70 



4. Genus L^idina. PI. VIII. 



Animal. As above. 



The principal difference between the Anodonta and the 

 Iridina, consists in the tuberculated hinge of the latter. 



Shell. Thin, oval, much elongated, inauriculated ; hinge very 

 long, linear, and crenulated throughout its length, ligament ex- 

 ternal and marginal ; tw^o distinct muscular impressions. Inhabits 

 the Nile and American coasts. Six species. 



Iridina exotica. Iridina Nilotica. 



I. caelistis.* I. elongata.* 



I. rubens.* I. McMurtria.* 



FAMILY XIV. 



Chamacea. Three genera. 

 1. Genus Dicer us. PI. VIII. 



Animal. 



Shell. Inequivalve, adherent ; beaks conical, very large, diverg- 

 ing in irregular spiral contortions; hinge with a large, thick, 

 concave, subauricular tooth in the larger prominent valve ; two 

 muscular impressions. One species. Fossil. 

 Diceras arietina. 



2. Genus Chama. PI. VIII. 



Animal. Body suborbicular terminated superiorly by a sort of 

 hook ; mantle very slightly opened for the passage of a foot, termi- 



J 



