OF THE GENUS UNIO. 265 



It is evident, that the word explained by the former of 

 these definitions is the most proper to express a genus of 

 shells ; and consequently, in Conchology, the word Unio is 

 masculine. 



1. Unio Calceolus. Plate III. fig. 1. 



Testa inaquilaterali, transversa, aliquantuluin cylindraced, tenuiter 

 rugatd ; dente cardinali prominente. 



Shell inequilateral, transverse, somewhat cylindrical, finely wrinkled ; 

 cardinal tooth prominent. 



Hab. Ohio. T. G. Lea. 



My Cabinet. 

 Cabinet of Prof. Vanuxem. 

 Diam. -6, Length -8, Breadth 1-5 inches. 



Shell ventricose, cylindrical, transverse — substance of the 

 shell thin, rather thicker anteriorly — ^beaks slightly elevated, 

 undulated and touching; not decorticated — ligament short, 

 partly concealed by the beaks — dorsal margin straight ; pos- 

 terior dorsal margin oblique and carinated ; posterior margin 

 angular ; posterior basal margin curved ; basal margin nearly 

 straight ; anterior and anterior dorsal and basal margins round- 

 ed — epidermis dark green at the margin and becoming lighter 

 towards the beaks ; rays indistinct — cardinal tooth of right 

 valve prominent and somewhat pointed ; the single tooth of 

 this valve shuts in before the tooth of the left valve, instead of 

 passing into it ; the tooth of the latter valve is emarginate — 

 lateral tooth very short and single in both valves — posterior 

 cicatrices confluent, as are also the anterior ones — cavity of 

 the beaks deep — nacre pearly, white and silvery, iridescent in 

 the posterior margin. 



Remarks. — This curious little shell is peculiar in its promi- 

 nent curved tooth, shutting in before that of the other valve. 



VOL. III. — 3 X 



