IV. MYSCA. 



Shell bivalve, transverse, equivalve, inequilateral, a 

 little open at the sides. Hinge with a transverse 

 crenate primary tooth, which in one valve is di- 

 vided into two lobes : lateral teeth at the anterior 

 side only, laminar, transversely elongated, and 

 double in one valve, without the terminal depres- 

 sion. Ligament external. 



10. MYSCA Batava. Shell oblong, rounded at both 

 ends, with the beaks rugged and warty. 



Mysca Batava. Turton, Dith. p. 244. 

 Mya Batava. Wood, p. 103. t.lQ.f.l, 2. 

 My a Pictorum. Montagu, p. 36. 



Shell an inch long, and two broad, greenish-brown, 

 without contraction in the front margin, by which 

 it is chiefly distinguished from the M. Pictorum ; 

 inside dark-bluish. 



In the river Kennet, above Newbury. 



11. MYSCA Pictorum. Shell somewhat angular and 

 pointed at the anterior side, with the front margin 

 a little contracted, and the beaks rugged and warty. 



