly smooth. Periostracum brown in juveniles, black in adults, and eroded at umbones. Nacre white or whitish, with or without pink or purple suffusions. Beak sculpture consists of a few coarse ridges parallel to the lines of growth. Hinge teeth incomplete: pseudocardinals erect and ser- rated, 1 in the right valve and 2 in the left; lateral teeth poorly developed or absent. Muscle scars in beak cavity only partly visible from below. The sexes are separate. The long and slightly bent shape, black- ish periostracum, strong pseudocardinal teeth, and obscure lateral teeth serve to readily distinguish this species. DISTRIBUTION Atlantic drainage of North America from Goose Bay, Labrador, to the Little Schuyl- kill River, Pennsylvania. Also occurs in Eurasia from northern Spain and Scandina- via east through northern USSR to Japan. Especially abundant in Newfoundland and Nova Scotia, but does not virtually pave the bottoms of streams as the western species M. falcata sometimes does. ECOLOGY Occurs in small and medium-sized running streams. Often found on sandy shoals and in pools under overhanging branches. The breeding season occurs between June and August. The glochidia are oval to almost circular, with a narrow inward-directed flange at the ventral edge of each valve, and very small (0.06 mm long and 0.07 mm high). Host fishes in Europe are the brown trout and the minnow Phoxinus phoxinus. In North America the native brook trout, as well as the introduced brown trout, may be a host. In Europe the species reaches at least 1 16 years of age. In North America it appears to be restricted to soft water. 248 91 Margaritifera margaritifera a,b,c,d: Burnt Berry Brook near Springdale, Nfid.; a and d 1 14.3 mm. The specimen illustrated in colour on page 229 is from the Parrsboro R. near Parrsboro, N.S. (x 2/3). 249 92 Margaritifera falcata (Gould, 1850) Western-River Pearl Mussel DESCRIPTION Similar to Margaritifera margaritifera ex- cept smaller (maximum length 125 mm, with purple rather than white or whitish nacre, relatively smaller anterior pseudocar- dinal tooth in left valve, and muscle scars in beak cavity entirely visible from below. Hermaphroditic, whereas inAf. margariti- fera the sexes are separate. DISTRIBUTION Distributed in Pacific drainages from Cali- fornia and New Mexico north to the southern interior of British Columbia, and farther north near the coast to Revillagigedo Island in southern Alaska. Also in the upper Missouri drainage in Montana. In favour- able localities in British Columbia the mussels may be so abundant and closely packed that they completely obscure the stream bed. ECOLOGY Occurs in running streams wider than 4 m. Found in sand or gravel substrates. Unlike M. margaritifera , it occurs in hard as well as in soft water. The gravid period is from mid May to late June. Hermaphroditic. The glochidia have not been described. Host fishes are the chinook salmon, rainbow trout, brown trout, brook trout, speckled dace, Lahontan redside, and Tahoe sucker. The greatest longevity so far determined forM. falcata is about 67 years, but older specimens probably occur. 250 92 Margaritifera falcata a,b,c,d: Koksilah R. near Duncan, Vancouver Is., B.C.; a and d 101.6 mm. The specimen illustrated in colour on page 229 is from the same locality (x 2/3). 251 FAMILY UNIONIDAE (Pearly Mussels) Shells small to large, bivalved, thin and fragile to thick and heavy, with pearly nacre, and with or without pseudocardi- nal hinge teeth and/or lateral hinge teeth. All four demibranchs (gills), or only one pair of demibranchs, are marsupial, and the microstructure is more complex than in Margaritiferidae. The glochidia are hookless or with hooks. The mantle is drawn together posteriorly by the diaphragm, and separate siphonal openings are present. The family is worldwide but occurs principally in Europe, Asia and North America, For many years North American Unionidae have been grouped into three subfamilies: Ambleminae (or Elliptioni- nae), characterized principally by heavy hinge teeth, all four demibranchs being marsupial, hookless glochidia, and a short breeding season; Anodontinae, with hinge teeth incomplete or absent, whole outer demibranchs only used as marsupia, hooked glochidia, and short breeding seasons; and Lampsilinae, with well-developed hinge teeth, posterior part of outer demibranchs only used as marsupia, hookless glochidia, and long breeding seasons. That classification is now being revised by several workers (see e.g. Heard and Guckert 1970), but the matter is still unsettled. In this book the traditional subdivisions of Unionidae are therefore retained. SUBFAMILY AMBLEMINAE (Button Shells and Relatives) 93 Gonidea angulata (Lea, 1839) Rocky Mountain Ridged Mussel DESCRIPTION Shell up to 125 mm long, 65 mm high, 40 mm wide, and with shell wall up to about 5 mm thick at mid-anterior; variable in form but typically rather thin, trapezoidal in shape, with posterior margin obliquely flattened and relatively broad, and with a sharp and prominent posterior ridge run- ning from the umbo to the angular basal posterior margin of each valve. Shell with obscure radial sculpturing on the posterior slope and readily apparent growth rests. Periostracum yellowish brown to blackish brown, without rays, smooth on the disc, and roughened on the posterior slope. Nacre centrally white or salmon, but pale blue posteriorly and near the margin. Beak sculpture composed of about 8 rather coarse, concentric ridges that are straight in the centre and curved at both ends. Hinge teeth irregular and poorly developed; pseu- docardinal teeth compressed, low, laterally expanded, 1 in the right valve and none or 1 in the left; lateral teeth absent. DISTRIBUTION Columbia River system in southern British Columbia (Okanagan and Kootenay rivers) and south in the Pacific drainage to southern California. ECOLOGY In Vaseux Lake near Oliver, British Colum- bia, large specimens occur in muddy sand at a depth of 0.6 to 0.9 m along the shore- ward edge of a bed of Potamogeton (pond weed). Elsewhere occurs in rivers and lakes and on various substrates. Four specimens were collected on 6 August 1972 from Vaseux Lake, and none were gravid. Nothing has been published about its reproduction, glochidia, or fish host. 254 93 Gonidea angulata a,b,c,d: Vaseux L. near Oliver, B.C.; a and d 123.8 mm. The specimen illustrated in colour on page 230 is from the same locality (X 2/3). 255 94 Amblema plicata (Say, 1817) Three-Ridge DESCRIPTION Shell to about 150 mm long, 105 mm high, 65 mm wide, and with mid-anterior shell wall 15 mm thick; ovate, more or less truncated posteriorly, and with heavy sculp- turing. Shells of most specimens bear 3 or 4 heavy, rounded, diagonal, more or less parallel centrally located ridges that are directed toward the lower posterior edge. In some old specimens the ridges are lacking. Surface also bears a few short ridges on the posterior slope perpendicular to the lines of growth and irregular concentric wrinkles over the whole shell. Periostracum brown to blackish and without rays. Nacre white and iridescent posteriorly. Beaks elevated above hinge line, located close to the anterior end, moderately inflated, and deeply excavated. Beak sculpture consisting of about 5 concentric single-looped ridges; early ridges expanded anteriorly. Hinge teeth massive and very strong; pseudocardi- nals thick and heavy, subtriangular, erect, deeply serrated, 2 or 3 in the right valve and 2 in the left; laterals of moderate length, straight or slightly curved, 1 in the right valve and 2 in the left. Has the heaviest and most ponderous shell of any mollusc in Canada. Easily recognized by its impressive size and thick- ness, and by its wide diagonal ridges. DISTRIBUTION Occurs in the Red River -Lake Winnipeg drainage area, in the Great Lakes- St, Lawrence system from Lake Michigan and Lake Huron to Lake Erie (in the lakes themselves and in their tributaries), and in the whole Ohio-Mississippi River system. ECOLOGY Common in southwestern Ontario and in southern Manitoba, Typically a river spe- cies. Lives on or in various substrates. Stunted individuals occur in Lake Erie. A short-term breeder, with gravid period ex- tending from May to July. Glochidia are oval, without hooks, and measure about 0,21 mm in length and 0.23 mm in height. Numerous fish hosts are known. 256 94 Amblema plicata a, d: Grand R. near Dunnville, Ont.; 123.8 mm. b, c: South Bay, Pelee Is., L, Erie, Ont The specimen illustrated in colour on page 230 is from McGregor Creek, Chatham, Ont. (x 2/3). 257 95 Fusconaia flava (Rafinesque, 1820) Pig-Toe DESCRIPTION Shell up to 100 mm long, 70 mm high, 40 mm wide, and with shell wall 8 mm thick at mid-anterior; roughly triangular, bluntly pointed at posterior basal region, with ventral margin straight or slightly concave posteriorly, and posterior ridge well marked. Periostracum with a dull lustre, brown in immature specimens and brownish black in adults, and without rays or with obscure rays only on the posterior slope. Nacre whitish or tinged with salmon. Umbones anterior of centre but in most specimens not close to anterior margin. Beak sculpture moderately fine and consisting of 3 to 5 small more or less concentric bars visible principally on the posterior ridge. Pseudo- cardinal hinge teeth moderately heavy and with radial furrow, 1 tooth in the right valve and 2 in the left; lateral teeth strong, of medium length, straight or slightly curved, 1 or 2 in the right valve and 2 in the left. Sometimes confused with the less com- mon species Pleurobema coccineum, with which it should be compared. DISTRIBUTION In Canada occurs only in the Lake Huron, Lake St. Clair and Lake Erie drainage basins of Ontario and in the Red River - Nelson River system of Manitoba. In the United States it lives in the same drainage systems but is also widespread in the Mississippi-Missouri system. ECOLOGY Relatively common within its range and always found in company with several other species of mussels. Occurs principally in medium or large rivers but also in large lakes, for example Lake Erie, Found in mud or sand and among sparse or moderate vegetation. Glochidia are ovate, hookless, and measure about 0.15 mm in height and width. Females are gravid in spring and summer, all four demibranchs are marsu- pial, and the host fish are bluegill, white crappie, and black crappie. 258 95 Fusconaia flava a, d: Sydenham R. near Strathroy, Ont.; 92.1 mm. b. c: Rondeau Harbour, L. Erie, Ont. The specimen illustrated in colour on page 231 is from Big Creek near Port Rowan, Ont. (x 2/3). 259 96 Quadrula quadrula (Rafinesque, 1820) Maple-Leaf DESCRIPTION Shell up to 125 mm long, 100 mm high, 50 mm wide, and with shell wall 8 mm thick at the mid-anterior; more or less quadrate, rounded anteriorly, somewhat truncated posteriorly, and sculptured on each valve with 2 bands of nodules radiating from the umbones, 1 centrally located and the other on the posterior ridge. Periostracum yellow- ish brown or brown, and with poorly defined green radial bands in some specimens. Annual growth rests well defined. Nacre white. Beak sculpture consisting of tiny nodules. Hinge teeth strong: pseudocardi- nal teeth erect, conical, and serrated; 1 major tooth (with a small one in front and another behind) in the right valve and 2 in the left; lateral teeth erect, 1 or 2 in the right valve and 2 in the left. Similar to Q. pustulosa except that the nodules are restricted to 2 radial bands, while in Q. pustulosa they occur over most of the shell surface. Also more quadrate and less ovate than Q. pustulosa . ECOLOGY Occurs in medium-to-large rivers where currents are slow to moderate. Usual sub- strates are mud or sand, and vegetation is ordinarily present and sometimes dense. Normally a minor element of unionid communities that contain several species. Adult females are gravid in late spring and summer, and the glochidia are ovate, without hooks, and measure about 0.08 mm in length and height. The host fish is the flathead catfish. DISTRIBUTION Southern Ontario in the Lake Erie and Lake St, Clair drainages and Manitoba in the Red River system. In the United States it occurs in those drainage systems as well as throughout the Ohio-Mississippi drain- age system. 260 96 Quadrula quadrula a,b>c,d: Grand R. near Byng, Ont; a and d 84,1 mm. The specimen illustrated in colour on page 231 is from the Grand R, near Dunnville, Ont. (x 2/3). 261 97 Quadrula pustulosa (Lea, 1831) Warty-Back DESCRIPTION Shell up to 100 mm long, 85 mm high, 65 mm wide, and with shell wall 8 mm thick at the mid-anterior; ovate-quadrate, rounded in front, truncated behind, and sculptured with elongate tubercles that are parallel to the lines of growth and distributed chiefly over the central part of each valve. If tuber- cles are numerous some are also present on the posterior slope. Periostracum yellow- ish brown to chestnut-brown in adults and yellowish with greenish rays in young individuals. Annual growth rests well marked in Canadian specimens. Nacre white. Umbones prominent and, when not corroded, sculptured with 3 or 4 coarse ridges. Hinge teeth heavy: pseudocardinal teeth erect, triangular, and serrated, 1 large tooth in the right valve (with a small tooth before and behind) and 2 in the left; lateral teeth short and slightly curved, 1 or 2 in the right valve and 2 in the left. Similar to Q. quadrula but is more ovate, has scattered rather than confined nodules, and is relatively heavier. DISTRIBUTION Lake Erie and Lake St. Clair drainages in southwestern Ontario and the United States. Also in the Lake Michigan and Ohio-Mississippi River drainages. ECOLOGY Not common in southwestern Ontario. Occurs in rivers of various widths. Found on gravel, sand, or mud bottoms. Females are gravid from mid May to late August. The glochidia are purse-shaped, without spines, and measure about 0.23 mm in length and 0.30 mm in height. The host fish are the channel catfish, shovelnose stur- geon, black bullhead, brown bullhead, flathead catfish, and white crappie. 262 97 Quadrula pustulosa a, d: Grand R., Port Maitland, Out.; 66.7 mm. b, c: South Bay, Pelee Is., L. Erie, Ont. The specimen illustrated in colour on page 23 1 is from L. Erie off Pelee Is., Ont. (x 2/3). 263 98 Cyclonaias tuberculata (Rafinesque, 1820) Purple Pimple-Back DESCRIPTION Shell about 100 mm long, 100 mm high, 50 mm wide, and with shell wall 8 mm thick anterio-centrally; outline circular except flattened dorsally and anteriorly, com- pressed, and with small or medium-sized nodules scattered over the posterior and central surfaces or more restricted. Nodules rounded or elongate, and oriented perpen- dicular to the lines of growth. Periostracum brown or blackish, with poorly defined brownish or greenish rays, and with annual growth rests well marked. Nacre purple. Beak sculpture of fine zigzag bars. Hinge teeth heavy and strong: pseudocardinal teeth massive and serrate, 1 in the right valve (with an additional small tooth in front and another behind) and 2 in the left; lateral teeth of medium length and nearly straight, 1 in the right valve and 2 in the left. Beak cavity narrow and deeply excavated. The circular and compressed shape, nodulous exterior, massive pseudocardinal teeth, and purple nacre readily distinguish it from all other species. DISTRIBUTION Lake Erie and the Sydenham River in southern Ontario. In the United States it occurs in Lake St. Clair, Lake Erie, Lake Michigan and their drainage areas, and in the Ohio-Mississippi River drainage system. ECOLOGY An uncommon species in Canada. Occurs in rivers of various sizes. Found on gravel or mud bottoms. Gravid females have been collected in the United States from late May to the middle of August. The glochidia are reported as 0.27 mm long and 0.35 mm high, with short hinge line and rounded anterior, and without spines. The host fish is unknown. 