294 NEW UNIONIDiE, MELANID^, ETC., 



Shell sulcate, elliptical, somewhat inflated, inequilateral, subangular behind, 

 rounded before ; substance of the shell rather thick, thicker before ; beaks some- 

 what prominent ; ligament very short and dark brown ; epidermis dark brown, 

 blackish and without rays; umbonial slope obtusely angular; posterior slope narrow 

 and very slightly raised; cardinal teeth rather small, compressed, erect and 

 crenulate ; lateral teeth oblique and slightly curved ; anterior cicatrices small, 

 distinct and well impressed ; posterior cicatrices distinct and moderately well im- 

 pressed ; dorsal cicatrices small, placed on the upper part of the cavity of the beaks ; 

 cavity of the shell rather deep ; cavity of the beaks rather deep and subangular ; 

 nacre white and iridescent. 



Remarhs. — Nearly a dozen of this small dark -colored species are before me. It is 

 easily distinguished from all the other species from Lake Nicaragua by its nearly 

 black epidermis, which is thin and easily rubbed off. None of the specimens having 

 it to remain on the beaks, and but little on the sides. In some of the specimens 

 there is a disposition to salmon color in the cavity of the beaks. In outline it is 

 nearly the same W\i\i fahalis (nobis) and germaims (nobis). It is also near to RoiveUii 

 (nobis), from Charges River, and, like it, it is sulcate, It may easily be distinguished 

 from it, however, by the blackish epidermis, the Rowellii being of a dark olive. It 

 is also more oblique, and not so large a species. 



Unio encarpus. pi. 42, fig. 105. 



Testa sulcata, subtriangulari, subinflata, aliquanto inicquivalva, insequilaterali, postice obtuse angulata, 

 antice rotundata ; valvulis subcrassis, antice crassioribus ; natibus prominentLbus ; epidermide 

 tenebroso-olivacea, encarpiformi, eradiata ; dentibus cardinalibus compressis, erectis, crenulatis, 

 in valvulo dextro subtripartitibus ; lateralibus obliquis rectisque ; margarita albida et iridescente. 



Shell sulcate, subtriangular, somewhat inflated, slightly inequivalve, inequilateral, 

 obtusely angular behind, rounded before; valves rather thick, thicker before; beaks 

 rather prominent; epidermis dark olivaceous, festoon-like, without rays; cardinal 

 teeth compressed, erect, crenulate, somewhat tripartite in the right valve; lateral 

 teeth oblique and straight ; nacre whitish and iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 95. 



Hah. — Lake Nicaragua, Central America, Mr. W. M. Gabb. 



My cabinet and cabinet of Acad. Nat. Sci. 

 Diam. -7, Length -1, Breadth 1-4 inch. 



Shell sulcate, subtriangular, somewhat inflated, slightly inequivalve, inequilateral, ob- 

 tusely angular behind, rounded before ; substance of the shell rather thick, thicker be- 

 fore ; beaks rather prominent ; ligament short and thin ; epidermis dark olivaceous, the 

 sulcations being festoon-like, without rays; umbonial slope obtusely angular; pos- 



