MYTILLUS. 



GENERIC CHARACTER. 



Shell equivalve, inequilateral, obliquely elongated, more 

 or less ovate-acute or subtriangular, or subcuneiform, reg- 

 ular ; summits posterior and terminal, acute ; anterior ex- 

 tremity obtusely rounded ; posterior base a little gaping to 

 permit the passage of the byssus; ligament marginal, deep- 

 ly seated, subinterior, rectilinear, elongated ; hinge edent- 

 ulous, or with one or two rudiments of teeth ; two princi- 

 pal remote muscular impressions, of which the anterior 

 one is large and elongated ; palleal impression entire. 



OBSERVATIONS. 



This genus has been considerably modified since it 

 came from the hands of our great master Linne, who uni- 

 ted in one assemblage shells of divers characters, and con- 

 structed by animals of opposite habits, forms and organiza- 

 tion. Bruguiere distinguished the widely different genera 

 Anodonta, and Avicula ; Lamarck separated Modiola, and 

 Leach parted from Avicula the celebrated pearl shell of 

 Ceylon under the name of Margarita, which was after- 

 wards called Melcagrina by Lamarck. Cuvier instituted 

 the genus Lithodomus, for M. lithodomus and some other 

 species which perforate and reside within calcareous rocks. 

 But of these the most closely allied to the present group 

 are unquestionably Modiola and Lithodomus, which two 

 are united together by Lamarck, and are considered by 



