CHAMA 



Testa irregularis, plerumque suborbicularis, iii- 

 aequivalvis, adherens, umbonibus inasqualibus, 

 distantibus, involutis. Cardo dente unico crasso, 

 oblique, subcrenato, fossulae valvae oppositae in- 

 serto. Impressiones musculares duae, distantes, 

 laterales. Ligamentum externum, divaricatum, 

 sub umbonibus revolutum. 



Linne had united in his Genus Chama, shells so dif- 

 ferent from each other, that the association could not pos- 

 sibly be preserved, for in his arrangement regular and 

 equivalve shells are placed with such as are irregular 

 and inequivalve ; free shells with others that are attached 

 to marine bodies ; and shells which have two distinct mus- 

 cular impressions with others which have only one. In- 

 deed it is very observable that the greater number of the 

 shells arranged together by Linne do not correspond with 

 the generic character he has drawn out for them, where- 

 fore Bruguiere has divided Linne's Chamce into several 

 Genera, to which Lamarck has added some others. We 

 now give that to which the name of Chama is retained, 

 which are irregular, thick, generally very inequevalve 

 shells, for the most part covered with irregular spines, or 

 foliated on the outside in the same manner as many Ostrece : 

 the umbones are also irregular, distant, unequal in size 

 and involute ; one of them, (that of the attached valve) is 

 salient at the base of the shelly and sometimes projects very 

 far beyond it, the other is generally turned over upon its 

 valve, so as to appear as it were imbedded in it. Lamarck 

 has divided the Chamce into two sections, in the first of 

 which the umbones turn from left to right, and in the other 

 from right to left, in both sections taking the attached valve 

 as the lower one : this circumstance arises from the re- 

 markable peculiarity in some of the species to attach them- 