264 98 Cyclonaias tuberculata a, d: Huron R., Ann Arbor, Mich.; 79.4 mm. b, c: South Bay, Pelee Is., L. Erie, Ont. The specimen illustrated in colour on page 231 is from the Huron R., Mich. (X 2/3). 265 99 Elliptio complanata (Lightfoot, 1786) Eastern Elliptio DESCRIPTION Shell up to about 125 mm long, 65 mm high, 40 mm wide, and with shell wall 6 mm thick at mid-anterior; unusually variable in form but typically of medium thickness, somewhat trapezoidal or ellipti- cal, obliquely truncated posteriorly, with rounded posterior ridge, and compressed. Shell unsculptured except for beak sculp- ture and lines of growth. Periostracum brownish or blackish and unrayed except in some young specimens and in adults from sandy substrates. Annual growth rests well marked. Nacre purple in most specimens, but pinkish or whitish in some. Beak sculpture of concentric U-shaped ridges. Hinge teeth well developed: pseudocardinal teeth compressed and conical, 1 in the right valve (a small accessory tooth may be present in front of the large one) and 2 in the left; lateral teeth narrow, of medium length and nearly straight, 1 in the right valve and 2 in the left. Muscle scars not deeply impressed. Usually distinguished from£, dilatata by its compressed and trapezoidal shape, obliquely flattened posterior margin, beaks that are not close to the anterior end, and often by its thinner shell. More inflated specimens are broadest near the posterior slope, whereas E . dilatata is broadest in the anterior region, more regularly tapered posteriorly, and has beaks close to the anterior end. Ligumia nasuta , which also has purple nacre, differs from E. complanata in its narrower shape, more delicate hinge teeth, and centrally pointed posterior margin. DISTRIBUTION Southern James Bay drainages and the St. Lawrence system (except Lake Huron south of Georgian Bay, Lake Michigan, and most of Lake Brie) south in the Atlantic drainage to Georgia. ECOLOGY Uncommon in James Bay drainages but abundant elsewhere. Lives in shallow water of permanent lakes, rivers and medium- sized streams. Found on gravel, sand, clay, or mud bottoms. Females are gravid in late spring and early summer, and mature glochidia are about 0.20 mm long, subovate, and without hooks. The yellow perch is its only known host. 266 99 Elliptic complanata a, d: Ottawa R. near Pembroke, Out.; 77.8 mm. b, c: Poucette L. near Port Elgin, N.R. The specimen illustrated in colour on page 232 is from the Ottawa R. near Pembroke, Ont. (x 2/3), 267 100 Elliptio dilatata (Rafmesque, 1820) Spike, or Lady-Finger DESCRIPTION Shell up to 125 mm long, 65 mm high, 45 mm wide, and with shell wall up to 12 mm thick at mid-anterior; variable in form but normally long-ovate, rather thick and strong, and somewhat inflated. Shell unsculptured except for beak sculpture and lines of growth. In some specimens the growth lines are not evenly concentric, but are disproportionately wide apart posteriorly and give the shell a deformed appearance. Periostracum yellowish brown to brown, with indistinct greenish rays in many specimens, and in Canadian specimens with dark growth rests. Nacre purple in most specimens but white or pale pink in some. Beak sculpture consisting of 4 or 5 rather heavy curved bars. Hinge teeth thick and strong: pseudocardinal teeth conical and serrated, 1 in the right valve (with 1 small tooth in front and another behind) and 2 in the left; lateral teeth of medium length and nearly straight, 1 (or 2) in the right valve and 2 in the left. Muscle scars rather deeply impressed. Sometimes confused with E. complanata. Compare with that species. DISTRIBUTION Common in the Great Lakes and their tributaries from Lake Michigan to Lake Erie; uncommon in Lake Ontario and in the St. Lawrence River. Widespread in the Ohio-Mississippi and Gulf of Mexico drainages. ECOLOGY Often abundant. Occurs in rivers and lakes of various sizes. Found on diverse sub- strates. Hermaphroditic. The breeding sea- son lasts from May to August. Glochidia are oval except for the straight hinge line, and measure about 0.20 mm in length and 0.22 mm in height. The host fish are gizzard shad, flathead catfish, white crappie, black crappie, and yellow perch. 268 100 EUiptio dilatata a, d: Grand R., Cayuga, Ont.; 85.7 mm. b, c: South Bay, Pelee Is., L. Erie, Ont. The specimen illustrated in colour on page 23 2 is from the Grand R. near West Montrose, Waterloo Co., Ont. (x 2/3). 269 101 Pleurobema coccineum (Conrad, 1836) False Pig-Toe DESCRIPTION Shell up to 90 mm long, 65 mm high, 40 mm wide, and with shell wall 8 mm thick at mid-anterior; more or less ovate, more sharply rounded posteriorly than anteriorly but not pointed, and with ventral margin convex throughout; posterior ridge obscure and rounded on most specimens. Periostracum shiny, yellowish brown to brown, but blackish in very old specimens, and without rays (or with obscure rays) only on the posterior slope. Nacre white or pinkish. Umbones in most specimens close to anterior margin. Beak sculpture coarse, irregular, and visible principally on poste- rior ridge. Pseudocardinal hinge teeth heavy and radially channelled and grooved, 1 large tooth in the right valve (with 1 additional small tooth in front and another behind) and 2 in the left; lateral teeth strong and straight or slightly curved, 1 in the right valve and 2 in the left. Similar to the more abundant species Fusconaia flava, with which it should be compared. DISTRIBUTION Within Canada found only in Lake Erie and tributaries of Lake Erie and Lake St. Clair in southwestern Ontario. Farther south it occurs throughout most of the Missis- sippi- Missouri system. ECOLOGY Rare in Canada. Occurs in medium-sized to large rivers and in Lake Erie. Found on mud or sand, and with associated vegetation sparse or absent. Moderate current is appar- ent in its river localities. Gravid in late spring and early summer. The glochidia are subovate, without hooks, and measure about 0.1 5 mm in height and width. The outer demibranchs only are marsupial. The host fish is unknown. 270 101 Pleurobema coccineum a, d: South Bay, Pelee Is., L. Erie, Ont.; 63.5 mm. b, c: Rondeau Harbour, L. Erie, Ont. The specimen illustrated in colour on page 232 is from Rondeau Harbour, L. Erie, near Shrewsbury, Ont. (x 2/3). 271 SUBFAMILY ANODONTINAE (Floater Mussels) 102 Alasmidonta viridis (Rafinesque, 1820) Brook Wedge Mussel DESCRIPTION Shell up to 50 mm long (usually less), 30 mm high, 18 mm wide, and with shell wall up to 2 mm thick; more or less rhomboid in shape, quite thin, and some- what inflated, especially at the rounded posterior ridge. Shell smooth except for lines of growth and beak sculpturing. Periostracum dull yellowish brown to greenish, and in many specimens covered with rather obscure greenish rays. Nacre white or bluish white, and iridescent poste- riorly. Beak sculpture consists of 6 to 8 concentric ridges that are gently and unevenly curved centrally and angular on the posterior slope. Hinge teeth moderately small; pseudocardinal teeth elevated, trian- gular, 1 in the right valve and 1 split tooth in the left (a smaller tooth may also be present anterior to the major tooth); lateral teeth irregularly developed, 1 or 2 in the right valve and 2 in the left, but these may be reduced or nearly absent. Alasmidonta viridis was formerly known as A. calceola (Lea, 1830). DISTRIBUTION Canadian specimens have come only from southern Ontario in the Lake Huron, Lake St. Clair, and Lake Erie drainages. In the United States, A. viridis occurs in the middle Great Lakes drainages and in the Mississippi system from the Ohio River drainage to the Tennessee River drainage. ECOLOGY Characteristic of small headwater streams, but also occurs in larger rivers and in lakes. Substrates are usually sand or gravel but sometimes mud. A long-term (bradytictic) breeder but details are not known. Glochid- ia are subtriangular, with a ventral spine on each valve, and measure about 0.30 mm long and 0,26 mm high. Host fish are the johnny darter and mottled sculpin. 272 102 Alasmidonta viridis a, d: Irvine Creek near Dracon, Ont. b, c: West branch of Grand R., Ayr, Ont.; 35.5 mm. The specimen illustrated in colour on page 232 is from Smith Creek, Poole, Ont. (x 2/3). 273 103 Alasmidonta heterodon (Lea, 1830) Dwarf Wedge Mussel DESCRIPTION Shell up to about 45 mm long, 25 mm high, 16 mm wide, and with shell wall about 1 mm thick in mid-anterior region; more or less ovate or trapezoidal, roundly pointed posterio-basally, thin but not unduly fragile, with rounded posterior ridge, and of me- dium inflation. Females more inflated pos- teriorly than males. Sculpturing absent except for lines of growth and beak sculp- ture. Periostracum brown or yellowish brown, and with greenish rays in young or pale-coloured specimens. Nacre bluish or silvery white, and iridescent posteriorly. Beak sculpture composed of about 4 curved ridges, which are angular on the posterior slope. Hinge teeth small but distinct; pseudocardinal teeth compressed, 1 or 2 in the right valve and 2 in the left; lateral teeth gently curved and reversed , that is, in most specimens, 2 in the right valve and 1 in the left. The small size, roundly pointed posterior- basal margin, and reversed lateral hinge teeth readily distinguish this species. DISTRIBUTION Discontinuously distributed in the Atlantic drainage from the Petitcodiac River in New Brunswick (its only Canadian population) to the Neuse River in North Carolina. Common in the Petitcodiac River and in portions of the Connecticut River system, but uncommon to rare elsewhere. ECOLOGY Characteristic of medium-sized rivers with slow-to-moderate current. Found on mud, sand, or (rarely) gravel bottoms. A long-term breeder, with gravid specimens recorded in February and April. Glochidia are roughly triangular, with hooks, and mea- sure about 0.30 mm in length and 0.25 mm in height. The host fish has not been determined. 274 103 Alasmidonta heterodon a,b,c,d: Ashuelot R. near Keene, N.H,; b and c 39,9 mm. The specimen illustrated in colour on page 233 is from the North R. near Salisbury, N.B. (X 2/3), 275 104 Alasmidonta marginata Say, 1819 Ridged Wedge-Mussel DESCRIPTION Shell up to about 90 mm long, 50 mm high, 35 mm wide, and with shell wall about 2.5 mm thick in mid-anterior region; roughly trapezoidal in shape, rather thin; and with a prominent, inflated, sharply rounded posterior ridge, and concave poste- rior slope. Shell sculptured on the posterior slope, with well-marked grooves and ridges perpendicular to the lines of growth. Perios- tracum yellowish, greenish, brownish or blackish, paler on the posterior slope, and prominently rayed in most specimens. Nacre bluish white, and exhibiting in some specimens greyish or greenish discoloura- tions or suffusions of pale salmon. Beak sculpture coarse and consisting of 5 or 6 heavy double-looped bars. Hinge teeth characteristic : pseudocardinal teeth dorso- ventrally compressed, well developed, 1 in each valve; lamellate interdental projection in left valve; lateral teeth absent. The inflated posterior ridge, unique hinge teeth, sculptured posterior slope, and more or less trapezoidal shape distinguish it from all other species except A. varicosa of the Atlantic coastal region. In A. varicosa the posterior ridge is evenly (not sharply) rounded, the periostracum of some speci- mens is paler anteriorly than posteriorly (not the reverse), the shell does not exceed 75 mm in length, and it is not sharply truncated posteriorly. DISTRIBUTION Great Lakes St. Lawrence system from Lake Huron to the Ottawa River and the vicinity of Cornwall, Ontario; Ohio- Mississippi River system and Susquehanna River system in the United States. ECOLOGY Occurs in rivers. Most common in riffles or rapids on gravel or rocky bottoms. Her- maphroditic. Gravid specimens have been noted in July; probably a long-term breeder. The glochidia bear hooks, and are about 0.34 mm in length and 0.37 mm in height. The host fish are white sucker, northern hog sucker, shorthead redhorse, rock bass, and warmouth. 276 104 Alasmidonta marginata a, d: Nottawasaga R. near Alliston, Ont.; 78.6 mm. b, c: Thames R., Chatham, Ont, The specimen illustrated in colour on page 233 is from the Sydenham R. near Shetland, Ont. (x 2/3), 277 105 Alasmidonta undulata (Say, 1817) Heavy-toothed Wedge Mussel DESCRIPTION Shell up to 75 mm long, 45 mm high, 35 mm wide, and with shell wall about 6 mm thick at mid-anterior; triangular- ovate, centrally inflated, and with thickened anterior and low posterior ridge. Shell smooth except for lines of growth and heavy beak sculpture. Periostracum yellowish, greenish, reddish brown or black, and with greenish or blackish rays that are obscured in old blackened specimens. Nacre whitish anteriorly and bluish posteriorly, or modi- fied with salmon or pink. Beak sculpture very heavy and composed of about 5 prom- inent single-looped curved ridges that ex- tend far out on the disc (about 10 mm from the umbonal apex). Hinge teeth incomplete: pseudocardinal teeth strong and deeply grooved, 1 in the right valve and 2 in the left (the posterior one larger); interdental projec- tion in left valve clearly apparent in many specimens; lateral teeth vestigial or absent. The pseudocardinal teeth are buttressed below by a heavy ridge located behind the impressed anterior adductor muscle scar. The triangular form, modest size, thick- ened anterior, characteristic hinge teeth, and heavy beak sculpture distinguish this species from all others. DISTRIBUTION Atlantic drainage from Nova Scotia and the St. Lawrence River and its tributary rivers south to Florida. ECOLOGY Occurs in rivers and lakes. Found especially on sand or gravel bottoms. Reaches maxi- mum size in outlet streams just below lakes. Breeds from the middle of July to the middle of the following June. Glochidia have strong hooks and measure about 0.34 mm in length and 0.36 mm in height. The fish host is unknown. 278 105 Alasmidoma undulata a,b,c,d; St. Lawrence R. near Quebec, Que.;a andd 73.0 mm. The specimen illustrated in colour on page 233 is from the St, Lawrence R. near Montreal, Que. f x 2/3). 279 106 Alasmidonta varicosa (Lamarck, 1819) Swollen Wedge-Mussel DESCRIPTION Shell up to about 70 mm long, 40 mm high, 30 mm wide and with shell wall about 2 mm thick in mid-anterior region; elliptical to trapezoidal but with flattened ventral margin and truncated dorso-posterior mar- gin, rather thin, and with an inflated and rounded posterior ridge and slightly concave posterior slope. Shell smooth, or lightly sculptured on the upper posterior slope, with short grooves and ridges perpendicular to the lines of growth. Periostracum yellow- ish, greenish, brownish or blackish, and (in most specimens) extensively rayed. Nacre bluish white with olive or pinkish suffusions. Beak sculpture coarse and con- sisting of a few heavy single- or double- looped ridges, but these ridges are rarely preserved. Hinge teeth not well developed: pseudocardinal teeth weak, flattened, 1 in the right valve and 1 (smaller) in the left; interdental projection in left valve poorly developed or absent; lateral teeth absent. Characters that distinguish it from the closely related A. marginata are discussed under that species. The inflated posterior ridge and complete absence of lateral teeth easily differentiate it from the other species that it partially resembles, that is Lasmigona compressa andL. costata. DISTRIBUTION Atlantic coastal drainage from Nova Scotia and New Brunswick to North Carolina. ECOLOGY Usually found in rapids or riffles on rocky or gravel substrates and in sandy shoals, that is habitats similar to those of A. marginata. More abundant in small rivers and creeks, whereas A. marginata is more abundant in larger streams. The breeding period lasts from August to the following May, and glochidia are similar to those of A. margi- nata. The host fish has not been determined. 