131 CONCmYU A— niTHYRA. 35 



Shell half an inch long, and rather more in breadth, yellowish- 

 white, somewhat oval and rather triangular, with numerous fine 

 laminar equidistant transverse ridges, which reflect a little, and 

 in both valves^ at the cartilage side, become confluent in pairs, 

 extending beyond the edges so as to form a fringe of short obtuse 

 spines, which turn back and form a cavity for the cartilage : 

 beaks small, nearly central, inclining a little to one side, with a 

 long narrow impression under them ; inside smooth, white, with 

 the margin plain. 



Young shells of the Venus Gallina something resemble it, the 

 transverse striae often shooting forward a little at the anterior 

 edges, as do those of the Venus fasciata; but the differeace of 

 the teeth and the laminar ridges distinguish them. 



35. CYPnm k— LAMARCK. 



Testa subcordata, fequivahis, suh^quilateralis, clausa 

 Cardo dentibus duobus vel tribus, snperne divergentibus, 

 cum lateraliantico. Ligamentum externum. 



Shell somewhat heart-shaped, equivalve, nearly equilateral, 

 closed. Hinge with two or three teeth, divergent at their 

 tops, and a lateral one at the anterior side. Ligament 

 external. 



