CONCHIFEKA. 



291 



Animal with the mantle-margins plaited ; siphons clothed with tentacular 

 filaments, anal orifice with a tubular valve: branchial fringed; foot long, 

 cylin rical, sickle-shaped, heeled. 



The cockle (C. edule) frequents sandy bays, near low-water; a small 

 variety lives in the brackish waters of the R. Thames, as high as Graves- 

 end ; it ranges to the Baltic, and is found in the Black Sea and Caspian. 

 C. rusticum extends from the Icy Sea to the Medit. Black Sea, Caspian, and 

 Aral. On the coast of Devon the large prickly cockle (C. aculeatum) is 

 eaten. 



Sub-genera. Hemicardium (Cardissa) Cuvier. C. hemicardium, PI. XIX. 

 fig. 3. Shell depressed, posterior slope flat, valves prominently keeled. 



Lithocardium aviculare, PI. XVIII. fig. 17. Shell triangular, keeled ; ante- 

 rior side very short; hinge-teeth 1.2, directed backwards; posterior laterals 

 2.1 ; anterior muscular pit minute, posterior impression large, remote from 

 the hinge. L. cymbulare, Lam. exhibits slight indications of a byssal sinus 

 in the front margins of the valves. Fossil, Eocene, France. These shells 

 present considerable resemblance to Tridacna. 



Serripes (groenlandicus) Beck. Hinge edentulous. Arctic Seas, from 

 C. Parry to Sea of Kara ; fossil in the Norwich Crag. 



Fig. 213. C. laeviusculum, Eichw. (after Middendorff.) 



Adacna, Eichwald. C. edentulum, PI. XIX. fig. 4. (Acardo, Sw. not Brug, 

 Pholadomya, Ag. and Mid. not Sby.) Shell compressed, gaping behind, thin, 

 nearly edentulous ; pallial line sinuated: Animal with the foot (/) com- 

 pressed ; siphons (s) elongated, united nearly to the end, plain. Distr. 8 sp, 

 Aral, Caspian, Azof, Black Sea, and the embouchures of the Wolga, Dnjestr, 

 Dnjepr, and Don ; burrowing in mud. C. Caspicum (Monodacna, Eichw.) 

 has a single hinge-tooth, and C. trigonoides (Didacna, E.) rudiments of two 

 teeth. The siphonal inflection varies in amount. 



Distr. 200 sp. World- wide ; from the sea-shore to 140 fathoms. Gre- 

 garious on sands and sandy mud. 



Fig. 214. Conocardium aliforme, Sby. Carb : Ireland. (Mus. Tennant.) 



