26$ [February, 



Buh-genera of TJnio. 



NODULARIA, Co7l. 



Shell nodose; cardinal teeth robust, single in the right valve ; in each valve 

 the principal cardinal tooth is parallel with the lateral teeth, or directed towards 

 the posterior extremity of the shell. 



Unio Douglasice, Gray. 



Iridea, Swains. South America. 



Shell with corrugated radiating folds on the beak or umbo ; cardinal teeth 

 granulated, senerally curved, elongated. Third muscular impression distinct, 

 not confluent, situated under the anterior portion of the cardinal tooth. 



Ufiio grauosics, Lam. To this subgenus I would refer Z7. so/istatia, D'Orb., 

 U. ParaJiensis, Lea, TJ. rMiacoica, D'Orb., U. Fontainiana^ D'Orb., JJ. hylcea, 

 D'Orb., Z7. Gaaraniana^ D'Orb., JJ. Mato)ua?iaiD'Oi'b., U. Psammotca, D'Orb., 

 Z7. charruana^ D'Orb. 



This sub-genus is very distinct from any of those existing in North America, 

 nor, indeed, does there appear to be any sub-genus in South America identical 

 with a Northern group. 



Mysca, Tnrton. Europe. 

 The type of this sub-genus, U. pictortim, has the third anterior muscular im- 

 pression deep, and more distinct from the large one, than occurs in any American 

 species of Unio. 



Lanceolaria, Cu7i. China. 



Shell elongated ; cardinal teeth widely bifid ; third muscular impression 

 situated at the base of the anterior lobe of the cardinal tooth, not confluent, 

 and very profoundly impressed; accessory impression small and confluent with 

 the superior margin of the large impression ; pallial impression slightly 

 deflected anteriorly. 



Tf. Grayanicsy Lea. 



Ccelatura, Con. Africa. 



Shell thin, not elongated ; beaks corrugated or subnodular ; cardinal teeth 

 laminar, greatly elongated, parallel with the anterior hinge margin ; anterior 

 accessory muscular impressions confluent with the lower part of the larger one ; 

 pallial impression slightly deflected. 



U. ^gyptiacusy Caill. 



CuNicuLA, Swains. North America. 



Shell compressed, thick, lateral teeth robust and receding from the dorsal 

 margin, posterior accessory muscular impression not confluent, and placed at 

 the extremity of the lateral teeth. 



JJ. fasciolaris^ lineolatus , EasthrooJclanus ^ sultentnSi ccelatus, arcus^ &c. 



I have founded this subgenus on other characters than those given by 

 Swainson. 



Glebula, Con. Lousiana. 



Shell with the cardinal teeth granulated and profoundly sulcated or divided 

 into 4 or 5 lobes, irregular, diverging, somewhat resembling those of Paxyodon; 

 posterior muscular impression very large and confluent with the accessory, 

 which is obsolete. 



JJ. rotundatiis^ Lam. 



Uniomerus, Con. 



Shell elongated, not thick, with parallel dorsal and basal margins ; beaks 

 with obliquely concentric plicae. 



U. declivis, camptodon, subcroceus, Sayii, rivularis, perrectus, symmetricus, 

 and excultus. 



The members of this group inhabit almost exclusively the small streams and 

 ponds in the Southern States. 



