30 ON THE NAIADES, 



trices situated on the under side of the cardinal tooth ; cavity of the 

 beaks obtiisely angular ; nacre pearly white and iridescent. 



Remarks. — 1 have had a single specimen of this shell for some years, 

 and although satisfied it differed from any described species, I deferred 

 bringing it forward until I should have an opportunity of examining 

 more. In the fine collection of the Academy of Natural Sciences 

 I found a second specimen, which so completely coincided in all its 

 characters with mine, that I deemed it unnecessary to hesitate erecting 

 it into a species. Both the specimens have that enlargement of the 

 inferior portion of the umbonial slope mentioned in the remarks on the 

 U. Haysianus herein described, which usually causes a remarkable and 

 curious denticulation of the margin, and a poverty of the deposition of 

 the nacre in that region. It has, perhaps, a stronger resemblance to 

 U. ellipsis (nobis) than to any other species. It is however more 

 rotund, more minutely rayed, and less oblique. 



Unio sub glob osus. Plate II. fia;. 3 



t3" 



Testa, subglobosd, subxquilaterali, inflata et postice subangulata ; valvuUs 

 crassis ; natibus jjrominulis rotundatisqiie ; denlibus cardinalibus latis striatis- 

 que, lateralibus subcurvis ; margaritd subrufd, vel colore caryophylli tinctd. 



Shell subglobose, nearly equilateral, inflated, subangular behind ; valves thick ; 

 beaks slightly prominent, rounded ; cardinal teeth wide and striated ; lateral teeth 

 somewhat curved : nacre pearly and pink coloured. 



Hab. Bayou Teche, Louisiana. W. M. Stewart. 



My Cabinet. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Mr Stewart. 

 Cabinet of William Hyde. 

 Cabinet of P. H. Nicklin. 

 Diam. 1-6, Length 2-1, Breadth 2-9 inches. 



Shell subglobose, subequilateral, subangular behind, inflated; sub- 

 stance of the shell thick ; umbonial slope carinate ; beaks slightly pro- 



