144 ON THE NAIADES, 



shell thick anteriorly and thin posteriorly ; beaks slightly elevated and 

 rounded ; ligament short and thick ; epidermis yellow, with numerous 

 small green rays ; cardinal teeth elevated, double and crested in both 

 valves; lateral teeth elevated and lamellar ; anterior cicatrices distinct; 

 posterior cicatrices confluent; dorsal cicatrices situated within the 

 cavity of the shell on the plate between the cardinal and lateral teeth 

 and on the base of the cardinal tooth ; cavity of the beaks wide and 

 obtusely angulate; nacre white on the anterior and iridescent on the 

 posterior portion. 



Remarks. — While engaged in my last memoir, this shell attracted 

 my attention. I had not, however, then, an opportunity of examining 

 more than two or three specimens, and finding they differed much in 

 some characters, I deferred noticing them. I owe to Mr Cooper the 

 advantage of examining his specimens, which convinced me the species 

 was distinct. This is one of those species which sometimes dilate or 

 increase about the region of the umbonial slope, and in this and its 

 rays it resembles, ia a slight degree, the U. perplexus (nobis). The 

 enlargement of this portion of the shell, which is generally a deep 

 green, causes it to have a different outline, being there more rounded 

 and causing the basal margin to be arcuate. 



Unio Ravenelianus. Plate III. fig. 5. 



Testa late ovatd, obliqud, insequilaterali, postice subangulutu ; valvulis antice 

 crassioribus ; dentibus cardinalibus crassis brevibiisque ; lateralibiis crassis rec- 

 tisque ; margaritd alba et iridescente. 



Shell widely ovate, oblique, inequilateral, subangulate posteriorly; valves thicker 

 anteriorly ; cardinal teeth short and thick ; lateral teeth straight and thick ; nacre pearly 

 white and iridescent. 



Hab. French Broad River, tributary to the Tennessee, near Ashe- 

 ville, N. C. Professor Ravenel. 



My Cabinet. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 



