UNITED STATES AND ARCTIC AMERICA. . 205 



single one was sent to me, among other molluscs, by Prof. Forshey. This speci- 

 men is larger than any from Lieut. Beale, and is more inflated, but it is very 

 imperfect. It is two inches and four-tenths wide, while the largest from Lieut. 

 Beale is one inch and three-tenths. None of them had beaks perfect enough to 

 observe the form of undulations of the tips, but they appear to be concentric, 

 somewhat like the pamis, Barnes, to which group it seems to belong. It is allied 

 to Texasensis, (nobis,) but of a darker color, more lenticular, not being so trans- 

 verse. It also has affinities to callostis, (nobis.) The nacre is rich in all the 

 specimens, and most of them are disposed to be slightly salmon-colored in the 

 cavity of the beaks. In some cases the salmon tint pervades the whole area. 

 I name this after Lieut. Beale, of the United States Navy, who obtained speci- 

 mens while on his professional duty in the State of Texas. 



Unio grandidens. PI. 30, fig. 274. 



Testa valde tuberculata, obliqua, ad urnbones inflata ; valvulis crassissimis, antice crassioribus ; natibus 

 valde tuinidis terminalibusque ; epidermide fusca ; dentibus cardmalibus pergrandis, perorassis 

 corrugatisque ; lateralibus crassis, sublongis, obliquis et valde corrugatis ; margarita alba et 

 iridescente. 



Shell very much tuberculate, oblique, inflated at the urnbones ; valves very 

 thick, thicker before ; beaks very much swollen and terminal ; epidermis brown ; 

 cardinal teeth very large, very thick and corrugate; lateral teeth thick, rather 

 long, oblique and very rough ; nacre white and iridescent. 

 Proe. Acad. Nat. Sei., 1862, p. 168. 



Hab. — Near Hot Springs, Arkansas, Byrd Powell, M. D. 



My cabinet and cabinet of Smithsonian Institution. 

 Diam. VI, Length 2-6, Breadth 3-6 inches. 



Shell very much tuberculate over nearly the whole disk, oblique, inflated on the 

 urnbones ; substance of the shell very thick, thicker before ; beaks very much 

 swollen, very much raised, incurved and terminal ; ligament thick and long ; 

 epidermis brown and with distant marks of growth ; umbonial slope raised and 

 rough ; posterior slope rather wide, corrugate, with oblique folds from the beaks to 

 basal margin ; cardinal teeth double in both valves, very large, very thick, corru- 

 gate and longitudinally and roughly striate ; lateral teeth disposed to double in 

 both valves, thick, rather long, oblique and very rough ; anterior cicatrices dis- 

 tinct, large, very deeply impressed and corrugate ; posterior cicatrices large, distinct 

 and well impressed ; dorsal cicatrices in a long row near the edge above the cavity 

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

 deep and angular ; nacre white and iridescent. 



Eemarks. — Two opposed valves of different individuals of nearly the same size 

 are before me. They were sent by Dr. Powell to the Smithsonian Institution 



