384 



SHELLS AND SHELL-FISH. 



PART II. 



FAMILY 3. AVICULID^E. Muscles and Pearl Oysters. 



Animal attached, byssiferous ; shells lamellar,, internally 

 perlaceous; the valves generally gaping, (fig. 126.) 



MYTILUS Linn. Oblong, transverse ; the bosses small,, 

 close to the anterior margin; both extremities rounded; 

 hinge margin straight, and generally forming an angle ; 

 valves not always gaping ; teeth (except in Brachi- 

 dontes) none. 



Brachidontes Sw. Umbones prominent, not terminal ; 

 valves corrugated ; hinge margin considerably angu 

 lated ; teeth many, small, and crenate. 

 sulcata. En. Meth. 220. f. 2. 



Modiola Lam. Resembling the last, but the hinge 

 without teeth, and the shell smooth ; valves slightly 

 gaping, (fig. 126. A.) 



M. tulipa. Sow. Gen. f. 160. 



Lithodomus Cuv. Animal perforating; shell oblong, 

 ventricose, nearly cylindrical ; the hinge margin not 



