FRESH WATER AND LAND SHELLS. 39 



Unio nigellus. pi. XXIV. Fig. 42. 



Testa Isevi, elliplica, anlice compressd, valde insequilalerali, postice ohluso-biangulata ; valvulis tenuibus ; 

 natibus prominulis; epidermide nitidu, nigra; dentibus cardinalibus parvis,acuminaiis, crenululis; luteralibus 

 prselongis curvisque; inargarita cseruleo-albd et valde iridescente. 



Shell smooth, elliptical, compressed before, very inequilateral, obtusely biangular behind; valves thin; beaks a 

 little prominent; epidermis shining, black; cardinal teeth small, pointed, crenulale ; lateral teeth long and 

 curved ; nacre bluish-white and very iridescent. 



Hab. Chatahoochee river, near Columbia, Georgia, Dr. Boykin. 

 My cabinet. 

 Diam. .5, Length .9, Breadth 1.6 inches. 



Shell smooth, elliptical, compressed before, very inequilateral, obtusely biangular behind ; 

 substance of the shell thin, thicker before; beaks a little prominent and placed near to the 

 anterior margin; ligament rather long and thin; epidermis shining, black, with distant 

 marks of growth; posterior slope rather compressed, and with an indented line from the 

 beaks to the margin; umbonial slope inflated and rounded; cardinal teeth small, pointed, 

 crenulate ; lateral teeth long, curved and removed from the cardinal teeth ; anterior cica- 

 trices distinct; posterior cicatrices confluent ; dorsal cicatrices placed above the centre 

 of the cavity of the beaks; palleal cicatrix impressed; cavity of the shell rather deep; 

 cavity of the beaks shallow and subangular; nacre white and beautifully iridescent. 



Remarks. — A single specimen of this species was received by me some years ago, from 

 my late friend. Dr. Boykin, to whose kindness I owe many interesting and new species 

 from the fruitful locality of Columbia. Having never been able to obtain other specimens, 

 I have delayed until now its description. Older or younger specimens may present dif- 

 ferent characters. This specimen is in good condition, but the beaks are not perfect, and 

 in younger and perfect specimens, the epidermis may not be so dark as this. It is allied 

 to U. occultus, (Nobis,) but is not so compressed nor so high in the carina. The occtiltus 

 is also much more rayed. 



Unio nux. PI. XXIV. Fig. 43. 



Testa Ixvi, elliplica, convexd, subinsequilaterali, postice subangulata ; valvulis percrassis ; natibus promi- 

 nentibus, rotimdatis ; epidermide tencbroso-f used, radiatd; dentibus cardinalibus subgrandibus ; laleralibus 

 brevis rectisque; margaritd argented et iridescente. 



Shell smooth, elliptical, convex, somewhat inequilateral, subangular behind ; valves very thick; beaks prominent, 

 rounded; epidermis dark-brown, radiated; cardinal teeth rather large; lateral teeth short and straight; nacre very 

 white and iridescent. 



Hab. Alabama river, Mr. Wheatley. 



My cabinet and cabinets of Dr. Budd and Mr. C. M. Wheatley, New York. 

 Diam. .6, Length .8, Breadth, LI inches. 



Shell smooth, elliptical, convex, somewhat inequilateral, rounded before, subangular 

 behind; substance of the shell very thick, much thinner behind; beaks prominent, inflated 

 towards the umbo; ligament very short and rather thick; epidermis dark-brown, obscurely 

 radiated, yellow on the posterior slope, with a single curved ray from the beak to the 



