Fam. 4. Crassatellidae.—Shell thick, with concentric striae, ligament external; foot short. Crassatella. Cuna.
Fam. 5. Carditidae.—Shell thick, with radiating costae; foot carinated, often byssiferous. Cardita. Thecalia. Milneria. Venericardia.
Fam. 6. Condylocardiidae.—Like Carditidae, but with an external ligament. Condylocardia. Carditella. Carditopsis.
Fam. 7. Cyprinidae.—Mantle open in front, with two pallial sutures; external gill-plates smaller than the internal. Cyprina; British. Cypricardia. Pleurophorus; Devonian to Trias. Anisocardia; Jurassic to Tertiary. Veniella; Cretaceous to Tertiary.
Fam. 8. Isocardiidae.—Mantle largely closed, pedal orifice small; gill-plates of equal size; shell globular, with prominent and coiled umbones. Isocardia; British.
Fam. 9. Callocardiidae.—Siphons present; external gill-plate smaller than the internal; umbones not prominent. Callocardia; abyssal.
Fam. 10. Lucinidae.—Labial palps very small; gills without an external plate. Lucina; British. Montacuta; British. Cryptodon.
Fam. 11. Corbidae.—Shell thick, with denticulated borders; anal aperture with valve but no siphon; foot elongated and pointed. Corbis. Gonodon; Trias and Jurassic. Mutiella; Upper Cretaceous.
Fam. 12. Ungulinidae.—Foot greatly elongated, vermiform, ending in a glandular enlargement. Ungulina. Diplodonta; British. Axinus; British.
Fam. 13. Cyrenellidae.—Two elongated, united, non-retractile siphons; freshwater. Cyrenella. Joanisiella.
Fam. 14. Tancrediidae.—Shell elongate, sub-triangular. Extinct. Tancredia; Trias to Cretaceous. Meekia; Cretaceous.
Fam. 15. Unicardiidae.—Shell sub-orbicular, nearly equilateral, with concentric striae. Extinct, Carboniferous to Cretaceous. Unicardium. Scaldia. Pseudedmondia.
Fam. 16. Leptonidae.—Shell thin; no siphons; foot long and byssiferous; marine; hermaphrodite and incubatory. Kellya; British. Lepton; commensal with the Crustacean Gebia; British. Erycina; Tertiary. Pythina. Scacchia. Sportella. Cyamium.
Fam. 17. Galeommidae.—Mantle reflected over shell; shell thin, gaping; adductors much reduced. Galeomma; British. Scintilla. Hindsiella. Ephippodonta; commensal with shrimp Axius. The three following genera with an internal shell probably belong to this family:—Chlamydoconcha. Scioberetia; commensal with a Spatangid. Entovalva; parasitic in Synapta.
Fam. 18. Kellyellidae.—Shell ovoid; anal aperture with very short siphon; foot elongated. Kellyella. Turtonia; British. Allopagus; Eocene. Lutetia; Eocene.
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Fig. 28.—Lateral view of a Mactra, the right valve of the shell and right mantle-flap removed, and the siphons retracted. (From Gegenbaur.) | |
| br, br′, | Outer and inner gill-plates. |
| t, | Labial tentacle. |
| ta, tr, | Upper and lower siphons. |
| ms, | Siphonal muscle of the mantle-flap. |
| ma, | Anterior adductor muscle. |
| mp, | Posterior adductor muscle. |
| p, | Foot. |
| c, | Umbo. |
Fam. 19. Cyrenidae.—Two siphons, more or less united, with papillose orifices; pallial line with a sinus; freshwater. Cyrena. Corbicula. Batissa. Velorita. Galatea. Fischeria.
Fam. 20. Cycladidae.—One siphon or two free siphons with simple orifices; pallial line simple; hermaphrodite, embryos incubated in external gill-plate; freshwater, Cyclas; British. Pisidium; British.
Fam. 21. Rangiidae.—Two short siphons, shell with prominent umbones and internal ligament. Rangia; brackish water, Florida.
Fam. 22. Cardiniidae.—Shell elongated, inequilateral. Extinct. Cardinia; Trias and Jurassic. Anthracosia; Carboniferous and Permian. Anoplophora; Trias. Pachycardia; Trias.
Fam. 23. Megalodontidae.—Shell inequilateral, thick; posterior adductor impression on a myophorous apophysis. Extinct. Megalodon; Devonian to Jurassic. Pachyrisma; Trias and Jurassic. Durga; Jurassic. Dicerocardium; Jurassic.
Fam. 24. Unionidae.—Shell equilateral; mantle with a single pallial suture and no siphons; freshwater; larva a glochidium. Unio; British. Anodonta; British. Pseudodon. Quadrula. Arconaia. Monocondylea. Solenaia. Mycetopus.
