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 striz 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 of Jsocardia cor. 
According to Knorr, this is called in France Ceur de Beuf, or bullock’s-heart, 
while in Holland it has the name of Zofs-Kappen, or foolscap. 
Genus Cyprina,* Lamarck. 1812. 
Venus (sp.) uct. 
Arctica. Schum., 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 
linguiform. 
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 Jsocardia. 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. xcumpes, one of the names of Venus. 
