52 CO^GEYLIA—DITHYRA. 10. 



16. AMPHIDESMA— L.4.V.^RCA' 



Testa ovata, wquivalvis, suhclausa. Car do clente cochleariformi cum 

 denticulis adjectis, et lateralibus. Ligavientum externum. 



Shell oval, equivalve, mostly closed. Hinge with a spoon-shaped 

 tooth and adjacent denticles, and lateral teeth. Ligament 

 external. 



All the British species, hitherto discovered of tliis genus, have a 

 lateral tooth on each side in one of the valves only. 



prismaticum. Amphidesma testd ovata-oblongd, latere aiillco ultcnuato, valvd altera 

 denticulo simplici et dentibus lateralibus. 

 Shell oval-oblong, tapering at the anterior side, with a plain denti- 

 cle and lateral teeth in one of the valves. 

 Tab. nost. 5, fig. 3. 

 Ligula prismatica Montagu, Suppl. p. 23, tab. 20, fig. 3. 



Pennant, Brit. Zool. iv. p. 1G9. 

 Mya prismatica. Wood, Conch, p. 101. 



Dillwyn, Descript. Catal. p. 47. 

 Turton, Conch. Diet. p. 103. 

 Mus. nost. Western coasts, British Channel, Scotland. 



Shell nearly half an inch long, and twice as broad, thin trans- 

 parent, glossy white reflecting metallic colors, elegantly tapering to 

 a point at one end and rounded at the other : beaks small, pointing 

 towards the longer side : inside smooth, glossy. 



