BIVALVIA. 289 



the shell is full grown. There is a small sinus in the mantle-mark, and the impressions 

 of the adductors are very distinct. Within these, on both sides, a ridge diverges from 

 beneath the umbo ; that on th anterior side is the more prominent. The ligament 

 appears to have been supported upon a prominent fulcrum, while the cartilage was 

 placed in a depressed line upon the dorsal edge, and there is a small gape on the 

 siphonal side. 



The shell above referred to, in the ' Hist, of Brit. Moll./ may possibly be the 

 descendant of our fossil, as I had supposed when compiling my Catalogue, (Ann. 

 and Mag. of Nat. Hist., 1840, p. 245, infra], but several dead valves of the recent 

 species, since obtained from the beach on Stone Point, at Walton Naze, cast a doubt 

 upon that identification, the recent shell having the siphonal side much broader than 

 the anterior, and is not quite so flat. 



I have no doubt of our fossil being distinct from Saxicava arctica, nor do I think 

 there is any good reason for believing it to be the fry of some larger species. It is 

 difficult to determine where it ought to be placed, but it appears to conform more 

 nearly with the diagnosis of Saxicava than with any other existing genus. I would 

 have adopted Arcinella, proposed by Philippi for the succeeding species, but that this 

 name had been twice previously used in the class Mollusca ; and Sphenia, the genus in 

 which I had provisionally placed it, has a different hinge with an internal ligament 

 like that of Mya, placed upon a spatulate projection. 



3. SAXICAVA ? CARINATA ? BroccU. Tab. XXIX, fig. 5, a e. 



MYTILUS CARINATUS? Broc. Coq. Foss. Subap., p. 585, t. 14, fig. 16. 



1 Gold/. Pet. Gerra., p. 179, pi. 131, fig. 14. 

 ARCINELLA CARINATA. Phil. En. Moll. Sic., vol. ii, t. 16, fig. 9. 

 SPHENIA ANGULATA. S. Wood. Catalogue, 1840. 



Spec. Char. Testa minutd, transversd, oblongd, valde inaequilaterali^ tenui,fragili ; 

 antice brevi, postice carinatd, angulatd, productd, granulosd ; cardine unidentato. 



Shell minute, transverse, oblong, very inequilateral, thin, and fragile ; anterior side 

 short, posterior angulated, carinated, and produced, with a granular surface ; hinge 

 with one tooth. 



Length, % inch. Height, \ inch. 



Locality. Cor. Crag, Sutton. 



A few specimens only of this species have come under my observation, and those 

 are all in my own cabinet. 



The shell it most resembles is the preceding, from which, however, it differs in 

 having the siphonal side much more angular, pointed, and carinated, with also a 

 roughened or shagreen-like exterior, most distinctly visible on the posterior slope. 



38 



