CARDIUM. 271 



semioval ; the upper pair are as long as the lower, but not 

 half the depth : palps very long, slender and pointed, strongly 

 striated on the inside and less so on the outside : foot finger- 

 shaped, closely striated lengthwise, covered with a flesh- 

 coloured or vermilion delicate skin, under which it is pure 

 white ; its length is at least twice that of the shell. 



Shell roundish, very convex, rather solid, opaque and 

 of a dull hue : sculpture, about 20 strong but somewhat com- 

 pressed ribs, which are a trifle broader than the furrows be- 

 tween them ; the crest of each rib has a numerous row of 

 triangular and short but stout spines, which are connected 

 together at the base and are usually curved towards the pos- 

 terior side ; all these spines are nearly equal in diameter and 

 length; both ribs and furrows (especially the latter) are crossed 

 by nexuous wrinkles, which are coarser and more distinct on 

 the posterior side; in young specimens are observable some 

 longitudinal lines and microscopical markings similar to those 

 noticed in the description of the last species : colour yellowish - 

 white : epidermis fibrous, mostly obliterated : margins rounded 

 on the anterior side, and sloping to the front, which is curved, 

 but much less obliquely than in C. aculeatum ; posterior side 

 not much produced, although considerably broader than the 

 other, slightly truncate, and exhibiting a narrow and indistinct 

 gape : beaks more or less contiguous ; umbones tumid ; below 

 the beaks on the anterior side is a nearly smooth heart-shaped 

 space, the lips of which project or pout, especially on the upper 

 part : ligament shaped like that of the last species, brownish - 

 homcolour : hinge-line obtusely curved : hinge-plate reflected, 

 occupying about one.-third of the circumference : teeth, in each 

 valve two erect nearly equal-sized cardinals, with laterals 

 similar to those of the other species : inside and scars the same. 

 L. 2-2. B. 2-3. 



Yar. 1. expansa. Shell rather more depressed and spread 

 out at each end. 



Var. 2. ovata. Shell transversely oval ; ribs sharp, obliquely 

 radiating, and much narrower than the furrows ; transverse 

 striae fewer than in typical specimens of a similar size ; dorsal 

 margin nearly straight ; there is only a single minute cardinal 

 tooth in each valve, besides indistinct laterals. L. 0-125. 

 B. 0-15. 



Habitat : All our sandy coasts, at various depths 

 from 5 to 100 fathoms. It occurs in almost every 