280 106 Alasmidonta varicosa a,b,c,d: Wallace R. near Pugwash, N.S.; a and d SI. 2 mm. The specimen illustrated in colour on page 233 is from Molunkus Stream, Macwahoc, Aroostook Co., Me. (x 2/3). 281 107 Lasmigona complanata (Barnes, 1823) White Heel-Splitter DESCRIPTION Shell up to 190 mm long, 125 mm high, 65 mm wide, and with shell wall 10 mm thick in mid-anterior; circular-trapezoid in juveniles but becoming ovate with age, diagonally truncate posteriorly, and thick- ened and rather strong anteriorly but thin and brittle posteriorly. A prominent and high dorsal projection (wing) occurs in juveniles and half-grown specimens. The wing is sculptured with radial ridges in some southern specimens but, except for growth rests and beak sculpture, the whole shell is unsculptured in Canadian material. Periostracum brown and indistinctly rayed in juveniles, blackish brown and unrayed in adults. Nacre white and tinged with bluish white posteriorly. Beak sculpture strong and composed of about 8 irregular or broken double-looped ridges that, in some specimens, are nodulous. Hinge teeth char- acteristic: pseudocardinal teeth large, thick, variable and irregular, 1 in the right valve (sometimes with 1 or 2 smaller teeth on either side of the large tooth) and 2 in the left; interdental projection present and low, or absent; lateral teeth vestigial or absent. Easily recognized by its compressed ovate shell, prominent dorsal wing, heavy pseudo- cardinal teeth, and white nacre. DISTRIBUTION Lake Winnipeg-Nelson River system from Alberta to western Ontario; middle Great Lakes -St. Lawrence River system in tribu- taries of Lake Michigan, Lake St. Clair and Lake Erie; Ohio-Mississippi River system throughout; and Alabama River system. ECOLOGY Occurs in rivers of various widths greater than about 7.5 m. Always found on sandy or muddy bottoms. The breeding season lasts from at least August to May. Glochidia are subtriangular, with hooks, and measure from 0.28 to 0.34 mm in length and 0.30 to 0.34 mm in height. The host fish are carp, green sunfish, largemouth bass, and white crappie. 282 107 Lasmigona complanata a, d: McGregor Creek, Chatham, Ont.; 127.0 mm. b, c: Minnedosa R. near Minnedosa, Man. The specimen illustrated in colour on page 234 is from the Seine R. near Winnipeg, Man. (x 2/3). 283 108 Lasmigona compressa (Lea , 1829) Brook Lasmigona DESCRIPTION Shell up to about 115 mm long, 55 mm high, 40 mm wide, and 4 mm in mid- anterior shell-wall thickness; trapezoid or rhomboid-ovate, with a low to moderate dorsal wing in immature specimens, com- pressed, and rather thin but not fragile. Rarely, a few faint radial grooves occur on the upper posterior slope, but ordinarily the shell is smooth except for beak sculpture and lines of growth. Periostracum yellowish brown, greenish or blackish brown, and extensively but not prominently rayed in most specimens. Nacre silvery white or bluish and, in some specimens, cream- or salmon-coloured near the beak cavities. Beak sculpture strong, and composed of about 8 variably irregular broken concentric ridges. Hinge teeth characteristic: pseudo- cardinal teeth strong, narrow, directed for- ward, typically 1 in the right valve and 2 in the left: interdental projection prominent in left valve; lateral teeth long and narrow, with 1 in the right valve and 2 in the left in most specimens, but undeveloped near the beaks or almost absent in some specimens. Well characterized by its shape, colour, beak sculpture, hinge teeth, and especially its prominent interdental projection. DISTRIBUTION Hudson Bay drainage from Saskatchewan to Ontario; Great Lakes- St. Lawrence drainage from Minnesota to Quebec and Vermont; Hudson River system in New York; and upper Ohio-Mississippi system south to West Virginia and Nebraska. ECOLOGY Occurs principally in rivers and streams of various sizes, even sometimes in very small creeks, 2 m wide or less. Rare in lakes. Found on substrates of gravel, sand, or mud. The breeding season lasts from August to the following June. Normally hermaphro- ditic. The glochidia are circularly triangu- lar, with hooks, and measure about 0.34 mm in length and 0.28 mm in height. The host fish is not known. 284 108 Lasmigona compressa a, d: Creek near Leggatt, Ont.; 78.6 mm. b, c: Turtlelake R., Edam, Sask, The specimen illustrated in colour on page 234 is from the Red Deer R. near Hudson Bay, Sask. (x 2/3). 285 109 Lasmigona costata (Rafinesque, 1820) Fluted Shell DESCRIPTION Shell up to about 150 mm long, 75 mm high, 50 mm wide, and with shell wall 6 mm thick in mid-anterior region; trape- zoid-ovate, without a posterior wing in all growth stages, of medium inflation, quite thick and strong, and heavily sculptured. The shell is sculptured on the posterior slope with up to 20 heavy radial ridges, with growth irregularities on the disc, and with beak sculpturing on the umbones. Perios- tracum yellowish, greenish or brownish, and with generally distributed narrow greenish or brownish rays that become mostly obscure in mature specimens. Nacre white or bluish white, with yellow or pink tints centrally. Beak sculpture composed of about 4 heavy double-looped concentric ridges. Hinge teeth well developed: pseudo- cardinal teeth strong and knob-like or lamellar, 1 in the right valve and 2 smaller ones in the left; interdental projection heavy and prominent in the left valve; lateral teeth rudimentary or absent. The large size, characteristic shape, and heavy posterior sculpturing make identifica- tion of most specimens very easy. Small specimens from some populations with reduced sculpture may resemble L. com- pressa , but they can be distinguished by characters of the hinge teeth, beak sculp- ture, and internal structure (that is relative proportion of males to females). DISTRIBUTION Hudson Bay drainage in the Red and Winnipeg River systems; Great Lakes- St, Lawrence system from southern Lake Huron and its tributaries to the Ottawa River and Lake Champlain ; and entire Ohio- Mississippi River system. ECOLOGY Occurs in canals, rivers, and lakes. Found on gravel, sand, or mud bottoms. Like other unionids it responds positively to increased water hardness by becoming unusually large and thick. The breeding season lasts from the beginning of August to the middle of May. The sexes are separate. Glochidia are triangular, and measure about 0.36 mm in length and 0.38 mm in height. A host fish is the carp. 286 109 Lasmigona costata a, d: Grand R. near Doon, Ont.; 109.5 mm, b, c: Baker Creek near Niagara R. near Fort Erie, Ont. The specimen illustrated in colour on page 235 is from the St. Lawrence R. near Cornwall, Ont. (x 2/3). 287 no Simpsoniconcha ambigua (Say, 1825) Mudpuppy Mussel DESCRIPTION Shell up to about 42 mm long, 20 mm high, 16 mm wide, and with shell wall almost 3 mm thick at mid-anterior; elongate ellipti- cal, and sharply rounded at the ends but more or less straight dorsally and ventrally. Periostracum brownish and without rays. Nacre whitish or with muted yellow or purple suffusions, especially near the beak cavity. Beak sculpture of 4 or 5 parallel, V-shaped bars with their apices directed toward the umbonal apex. Beaks sharp, narrow, inclined forward, and located about 1/4 the distance from anterior to posterior. Hinge teeth incomplete and irregular: 1 pseudocardinal tooth in each valve; lateral teeth either rudimentary or lacking entirely. This small, rare species resembles Carun- culina parva , but may be distinguished by the incomplete hinge teeth and characteris- tic beak sculpturing. Compare also with Alasmidonta heterodon and Villosa fabalis. DISTRIBUTION Lake St. Clair drainage (Sydenham River, one record) in southern Ontario; central Great Lakes drainages in the United States; and Ohio-Mississippi drainage from Michi- gan to Iowa and south to Arkansas and Tennessee. ECOLOGY Usually found under flat stones in rivers but also in mud or on gravel. The glochidial host is an amphibian, the mudpuppy {Nectu- rus maculosus). This is the only freshwater mussel known to utilize an animal other than a fish for glochidial attachment. 288 110 Simpsoniconcha ambigua a,b,c,d: Troublesome R. above Lost Creek, Ky.; a and d 33.3 mm. The specimen illustrated in colour on page 235 is from the same locality (x 2/3). 289 Ill Anodontoides ferussacianus (Lea, 1834) Cylindrical Floater DESCRIPTION Shell up to 95 mm long, 40 mm high, 40 mm wide, and with shell wall 1.5 mm thick in mid-anterior region; elliptical, much inflated, rather fragile, and with unusual oblique beak sculpturing. Shell unsculptured except for concentric lines and low ridges associated with growth rests and beak sculpture. Periostracum greenish or brownish, with prominent dark annuli; numerous, generally distributed, prominent or obscure, narrow green or brown rays and 2 or 3 broader dark rays on the low rounded posterior ridge and posterior slope. Nacre bluish white, slightly iridescent, and with tints of cream in the beak cavity of some specimens. Beak sculpture unique, fine, and composed of several curved ridges that are not parallel to the lines of growth but follow an anteriorly expanded arc. Several fine radial ridges also exist posterior to the curved ridges. Hinge teeth absent except for a narrow swelling of the shell margin in front of the beak. Characterized by its moderate size; thin, inflated and subcyclindrical shell; and espe- cially by its fine, oblique, subconcentric beak sculpture, DISTRIBUTION James Bay and Hudson Bay drainage from central Ontario to southeastern Saskatche- wan; Great Lakes- St. Lawrence system downstream to near Montreal; and Ohio Mississippi River system south to Colorado and Tennessee. ECOLOGY Usually found in slow-moving streams on mud bottoms but also occurs in lakes and sometimes on sand. The breeding season lasts from August until May. Glochidia are subtriangular, with hooks, and measure about 0.32 mm in length and height. The mottled sculpin and the sea lamprey are host fish. 290 Ill Anodontoides ferussacianus a, d: Baker Creek near Niagara R. near Fort Erie, Om.; 69.9 mm. b, c: Grand R., Riverview, Ont. The specimen illustrated in colour on page 235 is from the Souris R. near Souris, Man. (x 2/3). 291 112 Anodonta beringiana Middendorff, 1851 Yukon Floater DESCRIPTION Shell up to 150 mm long, 75 mm high, 55 mm wide, and with shell wall about 3 mm thick at mid-anterior; elliptical, broadly rounded anteriorly and more nar- rowly rounded posteriorly, without a dorsal wing, and moderately thin but relatively strong. Surface roughened by lines of growth but centrally shining. Periostracum olive-green in juveniles but dark brown to nearly black in old specimens. Nacre lead- colour to dull blue, Umbones inflated and elevated above hinge line. Beak sculpture consisting of a few rather straight, irregular bars parallel to the hinge line. Hinge teeth absent. Quite similar to very large specimens of A. kennerlyi but distinguished by its larger shell, dark periostracum, inflated beaks that clearly project above the hinge line, and lead-coloured to bluish nacre. Occurs in more northern drainages than A. kennerlyi. DISTRIBUTION Yukon River drainage in the Yukon Terri- tory and Alaska, and other drainages in Alaska and in Kamchatka, USSR. ECOLOGY Known from rivers and lakes within its range. The glochidia have been reported as 0.296 mm in height and width. Fish hosts are the sockeye salmon, chinook salmon, and three-spined stickleback. 292 112 Anodonta beringiana a,b: Old Crow R. near Old Crow, Y.T.; 133.4 mm. The specimen illustrated in colour on page 236 is from a lake in Porcupine Valley near Fort Yukon, Y.T. (x 2/3). 293 113 Anodonta cataracta cataracta Say, 1817 Eastern Floater DESCRIPTION Shell up to 150 mm long* 75 mm high, 65 mm wide, and with shell wall about 1.5 mm thick at mid-anterior; elliptical, roundly pointed posteriorly, inflated, thin, fragile, and with inflated beaks that project above the hinge line. Surface smooth except for low concentric wrinkles and growth rests. Periostracum shiny and grass-green, or modified with yellow or brown, or simply brown all over; in many specimens with numerous narrow green rays covering the disc and the central area, and a few broad green rays on the posterior ridge and slope. Nacre silvery or white, tinged with blue or yellow, and iridescent. Beak sculpture consisting of about 6 to 8 primarily double- looped, curved, concentric bars that are not nodulous. Hinge teeth absent. Similar to A. c.fragilis , but that subspe- cies has beak sculpture with 8 to 12 single- looped bars and lacks green periostracum (which is present in many, but not all, A . c. cataracta). Compare also A grandis grandis and A. g. simpsoniana. DISTRIBUTION Lower St. Lawrence River drainage and Maritime Provinces south in the Atlantic drainage to the Gulf of Mexico drainage. At the north end of its range it intergrades with A . c.fragilis , and in the middle of the St. Lawrence system with A. grandis grandis. ECOLOGY Occurs in ponds, lakes, and streams of various widths down to small brooks. Most abundant on mud (where it is commonly bright green) but also occurs on sand and, less frequently, on gravel. The breeding season lasts from July to the following April or May. Glochidia are roughly triangular, with hooks, and measure about 0.36 mm in length and 0.37 mm in height. The host fish are reported to be the pumpkinseed and the carp. 294 113 Anodotua cataracta cataracta a, d: Emerald L., North Dorset, Vt.; 101.6 mm. b, c: L, Edward, Denmark Parish, N.B. The specimen illustrated in colour on page 236 is from a ditch near Quebec, Que. (x 2/3). 