244 



GO^GRYLIA—DITHYRA. 55. 



transversa crenato, valvce alterius bilobo ; lateralibns anticis lamella- 

 tis transversim elongatis, valvce alterius didymis. Ligamentum 

 externum. 

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

 with the beaks wrinkled or warty. Hinge with a transverse 

 crenate tooth, which in one valve is divided into two lobes : 

 lateral teeth at the anterior side only, laminar, transversely elon- 

 gated, 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. 



Batava 

 1. 



Mysca testa oblongd, extremitatibus rotundatis, umbonibus rugoso- 



verrucosis. 

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



warty; 

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



Wood, Conch, p. 103. tab. 19, fig. 1, 2. 



Dillwyn, Descript. Catal. p. 49. 



Turton, Conch. Diet. p. 105. 



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



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



Donovan, British Shells, v. tab. 174. 



Mya Pictorum. 



