314 NEW UNIONID^, MELANIDiE, ETC:, 



growth ; umbonial slope slightly raised and rounded ; posterior slope very narrow 

 and slightly raised; cardinal teeth erect, compressed and crenulate; lateral teeth 

 long and straight; anterior cicatrices distinct and moderately well impressed; 

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

 placed in a row across the centre of the cavity of the beaks ; cavity of the shell 

 rather deep and very wide; cavity of the beaks rather shallow and rounded; nacre 

 bluish-white and very iridescent. 



RemarTcs. — Nearly a dozen specimens of this shell, of various ages and different 

 habitats, are before me. For many years I have had several, but its close 

 resemblance to nasuius, Say, on one side, and to RuttersvilJensis and Bairdianus 

 (nobis) on the other, made me hesitate. More recently I have better specimens from 

 other habitats in Kansas and Nebraska, which no longer leave any doubt. In outline 

 it is not so transverse as nasutus, and the undulations differ. In Topekaetisis the tips 

 of the beaks are embellished with two series of undulations, which meet in the 

 middle and form somewhat acute angles pointing to the vertex. Bairdianus is a 

 much smaller species, less transverse, and has concentric undulations on the beaks. 

 Like nasutus, this species has, in perfect specimens, green rays over nearly the whole 

 disk, and the enlargement of the female in the vicinity of the branchial uterus is 

 very much the same. In the character of the undulations of the beaks it is the same 

 as Ruttersvillensis, but that shell is not so transverse, and the female is more inflated. 



Unio corvunculus. pi. 50, fig. 127. 



Testa Isevi, elliptica, subinflata, valde inrequilaterali, antice et postice rotundata ; valvulis crassiuscuHs, 

 antice crassioribus ; natibus prominulis, ad apices subconcentrico-undulatis ; epidermide 

 nigricante, eradiata; dentibus cardinalibus parvis, erectis, subcompressis crenulatisque ; 

 lateralibus sublongis et subcurvatis ; margarita purpurea et iridescente. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, rounded before and 

 behind; valves a little thick, thicker before; beaks a little prominent, concentrically 

 undulate at the tij)s; epidermis blackish, without rays; cardinal teeth small, 

 erect, somewhat compressed and crenulate ; lateral teeth long and slightly curved ; 

 nacre purple and iridescent. 



Proc. Acad. Nat. Sci. 1868, p. 144. 



Hah. — Swamp Creek, Whitfield Co., Georgia, Major T. C. Downie. 



My cabinet and cabinets of Academy of Natural Sciences and Mr. C. M. Wheatley. 

 I^iam. -5, Length -7, Breadth 1-2 inch. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, rounded before and 

 behind; substance of the shell a little thick, thicker before; beaks a little 

 prominent, concentrically undulate at the tips; ligament short, thin and brown; 



