NKW FRKSII WATER AND LAND SIIKLLS. 36 



tlian the first, and more inllated than the latter, and the posterior slope is nearly 

 raised into a wing. It is' not obovate like pur^mratus. Young and perfect specimens 

 will probably be found to be quite alate. The purple color of the specimen before me 

 is not quite so dark as the alatus and purpuratm. In my specimen there is in 

 each valve an imperfect cicatrix, situated nearly in the centre of the interior of the 

 disk, and such may be the case with Dr. Budd's. If this should be found to be 

 developed in the species, it will resemble in this character the trapezoides, (nobis,) the 

 only Unlo I know to possess the additional muscle (ventral muscle). The beaks of 

 the specimen before me are too much eroded to give the character of the tips, but 

 they are evidently slightly undulate. 



It differs from Tampicoemis, (nobis,) to which it is allied, by being a larger species, 

 being higher in the carina of the posterior slope, in having a brown radiated epidermis 

 instead of a blackish rayless one, and in the purple color of the nacre. 



Unio poeyanus. pi. 32, fig. 30. 



Testa Ixvi, transversa, subcylindracea, ad basim subemarginata, valde inasquilaterali, ad latere planulata, 

 postic6 truncata et subbiangulata. ; valvulia subcrassis ; natibus prominulis, ad apices simplicibus ; 

 epidermide luteola et minute granulata ; dentibuscardinalibussubcoinpressis,acuminatis crenulatisque ; 

 lateralibus prjelongis, lamellatis rectisque ; margarlta luteola et iridescente. 



Shell smooth, transverse, subcylindrical, basal margin somewhat emarginate, very 

 inequilateral, flattened at the side, truncate and subbiangular behind ; valves a little 

 thickened ; beaks slightly elevated, simple at the tip ; epidermis yellowish and very 

 minutely granulate ; cardinal teeth somewhat compressed, acuminate and crenulate ; 

 lateral teeth very long, lamellar and straight; nacre yellowish and iridescent. 

 Proc. Acad. Nat. Sci. 1857. p. 85. 



Hah. — Rio de las Balsas, near Coyucan, Mexico. Prof. Felipe Poey, of Havana. 

 My cabinet and cabinet of Prof. Poey. 

 Diam. -G, Length 1, Breadth 2-2 inches. 



Shell smooth, transverse, subcylindrical, basal margin somewhat emarginate, very 

 inequilateral, flattened at the side, truncate and subbiangular behind and rounded 

 before; substance of the shell somewhat thick, thicker before ; beaks slightly elevated, 

 and without any undulations at the tip : ligament long and rather thin ; epidermis 

 yellow or yellowish olive, very minutely granulate, striate before ; umbonial slope 

 somewhat carinate ; marks of growth distant ; cardinal teeth somewhat compressed, 

 acuminate and crenulate ; lateral teeth very long, lamellar and straight ; anterior 

 cicatrices distinct ; posterior cicatrices nearly distinct ; dorsal cicatrices placed across 

 the cavity of the beaks ; pallial cicatrix slightly impressed ; cavity of the shell shallow ; 

 cavity of the boaks small and subangular ; nacre yellowish, paler before and iridescent. 



Remarks. — I owe to the kindness of Professor Poey the possession of two specimens 

 of this interesting species, and I dedicate it to him. In its outline it is nearly like 



