UNITED STATES AND NORTHERN MEXICO. IT, 



transverse, united only at the upper portion of the posterior edges. Mantle thin, 

 whitish, thickened at the border. Branchial open iiu/ large, with numerous very dark 

 brown papilla^ on the inner edges. Super-anal openuDj very large, colored on the 

 inner edges and united below. Color of the mass whitish. 



Remarl-s. — T have quite a number of this species from Bishop Elliott and Mr. Ilal- 

 lenbeck, but none with the soft parts. In outline it is very near to Rofiwcllensk 

 (nobis), but it is rather more transverse and less compressed. In the color of the epi- 

 dermis it is ver}- different, that species being dark brown or nearly black, while this 

 is usually light or reddish brown. In the cardinal teeth they also differ, the sale- 

 hrostts being single in the right valve, while in the other it is double. It is allied on 

 the other side to Eallenheclii (nobis), but is a much wider shell and is more Ijiangu- 

 lar at the posterior margin. Several of the si:»eci mens have well defined ventral cica- 

 trices. 



Unio inusitatis. pi. 52, fig. 158. 



Testa lajvi, oblongu. subcoiupressii, ad latere planulata et contracts, postici! obtuse" biangulata. valdO inwfjui- 

 laterali; valvulis crassiusculis ; natibus prominulis, ad apices minuto uiidulata; epidermide lutea et 

 fusca, supernt! glabra, inferne tenebroso-striatii, obsolete radiata ; dentibus cardinalibus parvis, acumi- 

 natis, crenulatis, in utroquc valvule duplicibus; lateralibus longis, lamellutis subrectisque ; maro-arita 

 vol alba vel purpurea vel salmonis colore tincta et valdfe iridescente. 



Shell smooth, oblong, rather compressed, flattened at the sides and contracted, ob- 

 tusely angular behind, very inequilateral ; valves somewhat thick ; beaks slightly 

 prominent and minutely undulate at the tip, epidermis yellowish and brown, smooth 

 above and dark and striate below ; cardinal teeth small, pointed, crenulate, double in 

 both valves; lateral teeth long, lamellar, and nearly straight ; nacre white, purple or 

 salmon color, and very iridescent. 



Proc. Acad. Nat. Sci. 1850, p. 171. 



Hah. — Swift Creek, below Macon, Georgia. Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. -8, Length 1-2, Breadth 2 3 inches. 



Shell smooth, oblong, rather compressed, flattened at the sides and contracted at 

 the second growth, obtusely angular behind and regularly rounded before, very ine- 

 quilateral; substance of the shell somewhat thick; beaks slightly j^rominent, with 

 numerous small, closely set undulations, which are angular on the umbonial slope • 

 ligament rather long and somewhat thick ; epidermis obscurely radiate and smooth 

 above, striate and usually banded with yellow below ; umbonial slope slightly raised 

 and obtusely angular ; posterior slope raised into a rather sharp carina and usually 

 with two obscure impressed lines in each valve ; cardinal teeth small, pointed, crenu- 

 late, double in l)oth valves, but only slightly so in the left one ; lateral teeth long. 



