264 SOLECURTID.E. 



of its area, with profound oblique more or less curved radia- 

 ting stria), which are so graven that each appears to imbri- 

 cate the succeeding. Those stritc which are beyond the 

 almost obsolete urabonal ridge, are more closely disposed 

 than the more distant ones situated in advance of it, from 

 which latter they diverge at acute angles, irregularly uniting 

 with them, and not leaving any intermediate unoccupied 

 space. A larger or smaller triangular surface, extending 

 from the acute sub-central but by no means prominent 

 beaks, is free from all sculpture, except a few antiquated 

 wrinkles which concentrically traverse the entire shell. 

 The sides, although nearly equal, vary a little in this 

 respect, at some the anterior, at others the posterior, being 

 the more produced ; both the extremities are rounded, but 

 assume nevertheless a very different aspect, the hinder 

 being very slightly attenuated and more symmetrically 

 arcuated, whilst the front, owing to the absence of declina- 

 tion, and the rectilinear outline of the anterior dorsal edge, 

 is bluntly angulated above, although strongly and obliquely 

 arcuated below. The hinder dorsal margin is sliglitly 

 retuse near the large and very broad olivaceous prominent 

 ligament, and slopes in but a very trifling degree, although 

 exceeding the anterior in that respect ; the ventral margin 

 is more or less incurved in the middle, and slightly convex 

 at either side, but rather more so anteriorly, where it curves 

 rapidly up in forming the front extremity. The structure 

 of the adult is firm or even solid, opaque, and of an uniform 

 dirty white externally : within it is of a purer white and 

 often polished. The hinge, which however is very rarely 

 found perfect, consists of two primary teeth in each valve, 

 variable in obliquity or erectness; those of the riglit valve 

 are strongly curved and much elevated, the hinder tooth 

 being greatly the longer, but from its compression at the 



