Section I. Platypoda.--Foot More or Less Flattened Ventrally.

FAM. 1. Naticidae.--Foot very large, produced before and behind, propodium reflected upon the head, eyes absent or buried in the integument, central and lateral tooth of the radula tricuspid, middle cusp strong; shell globular or auriform, outer lip simple, operculum corneous or calcareous, nucleus excentrical. Carboniferous ----. Principal genera: Natica, with many sub-genera; Ampullina (Tertiary); Amaura; Deshayesia (Tertiary); Sigaretus (Fig. 91, p. 186), shell auriform, last whorl very large, operculum much too small for the aperture.

FAM. 2. Lamellariidae.--Mantle reflected over more or less of the shell, shell delicate, no operculum. Eocene----. Principal genera: Lamellaria, shell completely internal, transparent, auriform; some species deposit their eggs on compound Ascidians (p. 74); Velutina, shell almost entirely external, paucispiral, with a thick periostracum; Marsenina, shell auriform, partly internal; Onchidiopsis, shell a membranous plate, internal.

FAM. 3. Trichotropidae.--Branchial siphon short, eyes on the outer side of the tentacles; radula closely allied to that of Velutina; shell conical, last whorl rather large, periostracum thick and hairy, operculum blunt claw-shaped, nucleus terminal. Cretaceous----. Genera: Trichotropis, Torellia.

FAM. 4. Naricidae.--Tentacles broad in the middle, with sessile eyes at the exterior base, propodium narrow, quadrangular, a large epipodial veil on each side of the foot; shell naticoid, cancellated, with velvety periostracum. Jurassic----. Single genus: Narica.

FAM. 5. Xenophoridae.--Foot divided by a groove, anterior portion the larger; central tooth heart-shaped, with blunt cusps, lateral large, roughly triangular, marginals long, falciform; shell trochiform, somewhat flattened, attaching various fragments externally. Devonian----. Single genus, Xenophora (Figs. 25, 26, p. 64).

FAM. 6. Capulidae.--Ctenidium deeply and finely pectinate, visceral sac scarcely spiral, penis long, behind the right tentacle; shell roughly patelliform, with scarcely any spire, interior polished, usually with a septum or internal plate of variable form, no operculum. Devonian----. Principal genera (Fig. 155, p. 248); Capulus, shell cap-shaped, no internal plate; Platyceras (Palaeozoic, see p. 76), Diaphorostoma (Palaeozoic), Addisonia (?); Crucibulum, internal appendage funnel-shaped; Crepidula (including Crepipatella and Ergaea), shell slipper-shaped, with a large septum; Calyptraea (including Galerus and Trochita), internal lamina semi-spiral.

FAM. 7. Hipponycidae.--Foot aborted, animal sedentary, adductor-muscle shaped like a horse’s hoof, fastened on the ventral side to the region of attachment, or to a thin calcareous plate which closes the aperture like a valve; ventral side of the body surrounded by a mantle with papillose border, which corresponds morphologically to the epipodia, head emerging between the dorsal and ventral mantles. Shell thick, bluntly conical, surface rugose. Eocene----. Genera: Hipponyx; Mitrularia, a narrow half funnel-shaped appendage within the shell.

FAM. 8. Solariidae.--Foot large, eyes sessile, near the outer base of the tentacles, radula abnormal (p. 224); shell more or less depressed, lip simple, umbilicus wide, margins often crenulated, operculum variable. The proper position of the family is quite uncertain. Ordovician----. (i.) Solariinae. Genera: Solarium, shell depressed, highly finished, angular at periphery, operculum corneous, central tooth absent, laterals and marginals numerous, long, and narrow; Platyschisma (Silurian). (ii.) Toriniinae. Genera: Torinia, whorls usually rounded, operculum (Fig. 183) conically elevated, spiral externally, central tooth present, marginals few, edge pectinated; Omalaxis. (iii.) Euomphalinae, shell planorbiform, whorls rounded. Genera: Euomphalus, Ophileta, Schizostoma, Eccyliomphalus (all Palaeozoic).

FAM. 9. Homalogyridae.--Tentacles absent, eyes sessile, central tooth unicuspid on a quadrangular base, laterals and marginals replaced by an oblong plate; shell very small, planorbiform. Recent. Single genus: Homalogyra, whose true position is uncertain.