295 114 Anodonta cataracta fragilis Lamarck^ 1819 Newfoundland Floater DESCRIPTION Shell up to about 90 mm long, 45 mm high, 25 mm wide, and with mid-anterior shell wall 1.5 mm thick; long-elliptical with bluntly pointed posterior located at or below the midline, rounded or nearly straight ventral ly, diagonally flattened dorso-posteri- orly, and typically thin and fragile. Surface marked by fine concentric wrinkles and prominent growth rests. Periostracum shiny or dull, straw-yellow to brown, and (in a few pale specimens) with obscure fine green rays on the disc and central area and a few poorly defined broad green rays on the posterior ridge and slope. Nacre silvery, white or bluish, and centrally discoloured with yellowish blotches in most specimens. Beak sculpture consisting of about 8 to 12 fine, irregular, concentric, single-looped bars that extend about 8 mm from the um- bonal apex. Hinge teeth absent. Characterized principally by its beak sculpture, lack of green periostracum, and small size. Compare with A. c. cataracta and A. kennerlyi. DISTRIBUTION Typical specimens occur principally in Newfoundland, but specimens exhibiting intermediate characteristics between A. c. fragilis and A. c. cataracta are common throughout northern Nova Scotia, New Brunswick, and eastern Quebec. Such specimens are considered to be intergrades and are referred to simply as Anodonta cataracta or, more precisely, as A. c. cata- racta x A, c. fragilis , or the reverse, with the dominant morph cited first. ECOLOGY Occurs in diverse, permanent-water habitats (ponds, lakes, and streams of various sizes) as does A. c. cataracta . Found principally in mud but also in sand and, less commonly, in gravel. Undoubtedly a long-term breeder, but no details are known about its reproduc- tive period, glochidia, or fish host. 296 114 Anodonta cataracta fragilis a, d: Wells Gully, Whitbourne, Nfld.; 69.9 mm. b, c: Poucette L. near Port Elgin, N.B. The specimen illustrated in colour on page 236 is from the same locality as a and d (x 2/3). 297 115 Anodonta grandis grandis Say, 1829 Common Floater DESCRIPTION Shell up to about 160 mm long, 100 mm high, 7 5 mm wide, and with shell wall 4 mm thick at mid-anterior and 8 mm thick near anterior pallial line. Shell highly variable in form but typically ovate, inflated, thin, and fragile. Surface smooth and shiny except roughened with low, concentric wrinkles and growth rests. Periostracum yellowish brown, greenish, greenish brown or blackish, and (in many specimens) with extensive but poorly defined green rays and concentric lighter and darker bands. Nacre white or bluish white, rarely pinkish. Umbones inflated, projecting well above hinge line, and located about 30% of the distance from anterior to posterior. Beak sculpture variable but ordinarily heavy, double-looped, and with the loop apices elevated and forming 2 radial rows of tubercules. Hinge teeth absent. The above description is of typical A. g. grandis. Most specimens from the lower St. Lawrence system are much smaller (about 75 mm long), are relatively more elongated, have a dark and roughened periostracum, and exhibit beak sculpture in which the nodules are poorly developed. Typical A, g, grandis , however, is character- ized by its ovate inflated form and its double- looped and nodulous beak sculpture. DISTRIBUTION Canadian Interior Basin from central Ontario to central Alberta; Great Lakes - St. Lawrence system east to near Montreal; Ohio-Mississippi system throughout; and Gulf of Mexico drainages in Louisiana and Texas. ECOLOGY Occurs in permanent ponds, lakes and rivers of various sizes. Found on all types of substrates but is most abundant on mud. The breeding season is reported to last from early August to the following April or May. Both dioecious (separate sexes) and monoe- cious (hermaphroditic) specimens occur. The glochidia are triangular-ovate, with spines, and measure from 0.31 to 0.36 mm long and 0.28 to 0.33 mm high. Numerous fish species have been shown to act as hosts (see Fuller in Hart and Fuller 1974). 298 115 Anodonta grandis grandis a, d: Gatineau R. near Kazabazua, Que.; 120.7 mm, b, c: L. Erie, Point Pelee, Ont. The specimen illustrated in colour on page 237 is from the Grand R. near Onondaga, Ont. (X 2/3). 299 116 Anodonta grandis simps oniana Lea, 1861 Northern Floater DESCRIPTION Shell up to about 125 mm long, 55 mm high, 45 mm wide, with shell wall 2 mm thick at mid-anterior; variable but com- monly elliptical, roundly pointed poste- riorly, of medium inflation, thin, and rather fragile. Surface roughened by fine concen- tric wrinkles and prominent growth rests. Periostracum brown in most specimens, greenish or yellowish in others, and with faint greenish rays and/or concentric darker and paler bands in some specimens. Nacre silvery, white, or bluish, and with or without salmon or yellow suffusions near the beak cavity. Beaks low but clearly projecting above hinge line and located about 25% of the distance from anterior to posterior. Beak sculpture composed of 4 to 6 single-looped or faintly double-looped curved bars that are not nodulous. Hinge teeth absent. May be distinguished from A. g. grandis principally by its beak sculpturing that is predominantly single-looped and not nodu- lous; in grandis s. str. it is double-looped and nodulous. Beak also farther forward and shell relatively more elongate and com- pressed than in A. g. grandis. Inter grades occur between the two subspecies in their zone of contact. DISTRIBUTION Canadian Interior Basin in the boreal forest region from northern Quebec west to central Alberta, and northwest to the mouth of the Mackenzie River. ECOLOGY Has been found in permanent ponds, in lakes, and in rivers more than about 9 m wide. All kinds of substrates are inhabited by this mussel. Gravid specimens with glochidia have been collected between July 22 and August 24, but the duration of its gravid period is not known. Glochidia are triangular-ovate, with hooks, and measure about 0.36 mm long and 0.35 mm high. The host fish is unknown. 300 116 Anodonta grandis simpsoniana a, d: L. St. Joseph near Rat Rapids, Ont.; 101.6 mm. b, c: L. Cache near Chibougamau, Que. (49°50'N, 74°24'W). The specimen illustrated in colour on page 237 is from Wilson L. south of Nellie Lake, Ont. (x 2/3). 301 117 Anodonta imbecilis Say, 1829 Paper Pond- Shell DESCRIPTION Shell up to about 90 mm long, 50 mm high, 40 mm wide, and with shell wall 1 mm thick at mid-anterior; elliptical, moderately in- flated, pointed at mid-posterior, slightly alate, and fragile. Shell smooth except for very fine concentric striae, growth rests, and beak sculpture. Periostracum green to greenish brown, shiny, with numerous fine green rays visible on the disc, and with a few broad green or brown rays clearly apparent on the posterior ridge and slope. Nacre bluish white, silvery, and iridescent posteriorly. Umbones flat and without pro- jections above the hinge line. Beak sculp- ture composed of about 6 fine, irregular, concentric ridges, with the earlier ones ridged and broken centrally, and the later ones somewhat double-looped. Hinge teeth absent. The flat unelevated beaks, greenish frag- ile shell, and characteristic beak sculpturing distinguish this species from all other Anodonta in Canada and the northern United States. DISTRIBUTION Lake Erie and Lake St. Clair drainages in southern Ontario (Grand and Sydenham rivers) and adjacent parts of the United States; Ohio-Mississippi system generally; Gulf of Mexico drainage from the Ochlock- nee River system in western Florida to the Rio Grande River system; and southern Atlantic coastal drainage from the Altamaha River system in Georgia to the Gunpowder River system in Maryland, ECOLOGY Occurs in muddy to somewhat sandy habitats in slow-moving rivers, canals, and lakes; rare on gravel bottoms. Hermaphro- ditic, A long-term breeder, with gravid periods probably overlapping in the summer in different individuals. Glochidia are roughly triangular, with hooks, and mea- sure about 0.23 mm in length and height. The creek chub and the green sunfish have been implicated as host fish. 302 117 Anodonta imbecilis a,b,c,d: Ohio Canal, Columbus, Ohio; a andd 69.9 mm. The specimen illustrated in colour on page 238 is from the Erie Barge Canal near Macedon, N.Y. (x 2/3). 303 118 Anodonta implicata Say, 1829 Alewife Floater DESCRIPTION Canadian specimens are up to about 125 mm long, 65 mm high, 40 mm wide, and with shell wall about 3.2 mm thick at mid-anterior and near the anteroventral margin below the pallial line. (More-south- ern specimens may be 20% larger and have a shell wall 5 mm thick.) Shell long-elliptical, thickened anteriorly, thinner posteriorly, inflated in females and more compressed in males, and with the posterior ridge well defined and double in most specimens. Surface marked with prominent concentric growth rests, and in most specimens with severe corrosion on the anterior and around the umbones. Periostracum heavy, yellow- ish, brownish or blackish, and in some young specimens obscurely rayed. Nacre ordinarily salmon or pinkish or, more rarely, white or bluish. Beaks inflated and some- what elevated. Beak sculpture composed of about 8 heavy double-looped concentric bars. Hinge teeth absent. Adult is well characterized by its promi- nent anteroventral thickening below the pallial line, large size, dark, rayless perios- tracum, and salmon or pinkish nacre. DISTRIBUTION Atlantic coastal plain from Nova Scotia (Cape Breton) and eastern Quebec south to the Potomac River system in Maryland. ECOLOGY Restricted to coastal streams and lakes that can be reached by its anadromous host fish, the alewife. Occurs principally in sand and gravel, rarely in mud; the largest individuals have been found in relatively rapid streams. The breeding season is not known in detail but probably occurs from about August or September to June. Glochidia are rather large, approximately triangular, and with hooks at the tip of each valve. The host fish is the alewife, a predominantly saltwater fish that in the spring migrates into fresh water to spawn. Some true freshwater fish (white sucker, white perch, and pumpkin- seed) have also been named as hosts, but the distribution of A. implicata makes this doubtful. Landlocked freshwater popula- tions of the alewife also occur in the Great Lakes, but A. implicata is not found there. 304 118 Anodonta imp It cam a, d: Darlings L., Lakeside, N.B. b, c: Branch of Denny Stream near Moores Mills, N.B.; 92.1 mm. The specimen illustrated in colour on page 238 is from Great Herring Pond near Buzzard’s Bay, Mass, (x 2/3). 305 119 Anodonta kennerlyi Lea, 1860 Western Floater DESCRIPTION Shell up to about 120 mm long, 65 mm high, 40 mm wide (but commonly much smaller), and with shell wall about 1.5 mm thick at mid-anterior and 3 mm at antero- ventral pallial line; elliptical, bluntly pointed posteriorly, without a dorsal wing, and relatively thin and fragile. Surface roughened by lines of growth but shiny in many specimens. Periostracum yellowish, yellowish brown or brown, tinged with green in some specimens, and with promi- nent dark-brown growth rests. Nacre whit- ish or bluish white, and in some individuals centrally suffused with salmon. Umbones flattened and barely projecting above hinge line. Beak sculpture consisting of about 1 5 irregular concentric ridges that extend up to 10 mm beyond the umbonal apex. Hinge teeth absent. The elliptical shape and lack of a dorsal wing separate this species from the only other Anodonta in British Columbia, namely A. nuttalliana. Similar to A. berin- giana but smaller and with lighter perios- tracum. Compare also with A. cataracta fragilh . DISTRIBUTION In British Columbia occurs abundantly on Vancouver Island and other coastal islands (including the Queen Charlone Islands) and on the mainland from the Columbia to the Fraser and Skeena River systems. Also crosses the Continental Divide and occurs in a few mountain lakes in the uppermost North Saskatchewan and Athabasca River systems of Alberta. Southward the species extends in the Pacific drainage to Oregon. ECOLOGY Often abundant. Occurs in muddy or sandy substrates in rivers and lakes. Probably a long-term breeder, with the breeding period beginning in early August. The glochidia are triangular, with a straight hinge and a spine at the ventral apex of each valve, and measure approximately 0.30 mm in length and height. The fish host is unknown. 306 119 Anodonta kennerlyi a, d: Aberdeen L., Aberdeen, Wash.; 93.7 mm. b, c: Still Creek, Queen Charlotte Islands, B.C. The specimen illustrated in colour on page 238 is from Horse L. east of 100 Mile House, Lillouet Dist., B.C (x 2/3). 307 120 Anodonta nuttalliana Lea, 1839 Winged Floater DESCRIPTION Shell up to about 1 10 mm long, 75 mm high, 45 mm wide, and with mid-anterior shell wall about 3 mm thick; highly variable in shape but ordinarily trapezoid-ovate, centrally inflated, with posterior margin obliquely flattened, and with a more or less prominent dorsal wing. Some specimens are relatively compressed, and in others the dorsal wing is not well developed. Surface roughened by lines of growth. Periostracum yellowish green, yellowish brown or brown, and with prominent dark-brown growth rests in some populations. Nacre white or bluish. Umbones flattened and projecting only very slightly, or not projecting, above hinge line. Beak sculpture consisting of up to 20 or more fairly strong concentric ridges that may be irregularly single- or double-looped and that extend about 1 0 mm beyond the tip of the umbones. Hinge teeth absent. The ovate and winged shape of A. nuttalliana easily distinguishes it from the other two Pacific-drainage A nodonta species in Canada, namely A. kennerlyi and A. beringiana , which are elliptical and lack a dorsal wing. The numerous umbonal ridges are characteristic of both A. kennerlyi and A, nuttalliana and differentiate them from all other Canadian species except A. cata- racta fragilis from the Maritime provinces. Synonyms include A. wahlamatensis Lea, 1839, and A. oregonensis Lea, 1839. In many localities A. nuttalliana occurs together with A. kennerlyi Lea, but intergrades have never been observed. The two species are therefore fully distinct. DISTRIBUTION Fraser and Columbia River systems in southern British Columbia, and south to central California. Absent from Vancouver Island. ECOLOGY Occurs in rivers and lakes on muddy and sandy bottoms. The largest Canadian speci- mens seen are from Vaseux Lake and Osoyoos Lake, both river-lakes in the Okanagan River, a tributary of the Colum- bia River. Little is known about its breeding season, although gravid specimens with immature larvae have been observed in October. The glochidia and host fish are unknown. 