82 



A N O M I 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 to- 

 wards the beak. One or both valves are frequently 

 perforated near the apex. Hinge toothless^ con- 

 sisting in some species of a prominent linear cal- 

 lus or cicatrix, with or without one or two internal 

 marginal teeth, and two bony rays in the tavity. 



Shape orbicular or obovate, rarely quadrila- 

 teral. 



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 compre- 

 hends species differing so greatly in essential cha- 

 racters, that it is hardly possible to form a de- 



