142 DIMYARIA. 



Hiatella arctica The Arctic Hiatella. Plate XVI. 



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

 and truncated; the valves virith 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— CYPRICARDIA.— Zcwmz-cA. 



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 Cai'dita, ■nith 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 Gninaica. — 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.— XflJwa/'cA. 



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 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. 



Genus 18.— CARDIUM Linnoeus. 



Generic Character. — Shell equivalve, subcordiform; beaks 



