CHIEFLY OF THE UNITED STATES. 279 



Unio evitatus, pi. 38, fig. 92. 



Testa Itevi, elliptica, valde infcqiiilaterali, postice subbiangulata, autice rotundata ; valvuHs subtenui- 

 bus, antice parum crassioribus ; natibus prominulis, ad apices divaricate undulatis ; epidermide 

 olivacea, obsolete radiata ; dentibus cardinalibus parviusculis, compressis, in utroque valvulo du- 

 plicibus ; lateralibus sublongis, subrectis lamellatisque ; margarita alba et iridescente. 



Shell smooth, elliptical, very inequilateral, subbiangular behind, rounded before ; 

 valves rather thin, sliglitly thicker before ; beaks a little prominent, divaricately fold- 

 ed at the tips; epidermis olivaceous, obscurely rayed ; cardinal teeth rather small, 

 compressed and double in both valves ; lateral teeth rather long, nearly straight and 

 lamellar; nacre white and iridescent. 



Proc. Acad. Nat. Sci. 1866, p. 183. 



Hah. — Bengal, W. A. Haines. 



My cabinet and cabinet of "\V. A. Haines. 

 Diam. "5, Length -8, Breadth 1-5 inch. 



Shell smooth, elliptical, very inequilateral, subbiangular behind and rounded be- 

 fore ; substance of the shell rather thin, slightly thicker before ; beaks a little promi- 

 nent, divaricately folded at the tips; ligament thin and light brown; epidermis oliva- 

 ceous, darker behind and obscurely rayed ; umbonial slope slightly raised and obtusely 

 angular; posterior slope narrow elliptical, very slightly carinate, with three green rays 

 in each valve ; cardinal teeth small, compressed and double in both valves ; lateral teeth 

 rather long, nearly straight, lamellar, single in the right and double in the left valve ; 

 anterior cicatrices distinct, large and well impressed ; posterior cicatrices confluent, large 

 and very indistinct ; dorsal cicatrices placed immediately over the centre of the cavity 

 of the beaks; cavity of the shell rather shallow; cavity of the beaks small and sub- 

 angular ; nacre white and iridescent. 



Bemarlcs. — Two specimens are before me, one of which is smoother than the other, 

 and differs slightly in outline. It belongs to the group of which cceruleus (nobis) may 

 be considered the type, and stands between that sjiecies and pilatus, herein described. 



It differs from coiruleus in being smaller, in not having a bluish epidermis and in 

 the cardinal teeth being stouter. From ji«7«^i<s it differs in being thinner, flatter 

 and less green. In the lateral teeth they are entirely different, inlatus being disposed 

 to be treble in hotJi valves, while evitatus is single in the right and double in the left 

 valve. These two last mentioned shells have been in my possession several years, 

 and I have avoided describing them in the hope of getting others more closely to 

 compare them. 



Unio Siamensis. PI. 38, fig. 93. 



Testa Icevi, transversa, subcylindracea, ad basim emarginata, valde inrequilaterali, subcompressa, ad 

 latere planulata, postice truncata, antice rotundata; valvnlis teuuissimis, diaphinis ; natibus promi- 

 nulis; epidermide luteo-oliva ; dentibus cardinalibus acicularis, sublongis, obliquis; lateralibus 

 longis, lamellatis subrectisque ; margarita alba et iridescente. 



