96 CONCHIFERA. DIMYAIRA. 



C. cardissa, Lin. Shell heart-shaped ; valves compressed, carinat- 

 ed, and the carina toothed ; umbones approximated ; colour whit- 

 ish, with clearer milky spots. 2 inches long. Inhabits Indian 

 seas. Rumph. Mus. pi. 43, fig. E. 



FAMILY V. CONCHACEA. 



Three primary teeth at least in one valve, the other with as 

 many, or less ; sometimes lateral teeth. 



The Conchacea constitute one of the most numerous and beautiful groups of the 

 Conchifera. Their shell is equivalve, orbicular, or transverse, always regular, and 

 in general close on the sides. The animal inhabitant often forms with its mantle 

 two tubes or syphons, which it projects from the shell, of which one serves for the 

 passage of the water to the branchiae and to the mouth, while the other is the exit 

 for dejected matters. The foot is lamelliform. Lamarck divides this large family 

 into two groups, according as the animals are marine or fluviatile. In the first, the 

 syphons of the animal are elongated and unequal, and the foot broad and project- 

 ing 4 in the second, the foot is long, narrow, and slightly projecting. All the ani- 

 mals of this family live in the sand or mud. 



I. MARINE. Generally without lateral teeth. 



Gen. 19. VENERICAHDIA, Lam. 



Shell equivalve, equilateral, suborbicular, generally with longi- 

 tudinal radiated ribs ; two oblique primary teeth, directed to 

 the same side. 



Almost all the species of this genus are extinct, and only known in the fossil state. 

 Those found in Britain are from the London clay and crag. In the smaller species 

 the character which distinguishes them from the Carditae is not always very per- 

 ceptible. 



V. Australis, Lam. Shell suborbicular, very small, tinged with 

 purple ; ribs narrow, with imbricated scales, subnodose. 2 lines 

 long. Inhabits seas of New Holland Lam. v. 611. 

 This species was found by M. Lamarck in sand from the coast of New Holland ; 

 and he conceives it to be analogous to the extinct species V. imbricata, found fossil at 

 Grignon, near Paris. It is a remarkable circumstance, that more than one fossil shell 

 found in Europe should be identified with living species in the Asiatic seas. 



Gen. 20. VENUS, Lam. Lin. 



Shell equivalve, inequilateral, transverse or suborbicular ; three 

 primary approximated teeth in each valve, the lateral ones 

 diverging at their summit ; ligament exterior. 



This genus, one of the most beautiful among the Conchifera, is very similar in 

 form to the next genus or the Cythereae ; and it is often necessary to ascertain the ge- 

 nus by reference to the hinge. They are all marine shells, and often beautifully varie- 

 gated in their colours. The animal has a mantle open before, and two more or less 

 projecting syphons. The foot is compressed, lamelliform, and of various size. Spe- 

 cies of this genus are found in all seas. They live in the sand at a small distance 

 from the coast. 



* Internal margins crenulated or dentated, and with lamellar stria?. 



V. puerpera, Lin. Shell rounded, heart-shaped, with decussated 

 striae, of which the longitudinal are membranaceous and reflect- 

 ed ; posterior depression ovate, surrounded by a groove, and ca- 

 rinated in the middle ; margin crenulated ; colour white or fer- 

 ruginous. 3 inches long. Indian seas. Lister, pi. 336, fig. 173. 



