66 CONCHOIiOGY, 



4. Genus IHdina. 

 Animal. As above. 



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

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

 nal and marginal ; two distinct muscular impressions. Inhabits 

 the Nile. Six species. 



Iridina exotica, Iridina Nilotica. 



I. cselistis.* I. elongata.* 



I. rubens,* I, McMurtria.* 



FAMILY XIV. 

 Chamacea. Three genera, 



1. Genus Dicer as. 

 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. 



Animal. Body suborbicular terminated superiorly by a sort of 

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

 nated at its extremity by a part much narrower than the base ; 

 superior lobes of the branchiae very short. 



Shell. Irregular, adhering, inequivalve, inequilateral ; summits 

 more or less twisted spirally, especially in the lower valve by 

 which these animals have the faculty of affixing themselves to 

 other bodies; hinge dissimilar, thick, formed by a single lamellous 

 tooth arcuated, subcrenulated, postcardinal and articulated in a 

 furrow of the same form ; ligament exterior and postapicial ; two 

 large muscular impressions, distant. Seventeen living species. 

 Fight fossil species. 



Chama damsecornis. Chama Florida.* 



C. crenulata. C. aeruginosa. 



C. arcinella. C. decussata. 



C. cristella. C. ruderalis. 



