228 ANATINID^. 



edge ; the inside is white, and the hinge-plate consists of 

 a large and very strong prominent tooth-like callus, whose 

 upper surface (which in the lesser valve is above, and in 

 the larger beneath the level of the margins,) is hollowed 

 out slightly near the middle, and profoundly so in front, for 

 the insertion of the ossicle, the intermediate space thus pre- 

 senting the appearance of a very blunt tooth ; this callus, 

 being entirely seated upon the angulated side, exposes the 

 cavity of the umbones in front, and is continued posteriorly 

 in a narrow rib-like line, which runs parallel to the margin, 

 and causes the intervening space to appear grooved. 



From the very rare occurrence of the young of this 

 species, whose extreme fragility materially diminished the 

 chances of its being captured in a good state of preserva- 

 tion, Montagu erroneously supposed that T. pJmseolina was 

 its immature state. Turton, too, although separating the 

 species, has delineated a large specimen of that shell as the 

 young of puhescens. This error we have avoided from an 

 examination of the long suite of examples belonging to 

 Mr. Jeffreys (taken at Exmouth by Mr. Clark), from 

 whence we are enabled to specify the points in which they 

 differ from pliaseolince of equal length. They are much 

 thinner and excessively brittle, much more scabrous, and 

 furnished with coarse concentric wrinkles, which become 

 folds upon the umbones. Moreover, their shape is very 

 dissimilar, the proportional distance from the beaks to the 

 ventral margin being considerably greater, and the hinder 

 dorsal edges (which are both of them flattened above) 

 being much incurved ; the ligament, likewise, is more 

 cinereous, and the cartilage plate more solid. 



The size of full-grown individuals is occasionally three 

 inches and a half in length, and two inches and a third in 

 breadth. 



