46 Trans. Acad. Sci. of St. Louis. 



common for Unios of this type. It has been found only in 

 the drainage of the Ohio, and the Mississippi river itself, but is 

 not yet known from streams beyond. South it ranges to the 

 Holston river, in east Tennessee, and to the Cumberland, at 

 Nashville. It is there quite abundant. There is certainly an 

 error in assigning to this species the distant habitat of Nova 

 Scotia, as was done by Lamarck in originally describing it. 

 The great traveler and naturalist, Michaud, had secured this 

 form, with numerous others, during his visit to the New World, 

 and from material furnished by him Lamarck drew his descrip- 

 tion. The localities were either confused by Lamarck, or 

 what would be more natural under the circumstances, had been 

 confounded by the collector. However this may be, the orig- 

 inal shells were most certainly obtained elsewhere than in the 

 region named by Lamarck. 



From specimens furnished by Professor Barton W. Ever- 

 mann, and taken in the White river, Indiana, the following 

 description is drawn: — 



Shell rotund, large, smooth, convex, heavy, rounded before, 

 circular behind; epidermis rather thin, polished, striate, dis- 

 posed to imbrication towards the margins, olivaceous, lines of 

 growth numerous, crowded, darker ; dorso-posterior margin 

 curved and rounded ; postero-dorsal umbonal slope lighter 

 horn-colored, with numerous capillary rays of green, which 

 are especially marked near the beaks, this slope is separated 

 from the lateral umbonal slope by a rather well marked angle, 

 it has also two slightly marked carina?; umbones large, prom- 

 inent, approximating closely, curved anteriorly, and projecting 

 slightly beyond the antero-ventral margin, smooth ; ligament 

 short, thick, curved with dorsal margin, light horn-color; 

 lunule large, cordate, scarious ; cardinal teeth single in the 

 right, double in the left valve, multi-tuberculate, striate, cren- 

 ulate, the folds all originating at a common point imme- 

 diately under the tip of the umbone, as a whole the 

 segments are triangular, massive, thick, short; lateral teeth 

 long, curved, commencing well toward the dorsal margin, 

 and nearly on a line with the anterior portion of the cardinals, 

 lamellar, somewhat thick, double in both valves, crenulate on 

 the margins; the plate connecting the cardinal with the laterals 



