298 MANUAL OF THE MOLLUSCA. 



Pacific Ids. In the mud of rivers, and in mangrove swamps, usually near 

 the coast. C. consobrina ranges from Egypt to Cashmere and China, and 

 is found fossil in the Pliocene formations of England,* Belgium and Sicily. 

 Fossil, 70 sp. Wealden . Europe, U. States. 



? CYRENOIDES, Joannis. 



Syn. CyreneUa, Desh. Type, C. Dupontii, PL XIX. fig. 19. 



Shell orbicular, ventricose, thin, eroded at the beaks ; epidermis dark 

 olive ; ligament external, prominent, elongated ; cardinal teeth 3:2, the 

 central tooth of the right valve bifid ; muscular impressions long, narrow ; 

 pallial line simple. 



Animal with the mantle open in front and below, margin simple, siphons 

 short, united ; palpi moderate, narrow ; gills very unequal, narrow, united 

 behind ; foot cylindrical elongated. 



Distr. 1 sp. R. Senegal. The marine sp. are Diplodonfa. 



FAMILY XII. CYPRINID^. 



Shell regular, equivalve, oval or elongated ; valves close, solid ; epider- 

 mis thick and dark; ligament external, conspicuous; cardinal teeth 1 3 in 

 each valve, and usually a posterior lateral tooth ; pedal scars close to, or 

 confluent with the adductors ; pallial line simple. 



Animal with the mantle-lobes united posteriorly by a curtain, pierced 

 with two siphonal orifices ; foot thick, tongue-shaped ; gills 2 on each side, 

 large, unequal, united behind, forming a complete partition ; palpi moderate, 

 lanceolate. 



One half the genera of this family are extinct, and the rest (excepting 

 Circe} were more abundant in former periods than at the present time. 

 Oyprina and Astarte are boreal forms ; Circe and Cardita abound in the 

 Southern seas. 



CYPRINA, Lamarck. 



Etym. Kuprinos (from Kupris] related to Venus. 

 Type, C. Islandica, PL XIX. fig. 22. Syn. Arctica, Schum, 

 Shell oval, large and strong, with usually an oblique line or angle on 

 the posterior side of each valve ; epidermis thick and dark ; ligament pro- 

 minent ; umbones oblique.; no lunule; cardinal teeth 2:2, laterals 1, 

 1 ; muscular impressions oval, polished ; pallial sinus obsolete. 



Animal with the mantle open in front and below, margins plain ; siphonal 

 orifices close together, fringed, slightly projecting ; outer . gills semilunar, 

 inner truncated in front. 



The principal hinge-tooth in the right valve of Cyprina represents the 



* Associated with the bones of Elephas meridionalis, Rhinoceros leptorhinus, 

 Mastodon Arvernensis, Hippopotamus major, &c. 



