﻿UNITED STATES AND NORTHERN MEXICO. 361 



before ; beaks raised and swollen and nearly medial ; ligament rather long, thick and 

 brown; epidermis dark brown, nearly black, without rays and transversely striate, 

 with distaut lines of growth; umbonial slope much raised and obtusely angular ; pos- 

 terior slope slightly raised and broad; cardinal teeth large, very much compressed, 

 quite lamellar, striate, crenulate, double in the right and single in the left valve; 

 lateral teeth long, thick, crenulate and curved ; anterior cicatrices confluent and 

 deeply impressed ; posterior cicatrices confluent and slightly impressed ; dorsal cica- 

 trices placed in the centre of the cavity of the beaks ; cavity of the shell very deep 

 and rounded ; cavity of the beak shallow and rounded ; nacre white and irides- 

 cent. 



Remarks. — Mr. Wheatley procured but a single specimen of this fine species. The 

 beaks being very much eroded, it is impossible to say if the tips be undulate. It is 

 nearly allied to Berlandierii (nobis), but is more quadrate, has a dark epidermis with- 

 out rays, and the cardinal teeth are more lamellar and longer. The beaks are also 

 more medial. The Berlandierii is usually pinkish in the nacre, while the specimens 

 from which this description is made is of a remarkably pure white. 



It is worthy of remark that the outline, inflation, position of the beaks, color and 

 roughness of the epidermis and thickness of the substance of the shell in this species 

 is so much like a specimen of Anodonta rotunda, Spix, sent to me by D'Orbigny, that, 

 lying side by side, any one would say they were of the same species, while U. quad- 

 rans has very large perfectly developed cardinal and lateral teeth, and A. rotunda is 

 of course without any. It is very likely that when perfect specimens of both shall 

 be observed, that they will be found to differ in the undulations of the beaks. 



Unio Bairdianus. PI. 61, fig. 186. 



Testa lsevi, elliptic*, paulisper. inflata, postice 1 compressa, valde insequilaterali ; valvulis subtenuibus, postice 

 crassioribus ; natibus prominulis, ad apices concentrice undulatis; epidermide tenebroso-fusca, obsolete 

 radiata ; dentibus eardinalibus pa-rvis, erectis, acurainatis crenulatisque ; lateralibus longis, lamellatis 

 subcurvisque ; margarita alba et valde iridescente. 



Shell smooth, elliptical, slightly' inflated, compressed behind, very inequilateral; 

 valves rather thin, thicker before ; beaks slightly prominent, concentrically undulate at 

 the tips; epidermis dark brown, obsoletely radiate; cardinal teeth small, erect, 

 acuminate and crenulate ; lateral teeth long, lamellar and somewhat curved ; nacre 

 white and very iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 102. 



flab. — Devil's River, Texas: Capt. Pope, U. S. A. 



My cabinet and cabinets of the Smithsonian Institution and J. G. Anthony. 

 Diam. -4, Length -7, Breadth 1-2 inches. 



92 



