Mr. Barnes on the Genera Unio and Alasmodonta, 121 



My collection. Cabinets of Lyceum and Dr. Mitchill. 

 Mr. Say^s cabinet, Philadelphia. 



Diam. '75 Length, 1.0 Breadth, 1*3 inches. 

 1-35 1-9 2-4 



1-9 2-3 3-2 



Shell thick ; posterior side very short, obtusely round- 

 ed ; anterior side compressed, wedge-shaped ; beaks very 

 prominent, large rounded and projecting backwards nearly 

 as far as the posterior side ; ligament passing under the 

 beaks, anterior lunule distinct and marked with longitudin- 

 al furrows ; hinge margin alated, compressed, carinated ; 

 epidermis green, becoming blackish as the shell advances 

 in age ; surface glabrous, deeply folded ; folds indenting 

 the anterior basal edge. Cardinal teeth crenate, sulcate ; 

 posterior cicatrix rough ; cavity of the beaks deep and di- 

 rected backwards. Naker very white, tinged on the an- 

 terior side with rose colour; surface polished and on the 

 fore part iridescent. 



Remarks. — In young specimens the folds are visible on 

 the inside, but in older ones the edge is not even indented. 

 This shell very much resembles the variety (rf.)of the Unio 

 Crassus. Both shells will stand erect when placed on the 

 posterior side, being supported by the projecting beaks. M. 

 Lamarck observes that his Rariplicata is nearly allied to his 

 Peruviana, but if we have not mistaken his short definitions, 

 they are much more unlike than the two above mentioned. 

 Our undulatus will not stand on the posterior side, as the 

 beaks project very little. 



4. Unio Undatus. Fig. 4. < z* '"''' • j* 

 *= i^b. outside. 



Shell, sub-triangular, sub-longitudinal, very tumid, waved : 



lateral teeth, two in each valve. 



Unio Obliqua? M. Lamarck. 



Hab. Ouisconsin and Fox Rivers. Mr, Schoolcraft. 

 Dr. MitchilPs cabinet. My collection. Mr. ,S'«?/'s col- 

 lection. 



Diam. 1-5 Length, 2-1 Breadth, 2-2 

 Shell thick, disks swelled behind ; depressed before ; 

 anterior side slightly produced, rapidly narrowed, angulated ; 

 beaks projecting backward nearly as far as the posterior 

 Vol. VI,...No. I, 16 



