244 CONCHYLW—DITHYRA. 55. 



transversa crenato, valca^ allerius biloho ; lateralibns anticis 

 lamellatis transversim elongatis, valvre allerius didymis. 

 Ligamenlum externum. 

 Shell transverse, equivalve, inequilateral, a little open at the 

 sides; with the beaks wrinkled or warty. Hinge with a trans- 

 verse crenate tooth, wiiich in one valve is divided into two 

 lobes : lateral teeth at the anterior side only, laminar, trans- 

 versely elongated, and double in one of the valves. Ligament 

 external. 



This genus is distinguished from the Unio by the strong trans- 

 verse notched teeth placed behind the beaks, the long lateral 

 teeth which reach to the end of the ligament and are double in 

 the left valve, and the want of the internal depression or sinus 

 at their anterior termination. The species are inhabitants of quiet 

 and placid rivers. 



Bafava, Mysca lestd ohlongd, extremitatibus rolundatis, umbonibus 

 rugoso-verrucosis. 

 Shell oblong, rounded at both ends, with the beaks rugged and 



warty. 

 Mya Batava. Linn. Trans, viii. p. 37. 



fVood, Conch, p. 103, tab. 19, fig. I, 2. 

 Dillwyn, Descript. Catal. p. 49. 

 Turton, Conch. Diet. p. lOo. 

 Pennant, Brit. Zool. iv. p. 161. 

 Mya Pictorum. Chemnitz, vi. p. 19, tab. 1, fig. 6. 



Donovan, British Shells, v. tab. 174. 