308 120 Anodonia nunalliana a, d: Osoyoos L., Osoyoos, B.C.; 114.3 mm. b, c: Okanagan L. near Vernon, B.C. The specimens illustrated in colour on pages 238 and 239 are from: a) Box L. south of Nakusp, B.C.; b) Vaseux L. north of Oliver, B.C. (x 2/3). J 309 121 Strophitus undulatus (Say,, 1817) Squaw-Foot DESCRIPTION Shell up to about 100 mm long, 55 mm high, 45 mm wide, and with mid-anterior shell wall about 3 mm thick; elliptical to trapezoid, somewhat compressed to moder- ately inflated, and of medium thickness. Surface roughened by concentric wrinkles and growth rests. Periostracum blackish brown in adults (paler near the umbones), and yellowish or greenish brown and with green rays in juveniles. Nacre white or bluish white, with suffusions of yellow or salmon near the beak cavity, and with a narrow band of olive-green or greenish brown at the border. Beak sculpture of 4 or 5 coarse concentric ridges that are approxi- mately parallel to the growth lines. Hinge teeth rudimentary: pseudocardinal hinge teeth vestigial and indicated by a swelling of the hinge line on each valve just anterior to the beak or, rarely, by small clearly discernable pseudocardinal teeth; lateral teeth entirely absent. The dark periostracum, vestigial pseudo- cardinal hinge teeth, and characteristic nacre readily distinguish this species. It is closest in appearance to Anodontoides ferus- sacianusj but that species is paler in colour, has a thinner shell, and has fine, clearly oblique beak sculpture. DISTRIBUTION Canadian Interior Basin in the Red River- Nelson River system from western Ontario to eastern Saskatchewan; Great Lakes - St. Lawrence system throughout; Ohio -Mississippi system from Minnesota to Texas and from Pennsylvania to Tennes- see; and Atlantic coastal drainage from Nova Scotia to South Carolina. ECOLOGY Occurs principally in rivers and creeks but occasionally in lakes. Inhabits all sub- strates, but the finest specimens are from sandy bottoms, especially in lake outlets. The breeding season lasts from July to the following April or May. The glochidia are subtriangular , with hooks, and have been reported as 0.36 mm long and 0.30 mm high in one population, and as 0.46 mm long and 0.36 mm high in another. The glochid- ia are reputed to be able to complete their development without a period of parasitism on fish. Successful metamorphosis has also been reported on fish, however, in particular on the largemouth black bass and the northern creek chub. 310 121 Strophitus undulatus a, d: Creek near Leggatt, Ont.; 63,5 mm, b, c: L. Winnipeg near Elk Is., Man. The specimen illustrated in colour on page 239 is from the Assiniboine R. near Amsterdam, Sask. posterior end much curved and anterior end begins back from inner edge of hinge-plate. Well characterized in most specimens by the prominent subconcentric ridge on each beak. In this it resembles the more abundant and widespread P. compressum , but in that species the hinge plate is more than 3/4 the length of the shell, the shell is propor- tionately much higher, and the anterior end is not extended and pointed basally. Com- pare also withP. lilljeborgi morph cristatum andP. subtruncatum . DISTRIBUTION Introduced, probably from Europe, and now widespread in the lower Great Lakes- St. Lawrence River system. Also occurs in Eurasia and Iceland. ECOLOGY Rare. In North America occurs chiefly in large bodies of water. In Europe it is also found in unpolluted rivers and canals. Litter sizes of from 1 to 7 young have been re- corded in Sweden. 404 166 Pisidium henslowanum a; L. Ontario near Collins Bay, Ont. (x 16). b,c,d: Prince Edward Bay, L, Ontario, Ont. (b x 22; c and d x 19). e,f,g,h: L, Ontario near Collins Bay, Ont. (x 1 1). 405 167 Pisidium (Cyclocalyx) lilljeborgi Clessin, 1886 Lilljeborg’s Pea Clam DESCRIPTION Shell up to about 4 mm long, proportion- ately high (H/L 0.82-0.94), moderately inflated (W/L 0.59-0.73), triangular-ovate, and rather thin shelled. Beaks prominent, high, full, and located posterior of centre. Dorsal margin short, posterior of centre, openly curved and joining anterior and posterior margins with angles; posterior margin roundly truncate and vertical; ante- rior margin elongate and distally rather sharply rounded; ventral margin long and curved. Hinge plate less than 3/4 of shell length and rather heavy. Surface of shell finely to rather coarsely striate, and slightly dull to moderately glossy. Details of hinge teeth, according to Her- rington (1962), are as follows: Laterals Al, A2 and P2 moderately long (Al and A3 form a V); cusp of Al proximal or on proximal side of center, or central (somewhat blunt on top), of A2 proximal (high and sharp on top), of P2 distal (high, a rather steep incline and sharp on top); cardinals close to anterior cusps; C3 rather long, usually bent with anterior end parallel with hinge-plate, posterior end quite expanded; C2 short and broad; C4 narrow, twice or more as long as C2 [but only as long as C2 in some specimens] . . . and extending . . . diagonally along hinge-plate. Occasionally specimens have ridges on the beaks and may be shorter than the typical form. These are called P . lilljeborgi morph cristatum Sterki, 1928. Differs from P, casertanum in that the anterior margin joins the dorsal margin at an angle, and the beaks are more elevated and more prominent. Compare also with P. subtruncatum. DISTRIBUTION Occurs throughout Canada as far north as southern Baffin Island and southern Victo- ria Island, throughout Alaska, in New England and the northern tier of states, and south in the Rocky Mountains to Colorado, Utah, and California. Also found in Iceland and in northern Europe. ECOLOGY Common. Lives in all permanent-water habitats, especially lakes. Inhabits clay, mud, sand, or gravel. Adult specimens containing mature young have been found only in summer, and litter sizes of up to 13 have been observed. NOTE Another species of Pisidium (P. waldeni Kuiper, 1975), closely related toP. lillje- borgi, has recently been recorded from arctic Canada. It is reported to differ by having a longer dorsal margin, a longer hinge plate, and shorter cardinal teeth in the left valve, as well as other characters. See Kuiper (1975) for details. 406 167 Pisidium lilljeborgi a: Oner L. near Shawville, Que. (x 14). b,c: L. Saint-Simon, Rimouski Co., Que. (x 11). 407 168 Pisidium (< Cyclocalyx ) milium Held, 1836 Quadrangular Pill Clam DESCRIPTION Shell small, up to 3 mm long, of moderate height (H/L 0.62-0.88), greatly inflated (W/L 0.60-0.95), and variable in shape but more or less triangular and flattened ven- trally (in end view). Beaks swollen, promi- nent, and located rather far back. Dorsal and ventral margins openly curved; posterior margin truncated; and anterior margin long, sloped above, and roundly pointed below. Hinge plate narrow and less than 3/4 the shell length. Surface with rather fine concentric striae and a few prominent growth rests. Periostracum thin, glossy, and pale yellowish brown. The dentition, according to Herrington (1962), is as follows: Laterals rather short; cusps inclined to be sharp on top; cusps of left valve toothpick-like, of A1 and A2 central or on distal side of center, of P2 somewhat distal; cardinals fairly near anterior cusps, but varying, sometimes subcentral; C3 slightly curved and uniform in width; C2 and C4 nearly same thickness and about parallel; C4 begins well over C2, slightly curving or straight (C2 is the shorter of the two). The small size, roughly triangular shape, prominent inflation, and flat but truncated ventral margin formed by the two appressed valves (when viewed from one end) are good diagnostic characters for this species. It resembles P. nitidum , but that species is higher, has a more sharply curved ventral margin, and the anterior cusps are more distal and not as sharp. DISTRIBUTION Occurs from the Maritime Provinces to British Columbia; in western Canada to north of Great Slave Lake. Also found in Alaska, the northern United States, south in the Rocky Mountains to Colorado and Utah, and in Europe. ECOLOGY Uncommon. Lives in lakes, ponds, and slow-moving streams. Occurs on muddy bottoms among vegetation. Swedish speci- mens were observed to produce young from June to September. 408 409 169 Pisidium (< Cyclocalyx ) nitidum Jenyns, 1832 Shiny Pea Clam DESCRIPTION Shell small, up to about 3 mm long, relatively high (H/L 0.80-0.92), of moderate inflation (W/L 0.57-0.64), roughly rhom- boidal in shape, and thin walled. Beaks posterior of centre, broad, low, and curved. Dorsal margin long and evenly curved; anterior margin curved and steep above and roundly pointed below; ventral margin long and broadly curved; and posterior margin roundly truncated and vertical or undercut. Surface sculptured with fine striae (more than 30 per mm). Periostracum pale yellow- ish or greyish brown and very glossy. The hinge teeth, according to Herrington (1962), are as follows: Laterals of moderate length, straight or flaring outward at distal end; cusps rather prominent, but inclined to be blunt on top; cusp of A 1 distal or on distal side of center, of PI, P2, and A2 rather distal; cardinals subcentral; C3 gently curved, of uniform width except at posterior end, and almost parallel with hinge-plate; C2 slightly heavier than C4; C4 straight or gently curved, about parallel with C2, space between the two of uniform width, straight or a little curved, and usually directed across hinge-plate at a gentle angle. Distinguished by its small size, relatively long hinge, shiny finely striate surface, and details of dentition. Two well-marked “ ‘forms” are known in addition to the typical form. Form contortum is longer, has a nearly straight ventral margin, and is more pointed in the anterior basal region. Form paupercu- lum is shorter, higher, heavier, and has a more curved dorsal margin and more- central cardinal teeth. DISTRIBUTION Broadly distributed throughout Canada, the United States, Mexico, Eurasia, and North Africa. ECOLOGY Common. Lives in all kinds of perennial- water habitats, on various substrates, and most commonly in shallow water. In each litter, 2 to 7 young are ordinarily produced. 410 169 Pisidium nitidum a,b,c,h,i: Typical nitidum: Pleasant Park, Cressy, Ont (i a,b,c x ll;)jandi x 18), d,e: Morph contortum: Klotz L. near Longlac, Ont. (x 11). f,g: Morph pauperculum: Rice L., Peterborough Co., Ont (x 11). 411 170 Pisidium (Cyclocalyx) rotundatum Prime, 1852 Fat Pea Clam DESCRIPTION Shell small, up to about 3.3 mm long, relatively high (H/L 0.80-0.92), greatly inflated (W/L 0.70-0.76), ovate, and thin. Beaks prominent, large, inflated, capped in some specimens, and located about 1/3 of the distance from posterior to anterior or (usually) more centrally. All margins rounded, the anterior and posterior margins more sharply rounded than the dorsal and ventral. Hinge plate short, narrow, curved, and posterior of centre. Surface covered with moderate-to-fine striae that are evenly spaced. Periostracum yellowish brown and glossy. The hinge teeth, according to Herrington (1962), are as follows: Laterals short; cusps short and high with near- vertical ends; cusps of A2 proximal, of P2 and A1 central or on distal side of center; cardinals close to anterior cusps; C3 curved, but not much enlarged at posterior end. . C2 and C4 short; C2 almost parallel with hinge- plate, straight, sometimes slightly curved, or just a peg; C4 straight or slightly curved, sometimes parallel with hinge- plate, but more often directed slightly downward, then not parallel with C2; proximal end of posterior sulcus of right valve closed by a pseudocallus on inner side of proximal end of P3 and, therefore, does not run out on top of hinge-plate. Distinguished from its close relative P. ventricosum by the more central position of the beaks and the narrow hinge plate (between the cardinals and A2). In P. ven- tricosum the beaks are nearly posterior, and the hinge plate is broad between the cardinals and A2. DISTRIBUTION Widespread in Canada south of the tree line. Also occurs in the northern tier of states in the United States, and south in the Rocky Mountains to Mexico. ECOLOGY Lives, as does P. ventricosum, in lakes, permanent ponds, rivers, and streams. Found among vegetation and in various substrates but typically in mud. Nothing is known about its life history. 412 170 Pisidium rotundatum a: Pond in Byron Bog, London, Ont. (x 23). b,c; Keefer L. near Kelowna, B.C. (x 19). 413 171 Pisidium {Cyclocalyx) subtruncatum Malm, 1855 Short-ended Pea Clam DESCRIPTION Shell rather small, up to almost 4 mm long, relatively high (H/L 0,74-0.94), inflated (W/L 0.54-0.74), ovate, variable in shape, and thin walled. Beaks narrow, prominent, projecting above the hinge line, and located far back. Dorsal margin short, curved, posterior of centre and joining anterior margin with an angle close to the anterior cusps; anterior margin long or short and rather sharply rounded centrally; ventral margin long and openly curved; posterior margin roundly truncate and joining dorsal margin with an angle. Hinge short and curved; hinge plate narrow. Striae evenly spaced, fine, and numbering 30 or more per mm. Periostracum glossy and yellowish brown. The hinge teeth, according to Herrington (1962), are as follows: Laterals rather long, cusps prominent; cusps of A1 and A2 proximal to central, of PI and P2 central; cardinals near anterior cusps or subcentral; C2 and C4 roughly parallel, posterior ends slightly nearer inner edge of hinge-plate; C3 long and not much curved; width of hinge-plate and size of shell influences cardinals considerably. Resembles P. walkeri , but that species is more compressed, the cusp of A1 is less proximal, the left cardinals are not parallel, and the periostracum is dull. Compare also withP. lilljeborgi. DISTRIBUTION Occurs in Prince Edward Island and throughout central Canada north to, and slightly beyond, the tree line. Also found from New York to Montana, south in the Rocky Mountains to California and Colo- rado, and in Europe. ECOLOGY Lives in lakes, ponds, muskeg pools, rivers, and streams. Found among vegetation and on various kinds of bottoms. Two litters of young are born each year, and life spans exceed 1 year. 414 415 172 Pisidium (Cyclocalyx) supinum Schmidt, 1850 Hump-backed Pea Clam DESCRIPTION Shell medium-sized, up to about 4.5 mm long, relatively high (H/L ca. 0.90), inflated (W/L ca. 0.67), roughly trianglular, and moderately thick to thick. Beaks high and full; and each beak surmounted by an oblique, more or less concentric raised ridge. Dorsal margin short, strongly curved, and joining the anterior and posterior margins without angles; anterior margin lengthened, flattened above, roundly pointed below, and curving smoothly into the long rounded anterior margin; posterior margin truncated and only slightly rounded. Hinge teeth typically thick and heavy. Surface sculptured with moderately heavy, concentric striae (about 16 to 18 per mm). Periostracum yellowish brown and moder- ately dull. Hinge teeth similar to those ofP. hen- slowanum , but much heavier and with the cardinals farther from the anterior cusps. Compare also with/ 3 , compressum and P. subtruncatum. DISTRIBUTION This Eurasian and Icelandic species was first discovered in North America near the eastern end of Lake Ontario in about 1959. It has not yet been observed elsewhere in the Great Lakes-St. Lawrence system. Living specimens were recently (1975) found, however, in the Eastmain and La Grande rivers in northern Quebec by B. T. Kidd. Has also been recorded in late Pliocene and Early Pleistocene deposits in Idaho. ECOLOGY Uncommon in North America. In Europe it is characteristic of rivers and is rare in lakes. 416 172 Pisidium supinum a,b,c: Athol Bay, L. Ontario, near Athol, Ont. (x 14), 417 173 Pisidium (i Cyclocalyx ) variabile Prime, 1852 Triangular Pea Clam DESCRIPTION Shell up to about 5 mm long, proportion- ately high (H/L 0.72-0.97), of medium inflation (W/L 0.54-0.68), triangular-ovate, thick walled, and variable in shape. Beaks prominent, full, and located posterior of centre. Dorsal and posterior margins round and continuous; ventral margin long and more openly curved; anterior margin roundly angled distally and joining the short dorsal margin without an angle. Hinge plate about 3/4 the length of the shell (or a little more), heavy, and rather steeply curved. Surface of shell glossy, and covered with rather fine to quite coarse striae (but less than 30 per mm). The hinge teeth are described by Herring- ton (1962) as follows: Laterals rather short, incorporated into hinge-plate; A3 and P3 tend to curve around pit of sulcus; cusps blunt on top; cusps of A1 distal, of PI, A2, and P2 central or on distal side of center; cardinals central; C3 short, much curved, posterior end much the larger; C2 short and stout like an inverted D; C4 fairly short, only slightly curved and directed toward cusp of P2; considerable space between posterior ends of C2 and C4. Distinguished by its rather heavy and roughly triangular shell, glossy surface, and characteristic hinge teeth. The hinge teeth are similar only to those ofP. compressum , but that species is smaller, with dull periostracum, and in most specimens bears a prominent concentric ridge on each beak. DISTRIBUTION Occurs throughout southern Canada and northward into the subarctic. Also recorded from most of the United States. ECOLOGY Common. Lives in virtually all natural perennial-water habitats. Found in various substrates (most frequently mud) and usu- ally amid vegetation. Litter size varies from at least 12 to 34. No anatomical studies have been done on this species. 