114 OBSERVATIONS ON NAIADES, 



passing from the beaks to basal margin. The figure represents a per- 

 fect and beautiful specimen. It sometimes occurs, however, with an 

 extended posterior portion so large as to be nearly as wide again as the 

 natural width of the shell. The pallial impression, nevertheless, does 

 not advance beyond its natural position, and the space beyond is covered 

 by a prolonged and hard portion of the fringe of the mantle. The 

 irregularity of the nodules is very remarkable and varies from one on 

 each valve to twelve. Where there are few, they are generally much 

 elevated, and there being a correspondent depression in the other valve 

 the specimen presents a remarkable, and distorted appearance. Speci- 

 mens are occasionally found of a beautiful rose colour. These, however, 

 are very rare. 



Unio Angustatus. Plate XVII. fig. 43. 



Testa transversa, sub-compressd, angusto-ellipticd; valvulis tenuibus; natibus 

 prominulis et apicibus undulatis; radiis obsoletis; dentibus cardinalibus elevatis et 

 compressis, later alibus longis, subrectisque ; margaritd purpurea et iridescente. 



Shell transverse, somewhat compressed, narrow-elliptical, valves thin ; beaks 

 slightly elevated and undulated at the tips; very obsolete; cardinal ^teelh elevated 

 and compressed; lateral teeth long and nearly straight; nacre purple and iri- 

 descent. 



Hab ^ Congaree river. South Carolina. 



c Cooper river. South Carolina, Professor Ravenel. 



My Cabinet. 



Cabinet of Professor Vanuxem. 



Cabinet of Professor Ravenel. 



Cabinet of Major Le Conte. 



Cabinet of the Academy of Natural Sciences. 



Diam. 7, Length M, Breadth 2-8 inches. 



Shell very transverse, somewhat compressed, very narrow-elliptical, 



inequilateral ; substance of the shell thin ; beaks slightly elevated and 



