VARIETIES OF OYSTERS. 141 



Mantle open and without tubes. 

 Family I. ANOMIID^ (Anomiadae), Gray. 



BODY roundish : mantle having very thin edges, which 

 are furnished with fine and extensile tentacular filaments : 

 gills circular and double : foot small : muscle divided into 

 two or three parts, the largest of which passes through a 

 hole in the hinder part of the lower valve, serving for 

 attachment to extraneous bodies, and forming on them a 

 fibrous or horny plug. 



SHELL generally circular and flat,' more or less inequi- 

 valve : orifice pear-shaped, being interrupted by a narrow 

 slit: cartilage internal, short, placed somewhat obliquely 

 "'below the beak. 



This family is connected with the Ostreidcz by the 

 genus Pododesmus of Philippi. Dr. Leach proposed to 

 raise it to the rank of an Order, which he called Trimya. 



Genus Anomia. Linne. 

 BODY compressed. 



SHELL inequilateral, of an irregular shape, dependent 

 on that of the substances to which it is attached : zipper 

 valve rather convex and thick : lower valve flat and thin : 

 hinge toothless. 



Fabius Colonna, the originator of this name, applied 

 it to species of Terebratula. About a century and a half 

 afterwards Linne used it in the same sense, for he described 

 the animal as having two arms, and the shell as furnished 

 with two bony processes or radii, the deeper valve being 

 often perforated at the base. But he included in the genus 

 many species which we now recognise as belonging, to 



