72 Mr. G. B. Sowerby on Jlinniles. 



praescrtim margine basali, picrumquc irregulariter depressa, 

 poHta. ' 



Shell oblong, thin, closely striated, striae radiating, scabrous ; 

 ears'unequal, with scabrous radiated striae; outside of the lower 

 valve, particularly the basal margin, generally flattened and 

 smooth. 



The regularity of this shell in its young state is remarkable, 

 particularly when contrasted with the irregular form it assumes as 

 it increases in age ; and it is such as to render it, when young, a 

 characteristic type of one of the divisions of the genus Peden. 



This is a common shell on the coast of Britain ; it difters in the 

 thinness of the shell and the distinctness of the ears from the other 

 species; it is the smallest of all, seldom exceeding two inches ia 

 height. The byssal groove is much more distinct than is usual in 

 the other species ; in one specimen, however, of the //. Cortesyi 

 which my brother possesses, this byssal groove is quite distinct. 

 For about half an inch in height this shell is generally quite 

 regular, afterwards it appears to be almost constantly pressed close 

 to the substance to which it is affixed by its byssus, and some- 

 times becomes fixed by the shell itself, by spreading the testa- 

 ceous matter close to the surface and in undercut hollows. 



From the whole of the above I think it will appear that Mr. 

 Gray had at first, though in error, come nearer to the truth in 

 placing this genus among the Pectiiiidcc, with Lima^ than after- 

 wards in associating it with Spondylus and Vlicatula ; it certainly 

 is much more nearly related to Peden than to either Spondylus 

 or Ostrea. It will also be observed that Defrance has partly 

 avoided an error into which Gray has stumbled, where he says of 

 the genus that is " adherente,^' whereas Gray says " adherent by 

 the apex of the right valve." Gray adds that it has " uo byssal 

 groove," which is also incorrect. 



