UNITED STATES AND NORTHERN MEXICO. 40 



displayed in a double row on eitch. In outline it closely resembles Traiitwiniana 

 (nobis), from Carthagena, but it is not so compressed, so thick, nor so dark a shell. 



In the young of many Amxlonta?, there is* slight disposition towards both cardinal 

 and lateral teeth of an indistinct lamellar structure. This may be perceived on 

 nearly all the young decora. In the specimen of Texasensis before me this char- 

 acter is well marked, the cardinal tooth in the left valve being distinctly raised and 

 separated into two divisions. 



Unio Eightsii. pi. 64, fig. 192. 



Testa plicata, quadrata, subcompressa, maxime undulata usrjue at natium apiecs, valdC' iiiiequilatcrali ; 

 valvulis crassissimis, anticc crassioribus ; natibus elevatis, compressis, ad apices rugoso-undulatis ; epider- 

 iiiide tenebroso-fusca, eradiata, striata ; dentibus cradinalibus raagnis, crassis et valde striatis ; laterali- 

 bus longis, crassis, lamellatis subcurvisque ; margarita alba et valde iridescente. 



Shell plicate, quadrate, rather compressed, very much undulated even to the tips of 

 the beaks, very inequilateral ; valves very thick, thicker .before ; beaks raised, com- 

 pressed and rugosely undulate at the tips ; epidermis dark brown, eradiate and striate ; 

 cardinal teeth large, thick and very much striate ; lateral teeth long, thick, lamellar 

 and somewhat curved ; nacre white and very iridescent. 

 Proc. Acad. Nat. Sci. 1800, p. 306. 



Hab. — Texas and in Sabinas River, New Leon, Mexico. James Eights, M. D. 



My cabinet and cabinet of the Smithsonian Institution. 

 Diam. 1-8, Length 3-3, Breadth 46 inches. 



Shell plicate, quadrate, rather compressed, very much undulated even to the tips 

 of the beaks, anterior portion only free from undulations, very inequilateral ; substance 

 of the shell very thjck, thicker before; beaks raised, compressed and rugosely undu- 

 late at the tips; ligament very long, thick and dark brown; epidermis dark brown, 

 without rays, striate, with rather distant lines of growth ; umbonial slope but slightly 

 raised and obliquely traversed by undulations increasing in size towards the margin ; 

 posterior slope raised into a high carina and covered with nearly parallel rib-like 

 undulations to the margin ; cardinal teeth lai'ge, thick, somewhat raised and very 

 rugosely striate; lateral teeth long, thick, lamellar and somewhat curved; anterior 

 cicatrices distinct, very large, very much corrugate and very deejjly impressed ; pos- 

 terior cicatrices confluent, very large and slightly impressed ; dorsal cicatrices placed 

 on the underside of the plate and on the base of the cardinal tooth ; palleal cicatrix 

 very deeply impressed and distant from the margin ; cavity of the shell rather shallow 

 and very wide ; cavity of the beaks very deep and angular, nacre white and very 

 iridescent. 



Remarks. — Several specimens were brought by Dr. Eights, of Albany, from the two 

 habitats mentioned, and I owe the possession of a specimen to him and one to the 