418 419 174 Pisidium (Cyclocalyx) ventricosum Prime, 1851 Globular Pea Clam DESCRIPTION Shell small, up to about 3 mm long, relatively high (H/L 0.82-1.00), greatly inflated (W/L 0.80-0,95), ovate, and rather heavy. Beaks large, swollen, and placed far back on the shell. Dorsal margin smoothly curved and passing imperceptibly into anterior margin; anterior margin sloped, broadly curved above, and roundly curved centrally or in an area just below the centre; ventral margin long, evenly rounded, and continuing in an uninterrupted curve into the posterior margin; posterior margin flatly curved and undercut. Hinge plate heavy and relatively short, that is less than 3/4 the length of the shell. Surface finely striate (more than 30 per mm) and with prominent growth rests in many specimens. Periostracum yellowish brown to greyish, and glossy. Hinge teeth similar to those in P. rotun - datum but heavier, and the hinge plate between the cardinal teeth and A2 is relatively wide, not thin. This small species is well characterized by its greatly inflated heavy shell and prominent, swollen, posteriorly -placed beaks. Compare with P. rotundatum and P. milium. DISTRIBUTION Occurs throughout central Canada south of the tree line and in isolated localities in eastern Canada. Also recorded from across the northern United States from Maine to Washington, and south in the Rocky Mountains to Mexico. ECOLOGY Lives in perennial-water lakes, ponds, rivers and streams of all sizes. Aquatic vegetation and muddy bottoms characterize typical habitats. Nothing is known about its anat- omy or reproduction. 420 174 Pisidium ventricosum a: Mechanic Lake Brook near Alma, N.B. (x 27). b,c: Reindeer L., Brocher, Man. (x 19). 421 175 Pisidium 0 Cyclocalyx ) walkeri Sterki, 1895 Walker’s Pea Clam DESCRIPTION Shell up to about 6 mm long, relatively high (H/L 0.80-0.90), moderately inflated (W/L 0.54-0.68), somewhat ovate but ante- riorly elongate, and rather thin walled. Umbones moderately large and located posterodorsally. Dorsal margin strongly curved and tilted posteriorly; anterior mar- gin long, slightly curved above and roundly pointed below the centre; ventral margin long and gently curved; posterior margin flattened and vertical. Hinge plate less than 3/4 the shell length and not entirely parallel with the dorsal margin. Surface of shell dull to somewhat shining and with less than 30 striae per mm. The hinge teeth, according to Herrington (1962), are as follows: Laterals rather long, cusps moderately sharp; cusps of A1 central or on distal side of center; of PI distal, of A2 proximal or on proximal side of center, of P2 central; cardinals subcentral; C2 short, much curved (sometimes an inverted D); C4 much lighter, short, curved, directed toward interior of shell; C3 parallel with hinge-plate, varying in degree of curva- ture, its posterior end enlarged. The “form” ofP. walkeri called mainense Sterki, 1903, is smaller and relatively short- er, and with finer striae, a more rounded anterior slope, left cardinal teeth that are more nearly parallel, and a longer C2. Differentiated from/ 5 , subtruncatum by its coarser striae. Compare also with P. casertanum . DISTRIBUTION Typical P. walkeri have been found from New Brunswick to James Bay, and in western Canada north into the Northwest Territories. Also widely distributed in the United States south to Virginia and Ari- zona. P . walkeri form mainense is more eastern, and is recorded from scattered sites in subarctic eastern Canada, from New Brunswick to Massachusetts, and in Illi- nois. Both forms are considered together on Map 175. ECOLOGY Rather uncommon. Occurs in permanent lakes, ponds, rivers, and streams. Found most frequently among vegetation and on a variety of substrates. A single litter of young are born during the 1-year lifetime of each individual. The anatomy of this species has not been studied. 422 423 176 Pisidium ( Neopisidium ) conventus Clessin, 1877 Arctic-Alpine Pea Clam DESCRIPTION Shell up to almost 3 mm long, of moderate height (H/L 0.68-0.88), rather compressed (W/L 0.44-0.65), more or less ovate or trapezoid, variable in shape, thin, and fragile. Beaks low, rounded, and located a little posterior of centre. All margins curved and with variable shape: for example, in some specimens the anterior and posterior margins are obliquely truncated and roughly parallel, in others the anterior margin is roundly pointed centrally and the posterior margin is vertically truncated. Hinge plate very long and narrow. Surface of shell covered with fine concentric striae and irregularly spaced growth rests. Perios- tracum thin and pale yellow or whitish. Details of the hinge teeth, according to Herrington (1962), are as follows: Laterals long and slender; cusps of Al, PI, and A2 distal or on distal side of center, of P2 distal; cardinals central or subcentral; C2 at or on proximal end of A2, short, close to inner edge of hinge- plate or overhanging and either about parallel with hinge-plate or with posterior end slightly more interior; C4 slightly longer than C2, slimmer, straight or slightly curved, beginning above center of C2 and parallel with it, or its posterior end directed a little more toward the interior; C3 moderately long, slightly curved, almost parallel with hinge-plate, posterior end enlarged somewhat, there- fore, nearer inner edge of hinge-plate. Well characterized by its small, thin, fragile, and pale-coloured shell, its over- hanging cardinal hinge teeth, its subtrape- zoidal shape (when present), and its unusual habitat. DISTRIBUTION Occurs in most of the nothern states of the United States and northward throughout most of Canada (to Victoria Island) and Alaska. Also found in alpine lakes across Eurasia and north to the Eurasian arctic coast. ECOLOGY A cold water species. Lives principally at considerable depths in large lakes within the temperate parts of its range, and at all depths within subarctic and arctic regions. Two broods of young are produced each year, 1 in summer and 1 in winter. 424 425 177 Pisidium ( Neopisidium ) cruciatum Sterki, 1895 Ornamented Pea Clam DESCRIPTION Shell up to about 2 mm long, proportion- ately high (H/L ca. 0.94 -0.95), quite inflated (W/L ca. 0.70-0.74), triangular, thick, and heavy. Beaks prominent, elevated, and pos- terior of centre. Each beak bears a heavy U-shaped ridge whose ends are directed ventrally and perpendicular to the lines of growth. Dorsal margin short and rounded, ventral margin long and flatly curved, anterior margin steep and roundly pointed basally, and posterior margin truncated and joining the dorsal margin in a smooth curve. Hinge plate very heavy and more than 3/4 the length of the shell. Surface dull and with coarse concentric striae (about 16 per mm). Details of the hinge teeth, according to Herrington (1962), are as follows: Laterals heavy and short, little more than cusps; cusps of A1 and PI distal, of A2 central or on either proximal or distal side of center, of P2 on distal side of center; cardinals central; C2 heavy, usu- ally an inverted D; C4 slim, slightly curved and directed toward cusp of P2 or slightly inside; C3 parallel with hinge- plate, curved somewhat on the outside, the [greatly enlarged] posterior end mak- ing the inside considerably curved; liga- ment pit very short and wide, width almost equalling length, and deepening as it approaches inside of hinge-plate where it breaks through, resembling in this respect the European species P. vincentianum. Characterized by its very small size, triangular shape, heavy shell, and strangely shaped ridges on the beaks. Unlike any other species. DISTRIBUTION Known only from a few mostly disjunct localities in Ontario (Thames River) and the central United States south to Arkansas and Alabama. ECOLOGY Very rare. Reported to live in mud among dead leaves and aquatic plants and to be so covered with a black or brown coat that it resembles a globule of soil. Its distribution implies that it occurs only in hard-water habitats. Nothing is known about its repro- duction or anatomy. 426 177 Pisidium cruciatum a,b: Honeoye Creek, Rush, N.Y. {a x 27; b x 41). c,d: Raisin R, near Norwell, Mich, (c x 27; d x 1 1). e-j: Grand R., Pottawattomie Bayou, Ottawa Co., Mich, (x 16). 427 178 Pisidium (Neopisidium) insigne Gabb, 1868 Tiny Pea Clam DESCRIPTION Shell very small, up to about 2 mm long, relatively high (H/L 0.82-0,84), compressed (W/L 0.47-0.59), elliptical, and thin shelled. Beaks low, rounded, and close to centre. Dorsal margin long and gently curved, anterior end broad and roundly pointed, ventral margin long and very gently curved, and posterior margin roundly truncate. Hinge plate narrow, long, and openly curved. Surface finely striate (about 25 to 30 per mm). Periostracum brownish and (in many specimens) with foreign material adhering to it. The hinge teeth, according to Herrington (1962), are as follows: Laterals long and slim, cusps rather sharp on top; cusp of A2 distal or on distal side of center, of P2 very distal (the distance from this cusp to the cardinals seems very great), of A1 distal or on distal side of center, of PI distal; cardinals of right valve subcentral or nearer anterior cusps; C2 small, almost straight, parallel with inside of hinge-plate; C4 small, rather indistinct, slightly curved, almost parallel with C2, posterior end a little nearer inside of hinge-plate and a little more posterior than C2; C3 slim, straight, or slightly curved, frequently slightly enlarged at posterior end, which is a little nearer the inside of hinge-plate. Characterized by its very small size, low and elongate form, and broad rounded anterior end. Compare with/ 5 , conventus and with juvenile P. casertanum. DISTRIBUTION Known in Canada only from Prince Edward Island, southern Ontario, and southern British Columbia. Also occurs across the northern United States and south in the Rocky Mountains to Arizona and New Mexico. ECOLOGY Found principally in slow-moving creeks and spring creeks. Almost nothing is known about its biology. 428 178 Pisidium insigne a: Lidstone Creek, Prince Co., P.E.I. (x 22). b,c: Long L., Wellington, B.C. (x 22). 429 179 Pisidium ( Neopisidium ) punctatum Sterki 5 1895 Perforated Pea Clam DESCRIPTION Shell minute, up to about 1.7 mm long, relatively high (H/L 0.82-0.94), inflated (W/L 0.56-0.71), ovate, quite thin, and full of tiny holes that are clearly visible at magnification of 50 x . In many specimens a transverse more or less concentric ridge is present near the umbones. Dorsal and ventral margins openly curved; anterior margin roundly pointed centrally and flat- tened above; posterior margin somewhat truncated, curved, and joining the dorsal margin with an angle. Hinge plate more than 3/4 shell length. In addition to the tiny holes, the surface is covered with rather coarse, concentric, evenly spaced striae. Periostracum very thin and pale yellowish brown. The hinge teeth, according to Sterki (1895), are as follows: Hinge moderately strong; cardinal teeth fine, in the left valve two, lamellar, longitudinal, about equally long, a little curved, almost parallel, the upper little anterior; in the right valve one, longitudi- nal, little curved, lamellar, the posterior end slightly thickened; lateral teeth rather small and thin, in the left valve one, pointed, in the right valve two, the outer quite small. Best distinguished by its very small size, regular but rather coarse striae, and tiny holes (or punctae) that cover the shell. The umbonal ridge, when present, is also dis- tinctive. Closely related to P. punctiferum Guppy, but that species is much larger, more finely striate, and occurs only in the southern United States. DISTRIBUTION Found in scattered localities in southern Canada from Ontario to British Columbia, and in the northern United States. ECOLOGY Uncommon. Occurs in lakes and in slow- moving portions of rivers and streams. Found among vegetation and usually on muddy bottoms. Adults bear 2 litters of young each year, 1 in the spring and 1 in the fall. 430 179 Pisidium punctatum a,b,c: Athol Bay, L. Ontario, Prince Edward Co., Ont. (x 27). 431 Glossary abaxial outward, away from shell axis. adaxial inward, toward shell axis. adductor muscle a large muscle which closes the valves of a bivalved mollusc shell. alate expanded like a wing. ann uli (sing, annulus) ringlike thickenings, generally related to previous growth pauses. apex top of the spire, the first formed part of a gastropod (snail) shell, pointed in most species. arcuate bent or arc-like. beak the earliest formed part of a bivalved shell. See umbo. bifid partly but not wholly split into two similar parts. biconvex convex on both sides. calcareous containing and/or resembling calcium carbonate. callus thickened shelly structure that covers inner lip or columellar region of a gastropod shell. cardinal central or major, as in cardinal hinge teeth. Carina prominent spiral keel or ridge. carinate bearing one or more spiral keels or ridges. collabral conforming to shape of outer lip at an earlier growth stage as shown by growth lines. columella centrally located pillar surrounding the axis of coiling of a spiral gastropod shell. conoid shaped like a cone. cusp a projecting peak on a radular tooth, decurrent flowing downward. dextral right-handed or coiled in a clockwise direction when viewed from above; when viewed from the front (apex above) the aperture is on the right. dimorphism the condition of having two distinct forms, especially as in sexual dimorphism, in which males and females are visibly different. dioecious having the male reproductive system in one individual and the female in another. disc the rounded anterior portion of a freshwater mussel shell. distal far from the point of origin or attachment, opposite from proximal. dorsal the back, or, in bivalved molluscs, the area that includes the umbones and the ligament. eutrophic lake a shallow lake ordinarily characterized by an abundance of plant and animal life and a muddy bottom with high organic content. Oxygen concentrations are low in deeper water during the summer. This is a late stage in normal lake succession from the oligotrophic condition through mesotrophic to eutrophic, leading eventually to a marsh and finally to dry land, globose inflated and approaching the shape of a sphere. glochidia (sing, glochidium) the larvae of freshwater mussels (superfamily Unionacea). gravid pregnant, that is with fertilized eggs or unborn young within the body. 433 growth rest a ridge formed during an intermediate stage of growth when this area was the edge of the shell. helicone a cone twisted into a spiral form; the distally expanded coiled tube that forms most gastropod shells. hermaphrodite an individual that has both male and female sexual organs, hinge the structure that joins the two halves of a bivalve shell at the dorsal margin. It is generally composed of an elastic ligament and articulating hinge teeth. hinge plate the thickened edge of a