CHIEFLY OF THE UNITED STATES. 297 



in the upper part of the cavity of the bealis; cavity of the shell rather shallow and 

 wide; cavity of the beaks rather deeja and obtusely angular; nacre silver-white and 

 iridescent. 



Remarks. — One only of the four specimens before me appears to be adult. This is 

 the most perfect one. The others are apparently only half-grown. This species may 

 be distinguished from Neiocomhianus (nobis) by being less solid, being more com- 

 pressed, and in having smaller and compressed cardinal teeth. It belongs to the 

 deltoid form of the sulcate group, which group has so many representatives in the 

 Central American Uniones. It is somewhat allied in color and sulcation to Caldioellii 

 (nobis), but that species is elliptical and the sulcations are not so regular. In the 

 youngest specimen the beaks are nearly perfect. There is no sign of undulations, but 

 there are capillary green rays from the tips. The tripartite character of the cardinal 

 tooth of the right valve is more or less developed in most of these Nicaraguaa 

 Uniones ; some are very slightly so. It is a very remarkable feature of some of the 

 small Unionidce of Lake Nicaragua to be inequivalve. Three species described herein 

 are so, plainly showing one beak to be higher than the other, and the plane of the 

 valves may easily be observed to be slightly curved. Having received several perfect 

 specimens of U. Neiocomhianus, I was surprised to find in every case that the inequi- 

 valve character was also possessed by it. 



' Unio Beaveeensis. pi. 44, fig. 109. 



Testa Isevi, oblonga, compressa, ad latere planulata, infequilaterali, postice obtuso-biangulari, antice 

 rotunda ; valvulis subcrassis, antice parum crassioribus ; natibus subprominentibus ; epidermide 

 vel rubiginosa vel luteola, micanti, radiata ; dentibus cardiualibus crassis sulcatisque; lateralibus 

 longis, crassis, lamellatis subrectisque ; margarita vel alba vel purpurea et valde iridescente. 



Shell smooth, oblong, compressed, flattened at the sides, inequilateral, obtusely 

 biangular behind, round before; valves rather thick, slightly thicker before; beaks 

 somewhat prominent; epidermis rubiginose or yellowish, shining and obscurely 

 radiate; cardinal teeth thick and sulcate; lateral teeth long, thick, lamellar and 

 nearly straight ; nacre white or purple and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 161. 



Hah. — Beaver Creek and Long Creek, N. C, C. M. Wheatley, and Carter's Creek, 

 Geo., J. Postell. 



My cabinet and cabinet of Mr. Wheatley. 

 Diam. '8, Length I'G, Breadth 2*8 inches. 



Shell smooth, oblong, compressed, flattened at the sides, inequilateral, obtusely 

 biangular behind, round before ; substance of the shell rather thick, sliglitly thicker 

 before; beaks somewhat prominent; ligament rather short and dark brown; 