FAM. 10. Littorinidae.--Proboscis short, broad, tentacles long, eyes at their outer bases, penis behind the right tentacle; reproduction oviparous or ovoviviparous, radula very long; shell turbinate, solid, columella thickened, lip simple, operculum corneous, nucleus excentrical. Jurassic----. Principal genera: Littorina (radula, Fig. 16, p. 20), Cremnoconchus (p. 16), Fossarina; Tectarius, shell tubercled or spinose; Risella, base slightly concave; Lacuna, shell thin, grooved behind the columellar lip.

FAM. 11. Fossaridae.--Shell turbinate, solid, small, white, spirally ribbed, outer lip simple. Miocene----. Principal genus, Fossarus.

FAM. 12. Cyclophoridae.--Ctenidium replaced by a pulmonary sac, tentacles long, thread-like (radula, Fig. 17, p. 21); shell variously spiral, peristome round, often reflected, operculum circular. Terrestrial only. Cretaceous----. (i.) Pomatiasinae, shell high, conical, longitudinally striated, operculum consisting of two laminae united together. Single genus, Pomatias. (ii.) Diplommatininae, shell more or less pupiform, peristome thickened or reflected, often double. Genera: Diplommatina (subg., Nicida, Palaina, Paxillus, Arinia), shell dextral or sinistral, small, columella often denticulated; Opisthostoma (Fig. 208, p. 309), last whorl disconnected, often reflected back upon the spire. (iii.) Pupininae, shell more or less lustrous, bluntly conical, lip with a channel above or below. Genera: Pupina (subg., Registoma, Callia, Streptaulus, Pupinella, Anaulus), Hybocystis (Fig. 205, p. 305), Cataulus, Coptochilus, Megalomastoma. (iv.) Cyclophorinae, shell turbinate or depressed, operculum corneous or calcareous. Genera: Alycaeus, Craspedopoma, Leptopoma, Lagochilus, Cyclophorus (Fig. 206, p. 306); including Diadema, Aulopoma, Ditropis, and others), Aperostoma (including Cyrtotoma and others), Cyathopoma, Pterocyclus (subg., Myxostoma, Spiraculum, Opisthoporus, and Rhiostoma (Fig. 180, p. 266), Cyclotus, Cyclosurus, and Strophostoma.

FAM. 13. Cyclostomatidae.--Ctenidium replaced by a pulmonary sac, tentacles obtuse, foot with a deep longitudinal median groove; central tooth, lateral, and first marginal more or less bluntly cusped, second marginal large, edge pectinate; shell variously spiral, spire usually elevated, aperture not quite circular; operculum generally with an external calcareous and an internal cartilaginoid lamina, rarely corneous. Terrestrial only. Cretaceous----. Genera: Cyclostoma (subg., Leonia, Tropidophora, Rochebrunia, Georgia, Otopoma, Lithidion, Revoilia), Cyclotopsis, Choanopoma (subg., Licina, Jamaicia, Ctenopoma, Diplopoma, Adamsiella), Cistula (subg., Chondropoma, Tudora), Omphalotropis (subg., Realia, Cyclomorpha), Hainesia, Acroptychia.

FAM. 14. Aciculidae.--Ctenidium replaced by a pulmonary sac, tentacles cylindrical, pointed at the end, eyes behind their base, foot long and narrow; central tooth and lateral very similar, pinched in at the sides, external marginal broad, edge finely pectinate; shell small, acuminate, with a blunt spire, operculum corneous. Terrestrial only. Tertiary----. Genus, Acicula (= Acme).

FAM. 15. Truncatellidae.--Ctenidium replaced by a pulmonary sac, proboscis very long, eyes sessile, behind the base of the tentacles, shell small, evenly cylindrical, apex truncated in the adult. Eocene----. Genera: Truncatella (subg., Taheitia, Blanfordia, and Tomichia), Geomelania (subg., Chittya and Blandiella), Cecina (?).

