NEW FRESH WATER AND LAND SHELLS. 235 



Shell elliptical, inflated, inequilateral, subbiangular behind ; substance of the shell thick; beaks some- 

 what prominent; epidermis nearly black, shining; cardinal teeth large; lateral teeth large and somewhat 

 curved ; nacre purple or salmon-coloured and iridescent. 



Hab. Tecomate River, near Tlocatalpam, Mexico. Dr. Burrough. 

 My Cabinet, and Cabinet, of Dr. Burrough. 

 Diam. 1.6, Length 2.5, Breadth 3.5 inches. 



Shell elliptical, inflated, inequilateral, subbiangular behind; substance of the 

 shell thick, thinner behind; beaks rather prominent; ligament long and thick; 

 epidermis very dark, nearly black, shining, wrinkled towards the margin; car- 

 dinal teeth large, erect and double in both valves; lateral teeth large and some- 

 what curved; anterior cicatrices distinct; posterior cicatrices confluent; dorsal 

 cicatrices large and placed in a row immediately under the cardinal tooth; 

 cavity of the shell rather deep and rounded; cavity of the beak rather deep and 

 subangular; nacre purple or salmon-coloured and iridescent. 



Remarks. — Two specimens only of this species were brought by Dr. Bur- 

 rough, one of a fine salmon colour, the other of a deep purple. It probably 

 occurs also perfectly white, resembling in this variety of colour many other 

 species, particularly the JJ. complanatus. In form it resembles U. crassus, Say, 

 but differs altogether in the colour of the epidermis and the colour of the nacre. 

 I have seen no young specimens, and the beaks of those before me, being much 

 eroded, their character cannot be ascertained. In the colour of the epidermis it 

 resembles old individuals of U. pliciferus, (nobis,) but being without the folds 

 and being less transverse, ought not to be confounded with that shell. 



Unio GeorGianus. Plate 21, Fig. 49. 



Testa ellipticd, subcompressd,in<Bquilaterali,postice subangulatd; valvuUs subtenuibus ; natibus suh- 

 prominentibus ; epidermide luteo-fuscd; dentibus cardinalibus parvis; lateralibus brevibus rectisque; 

 margaritd alba. 



Shell elliptical, rather compressed, inequilateral, subangular behind; substance of the shell rather thin; 

 beaks somewhat prominent ; epidermis yellowish brown ; cardinal teeth small ; lateral teeth short and 

 straight; nacre white. 



Hab. Stump Creek, Geo. T. R. Dutton. 



Cabinet of Mr. Dutton. 



Diam. .6, Length 1.1, Breadth 1.6 inches, 



vin. — 3 K 



