BEEDE AND ROGERS: NEW AND LITTLE KNOWN PELECYPODS. 1 33 



This shell is more closely related to N. illi>ioiensis Worthen, from 

 the St. Louis limestone, than to any other species, perhaps, but 

 differs from that species in having the angles of the outline much 

 more sharp, in being smaller, and very distinctly concentrically 

 striated. With a strong lens these stride can be seen to be occa- 

 sionally minutely crenulated. The furrows are twice or more as 

 wide as the striae. Several specimens of this interesting little 

 shell have been secured from Cameron's Bluff in almost perfect 

 preservation. 



Yoldia glabra, n. sp. Plate XXXIV, Figs. 4a, 4b. 



Shell medium size for this genus, truncate-subelliptical in out- 

 line, nearly flat, greatest convexity at the umbo, sloping gently in 

 all directions from the central portion of the valve; anterior dorsal 

 outline nearly straight, sloping gently, and broadly rounded into 

 the anterior ventral margin, which forms an elliptical curve to the 

 posterior end, where it is somewhat truncate, meeting the hinge at 

 an obtuse angle. Hinge-line back of the beak nearly straight. 

 Beak depressed, nearly central. Surface nearly smooth, with 

 traces of obscure, distant, concentric striae parallel to the ventral 

 outline; lines of growth visible on the postero-dorsal region. 



Measurements: Length, 14)4 mm.; height, 7 mm.; convexity of 

 single valve, 1% mm. 



Cameron's Bluff, near Lawrence, Kansas. Type specimen in 

 Mr. Rogers' collection. 



This shell differs from Y. levistriaia M. and W., from the St. 

 Louis group, in having its posterior border truncated, strice distant 

 rather than closely arranged, and in being much less convex. It 

 differs from Y. subscitula? Meek (or Y. propinqiia Meek, if it is dis- 

 tinct), in being more depressed and the posterior (anterior) end 

 much more broadly rounded. Otherwise it is very similar to it. 



Monopteria? subalata, n. sp. Plate XXXIV, Figs. 3a, 3b 



Shell moderately small, subcrescentic in outline, gibbous, a little 

 longer than high; valves subequal, beak prominent, slightly pro- 

 jecting, somewhat inflated, situated about one-fifth the length of 

 the shell from the anterior margin, which is truncated on account 

 of the lunule which is formed by the turning in of the shell. The 

 anterior margin is convex below. Ventral margin broadl}' rounded 

 to the postero-ventral extremity where it is abruptly rounded to 

 meet the concave posterior. Hinge short and straight; posterior 

 ear but slightly developed; umbonal ridge prominent, somewhat 

 sickle-shaped, sloping abruptly posteriorly forming a concavity, 



