Beedk.] Carboniferous Invertebrates, 153 



Range and distribution : Upper Coal Measures ; Topeka. 



Only a single left valve of this species has been collected by 

 the writer, at Topeka, Kan. It agrees so well with this descrip- 

 tion that it is referred to it, though the lines of growth pass 

 forward on approaching the hinge and become nearly parallel 

 to it. 



Yoldia glabra. Plate XXI, figs. 4a, b. 



Y t,hl in glabra Beede and Rogers, Kans. Univ. Quart., viii, p. 133, pi. 

 xxxiv, ff. 4a, b, (1899). 



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

 outline, 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. Beaks depressed, nearly 

 central. Surface nearly smooth, with traces of obscure, dis- 

 tant, concentric striae parallel to the ventral outline ; lines of 

 growth visible on the postero-dorsal region. Measurements : 

 Length, 14+ mm. ; height, 7 mm. ; convexity of single valve, 

 1+ mm. 



Range and distribution : Upper Coal Measures ; Lawrence. 



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

 Louis group, in having its posterior border truncated, stria? 

 distant rather than closely arranged, and in being much less 

 convex. It differs from Y. subscitula f Meek, or Y. propinqua 

 Meek, in being more depressed and the posterior end much 

 more broadly rounded. 



11— vi 



