MODIOLA. 



GENERIC CHARACTER. 



Shell cquivalve, inequilateral, obliquely elongated, more 

 or less subovate, regular ; summits near the posterior ex- 

 tremity, but not terminal ; anterior margin obtusely 

 rounded ; posterior margin short, rounded ; posterior base 

 a little gaping to permit the passage of the byssus ; liga- 

 ment marginal, rectilinear, subinterior, elongated ; hinge 

 edentulous ; two principal, remote muscular impressions, 

 of which the anterior one is larger, and securiform : palleal 

 impressions entire. 



OBSERVATIONS. 



A genus of marine bivalves, separated by Lamarck from 

 the Linnaian genus Mytillus, in consequence of the beaks 

 not being terminal, as they arc in that group. It must be 

 confessed however that they are very closely related, cor- 

 responding in the other characters of the shell, as well as 

 in the habits of the animal, the organization of which, ac- 

 cording to the anatomist Poli is similar, and to which col- 

 lectively he appropriates the name of Callitriche ; for a 

 description of it the reader is refered to the genus Mytil- 

 lus. Several species blended by Lamarck in Modiola, 

 were separated by Cuvier under Ihe name of Lithodomus, 

 in consequence of their habit of penetrating and dwulHng 

 in the interior of calcareous rocks and other soliil substan- 

 ces 5 their shell, excepting its more cylindrical form, has 



