286 NEW UNIONIDiE, MELANID^, ETC., 



Unio tortuosus. pi. 39, fig. 98. 



Testa inpequivalva, contorta, plicata, valde obliqua, inflata, postiee obtuse angulata, antics oblique ciir- 

 vata ; valvulis percrassis, antice crassioribus ; natibus prominentibus, crassis terminalibusque ; 

 epidermide tenebroso-oliva, obsolete radiata ; dentibus cardinalibus permagnis, crassis, rectis corru- 

 gatisque ; lateralibus sublongis, subrectis, striis perpendicularis instructis ; margarita argentea et 

 valde iridescente. 



Shell inequivalve, twisted, plicate, inflated, very oblique, obtusely angular behind 

 and obliquely curved before ; valves very thick, thicker before ; beaks prominent, 

 thick and terminal; epidermis dark olive, obscurely rayed ; cardinal teeth very large, 

 thick, straight and corrugate ; lateral teeth rather long, nearly straight and furnished 

 with perpendicular strise ; nacre silver white and very iridescent. 

 Proc. Acad. Nat. Sci. 1865, p. 76. 



Sa6.— China, A. R. Wright, M. D. 



Cabinet of the Buffalo Society of Natural History, New York. 

 Diam. Vl, Length 1-5, Breadth 2-1 inches. 



Shell inequivalve, twisted, plicate, very oblique, inflated, obtusely angular behind, 

 obliquely curved before ; substance of the shell very thick, thicker before ; beaks 

 prominent, thick and terminal ; ligament rather short and thin ; epidermis dark olive, 

 obscurely rayed and with distant marks of growth ; umbonial slope slightly raised 

 and rounded ; posterior slope with unequal sides and nearly covered with oblique 

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

 long, nearly straight and furnished with perpendicular, parallel striae on the upper 

 half; anterior cicatrices distinct and deeply impressed ; posterior cicatrices distinct 

 and slightly impressed; dorsal cicatrices placed under the posterior part of the car- 

 dinal tooth ; cavity of the shell rather deep and rounded ; cavity of the beaks very 

 deep and obtusely angular; nacre silver white and very iridescent. 



RemarTcs. — This very remarkable shell was, among other shells from China, sent to 

 me for examination by the Buffalo Society of Natural History. It was accompanied 

 by the gigantic specimen of U. Cumingii (nobis) mentioned above. This is the first 

 Unio which has been found possessing an irregular plane of the margin and being 

 inequivalve. When looking on the anterior end, with the ligament above, the line of 

 the opening of the valves curves to the right. The beak of the left valve is higher 

 than that of the right and projects anteriorly. The left valve, therefore, is larger 

 than that of the right, and the weight differs — the left being 257 grains and the right 

 242 grains. In the specimen before me the marks of growth are but two and they are 

 distant. The cardinal teeth are large and nearly in a line with the lateral teeth. The 

 very remarkable perpendicular strife on the lateral teeth of this specimen, if always 

 present in other individuals, will demand its being placed in the genus Prisodon, 



