CHIEFLY OF THE UNITED STATES. 309 



Shell smooth, widely elliptical, somewhat cylindrical, very inequilateral, rounded 

 before and behind ; substance of the shell thick, thicker before ; beaks slightly 

 prominent ; ligament rather long and thin ; epidermis yellowish, without rays, with 

 rather distant marks of growth; umbonial slope rather high and rounded; posterior 

 slope elliptical, low, with a line from the tip to the posterior margin in both valves; 

 cardinal teeth small, subcouical and corrugate ; lateral teeth long and somewhat 

 curved; anterior cicatrices distinct, small and well impressed; posterior cicatrices 

 distinct, rather small and slightly impressed; dorsal cicatrices placed in the centre 

 of the cavity of the shell ; cavity of the shell rather deep and wide ; cavity of the 

 beaks rather deep and subangular; nacre purple within the cavity and very 

 iridescent. 



Remarks. — I have two specimens and an odd valve of this interesting species 

 before me. These are adults. The thickened margin of the nacre below the palleal 

 impression is white in thi'ee specimens. Neither of the specimens have any rays. 

 In outline it is nearly allied to granulatus (nobis), and parvus, Barnes, but is not 

 easily confounded with either, being more cylindrical than either, being more solid, 

 and in having a yellowish epidermis, while the others are dark greenish. 



Unio Brazosensis. PL 48, fig. 122. 



Testa plicata, subrotunda, ventricosa, valde insequilaterali, antice et postice rotundata ; valvulis 

 percrassis, antice crassioribus ; natibus prominentibus, tumidis, incurvis, ad apices minute 

 undulatis ; epidermide tenebroso-rufo-fusca, eradiata ; dentibus cardinalibus percrassis, solidis, 

 erectis corrugatisque ; lateralibus longis subcrassis et obliquis; margarita argentea et valde 

 iridescente. 



Shell folded, subrotund, ventricose, very inequilateral, rounded before and behind ; 

 valves very thick, thicker before ; beaks prominent, swollen, incurved and minutely 

 undulate at the tips; epidermis dark reddish-brown, without rays ; cardinal teeth 

 very thick, solid, erect and crenulate; lateral teeth long, rather thick and oblique; 



nacre silver-white and beautifully iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 144. 



Hah. — Dallas Co., Texas, Prof. Forshey ; Brazos River, Dr. Lincecum. 



My cabinet and cabinet of Smithsonian Institution. 

 Diam. 1*5, Length 2-1, Breadth 2-7 inches. 



Shell plicate, subrotund, ventricose, very inequilateral, rounded before and behind; 

 substance of the shell very thick, thicker before ; beaks prominent, swollen, incurved 

 and minutely undulate at the tips; ligament very large and light brown; epidermis 

 dark reddish-brown, without rays, with distant broad marks of growth ; umbonial 

 slope raised, rounded, with two irregular raised lines from the tips to posterior 

 margin ; posterior slope cordate and carinate ; cardinal teeth very thick, solid, erect 



