142 DIMYARIA. 



Hiatella arctica The Arctic Hiatella. Plate XVI. 



fig. 12. Transversely oblong; with 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 rugosa. 



Genus 16.— CYPRTCARDIA.—Iowm/c/fe. 



Generic Character Shell free, equi valve, inequilateral, 



obliquely or transversely elongated ; teeth of the hinge three, 

 situated under the beaks, and one lateral elongated tooth. 



Distinguished from Cardita, -with which they are closely allied in 

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

 in addition to the lateral lengthened tooth or ridge. 



Cypricardia Guinaica. — The Guinea Cypricardia. 

 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 17.— CARDITA.— Za?«arcA. 



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 from the Venericardia. 



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. 



Genus 18.— CARDIUM Linnceus. 



Generic Character — Shell equivalve, subcordiform ; beaks 



