6S 



A N O M [ A. 



A. Perforated in the apex. (Plate X. Fig, 1.) 



B. Perforated in the disk. (Fig. 2.) 



C. Imperforate. 



Shell inequivalve ; one valve flatter, the other 

 more gibbous, often produced and incurved towards 

 the beak. One or both valves are frequently per- 

 forated near the apex. Hinge toothless, consisting 

 in some species of a prominent linear callus or ci- 

 catrix, with or without one or two internal mar- 

 ginal teeth, and two bony rays in the cavity. 



Shape orbicular or obovate, rarely quadrilateral. 



The definition of the Anomia, given by Linnaeus, 

 is very unintelligible : it is therefore attempted to 

 render it less so, by altering some parts of the 

 description which appear unnecessary and tend 

 only to obscurity. This genus in fact comprehends 

 species differing so greatly in essential characters, 

 that it is hardly possible to form a description 

 which shall not be contradicted by some among 

 them. The perforation in one or other of the 

 valves, for the emission of a ligature, by which the 