bivalved mollusc shell to which hinge teeth (if present) are attached. immersed depressed below the adjacent whorls, as an immersed nuclear whorl. impressed lying below the general adjacent surface as if stamped into it. inflated expanded and distended. mterdentum in freshwater mussels the area of the hinge plate between the pseudocardinal and the lateral hinge teeth, lamellae thin plates or blade-like ridges. lentic characteristic of standing water, opposite to lotic. lip the structure surrounding, either entirely or in part, the mouth or aperture of a snail shell. lotic characteristic of running water, opposite to lentic. lymnaeiforxn shaped more or less like a rypical Lymnaea, that is like L. stagnalis. malleate bearing flattened areas as if hammered. man tle the fleshy sheet of tissue that secretes the shell of a mollusc and is appressed to its inner surface. It encloses the mantle cavity and most, or all, of the internal organs. marsupial in molluscs refers to the possession of a structure for containing or enclosing the young. mesotrophic lake a lake of moderate depth with intermediate abundance of plants and animals. See oligo trophic lake and eu trophic lake. monoecious having both the male and female reproductive systems in the same individual. morph a distinct form or colour phase of a variable species. nacre the pearly inner layer characteristic of some mollusc shells. nuclear whorl the first turn of a spiral shell, beginning at the apex and corresponding to part or all of the larval shell. obtuse an angle exceeding 90°. oligotrophic lake a deep lake with sparse plant and animal life, and with low organic content in bottom deposits. Oxygen concentrations in such a lake remain high in deep water throughout the year. This is the first stage in normal lake succession. See eutrophic lake and mesotrophic lake. operculum a horny or shelly plate- like structure attached to the foot of most prosobranch gastropods. It seals the shell aperture when the animal is contracted within the shell. ovate oval; used also in combinations such as ovate-quadrate, meaning intermediate between ovate and quadrate. palatal lip the outer lip of a snail shell, that is the portion of the lip on the outer side of the aperture. pallial line an impressed line on the inner surface of a bivalved mollusc shell that marks the zone of attachment of the mantle to the shell. parietal in gastropods, pertaining to that pan of the aperture adjacent to, or pressed against, the preceding whorl. parthenogenic capable of reproduction by direct development, without fertilization of the eggs. 434 patulous broadly expanded or limpet-like. pauci spiral consisting of few spirals or of less than one complete spiral. pelagic capable of swimming, or floating, in open water for extended periods. penultimate next to the last. The penultimate whorl is the one just above the body whorl. peristome lip. periostracum the outer parchment-like layer of a mollusc shell. plait a spiral, flattened ridge on the columella. planorboid coiled approximately in a single plane or resembling typical species of the family Planorbidae. planospiral coiled in a single plane. plicae broad ridges. post-basaJly located in the basal (ventral) region near the posterior end. prosocline with plane of aperture inclined away from the axis in its upper part, and toward the axis in its lower part. This is characteristic of most prosobranch gastropods. protoconch the larval shell of a mollusc. It is still visible in some partly mature and adult specimens. pseudocardinal the centrally located, short (or stump-like) hinge teeth of most bivalve molluscs. punctate the surface pitted with tiny holes. quadrate more-or-less four-sided, resembling a square or rec- tangle. scalariform loosely coiled with whorls not touching at the sides or tending toward this condition. See illustration of Valvata sincera ontariensis. sculpture impressed or raised markings. sensu lato in the broad sense (abbreviated s. lau) sensu stricto in the strict sense (abbreviated s. sir.) septate with one or more internal shelly partitions, serrate with a series of notches or grooves at the edge, like a saw or a file. shouldered shaped like a shoulder, with a flattened upper surface bounded by a definite angle. sigmoid shaped like an S. sinistra! left-handed or coiled in a counterclockwise direction when viewed apically, that is from above. Viewed from the front (apex above) the aperture is on the left. sinuate wavy or sinuous. spire the upper surface of a spiral snail shell. In most species it is cone-shaped and tapers to a point (the apex). The last whorl (the body whorl) is not considered to be pan of the spire. In flatly coiled snails, especially ramshorn snails (Planorbidae), the spire may be flat or concave but is recognizable because it is less concave than the base of the shell that contains the umbilicus. spire angle the angle at the apex formed by the cone of the spire, sp. abbreviation for species (singular). spp. abbreviation for species (plural). ssp. abbreviation for subspecies (singular), sspp, abbreviation for subspecies (plural). 435 striae impressed lines or narrow grooves. sub globose inflated but not so much as to be round or globose. substrate the substance on which an organism lives or grows, such as soil, gravel, or rocks. suffusion an overspreading, as with a tint of colour. suture a spiral line or groove marking the junction of adjacent whorls, tabulate shaped like a table. trapezoidal shaped like a trapezoid, that is a four-sided geometric figure similar to a rectangle but with only two parallel sides. truncate shaped as if cut off. umbilicus the hollow centre (if present) of the axis of rotation of a snail shell, visible from the base of the shell. umbo the apex, or juvenile shell, of one half (a valve) of a bivalve mollusc. umbones plural of umbo. varix a prominent ridge or protrusion formed by expansion of the shell aperture during a previous stage of growth. ventral the underside or lower pan of the shell. In bivalves it is on the opposite side from the beaks and hinge. verge in some gastropods an organ of the male genital tract that bears the penis. vernal occurring in the spring, for example a vernal pool. whorl a single complete turn of a spiral shell. 436 References Serious students are referred to the following literature for additional information. The list includes not only the references cited elsewhere in this book by author and date only, but also the important works published in this field since 1968. For more extensive bibliographies of Canadian freshwater molluscs, consult especially Clarke (1973), LaRocque (1953), Taylor (1975), and the section on Mollusca in th e Zoological Record, published annually (since 1864) by the Zoological Society of London. Abbott, R.T. (1974). American Seashells: The Marine Mollusca of the Atlantic and Pacific Coasts of North America. 2nd ed. New York: Van Nostrand Reinhold. 663 pp. Bailey, R.M.; Fitch, J.E.; Herald, E.S.; Lachner, E.A.; Lindsey, C.C.; Robins, C.R.; and Scott, W.B. (1970). A List of Common and Scientific Names of Fishes from the United States and Canada. 3rd ed. American Fisheries Society, Special Publication 6. 150 pp. Baker, F.C. (1928a). The Fresh- Water Mollusca of Wisconsin, Part I: Gastropoda. Wisconsin Geological and Natural History Survey, Bulletin 70. 507 pp. (19286). The Fresh- Water Mollusca of Wisconsin, Pan II: Pelecypoda. Wisconsin Geological and Natural History Survey, Bulletin 70. 495 pp. Baker, H.B. (1925). Anatomy of Lanx, a Limpet-like Lymnaeid Mollusk. Proceedings of the California Academy of Sciences, Series 4, 14(8): 143-69. Basch, P.F. (1963). A Review of the Recent Freshwater Limpet Snails of North America (Mollusca: Pulmonata). Harvard University, Museum of Comparative Zoology Bulletin 129(8): 401-61. Berry, E.G. (1943). The Amnicolidae of Michigan: Distribution, Ecology, and Taxonomy. Miscellaneous Publications, Museum of Zoology, University of Michigan, No. 57. 68 pp. Bousfield, E.L. (1960). Canadian Atlantic Sea Shells. Ottawa: Depart- ment of Northern Affairs and National Resources, National Museum of Canada. 72 pp. Burch, J.B. (1962). How to Know the Eastern Land Snails. Dubuque, Iowa: Brown. 214 pp. (1975a) Freshwater Sphaeriacean Clams (Mollusca: Pelecypoda) of North America. Rev. ed. Hamburg, Mich.: Malacologieal Publications. 96 pp. (Previously published in 1972 by the U.S. Environmental Protec- tion Agency in Biota of Freshwater Ecosystems, Identification Manual No. 3. Washington, D.C.: U.S. Government Printing Office. 31 pp.) (19756) Freshwater Unionacean Clams (Mollusca: Pelecypoda) of North America, Rev. ed. Hamburg, Mich.: Malacologieal Publications. 204 pp. (Previously published in 1973 by the U.S. Environmental Protec- tion Agency in Biota of Freshwater Ecosystems, Identification Manual No. 11. Washington, D.C.: U.S. Government Priming Office. 176 pp.) Clampitt, P.T. (1970). Comparative Ecology of the Snails Physa gyrina and Physa Integra (Basommatophora: Physidae). Mala- cologia 10(1): 113-51. Clarke, A.H. (1973). The Freshwater Molluscs of the Canadian Interior Basin. Malacologia 13(1-2). 509 pp. (1976). Endangered Freshwater Mollusks of Northwest- ern North America. Bulletin of the American Malaco- logical Union Inc. for 1976: 18-19. Clarke, A.H., and Berg, C.O. (1959). The Freshwater Mussels of Central New York, with an Illustrated Key to the Species of Northeastern North America. Cornell University, Agricultural Exper- iment Station, Memoir 367. 79 pp. Dazo, B„C. (1965). The Morphology and Natural History of Pleurocera acuta and G onto basis livescens (Gastropoda: Cerithiacea: Pleuroceridae). Malacologia 3(1). 80 pp. Dundee, D.S. (1957). Aspects of the Biology of Pomatiopsis lapidaria (Say) (Mollusca: Gastropoda: Prosobranchia). Miscella- neous Publications, Museum of Zoology, University of Michigan, No. 100. 37 pp. Goodrich, Calvin (1942). The Pleuroceridae of the Pacific Coastal Drainage, including the Western Interior Basin. Occa- sional Papers of the Museum of Zoology, University of Michigan, No. 469. 4 pp. (1945). Goniobasis livescens of Michigan. Miscellaneous Publications, Museum of Zoology, University of Mich- igan, No. 64. 36 pp. 437 Haas, Fritz (1969). Superfamilia Unionacea. Das Tierreich 88. 663 pp. Hanna, G.D. (1966). Introduced Molluscs of Western North Amer- ica. Occasional Papers, California Academy of Sci- ences, No. 48, 108 pp. Hart, C.W., Jr., and Fuller, S.L.H. (eds.) (1974). Pollution Ecology of Freshwater Invertebrates. New York and London: Academic Press. 389 pp. Heard, W.H. (1965). Comparative Life Histories of North American Pill Clams (Sphaeriidae: Pisidmm). Malacologia 2(3): 381-411. (1975). Sexuality and other aspects of reproduction in Anodonta (Pelecypoda: Unionidae). Malacologia 15(1): 81-103. Heard, W.H., and Guckert, R.H. (1970). A Re-evaluation of the Recent Unionacea (Pelecypoda) of North America. Malacologia 10(2): 333-55. Herrington, H.B. (1962). A revision of the Sphaeriidae of North America (Mollusca: Pelecypoda). Miscellaneous Publications, Museum of Zoology, University of Michigan, No. 118. 74 pp. Hubendick, Bengt (1951). Recent Lymnaeidae, Their Variation, Morphol- ogy, Taxonomy, Nomenclature, and Distribution. Kunglica Svenska Vetenskapsakademiens Handlingar, Fjarde Serien, 3(1). 223 pp. (1964). Studies on Ancylidae, the subgroups. Goteborgs Kungliga Vetenskaps och Vitterhets-Samhalles Hand- lingar, Sjatte Foljden, Series B, 9(6): 1-72. Johnson, R.I. (1970). The Systematies and Zoogeography of the Unionidae (Mollusca: Bivalvia) of the Southern Atlan- tic Slope Region. Harvard University, Museum of Comparative Zoology Bulletin 140(6): 263-449. Kuiper, J.G.J. (1975). Zwei neue boreal e Ptsidium-Arten: P. hinzi und P. waldeni. Archivfiir Molluskenkunde 106(1/3): 27-37. LaRocque, Aurele (1953). Catalogue of the Recent Mollusca of Canada, National Museum of Canada Bulletin 129 (Biological Series 44). 406 pp. Mackie, G.L. (1973). Biology ofMusculium securis (Pelecypoda: Sphaeriidae). . . . Ph.D. dissertation, University of Ottawa. 175 pp. Mayr, Ernst (1969). Principles of Systematic Zoology. New York: McGraw-Hill. 428 pp. Moore, R.C. (ed.) (1969). Treatise on Invertebrate Paleontology, Part N. Mollusca 6, Bivalvia. Vol. 2 of 3. New York and Lawrence, Kans.: Geological Society of America and University of Kansas. N491-N951. Morrison, J.P.E. (1955). Notes on the Genera Lanx and Fisherola (Pulmonata). Nautilus 68(3): 79-83. Odhner, N.H. (1929). Die Molluskenfauna des Takern. Sjon Takerns Fauna och Flora, utgiven av K. Svenska Vetenskaps- akademien. Stockholm: Almqvist and Wiksells. 129 pp. Pilsbry, H.A. (1925). The Family Lancidae Distinguished from the Ancylidae. Nautilus 38(3): 73-75. (1939-48). Land Mollusca of North America (North of Mexico). Monographs of the Academy of Natural Sciences of Philadelphia, No. 3, 1(1): 1-573 (1939); 1(2): 575-994 (1940); 2(1): 1-520(1946); 2(2): 521-1113 (1948). Ross, H.H. (1974), Biological Systematies. Reading, Mass.: Addi- son- Wesley Publishing Co. 345 pp. Sinclair, R.M., and Isom, B.G. (1963). Further Studies on the Introduced Asiatic Clam (Corbicula) in Tennessee. Tennessee Department of Public Health, Tennessee Stream Pollution Control Board. 76 pp. Solem, G.A. (1974). The Shell Makers: Introducing Mollusks. Toronto: John Wiley and Sons. 289 pp. Sterki, V. (1895). Two New Pisidia. Nautilus 8(9): 97-100. Taylor, D.W. (1966). Summary of North American Blancan Non- Marine Mollusks. Malacologia 4(1): 1-172. (1975). Index and Bibliography of Late Cenozoic Freshwater Mollusca of Western North America. Claude W. Hibbard Memorial Vol. 1. Museum of Paleontology Papers on Paleontology, No. 10. 384 pp. Taylor, D.W., and Sohl, N.F. (1962). An Outline of Gastropod Classification. Mala- cologia 1(1): 7-32. Taylor, D.W.; WUter, H.J.; and Burch, J.B. (1963). Freshwater Snails of the Sub-genus Hinkkyia (Lymnaeidae: Stagnicola) from the Western United States. Malacologia 1(2): 237-81. 