439 



CYPRINIDiE. 



In the arrangements of the older conchologists many 

 shells were associated with Venus which, though they bore 

 a near resemblance to the true members of that group, so 

 far as external aspect and characters of dentition went, j^re- 

 sented an unsinuated pallial impression, thereby indicating 

 a very differently formed animal. Among these were the 

 shells out of which the genera Ci/prina and Astarte were 

 constituted. We associate with them in one family the 

 Venus minima of Montagu, and the Isocardia cor. 



The members of this family have substantial shells, 

 often thick and heavy, almost always strong in proportion 

 to their size, and frequently invested with a strongly-de- 

 veloped epidermis ; some of them are very brilliantly 

 coloured, others dull and dusky. Their surface is either 

 smooth, or nearly so, or, if sculptured, marked with con- 

 centric striae or furrows. The greater or less prominence 

 and direction of the beaks, and the presence or absence of 

 a lunule, are variable characters, and serve to distinguish 

 the genera. The hinge has strongly developed cardinal 

 teeth, and the ligament is well formed and external. The 

 pallial impression is either quite entire, or presents only the 

 slightest indication of a sinus. This depends on the pecu- 

 liar feature in the organization of the animal, which has, 

 instead of distinct and produced siphonal tubes, only rudi- 

 mentary ones in the shape of two scarcely separated 



