CHIEFLY OF THE UNITED STATES. 293 



Shell smooth, obovate, compressed, inequivalve, inequilateral, rounded before and 

 behind; substance of the shell rather thin; beaks somewhat prominent; ligament 

 short, thin and dark brown ; epidermis dark green or yellowish-green and obscurely- 

 radiated ; umbonial slope rather depressed and rounded ; posterior slope narrow ellip- 

 tical and carinate ; anterior cicatrices confluent, large and very slightly impressed ; 

 posterior cicatrices confluent, large and very slightly impressed ; dorsal cicatrices 

 scarcely perceptible; cavity of the shell rather shallow and wide; cavity of the 

 beaks shallow and obtusely angular ; nacre bluish-white and very iridescent. 



EemarJcs. — Several specimens of this remarkable Anodonta are before me. They 

 are all slightly inequivalve, having the beak of the left valve a little higher than 

 that of the right, and having a slight flexure on the superior anterior margin. In 

 this unusual character of being inequivalve, it resembles Spatha Natalensis (nobis), 

 from South Africa, described in my eleventh volume of " Observations on the Genus 

 Unio." I have not before observed this character on any of our American Anodonta, 

 but we have a Unio and a Triquetra, it will be remembered, from Northern China, 

 published by me, which are so. To these may now be added several new Uniones 

 from Lake Nicaragua, described herein. [See remarks on U. Nicaraguensis^ In 

 outline it is near to luteola (nobis), but it is a smaller species, thinner and more 

 inflated. Several specimens which accompanied the four before me are nearly of the 

 same size and thinness, but they differ in outline and constitute, I think, different 

 species, and will be described herewith. The epidermis on most of the small Ano- 

 dontoi of this collection is worn and bleached. The one figured has a dark green 

 epidermis, wUh a broad border. The other three are pale yellow, with obsolete 

 green rays well marked on the posterior slope, with three distinct ones on each 

 valve. 



Unio Granadensis. PI. 42, fig. 103. 



Testa sulca, elliptica, subinflata, intequilaterali, postice subangulari, antice rotundata ; valvulis 

 crassiusculis, antice crassioribus ; natibiis subpromiuentibus ; epiderraide teuebroso-fusca, 

 nigricante, eradiata ; deiitibus cardinalibus parviusculis, compressis, erectis crenulatisque ; 

 lateralibus obliquis ; margarita alba et iridescente. 



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

 rounded before; valves somewhat thick, thicker before; beaks somewhat prominent; 

 epidermis dark brown, blackish, without rays; cardinal teeth rather small, 

 compressed, erect and crenulate; lateral teeth oblique; nacre white and iridescent, 

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



Eah. — Lake Nicaragua, Central America, Col. E. Jewett and Mr. Gabb. 



My cabinet and cabinets of Acad. Nat. Sci. and Col. Jewett. 

 Diam. -6, Length -9, Breadth 14 inch. 



