SHELLS. 239 



forms. The only species known in Bermuda is the 

 Chama arcinella. 



The fourth family of the Acephala Testacea com 

 prise the Cardicea, the greater pE^rt of which are 

 furnished with longitudinal ribs, and have the shape 

 of a heart when viewed anteriorly. To this family 

 belong the following genera, viz : — 



1. Genus Cardium (Cockles). — The species of 

 cockle are numerous on our shores, among which we 

 may notice Cardium leevigatum (the smooth cockle), 

 Cardium unedo, and Cardium cardissa. In the latter 

 species the valves are flattened, but in a contrary 

 manner to the generality of flat bivalves. 



2. Genus Tellina. — The Tellinas are all attractive, 

 from their beautiful colour and elegant shape. The 

 species are as follows : Tellina radiata, Tellina de- 

 pressa, and Tellina tenuis. 



3. Genus Venus is one of the most beautiful among 

 the conchifera. The following species are some- 

 times found: — Venus gemma, Venus granulata, and 



Venus plicata. 



4. Genus Cytherea, — This genus resembles much 

 the Venus in beauty and colouring, but the fourth 

 cardinal tooth, which is supposed to distinguish it, is 

 sometimes scarcely visible. The species are Cytherea 

 tigerina and Cytherea castrensis. 