438 Te, G.A, (1975). Michigan Physidae, with Systematic Notes on Physella and Physodon (Basommatophora: Pulmonata). Malacological Review 8 (1/2) 7-30. Vkn der Schalie, H., and Dundee, D.S. (1955). The Distribution, Ecology and Life History of Pomatiopsis cincinnatiensis (Lea), an Amphibious Operculate Snail. Transactions of the American Micro- scopical Society 74(2): 119-33. Index to Scientific and Common Names References are to the consecutive numbers assigned to the species in the text. Italic numbers indicate that the taxon is briefly discussed under that species entry. Family names are listed in the table of contents, Acella haldemani 36 Acroloxus coloradensis 23 Actinonaias carinaia 131 acuta, Pleurocera 20 adamsi , Pisidium 160 Adam’s Pea Clam 160 Alaskan Pond Snail 40 Alasmidonta calceola (= Alasmidonta viridis) 102 heterodon 103 marginata 104 undulata 105 varicosa 106 viridis 102 alata, Prop ter a 1 26 alberta, Bakerilymnaea bulimoides morph 31 Alewife Floater 118 ambigua, Simpsoniconcha 110 Amblema plicata 94 American Ear Snail 35 Amnicola limosa 14 walkeri 15 amnicum, Pisidium 1 57 Amphibious Fossaria 29 anceps, Helisoma anceps 77 angulata , Gonidea 93 A nodonta beringiana 1 12 cataracta cataracta 113 cataracta fragilis 1 14 grandis grandis 115 g randis simpsoniana 116 imbed lis 117 implicata 118 kennerlyi 119 nuttalliana 120 oregonensis {— Anodonta nuttalliana) 120 zoahlamatensis (— Anodonta nuttalliana) 120 A nodontoides feruss acianus 111 Aplexa hypnorum 65 appressa, Lymnaea stagnalis (= Lymnaea stagnalis jugularis) 38 arctica, Stagnicola 43 Arctic-Alpine Fingernail Clam 147 Arctic-Alpine Pea Clam 176 armigera,Planorbula 75 A rmiger crista 70 Asiatic Clam 144 atheami, Physa jennesst 5 6 atkaensis, Lymnaea 40 auricularia, Radix 33 Bakerilymnaea bulimoides 3 1 bulimoides morph alberta 31 morph bulimoides 3 1 morph cockerelli 3 1 morph perplexa 3 1 morph techella 31 morph vancouverensis 3 1 dalh 32 Banded Mystery Snail 2 Banff Springs Physa 5 8 BeanVillosa 140 Bell-mouthed Ramshorn 79 beringiana, Anodonta 112 binneyi, Helisoma trivolvis 85 Burney’s Stout Ramshorn 85 Bithynia tentaculata 19 Black Sand-Shell 133 Blade-ridged Stagnicola 41 Blunt Albino Physa 56 Blunt Arctic Physa 5 5 Blunt Prairie Physa 57 British Columbia Menetus 74 Broad Promenetus 72 Brook Lasmigona 108 Brook Wedge Mussel 102 Brown Mystery Snail 1 Bulimnea megasoma 37 bulimoides, Bakerilymnaea 3 1 bulimoides, Bakerilymnaea bulimoides morph 31 Bulimus tentaculatus (= Bithynia tentaculata) 19 Bythinia tentaculata (= Bithynia tentaculata) 19 calceola, Alasmidonta (= Alasmidonta viridis) 102 campanulatum , Helisoma campanulatum 79 Gampeloma decisum 1 integrum 1 Gampeloma Spire Snail 10 campestris, Planorbula 76 Capacious Manitoba Ramshorn 8 1 caperata, Stagnicola 41 carinata, Actinonaias 131 cariosa, Lampsilis 134 Carunculina parva 127 casertanum, Pisidium 161 cataracta, A nodonta cataracta 113 catascopium, Stagnicola catascopium 44 chinensis, Cipangopaludina 3 Cincinnatia cincinnatiensis 10 dncinnatiensis, C incinnatia 1 0 cincinnatiensis, Pomatiopsis 1 8 Cipangopaludina chinensis 3 circumstriatus, Gyraulus 66 coccineum, Pleurobema 101 cockerelli, Bakerilymnaea bulimoides morph 31 441 collinsi, Helisoma campanulatum 80 coloradensis, Acroloxus 23 Columbiana, Physa 59 Columbia River Physa 59 columella, Pseudosuccinea 35 Common Floater 1 1 5 Common Stagnicola 47 complanata, Elliptio 99 complanata, Lasmigona 107 compressa, Lasmigona 1 08 comp res sum, Pisidiu m 162 concolor, Physa 60 contectoideSy Viviparus (= Viviparus georgianus) 2 contortum , Pisidium nitidum form 169 convenvus, Pisidium 176 cooperi, Menetus 74 Corbicula fluminea 144 leana (= Corbicula fluminea ) 144 manilensis (= Corbicula fluminea) 144 comeum, Sphaerium 145 corpulentum, Helisoma corpulentum 8 1 costata, Lasmigona 109 crista, Armiger 70 cristatum, Pisidium lilljeborgi morph 1 67 cruciamm, Pisidium 1 77 Cyclonaias tuberculata 98 Cylindrical Floater 111 dalli, Bakerilymnaea 32 decampi,Fossaria 25 decepta, Marswnia 12 decisum, Campeloma 1 Deep-Water Spire Snail 16 Deer-Toe 125 deflectus , Gyraulus 67 Delicate Lamp-Mussel 136 dilataia, Elliptio 100 donaciformis, Truncilla 124 dubium, Pisidium 158 Dusky Lily-Pad Limpet 87 Dwarf Wedge Mussel 103 Dysnomia torulosa rangiana 142 triquetra 143 Eastern Elliptio 99 Eastern Floater 113 Eastern Lamp-Mussel 137 Eastern Physa 53 Eastern-River Pearl Mussel 9 1 Elliptio complanata 99 dilatata 100 e lodes, Stagnicola 47 equilaterale, Pisidium 163 European Ear Snail 33 European Fingernail Clam 145 European \hlve Snail 5 exacuous, Promeneius exacuous 7 1 exigua, Fossaria 26 fab ale, Sphae rium 146 fabalis, Villosa 140 falcata, Margaritifera 92 fallax, Pisidium 1 64 False Pig-Toe 101 fasciola, Lampsilis 135 fasciolaris, Ptychobranchus 122 FatMucket 138 Fat Pea Clam 170 Faucet Snail 19 Fawn’s-Foot 124 Ferrissia fragilis 88 fragilis form isabellae 88 parallela 89 rivularis 90 ferruginea, Fossaria 27 ferrugineum, Pisidium 165 ferussacianus, Anodontoides 111 Flat-ended Spire Snail 1 1 Flatly Coiled Gyraulus 66 Flat-sided Horn Snail 20 Flat-sided Lake Limpet 89 Flat \hlve- Snail 4 flava , Fusconaia 95 Flumincola virens ( = Lithoglyphus virens ) 1 7 fluminea, Corbicula 144 Fluted Shell 109 Fossaria decampi 25 exigua 26 ferruginea 27 modicella 28 modicella morph rustica 28 parva 29 truncatula 30 Fragile Fossaria 27 Fragile Paper-Shell 130 fragilis, A nodonta cataracta 114 fragilis, Ferrissia 88 fragilis, Leptode a 130 Fusconaia flava 95 fuscus, Laevapex 87 Gatineau Tadpole Snail 52 georgianus, Viviparus 2 Giant Columbia- River Limpet 24 Giant Columbia- River Spire Snail 1 7 Giant Fingernail Clam 150 Giant Manitoba Ram shorn 8 1 Giant Northern Pea Clam 1 59 Giant Promenetus 72 Giant Western Physa 62 Giant Western Spire Snail 17 Globular Pea Clam 174 Gonidea angulata 93 Goniobasis livescens 21 Graceful Fossaria 26 Graceful Keeled Horn Snail 22 grandis, Anodonta grandis 115 granum, Lyogyrus 13 442 Greater Carinate Ramshorn 83 Greater Columbia-River Limpet 24 Greater Eastern Pea Clam 1 58 Greater European Pea Clam 1 57 Great Lakes Horn Snail 21 Great Pond Snail 38 Grooved Fingernail Clam 150 Gyraulus circumstriatus 66 deflecms 61 parvus 68 vermicularis 69 gyrina, Physa gyri na 51 haldemani, Acella 36 Haldeman’s Physa 60 Heavy-toothed Wedge Mussel 105 helicoidea, Valvata sincera 7 Hdisoma anceps anceps 77 anceps royalense 78 campanulatum campanulatum 79 campanulatum collinsi 80 corpulentum corpulentum 81 corpulenium vermilionense 82 corpulentum white avesi 82 multivolvis 80 pilsbryi infracarinatum 83 trivolvis binneyi 85 trivolvis subcrenatum 86 trivolvis trivolvis 84 henslowanum, Pisidium 166 Henslow’s Pea Clam 166 Herrington’s Fingernail Clam 152 heterodon, A lasmidonta 1 03 keterostropha, Physa 53 hindsii, Lithoglyphus 1 7 hordacea, Physa 61 Hump-backed Pea Clam 172 Hy dr obi a nickliniana 18 hypnorum, Aplexa 65 idahoense, Pisidium 159 imbecilis, Anodonta 1 17 implicata, Anondonta 118 infracarinatum, Hdisoma pilsbryi 83 insigne, Pisidium 178 integra , Physa 54 integrum, Campeloma 1 iris, Villosa 141 Irregular Gyraulus 67 isabellae, Ferris si a fragilis form 88 japonicus, Viviparus (= Cipangopaludina chinensis) 3 jenksii, Planorbula (= Planorbula armigera) 75 jennessi, Physa jennessi 55 johnsoni, Physa 58 Juga plicifera 22 silicula (= Juga plicifera) 22 jugularis, Lymnaea stagnalis 38 Keeled Promene tu s 71 kennerlyi, A nodonta 119 kennicotti, Stagnicola 48 Kidney Shell 122 lacustre, Sphaenum 153 lacustris, Probythinella 1 1 Lady-Finger 100 Laevapex fuscus 87 Lake Fingernail Clam 153 Lake Stagnicola 44 Lake Superior Ramshorn 78 Lampsilis cariosa 134 fasciola 135 ochracea 136 ovata 139 ovata ventricosa (= Lampsilis ventricosa ) 139 radiata radiata 137 radiata siliquoidea 138 ventricosa 139 Lanx nuttalli 24 lapidaria, Pomatiopsis 18 Larger Eastern Ramshorn 84 Larger Prairie Ramshorn 86 Lasmigona compla nata 107 compressa 108 costata 109 latchfordi , Physa gyrina 52 leana, Corbicula (= Corbicula fluminea) 144 Leptodea fragilis 130 letsoni, Pyrgulopsis 12 Ltgumia nasuta 132 recta 133 Lilliput Mussel 1 27 lilljeborgi, Pisidium 167 Lilljeborg’s Pea Clam 167 limosa, A mnicola 1 4 Lithoglyphus hindsii 1 7 virens 17 Liver-Fluke Fossaria 30 livescens, Goniobasis 21 Long Fingernail-Clam 156 Loosely Coiled \hlve Snail 8 lordi, Physa 62 Low-spired Ramshorn 80 Lymnaea atkaensis 40 palustris (= Stagnicola elodes) 47 peregra ( = Radix peregra ) 34 stagnalis appressa (= Lymnaea stagnalis jugularis) 38 stagnalis jugularis 38 stagnalis sanctaemariae 39 stagnalis wasatchensis (= Lymnaea stagnalis jugularis) 38 Lyogyrus granum 1 3 443 macrodon, Truncilla 124 mainense, Pisidium walkeri form 175 malleatus, Viviparus (= Cipangopaludina chinensis) 3 manilensis, Corbictda (= Corbicula flwninea) 144 Maple-Leaf 96 Margatitifera falcata 92 margaritifera 91 margaritifera, Margaritifera 91 ma rgmaia, A las mido nta 1 04 Mar stoma decepta 12 me gas, Promenetus exacuous 72 megasoma, Bulimnea 37 Menetus cooperi 74 mergella, Valvata 6 milium, Pisidium 1 68 Miniature Lake-Stagnicola 45 Modest Fossaria 28 Modest Gyraulus 68 modicella , Fossaria 28 montanensis, Stagnicola 42 Mountain-Spring Stagnicola 42 Mucket 131 Mudpuppy Mussel 110 multivolvis, Helisoma 80 Muskeg Stagnicola 43 nasoni, Stagnicola catascopium 45 nasuta, Ligumia 132 Newfoundland Floater 1 14 mcklintana, Hydrobta 18 nitidum, Pisidium 169 nitidum, Sphaerium 147 Northern Floater 116 Northern Riffle Shell 142 Northern V&lve Snail 7 nuttalli, Lanx 24 nuttalli, Physa 63 nuttalliana, Anodonta 120 Nuttall’s Physa 63 Obliquaria reflexa 123 Obovaria olivaria 128 subrotunda 129 Occident ale, Sphaerium 152 ochracea, Lampsilis 136 olivaria, Obovaria 128 Olive Hickory-Nut 128 ontariensis, Valvata sincera 8 Ordinary Spire Snail 14 oregonensis, Anodonta ( = A nodonta nuttalliana ) 1 20 Oriental Mystery Snail 3 Ornamented Pea Clam 1 77 Oval Lake-Limpet 88 ovata, Lampsilis 139 Pacific Coast Gyraulus 69 palustris, Lymnaea (= Stagnicola elodes ) 47 palustris, Stagnicola (= Stagnicola elodes) 47 Paper Pond-Shell 117 parallela, Ferrissia 89 partumeium, Sphaerium 1 54 parva, Carunculina 127 parva, Fossaria 29 parvus, Gyraulus 68 patella, Sphaerium 148 pauperculum, Pisidium nitidum form 169 perdepressa, Valvata 4 peregra , Radix 34 Perforated Pea Clam 1 79 perplexa , Bakerilymnaea bulimoides morph 31 Physa columbiana 59 concolor 60 gyrina gynna 51 gyrina latchfordi 52 heterostropha 53 hordacea 61 integra 54 jennessi atheami 56 jennessi jennessi 55 jennessi skinneri 57 Johns om 58 lordi 62 nuttalli 63 propinqua 64 vinosa 51 virginea 62 Pig-Toe 95 Pilsbry’s Spire Snail 12 Pink Heel-Splitter 126 piscinalis, Valvata 5 Pisidium adamsi 160 amnicum 157 casenanum 161 compressum 1 62 conventus \16 crudatum 177 dubium 1 58 equilaterale 163 fallax 164 ferrugineum 165 henslowanum 166 idahoense 159 insigne 178 lilljeborgi 167 lilljeborgi morph cristatum 167 milium 168 nitidum 169 nitidum form contortum 1 69 nitidum form pauperculum 169 punctatum 179 punctiferum 179 rotundatum 170 subtruncatum 171 supinum 172 444 variabile 173 ventricosum 174 vincentianum 177 waldeni 167 walkeri 175 walkeri form mainense 175 Planorbula armigera 75 campestris 76 jenksii (= Planorbula armigera) 75 Pleurobema coccineum 101 Pleurocera acuta 20 plicata, Amblema 94 plicifera,Juga 22 Pocket-Book 139 Pointed Lake Limpet 23 Pointed Sand-Shell 132 Polished Tadpole Snail 65 Pomatiopsis cincinnatiensis 18 lapidaria 18 Pond Fin gemai l Clam 155 Prairie Pond Snail 31 Prairi e T oothed Planorbid 7 6 preblei, Stagnicola catascopium 46 Probyth ine lla la custris 1 1 Promenetus exacuous exacuous 71 e: vacuous megas 72 umbilicatellus 73 propinqua, Physa 64 Proptera alata 1 26 proximo, Stagnicola 49 Pseudo succinea columella 35 Ptychobranchus fasciolaris 122 punctatum, Pisidium 179 punctiferum, Pisidium 179 Purple Pimple-Back 98 pustule sa, Quadrula 97 Pyrgulopsis letsoni 12 Quadrangular Pill Clam 168 Quadrula pustulosa 97 quadrula 96 quadrula, Quadrula 96 radiata, Lampsilis radiata 137 Radix auricularia 33 peregra 34 Rainbow Shell 141 rangiana, Dysnomia torulosa 142 recta, L igumia 133 reflexa, Obliquaria 123 reflexa, Stagnicola 50 rhomboideum , Sphaerium 149 Rhomboid Fingernail Clam 149 Ribbed Valve-Snail 6 Ridged-Beak Pea Clam 162 Ridged Wedge-Mussel 104 River- Bank Looping Snail 18 River Fingernail Clam 146 River Pea Clam 164 rivularis, Ferrissia 90 Rocky Mountain Fingernail Clam 148 Rocky Mountain Ridged Mussel 93 Rocky Mountain Stagnicola 49 rotundatum, Pisidium 1 70 Round Hickory-Nut 129 Round Pea Clam 163 rowelli, Stagnicola proximo (= Stagnicola proximo) rqyalense, Helisoma anceps 78 rustica, Fossaria modicella morph 28 Rusty Pea Clam 165 Rusty Spire Snail 13 sanctaemariae, Lymnaea stagnalis 39 Say’s Toothed Planorbid 75 securis, Sphaerium 155 Shiny Pea Clam 169 Short-ended Pea C lam 171 Shouldered Northern Fossaria 25 Showy Pond Snail 37 silicula,Juga (= Juga plicifera) 22 siliquoidea, Lampsilis radiata 138 simile, Sphaerium 150 simpsoniana, Anodonta grandis 1 1 6 Simpsoniconcha ambigua 110 sincera , Valvata sine era 6 skinneri, Physa jennessi 57 Slender Pond Snail 36 Small Pond-Snail 32 Small Spire-Snail 15 Solid Lake-Physa 54 Somatogyrus subglobosus 16 Sphaerium comeum 145 f abate 146 lacustre 153 nitidum 147 ocddentale 152 partumeium 154 patella 148 rhomboideum 149 rerun's 155 simile 1 50 striatinum 151 transversum 1 56 Spike 100 Squaw-Foot 121 Stagnicola arctica 43 caperata 41 catascopium catascopium 44 catascopium nasoni 45 catascopium preblei 46 elodes 47 kennicotti 48 montanensis 42 palustris (= Stagnicola elodes ) 47 proximo 49 proxima rotvelli (= Stagnicola proximo) 49 reflexa 50 yukonensis (= Stagnicola arctica) 43 Striated Fingernail Clam 151 striatinwn , Sphaerium 151 Striped Stagnicola 50 Strophitus undulatus 121 Sturdy River Limpet 90 Subarctic Lake-Stagnicola 46 subcrenatum, Hdisoma trivolvis 86 subglobosus, Somatogyrus 16 subrotunda, Obovaria 129 subtruncatum, Pisidium 171 supinum, Pisidium 172 Swamp Fingernail Clam 1 54 Swollen Wedge-Mussel 106 Tadpole Snail 51 techella, Bakenlymnaea bulimoides morph 3 1 tentaculata, Bithynia 19 tentaculata, Bythinia {= Bithynia tentaculata) 19 tentaculatus, Bulimus (= Bithynia tentaculata) 19 Three-homed Warty-Back 1 23 Three-keeled Valve Snail 9 Three-Ridge 94 Tiny Nautilus Snail 70 Tiny Pea Clam 178 transversum, Sphaerium 156 Triangular Pea Clam 1 73 tricarinata, Valvata 9 Tricorn Pearly Mussel 143 triquetra, Dysnomia 143 trivolvis, Helisoma trivolvis 84 truncata, T runcilla 125 truncatula , Fassaria 30 T runcilla donaciformis 124 macrodon 124 truncata 125 luberculata, Cyclonaias 98 Two-ridged Ramshorn 77 Ubiquitous Pea Clam 161 umbilicatellus, Promenetus 73 Umbilicate Promenetus 73 undulata, A lasmidonta 1 05 undulatus, Strophitus 121 Valvata mergella 6 perdepressa 4 piscinalis 5 sincera heltcoidea 1 sincera ontariensis 8 sincera sincera 6 tricarinata 9 virens 6 vancouverensis, Bakerilymnaea bulimoides morph 3 1 Vancouver Island Physa 61 variabile, Pisidium 173 varicosa, A lasmidonta 1 06 ventricosa, Lampsilis 139 ventricosa, Lampsilis ovata (= Lampsilis ventricosa) 139 ventricosum, Pisid ium 1 74 vermicularis, Gyraulus 69 vermiiionense, Helisoma corpulentum 82 Villosa fab alls 140 iris 141 vincentianum, Pisidium 177 vinosa, Physa 51 virens, Lithoglyphus 17 virens, Valvata 6 virginea, Physa 62 viridis, Alasmidonta 102 Viviparus contectoides (= Viviparus georgianus) 2 georgianus 2 japonicus (= Cipangopaludina chinensis) 3 malleatus (= Cipangopaludina chinensis) 3 viviparus 2 viviparus, Viviparus 2 wahlamatensis, Anodonta (= Anodonta nuttalliana) 120 waldeni, Pisidium 167 walkert, Amnicola 1 5 walkeri, Pisidium 1 7 5 Walker’s Pea Clam 175 Walker’s Pond Snail 39 Wandering Snail 34 Warty-Back 97 zuasatchensis, Lymnaea stagnalis (= Lymnaea stagnalis jugularis) 38 Wavy-rayed Lamp-Mussel 135 Western Arctic Stagnicola 48 Western Floater 1 19 Western Lake Physa 64 Western-River Pearl Mussel 92 whiteavesi, Helisoma corpulentum 82 Whiteaves’s Capacious Ramshorn 82 White Heel-Splitter 107 Winged Floater 120 Yellow Lamp-Mussel 134 yukonensis , Stagnicola (= Stagnicola arctica) 43 Yukon Floater 112 446 n:ay MAI 3 1982 V The Shell of a Freshwater Mussel or Clam 0 Quadrula quadrula) Outside View Disc Posterior ridge Lines of growth Ligament Posterior slope j Umbo, or beak Anterior margin Inside View Interdentum Lateral hinge teeth Posterior pedal retractor (muscle scar) Posterior adductor (muscle scar) Anterior pedal retractor (muscle scar) Anterior adductor (muscle scar) Pedal protractor (muscle scar) Beak cavity Umbo Pseudocardinal teeth Pallial line The Shell of a Pea Clam or Pill Clam ( Pisidium ) Inside View of Left Valve Anterior lateral (A2) Cusp (C4) Ligament Posterior lateral (P2) Cusp Cardinal teeth Beak Anterior inner lateral (Al) Inside View of Right Valve Cardinal tooth (C3) Ligament Posterior outer lateral (P3) Anterior outer lateral (A3) Posterior inner lateral (PI) Drawings by Charles Douglas (reprinted from Clarke 1973)