ANOMIA. 29 



* Mantle open and without tubes. 



Family I. ANOMI'IDiE, (Anomiadce) 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 extra- 

 neous bodies, and forming on them a fibrous or horny plug. 



Shell generally circular and flat, more or less inequivalve : 

 orifice pear-shaped, being interrupted behind by a narrow slit : 

 cartilage internal, short, placed somewhat obliquely below the 

 beak. 



This family is connected with the Ostreida by the 

 genus Pododesmus of Philippi. Dr. Leach proposed to 

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

 Trimya. 



Genus ANO'MIA* Linne. PI. I. f. 4. 



Body compressed. 



Shell inequilateral, of an irregular shape, dependent on 

 that of the substances to which it is attached : upper valve 

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

 toothless. 



As I have before observed, Fabius Colonna, the origi- 

 nator of this name, applied it to species of Terebratula. 

 About a centurv 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 bonv 

 processes or radii, the deeper valve being often per- 

 forated at the base. But he included in the genus 

 many species which we now recognize as belonging to 

 Anomia thus restricted, and long custom has sanc- 



* Irregularity. 



