296 NEW UNIONlD^, MELANID^E, ETC., 



cardinal tooth within the cavity of the beaks ; cavity of the shell rather deep and 

 rounded ; cavity of the beaks deep and angular ; nacre silver-white and iridescent. 



Remarks. — There are nine specimens before me from Col. Jewett and Mr. Gabb. 

 They are very perfect, having beaks without erosion, but not exhibiting any undula- 

 tions at the tips, while minute green rays are very apparent. In all the specimens 

 perfect enough the disks exhibit very obscure rays, which are capillary at the apex, 

 and these are beautifully distinct. The furrows are extremely regular and beautiful, 

 and are without festoons as in encarjnis, herein described. In outline it is near to 

 cyrenoides, Phil., but it is a smaller and less solid shell, and the teeth are not massive, 

 but thin, delicate and compressed. I have pleasure in dedicating this pretty little 

 species to Mr. W. M. Gabb, who, while devoting his time to his palreontological 

 duties as one of the geologists of the California Survey, has brought here a number of 

 new species, which were collected by the late botanist Th. Bridges in Lake Nicaragua. 



Unio Nicaraguensis. pi. 43, fig. 107. 



Testa sulcata, triangulari, compressa, aliquanto inccquivalva, inrequilaterali, postice obtuse angulata, 

 antice oblique truncata; valvulis crassiuscuiis ; natibus prominentibus, subacutis ; epidermide 

 olivacea, crebris sulcatia indutis, eradiata ; dentibus cardinalibus ereetis, compressis, crenulatis et 

 in valvule dextro subtripartitibus ; lateralibus brevibus fornicatisque ; margarita argeutea et 

 iridescente. 



Shell sulcate, triangular, compressed, slightly inequivalve, inequilateral, obtusely 

 angular behind, obliquely truncate before ; valves rather thick ; beaks prominent, 

 rather pointed ; epidermis olivaceous, covered with close furrows, without rays ; 

 cardinal teeth erect, compressed, crenulate, and in the right valve somewhat tri- 

 partite J lateral teeth short and arched ; nacre silver-white and iridescent. 

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



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



My cabinet and cabinet of Acad. Nat. Sci. 

 Diam. "7, Length 1-1, Breadth 1-5 inch. 



Shell sulcate, triangular, compressed, slightly inequivalve, inequilateral, obtusely 

 angular behind, obliquely truncate before ; substance of the shell rather thick ; beaks 

 prominent, pointed at the tips ; ligament short, thin and light brown ; epidermis oliva- 

 ceous, covered with transverse close furrows and without rays ; umbonial slope angular 

 and placed near the posterior margin; posterior slope very narrow elliptical, depressed, 

 with a small elevated line in each valve from the beaks to the posterior margin ; 

 cardinal teeth erect, compressed, crenulate, and in the right valve somewhat tripar- 

 tite ; lateral teeth short, lamellar and arched ; anterior cicatrices distinct and well 

 impressed ; posterior cicatrices distinct and well impressed ; dorsal cicatrices placed 



