322 NEW UNIONID^, MELANIDiE, ETC., 



lamellar, curved and roughened ; anterior cicatrices distinct, large, well impressed 

 and divided into three rounded impressions ; posterior cicatrices confluent, large and 

 slightly impressed ; dorsal cicatrices placed in a row across the centre of the cavity of 

 the beaks ; cavity of the shell shallow, very wide and with a broad furrow from the 

 beaks to the posterior basal margin ; cavity of the beaks very shallow and scarcely 

 perceptible ; nacre whitish and very iridescent. 



BemarJcs. — A single valve only — the right one — is before me. This is a matter of 

 great regret, because this is a very remarkable shell, entirely new, and we have the 

 advantage of seeing only an imperfect valve, for this has been ground on the margins 

 so that I cannot determine whether it does not belong to the alate division and come 

 near to U. Myersianus (nobis), from Siam. The outline is nearly the same, and per- 

 fect specimens may be alate if not bialate. The cardinal teeth of the young may also 

 be quite different, as in Myersianus. There is a very marked difference in Ortonii 

 from any species of the Unionidce I have seen. There are two wide ridges from the 

 beaks to the posterior margin, and these enlarge as they are projected towards the 

 margin. On the posterior ridge, which really forms the umbonial slope, there are six 

 folds of low elevation. The nacre is remarkably beautiful, being satin-like. The 

 epidermis is unusually thin and very nearly all lost from the specimen. I have 

 great pleasure in naming this shell after Prof. Orton, who brought it from the River 

 Napo. The lateral tooth is long and lamellar, like any wide Unio, but the cardinal 

 tooth is divided more like Iridina, and in this it is somewhat like an old Unio 

 Myersianus (nobis), the teeth of which differ very much from the young. 



Anodonta Strebelii. pi. 52, fig. 135. 



Testa Ijevi, elliptica, insequilaterali, postice obtuse angulata, antice rotundata ; valvulis pertenuis ; 

 natibus prominulis ; epidermide tenebroso-viridi, radiis capillaris indutis ; margarita cserulea et 

 valde iridescente. 



Shell smooth, elliptical, inequilateral, obtusely angular behind, rounded before ; 

 valves very thin; beaks a little prominent; epidermis dark green, covered with 

 capillary rays ; nacre bluish and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 150. 



Hob. — Vera Cruz, Mexico, G. Strebel, M. D. 



Cabinet of the Smithsonian Institution. 

 Diam. -6 Length -9 Breadth 1-5 inch. 



Shell smooth, elliptical, inequilateral, obtusely angular behind and rounded before ; 

 substance of the shell very thin, not thickened before, translucent, so as to show the 

 rays ; beaks a little prominent and slightly inflated ; ligament rather long, thin and 

 nearly concealed ; epidermis dark green, with very numerous, close capillary rays, 



