ANODONTA. 



GENERIC CHARACTER. 



Shell equivalve, inequilateral, transverse, regular ; hinge 

 margin linear, without teeth having a sinus before ; liga- 

 ment external, elongated, terminating in the anterior sinus ; 

 muscular impressions two, remote, posterior one com- 

 pound. 



OBSERTATIONS. 



These are shells of rather large size, resijling in fresli 

 water streams and lakes. They are generally perlaceous 

 W'ithin and greenish on the exterior. Although the gene- 

 ra Anodonta and Unio are closely allied, yet the species 

 were widely separated by Linnc who referred those of the 

 present genus to Mytilus, whilst those of Unio he associa- 

 ted with the Myae ; but an arrangement so artificial could 

 not escape Bruguiercs. He perceived their affinities, and 

 grouped them under the above mentioned denominations. 

 Several other allied genera have been formed by subse- 

 quent naturalists, distinguished from the present by the ex- 

 istence of either cardinal or lamellar teeth, with the excep- 

 tion however of Iridina of I^amarck, which has an elonga- 

 ted, linear, crenulated hinge and was placed by Bruguicres 

 in Anodonta, to which indeed it is intimately linked by the 

 I. nilotica. Ferussac, in his Tableaux Sj'st.. iuchuled all 

 the genera of this family in four, viz. Anodonta, Hyria, 

 Unio, and Castalia. Sowerby hiis since proposed to retain 



PLATE XI. F 



