93 



flakes: this compound tooth is not erect, but slopes in 

 an inclined position towards the posterior side. The 

 substance of the shell is solid, and beautifully pearly. 

 Shell equivalve, obliquely triangular, auriculated, base 

 truncated and straight: hinge with two projecting 

 teeth, the one posterior or cardinal, divided into nu- 

 merous divergent parts, the anterior ones smaller, and 

 the others, anterior or lateral, being very long and la- 

 mellar; ligament linear and external. This genus, 

 with that of Dr. Leach's Dipsas, form the transitions to 

 the genus Anodon. 



Hyria avicularis Hyria corrugata 



ANODONTA. 



mytilus cygneus, — Linn. 



Swainsons Exotic Conchology. 

 The genus Anodon, as it properly should be called, 

 has been separated from the G. Mytilus of Linnaeus; 

 it consists of fresh water shells, so nearly allied to the 

 G. Unio that they cannot easily be distinguished from 

 them without a careful examination of the hinge, which 

 in this genus wants the cardinal and lateral teeth, 

 and merely presents a smooth internal rim round the 

 edge, terminated at the anterior end by a sinus or 