Fam. 25. Mutelidae.—Differs from Unionidae in having two pallial sutures; freshwater. Muleta. Pliodon. Spatha. Iridina. Hyria. Castalia. Aplodon. Plagiodon.
Fam. 26. Aetheriidae.—Shell irregular, generally fixed in the adult; foot absent; freshwater. Aetheria. Mulleria. Bartlettia.
Sub-order III.—Tellinacea.
Mantle not extensively closed; two pallial sutures and two well-developed siphons. Gills smooth. Foot compressed and elongated. Labial palps very large. Dimyarian; pallial line with a deep sinus.
Fam. 1. Tellinidae.—External gill-plate directed upwards; siphons separate and elongated; foot with byssus; palps very large; ligament external. Tellina; British. Gastrana; British. Capsa. Macoma.
Fam. 2. Scrobiculariidae.—External gill-plates directed upwards; siphons separate and excessively long; foot without byssus. Scrobicularia; estuarine; British. Syndosmya; British. Cumingia.
Fam. 3. Donacidae.—External gill-plate directed ventrally; siphons separate, of moderate length, anal siphon the longer. Donax; British. Iphigeneia.
Fam. 4. Mesodesmatidae.—External gill-plate directed ventrally; siphons separate and equal. Mesodesma. Ervilia; British.
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Fig. 29.—The same animal as fig. 28, with its foot and siphons expanded. Letters as in fig. 28. (From Gegenbaur.) |
Fam. 5. Cardiliidae.—Shell very high and short; dimyarian; posterior adductor impression on a prominent apophysis. Cardilia.
Fam. 6. Mactridae.—External gill-plate directed ventrally; siphons united, invested by a chitinous sheath; foot long, bent at an angle, without byssus. Mactra; British (figs. 28, 29). Mulinia. Harvella. Raeta. Eastonia. Heterocardia. Vanganella.
Sub-order IV.—Veneracea.
Two pallial sutures, siphons somewhat elongated and partially or wholly united. Gills slightly folded. A bulb on the posterior aorta. Ligament external.
Fam. 1. Veneridae.—Foot well developed; pallial sinus shallow or absent. Venus; British. Dosinia; British. Tapes; British. Cyclina. Lucinopsis; British. Meretrix. Circe; British. Venerupis.
Fam. 2. Petricolidae.—Boring forms with a reduced foot; shell elongated, with deep pallial sinus. Petricola. P. pholadiformis, originally an inhabitant of the coast of the United States, has been acclimatized for some years in the North Sea.
Fam. 3. Glaucomyidae.—Siphons very long and united; foot small; shell thin, with deep pallial sinus; fresh or brackish water. Glaucomya. Tanysiphon.
Sub-order V.—Cardiacea.
Two pallial sutures. Siphons generally short. Foot cylindrical, more or less elongated, byssogenous. Gills much folded. Shell equivalve, with radiating costae and external ligament.
Fam. 1. Cardiidae.—Mantle slightly closed; siphons very short, surrounded by papillae which often bear eyes; foot very long, geniculated; pallial line without sinus; two adductors, Cardium; British. Pseudo-kellya. Byssocardium; Eocene. Lithocardium; Eocene.
Fam. 2. Limnocardiidae.—Siphons very long, united throughout; shell gaping; two adductors; brackish waters. Limnocardium; Caspian Sea and fossil from the Tertiary. Archicardium; Tertiary.
Fam. 3. Tridacnidae.—Mantle closed to a considerable extent; apertures distant from each other; no siphons; a single adductor; shell thick. Tridacna. Hippopus.
Sub-order VI.—Chamacea.
Asymmetrical, inequivalve, fixed, with extensive pallial sutures; no siphons. Two adductors. Foot reduced and without byssus. Shell thick, without pallial sinus.
Fam. 1. Chamidae.—Shell with sub-equal valves and prominent umbones more or less spirally coiled; ligament external. Chama. Diceras; Jurassic. Requienia; Cretaceous. Matheronia; Cretaceous.
Fam. 2. Caprinidae.—Shell inequivalve; fixed valve spiral or conical; free valve coiled or spiral; Cretaceous. Caprina. Caprotina. Caprinula, &c.
Fam. 3. Monopleuridae.—Shell very inequivalve; fixed valve conical or spiral; free valve operculiform; Cretaceous. Monopleuron. Baylea. The two following families, together known as Rudistae, are closely allied to the preceding; they are extinct marine forms from Secondary deposits. They were fixed by the conical elongated right valve; the free left valve is not spiral, and is furnished with prominent apophyses to which the adductors were attached.
