94 University Geological Survey of Kansas. 



Pug n ax Utah Hall and Clarke, Pal. N. Y., vni, pt. n, p. 204, pi. lx, ff. 39- 



42, (1893). 

 Rhynchonella uta Keyes, Geol. Surv. Mo., v, p. 103, pi. xli, f. 7, (1895). 



Meek's description: " Shell small, more or less variable in 

 form, often subtrigonal, generally wider than long, more or less 

 gibbous ; front truncated, or sometimes sinuous in outline ; an- 

 terior lateral margins rounded in outline ; posterior lateral mar- 

 gins convex, or nearly straight and converging toward the 

 beaks at an angle of from 90 deg. to 120 deg. Dorsal valve 

 more convex than the other, greatest convexity near the middle 

 or between it and the front, which has a broad, rather deep, 

 marginal sinus, for the reception of the corresponding projec- 

 tion of the front of the other valve ; mesial fold somewhat flat- 

 tened, but slightly prominent, and rarely traceable back of the 

 middle of the valve ; generally composed of three, but some- 

 times four — rarely more — plications; sides rounding down 

 rapidly on each side of the mesial fold, and each occupied by 

 about three or four simple plications ; beak curving strongly 

 beneath that of the other valve ; interior with a faint linear 

 mesial ridge, on each side of which is a raised curved line en- 

 closing an ovate space, occupied by the adductor muscular 

 impressions. Ventral valve distinctly less convex than the 

 other, with abroad, shallow, short sinus occupied by about two 

 or three short plications ; anterior lateral margins on each side 

 of the sinus, with from two to four plications ; beak moderately 

 prominent, and more or less arched, rather pointed; foramen 

 small." Measurements : Length, 8 mm. ; width, 9 mm. ; con- 

 vexity, 7 mm. 



Range and distribution : Upper Coal Measures ; Bronson, 

 Bourbon county, Kansas City, Iola, Olathe, Lawrence, Lecomp- 

 ton, Topeka, Beaumont, Grand Summit. 



The young of this species are perfectly plain and betray no 

 indication that they are of the same kind as the folded, plicated 

 adults. It can be readily distinguished from the previous spe- 

 cies by its smaller size, shallower and more ill-defined sinus, and 

 the presence of plications on its sides. 



