62 



C H A M A. 



(Plate VIII. fig. 2.) 



A. Gaping. B. Closed. 



Shell thick. Hinge furnislied with a gibbous cal- 

 losity, obliquely inserted in a corresponding chan- 

 nel. This callosity or tooth is either simple or 

 crenate, occasionally double or triple, (fig. 1.) 



Some species of this genus are truncate, and 

 gape on the posterior margin ; and though all do 

 not so, they agree in being equivalve, and sub- 

 equilateral, in having recurved beaks, and no pro- 

 minent lips. The form differs much, being sub- 

 globose, reniform, cordate, or rliombic. No genus, 

 perhaps, contains two species so dissimilar in out- 

 ward appearance as C. Co7- and C. G'lgas ; still 

 they are linked together by the Linna?an bond of 

 relationship, the hinge. This genus, indeed, were 

 it formed only upon the name, derived from x^iMt 

 a gaping, would exclude a large proportion of its 

 shells, and would properly retain only one species, 

 C, Gigas, which is the largest of all testaceous 