FAM. 16. Rissoidae.--Eyes at the external base of the tentacles, epipodium with filaments, operculigerous lobe with appendages; central tooth pleated at the basal angles, lateral large, bluntly multicuspid, marginals long, narrow, denticulate at the edge; shell small, acuminate, often elaborately sculptured, mouth entire or with a shallow canal, operculum corneous. Marine or brackish water. Jurassic----. Principal genera: Rissoa (subg., Folinia, Onoba, Alvania, Cingula, Nodulus, Anabathron, Fenella, Iravadia, and others), Scaliola (shell agglutinating fragments of sand, etc.), Rissoina (lip thickened, operculum with an apophysis as in Nerita), Barleeia, Paryphostoma (Eocene).

FAM. 17. Hydrobiidae.--Eyes at the outer base of the tentacles, penis behind the right tentacle, prominent, operculigerous lobe without filaments; radula rissoidan, central tooth often with basal denticulations; shell more or less acuminate, small, aperture entire, operculum corneous or calcareous. Brackish or fresh water. Jurassic----. Principal genera: Baicalia, with its various sub-genera (p. 290); Pomatiopsis, Hydrobia, Bithynella, Micropyrgus (Tertiary), Pyrgula, Emmericia, Benedictia, Lithoglyphus, Tanganyicia, Limnotrochus (?), Jullienia, Pachydrobia, Potamopyrgus, Littorinida, Amnicola, Fluminicola (subg., Gillia, Somatogyrus), Bithynia, Fossarulus (Tertiary), Stenothyra.

FAM. 18. Assimineidae.--Ctenidium replaced by a pulmonary sac, no true tentacles, eye-peduncles long, retractile; radula that of Hydrobia; shell small, conoidal, operculum corneous, nucleus sub-lateral. Eocene----. Genera: Assiminea, Acmella.

FAM. 19. Skeneidae.--Radula resembling that of Hydrobia; shell very small, depressed, widely umbilicated, operculum corneous. Pleistocene----. Single genus, Skenea.

FAM. 20. Jeffreysiidae.--Mantle with two pointed ciliated appendages in front, tentacles ciliated, eyes sessile, far behind the base of the tentacles; marginal teeth sometimes absent; shell small, thin, pellucid, whorls rather swollen, operculum with marginal nucleus, divided by a rib on the inner face. Recent. Genera: Jeffreysia, Dardania. Marine, living on algae.

FAM. 21. Litiopidae.--Epipodium with cirrhi on each side, operculigerous lobe with appendages; radula rissoidan; shell small, conical, columella truncated, operculum corneous. Eocene----. Genera: Litiopa, living on the Sargasso weed, suspended by a long filament; Alaba, Diala.

FAM. 22. Adeorbidae.--Radula essentially rissoidan; shell depressed, circular or auriform, widely umbilicated, operculum corneous, paucispiral, nucleus excentrical. Pliocene ----. Principal genera: Adeorbis, Stenotis, Megalomphalus.

FAM. 23. Viviparidae.--Snout blunt, tentacles long, right tentacle in the male deformed, pierced with a hole corresponding to the aperture of the penis, two cervical lobes, the right being siphonal, foot with an anterior transverse groove; teeth broad, shallowly pectinate at the ends; shell turbinate, whorls more or less rounded, aperture continuous, operculum corneous, nucleus sub-lateral, with a false sub-central nucleus on the external face. Animal ovoviviparous. Fresh-water. Cretaceous ----. Genera: Vivipara (= Paludina), subg., Cleopatra, Melantho, Tulotoma; Tylopoma (Tertiary), and Lioplax.

FAM. 24. Valvatidae.--Branchia exserted, bipectinate, carried on the back of the neck, a filiform appendage (Fig. 66, p. 159) on the right of the neck, penis under the right tentacle, prominent, eyes sessile, behind the tentacles; radula like that of Vivipara; shell small, turbinate or flattened, operculum corneous, nucleus central. Fresh water. Jurassic ----. Single genus, Valvata.

FAM. 25. Ampullariidae.--Snout with two tentacles, tentacles proper very long, tapering, eyes prominently pedunculate, two cervical lobes, the left siphonal, respiratory cavity divided by a partition, a large branchia in the right chamber, the left functioning as a pulmonary sac (Fig. 65, p. 158); radula large, central tooth multicuspid, base broad, lateral and marginals falciform, simple or bicuspid; shell large, turbinate or flattened, spire small, whorls rounded; operculum generally corneous, nucleus sub-lateral, false nucleus as in Vivipara. Fresh water. Cretaceous ----. Single genus, Ampullaria (subg., Ceratodes, Pachylabra, Asolene, Lanistes, and Meladomus).

