CONCHYLIA— D/THYi?^. 56. 247 



Tah.nost. 16, fig. 2. 

 Mya ovata. Donovan, British Shells, iv. tab. 122. 



Mus. nost. From the Avon, near Bristol. 



Shell two inches long, three and a half broad, and nearly as deep 

 as it is long, covered with a blackish-brown skin, under which it is 

 of the richest pearly lustre ; thick and [ponderous, with the margin 

 thick and very obtuse, nearly cylindrical about the hinge, from 

 which it regularly tapers in a conical manner to the anterior side : 

 beaks rugged, and often decorticated. 



Montagu, at p. 36, is of opinion, that this is only a variety of 

 Mysca ovata : but a series of each of them, from the Avon and the 

 Froome, has sufficiently convinced us of their specific distinction. 

 One is uniformly flat and thin ; the other is nearly cylindrical and 

 thick. 



56. GYCLAS—BRUGUIERE. 



Testa orbicularis vel ovata, cequivalvis, clausa. Cardo dentibus duobus 



ininutis divergentibus : lateralibus utrinque, valvce alterius didymis. 



Ligamentum externum. 

 Shell orbicular or oval, equivalve, closed. Hinge with two minute 



divergent teeth : and lateral ones on each side, which are doublo 



in one of the valves. 



