In the Devonshire whetstone-pits, a shell is found, measuring from 

 three to five inches in width ; and which, I suspect, fronrthe particular 

 oblique turn of its beak, and from so much of the hinge as I have been 

 able to expose, belongs to this genus. This shell is very unequal sided 

 and the upper part of its produced side has been set with minute spines, 

 regularly disposed. 



CL. Anomia. An irregular shell, with unequal valves; the inferior 

 valve pierced or notched at its beak, which is sometimes closed by a little 

 operculum, or third valve, attached to a cartilage passing out of the hole 

 or notch, and serving to fix the animal on other bodies. The hinge 

 without teeth. 



With the shells of the genus Ano?nia t as formed by Linnaeus, Bru- 

 guiere and Lamarck have composed six genera : Anomia, Placuna, Cra- 

 nia, Terebratula, Calceola, and Hyal<za. 



The shells of the present genus differ from others chiefly in possessing 

 a valve or operculum, with which the animal fixes itself to adjacent 

 bodies. This circumstance, it is to be observed, can only be ascertained 

 in the recent shell ; and therefore cannot be called into aid, when com- 

 paring the fossil shells of this genus with those of Terebratula ; since, each 

 having an opening in the under valve, there exists no particular dif- 

 ference in that state ; excepting, that the shells of the genus Anomia are 

 more rude and irregular than those of Terebratula. I am therefore unable 

 to point out any fossil shell which shows any proof of having possessed 

 the characteristic valve or operculum of this genus. Anomia ephippium, 

 Linn. List. Conch. Tab. 204, /. 38, is instanced as a species of this 

 genus. 



CLI. Crania. A regular inequivalved bivalve : the lower valve flat 

 and nearly round, and pierced in its inner face with three unequal and 

 oblique holes; the upper very convex, furnished interiorly with two 

 projecting callosities. 



These shells had been ranged among the Anomiae, and formed the 

 Anomia craniolaris, Linn. ; but Bruguiere and Lamarck considered the 