FAM. 26. Cerithiidae.--Branchial siphon present, short, eyes variable in position; central tooth small, evenly cusped, lateral hollowed at base, multicuspid, marginals narrow; shell long, turriculate, whorls many, generally tuberculate, varicose or spiny, aperture sometimes strongly channelled; operculum corneous, subcircular, nucleus nearly central. Marine or brackish water. Trias ----. Principal genera: Triforis, shell small, generally sinistral; Fastigiella, Cerithium (Fig. 12, p. 16), Bittium, Potamides (subg., Tympanotomus, Pyrazus, Pirenella, Telescopium, Cerithidea, Lampania, all brackish water), Diastoma (Eocene), Cerithiopsis; Ceritella (Jurassic), Brachytrema (Jurassic), and Planaxis (subg., Quoyia and Holcostoma).

FAM. 27. Modulidae.--No siphon, radula of Cerithium; shell with short spire, columella strongly toothed at the base, aperture nearly circular. Recent. Single genus, Modulus.

FAM. 28. Nerineidae.--Shell solid, long, sub-cylindrical, aperture channelled, columella and interior of whorls with continuous ridges, extending up the spire. Genera: Nerinea (Trias to Cretaceous), Aptyxiella (Jurassic).

FAM. 29. Melaniidae.--Border of mantle festooned, foot broad, with an anterior groove, penis present; radula closely resembling that of Cerithium; shell long, spiral, with a thick periostracum, surface with tubercles, ribs, or striae, suture shallow; operculum corneous, paucispiral, nucleus excentrical. Animal ovoviviparous. Fresh water. Cretaceous ----. Principal genera: Melania (with many sections or sub-genera), Pachychilus, Claviger (= Vibex), Hemisinus, Pirena, Melanopsis, Tiphobia, Paludomus (subg., Philopotamis, Tanalia, Stomatodon), Hantkenia (Eocene), Larina (?).

FAM. 30. Pleuroceridae.--Mantle edge not festooned, no copulatory organ, otherwise like Melaniidae; operculum with nucleus sub-marginal. Animal oviparous. Fresh-water. Cretaceous ----. Genera: Pleurocera (including Io, Fig. 12, p. 16, Angitrema, Lithasia, Strephobasis), Goniobasis, Anculotus, Gyrotoma.

FAM. 31. Pseudomelaniidae.--Shell resembling that of Melaniidae, but marine. Genera: Pseudomelania, Loxonema, Bourguetia, Macrochilus. Palaeozoic to Tertiary strata.

FAM. 32. Turritellidae.--Mantle with a siphonal fold on the right side; radula variable (p. 224); shell long, whorls many, slowly increasing in size, transversely ribbed or striated, aperture small; operculum corneous, nucleus central. Jurassic ----. Principal genera: Turritella, Mesalia, Protoma, Mathilda (?).

FAM. 33. Coecidae.--Tentacles long, eyes sessile at their base; shell small, spiral in the young form, spire generally lost in the adult, the shell becoming simply a straight or curved cylinder; operculum corneous, multispiral. Eocene ----. Single genus, Coecum.

FAM. 34. Vermetidae.--Visceral sac greatly produced, irregularly spiral, no copulatory organs (radula, Fig. 126, p. 223), shell tubular, irregularly coiled, last whorls often free, aperture circular; operculum corneous, circular, nucleus central. Carboniferous ----. Principal genera: Vermetus; Siliquaria (Fig 153, p. 248), a long fissure, or series of holes, runs along a considerable part of the shell, operculum with outer face spiral, elevated.

FAM. 35. Strombidae.--Foot narrow, arched, metapodium greatly produced, snout long, eye peduncles long, thick, eyes elaborate, siphon short, penis prominent, bifurcate; central tooth with strong median cusp, marginals falciform, slender, edge more or less denticulate; shell solid, spire conical, outer lip generally dilated into wings or digitations, channelled before and behind, a labial sinus at the base, distinct from the anterior canal; operculum small for the aperture, corneous, claw-shaped, edge notched. Lias ----. Genera: Strombus (Fig. 99, p. 200); Pereiraea (Miocene), Pteroceras (Fig. 277; digitations of the outer lip very strong), Rostellaria (spire produced, anterior canal very long), Rimella, Pterodonta, Terebellum (base of shell truncate, spire short).

