BIVALVIA. 195 



the recent shell are scarcely more than skin deep, or penetrate beneath the epidermis, 

 as may be seen at the umbo of the recent shell, which is generally eroded, but by a 

 close inspection, these granulated striae may be detected even in the fossil state. 



In the Campinian beds of Belgium this shell does not appear to have been rare, 

 but to have presented considerable diversity of form, and M. Nyst himself seems to 

 admit, at page 199, the probability of his own three species being modifications or 

 variations oS* Isocardia cor. 



According to Knorr, this is called in France Coeur de Boeuf, or bullock's -heart, 

 while in Holland it has the name of Zots-Kappen^ or foolscap. 



Genus Cyprina,* Lamarck. 1812. 



Venus (sp.) Auct. 

 Arctica. Schutn., 1817. 



Gen. Char. Shell equivalved, inequilateral, more or less orbicular, or obliquely 

 heartshaped ; smooth, or covered with irregular lines of growth, and in the recent 

 state invested with an epidermis ; umbones sharp, with a slight inclination to curve ; 

 the ventral margin smooth. Hinge with strong and prominent cardinal teeth in each 

 valve, and one posterior lateral tooth. Muscle marks large, anterior one deeply 

 impressed. Mantle mark with a small or incipient sinus. Ligament external. 



Animal suborbicular, with mantle freely open, and finely serrated at the edges ; 

 siphonal tubes very short, and the margins of the openings fringed ; foot large and 

 hnguiform. 



The shells of this genus closely resemble in outward appearance some of the 

 species of Venus, from which they were separated by Lamarck, who thought them of 

 scarcely sufficient importance for generic distinction ; there is, however, a marked 

 difference in the impression of the mantle, which in this is without a sinus, denoting 

 the possession in the animal of very short siphons ; a large lateral tooth on the 

 posterior margin is another character by which the shell may be distinguished. It 

 appears to be very closely related to Isocardia. The species as yet known are all 

 inhabitants of salt water, and in the living state are frequenters of gravelly sand or 

 mud ; they are somewhat of a large size, and of considerable solidity, and, as a genus, 

 may perhaps date its existence as far back as the period of the Greensand Formation, 

 continuing, though sparingly, through the Tertiaries to the present day, without 

 numbering many species either in the existing state or in the ancient seas. 



* Etym. Kvirpii, one of the names of Venus. 



