xlvi. CONCUYLIA—DITHYRA. 



53. Anodon. 



1. Cygneus, in(Equilateralis, antich aiigustalo-acuminatus. 



inequilateral, narrowed to a point at the anterior 

 side. 



2. paUHlosas, suhcequilateralis, antich simialo-suhangulalns. 



nearly equilateral, sinuous and somewhat angular 

 at the anterior side. 



3. Anatinus, antice alatus, umbonibus erosis. 



winged at the anterior side, and eroded about 

 the beaks. 



4. Avonensis, laleribus rotandatis, umbonibus subterminalibus. 



rounded at the sides, and the beaks nearly tenuiual. 



54. Unio. 



1. margaritiferus, subarcuatus, epidermide nigid. 



slightly arched, and clothed with a black skin. 



35. Mysca. 



1. Batava, exlremitatibus rotaudutls. 



rounded at both sides. 



2. Pictorum, oblonga, antich acumiuala, marqine coorctalo. 



oblong, pointed at the anterior end, with tiib 

 margin contracted. 



3. ovata, ovata, margine subarcnalo. 



oval, with the margin slightly curved. 



4 suliila, crassa subcylindrica, antice acuminata. 



thick somewhat cylindrical, and pointed at the 

 anterior end. 



