600 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Judith River beds; — south of Cow Islaud, Upper Missouri Eiver, Mon- 

 tana Territory. 



Unio cryptorhynchus (sp. nov.). — Shell of medium size, ventricose, 

 subelliptical in marginal outline; height a little greater forward of 

 the mid-length; test moderately thick ; dorsal margin nearly straight, 

 or slightly convex ; basal margin broadly convex ; posterior margin reg- 

 ularly rounded ; front margin also regularly rounded from beneath the 

 beaks to the ventral margin ; beaks rather large, distinctly defined from 

 the body of the shell, not elevated but projected forward and turned 

 strongly inward, placed near the anterior end of the shell, but notreacTi- 

 ing quite so far forward as the anterior border, between which and the 

 beak there is a distinct sulcation ; cardinal teeth strong, each having 

 behind it a moderately deep crypt or cavity of the beak; lateral teeth 

 well developed but rather thin and sharp. 



Surface marked only by the ordinary lines of growth. 



Length 7 centimeters; greatest height from base to umbo 4^- centi- 

 meters. 



This species bears some resemblance to U. proavitus White from the 

 Wahsatch group, at Black Buttes Station, Wyoming Territory, but it 

 differs in being subelliptical instead of subtetrahedral in marginal out- 

 line; in wanting the umbonal and postero-dorsal ridges and oblique pos- 

 terior truncation of that species; and also in having the front margin 

 projecting a little beyond the beaks, instead of the beaks projecting 

 beyond the front margin, as they do in U. proavitus. 



Position and locality. — Judith Eiver group; — Dog Creek, a tributary 

 of the Upper Missouri River, Montana Territory. 



Unio sbnectus (sp. nov.). — Shell elongate-subelliptical in marginal 

 outline ; covexity of the valves comparativ^ely slight and nearly uniform 

 over the- whole surface; test thin ; both basal and dorsal margins broadly 

 convex, or the latter sometimes straightened ; front regularly rounded; 

 posterior margin also rounded, but more abruptly so than the front ; 

 beaks scarcely definable as such from the body of the shell, situated at 

 about one-fifth the length of the shell from the front ; hinge well devel- 

 oped; cardinal teeth prominent; lateral teeth long and well formed, but 

 between their anterior end and the cardinal teeth there is considerable 

 space. Above and behind a line drawn from the beak to the postero-basal 

 margin — the place of the umbonal ridge when one is present — the sur- 

 face is marked by very numerous, small, crenulated undulations, which 

 increase in number both by implantation and bifurcation with the increas- 

 ing size of the shell ; their general direction being backward, but along 

 the dorsum they are flexed upward and end along the dorsal margin. 

 Below and in front of this line, the surface is plain, being marked only 

 by the ordinary lines of growth, except the fine radiating lines, which 

 appear in the substance of the shell where it is exfoliated. 



Length 8 centimeters; height 4 centimeters. 



In its general form and s;jrface-characters, this species somewhat 



