68 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



PL XLVIII. Fig. 5. 



Amphidesma purpurascens, Sowerby, Proceedings Zool. Soc, 1832, 



p. 199. 



PI. XLVIII. Fig. 6. 



Amphidesma l^ve, Sowerby, Proceedings Zool. Soc, 1832, p. 200. 



PI. XLVIII. Fig. 7. 

 Amphidesma formosum, Sowerby, Proceedings Zool. Soc, 1832, p. 199. 



CUMINGIA, Sowerby. 



Testa insequilateralis, requivalvis, latere antico rotundato, postico sub- 

 acuminato ; dentibus, cardinali in utraque valva unico, parvo, an- 

 tico, lateralibus in altera valva ad utrumque latus uno, valido, in 

 altera nullo. Ligamentum internum, foveolae cocbleariformi atlixo. 

 Impressiones musculares distincte imbuta?, antica irregulari, postica 

 subrotundata ; irapressio muscularis pallii sinu maximo. 



This genus was established by Sowerby for the introduction of a series 

 of new and interesting species of Mactracea, brought to England by 

 Mr. Cuming. Their shell exhibits the unusual character of having two 

 strong lateral teeth in one valve and none in the other, but approximates 

 in other respects to that of the. Amphidesmata. 



Mr. Sowerby describes the shell of Cumingia as being " inequilateral, 

 equi valve, with the anterior side rounded and the posterior rather acu- 

 minated. A single small anterior cardinal tooth is observable in each 

 valve ; and there is one strong lateral tooth on each side of the hinge in 

 one valve, but no lateral tooth in the other ; the ligament is internal, 

 and affixed to a somewhat spoon-shaped pit in each valve. The anterior 

 muscular impression is irregular and oblong, the posterior rounded, and 

 there is a very large sinus in the muscular impression of the mantle." 