FAM. 36. Chenopodidae (= Aporrhaidae).--Foot flat; lateral and marginal teeth not denticulate; shell resembling that of Strombus, outer lip dilated, wing-like, no labial sinus. Jurassic ----. Genera: Chenopus (= Aporrhais, Diastema, Malaptera, Harpagodes, Alaria) (last four from Secondary strata).

FAM. 37. Struthiolariidae.--Radula allied to that of Strombus, marginals occasionally multiplied; shell buccinoid, very solid, outer lip thickened, canal short, operculum claw-shaped, notched, nucleus terminal. Tertiary ----. Single genus, Struthiolaria (subg., Perissodonta, marginal teeth multiplied).

FAM. 38. Cypraeidae.--Mantle with two large lateral lobes reflected and meeting over the shell, siphon small; central and lateral teeth bluntly tricuspid or multicuspid, laterals fairly broad, edges cusped or finely pectinate; shell polished, solid, spire generally concealed in the adult or overlaid with enamel, aperture straight, narrow, nearly as long as the shell, toothed at the sides, channelled at each end, labium inflected; no operculum. Jurassic ----. Genera: Ovula (including Amphiperas, Transovula, Cyphoma, Radius, Simnia), Pedicularia, Cypraea (with subg., Cypraeovula, Cypraedia, and Trivia), and Erato.

FAM. 39. Doliidae.--Foot expanded, wider and longer than the shell, truncated and thickened in front, siphon very long and narrow; central tooth with very strong median and small lateral and basal cusps, lateral and marginals bluntly falciform; shell ventricose, without varices, spire short, outer lip generally simple, anterior canal rather wide, no operculum. Cretaceous ----. Genera: Dolium (subg., Malea, outer lip thickened, denticulate, reflected); Pirula, mantle with two lateral lobes reflected over part of the shell, shell fig-shaped (Fig. 278).

FAM. 40. Cassididae.--Foot broad, siphon long (radula, Fig. 125, p. 223); shell ventricose, with varices, spire short, outer lip reflected or thickened, anterior canal short, recurved narrow; operculum semi-lunar, with ribs radiating from a marginal nucleus. Cretaceous ----. Genera: Cassis (subg., Semicassis and Cypraecassis), Morio (= Cassidaria), Oniscia.

FAM. 41. Columbellinidae.--Shell solid, ribbed, usually cancellated, with an oblique posterior canal, columella callous, more or less reflected. Genera: Columbellina, Columbellaria, Zittelia, Petersia, Alariopsis (?). Secondary strata only.

FAM. 42. Tritonidae.--Foot short, narrow; siphon short, not prominent; radula allied to that of Cassididae; shell thick, varicose; outer lip inflected and thickened, canal long, periostracum often thick and hairy, operculum corneous, nucleus terminal or sub-marginal. Cretaceous ----. Genera: Triton (Fig. 191, p. 275; subg., Epidromus, Plesiotriton, Simpulum, Ranularia, Argobuccinum); Persona, aperture toothed, narrow; columella reflected upon the last whorl; Ranella, shell dorso-ventrally compressed, generally with two continuous lateral varices, posterior canal present.

The position of the following four families is doubtful:--

FAM. 43. Oocorythidae.--Siphon short, foot broad, eyes absent, radula taenioglossate; shell buccinoid or cassidiform, operculum corneous, spiral. Recent. Single genus, Oocorys.

FAM. 44. Subulitidae.--Shell elongate, fusiform, smooth; suture shallow, base truncate or rounded, aperture channelled or notched. Ordovician to Trias. Genera: Subulites, Fusispira, Euchrysallis.

FAM. 45. Seguenziidae.--Radula taenioglossate, shell trochiform, aperture channelled, columella twisted, operculum multispiral, nucleus central. Pliocene ----. Single genus, Seguenzia.

FAM. 46. Choristidae.--Anterior tentacles united by a frontal veil, posterior simple; eyes absent, foot with tentaculae before and behind; three central teeth, outer marginal with a basal plate; shell helicoid, suture deep, peristome continuous, operculum corneous, paucispiral. Pliocene ----. Single genus, Choristes.