142 DIMYARIA. 



Hiatella arctica The Arctic Hiatella. Plate XVI. 



fig. 12. Transversely oblong; witli the anterior end longer 

 and truncated; the valves with two divergent spiny ridges; 

 yellowish- white, with decussated striae; inside perlaceous. 

 Half an inch long, and one inch broad. Inhabits the British 

 seas. 



It appears to be the same as Saxicava lugosa. 



Genus 16.— CYPRICARDIA Lamarck. 



Generic Character. — Shell free, equivalve, inequilateral, 



obliquely or transversely elongated; teeth of the hinge three, 



situated under the beaks, and one lateral elongated tooth. 



Distinguished from Cardita, viith which they are closely aUied in 

 form, by having three teeth beneath the apices, like the genus Venus, 

 in addition to the lateral lengthened tooth or lidgo, 



Cypricardia Guinaica. — The Guinea Cvpricardia. 

 Plate XVI. fig. 13. Transversely oblong, oblique, angu- 

 lated, white, and covered with decussated striae; compressed 

 before, and the apex rounded; yellowish- white. Two inches 

 long. Inhabits the coast of Guinea. 



Genus \7.—C\RT>lT A.— Lamarck. 



Generic Character. — Shell free, regular, equivalve, in- 

 equilateral; hinge with two unequal teeth; primary tooth 

 short, straight, placed under the umbo; the other tooth 

 oblique, marginal, and elongated. 



Some of the species require minute attention to the teeth, to distin- 

 guish them ti'om the Yenericardia. 



Cardita sulcata The Furrowed Cardita. Plate 



XVI. fig. 15. Subcordate, white, tessellated with brown; 

 having longitudinal, convex transversely striated ribs; pos- 

 terior depression heart-shaped. One inch long. Inhabits 

 the Mediterranean. 



Gc7ius 18.— CARDIUM Linnceus. 



Generic Character. — Shell equivalve, subcordiform ; beaks 



