PART II. 



ATRACHIA- 



•OSTRAClDiE. 



387 



umbones lateral or sublateral ; byssus protruded near 

 the umbones. 

 Margarita Leach. (I8I7.) Shell more or less rounded; 

 auricles small ; umbones sub-lateral ; the hinge mar- 

 gin straight, but not lengthened ; teeth small, tuber- 

 culated, nearly obsolete, {fig. 126. e.) 

 crocata. Zool. 111. ii. pi. 55. 



Aviciila Lam. Shell obliquely oval ; the hinge margin 

 very much lengthened, and forming unequal auricles ; 

 teeth tuberculous, nearly or quite obsolete, {^fig. 1'2,1. 

 h, c, c?.) 

 A. heteroptera. Sow. Gen. f. 1. aculeata. lb. f. 2. 



PiiNNA. Shell equivalve, wedge-shaped or triangular ; 

 umbones terminal ; the other extremity widely gaping ; 

 hinge margin straight ; teeth none ; anterior margin 

 slightly gaping.* {fig. 19.6. f, g.) 

 P. serrata. Sow. Gen. 



Family 4. OSTRACTD^. Oysters. 



Animal sedentary, generally affixed by their under valve ; 

 shell foliaceous, rarely pearly, {fig. 129.) 



Peoten Linn. Shell regular, depressed, nearly orbicular, 

 auriculated ; umbones central ; ligament small ; in- 

 ternal hinge margin short ; teeth straight. 



* This genus, by coining close to Mytilus corapletes the circle of thi» 

 family. 



c c 2 



^ 



