CHIEFLY OF THE UNITED STATES. 313 



cavity of the shell deep and rounded ; cavity of the beaks very deep and sharply 

 angular ; nacre silver-white and very iridescent. 



RemarJcs. — Three specimens of this shell are before me. Two I have had for some 

 years from Prof. Forshey; the third was recently received from the Smithsonian 

 Institution, having been collected by Dr. Lincecum and presented to that Institution. 

 This species is remarkable among the plicate shells for its globose form and its black 

 epidermis. In the remarks on Brazosensis I have stated the difference between these 

 species. It differs from plicatm, Lesueur, in being rotund and globose. A very in- 

 distinct raised line passes down the umbonial slope and cuts the folds, of which there 

 are five or six. Plicatns usually has three or four folds, which are much larger. The 

 marginal line is reddish, somewhat like Brazosensis. The epidermis of the most 

 perfect specimen is almost polished, and the nacre of remarkable brilliancy. The 

 undulations of the tips are small, subconcentric, and are four or five in number. This 

 species need not be confounded with either purplicatus, Con., Elliottii, or atrocostatus, 

 nobis. I have pleasure in naming this species after Dr. Lincecum, of Texas, who, 

 while collecting plants, has also gathered the interesting inhabitants of the waters of 

 his State. 



Unio Topekaensis. PL 49, fig. 126. 



Testa Itevi, lata, subcompressa, valde insequilaterali, postice obtuse angulata, autice rotundata ; valvulis 

 crassiusculis, antics crassioribus ; natlbus promiuulis, ad apices undulatis ; epidermide tenebroso- 

 fusca, radiata ; dentibus cardinalibus erectis, compressis crenulatisque ; lateralibus longis 

 rectisque ; margarita CEeruleo-alba et valde iridescente. 



Shell smooth, wide, somewhat compressed, very inequilateral, obtusely angular 

 behind, rounded before; valves a little thick, thicker before; beaks a little promi- 

 nent, undulate at the tips ; epidermis dark brown, radiate ; cardinal teeth erect, 

 compressed and crenulate ; lateral teeth long and straight ; nacre bluish-white and 

 very iridescent. 



Proc. Acad. Nat. Sci. 1868, p. U4. 



Hah. — Topeka, Kansas, Prof. Daniels ; Little Arkansas River, Dr. Le Conte ; Rock 

 Creek, Kansas, F. Hawn ; Walnut Creek, Santa Fe Road, Mr. Idler ; Falls City, 

 Nebraska, Prof Hayden ; Verdigris River, Kansas. 



My cabinet and cabinets of the Academy of Natural Sciences and Smithsonian 

 Institution. 

 Diam. "6, Length -9, Breadth 2 inches. 



Shell smooth, wide, somewhat compressed, very inequilateral, obtusely angular 

 behind, rounded before ; substance of the valves a little thick, thicker before ; beaks 

 a little prominent, much undulated at the tips ; ligament long, thin and brown ; 

 epidermis dark brown, smooth, shining, radiated all over, with distant marks of 



