84 University Geological Survey of Kansas. 



defined on the ears ; over the whole there are also regularly 

 arranged in quincunx, very slender spines, .20-. 30 inch in 

 length, rising from the slight prominences or swellings of the 

 radiating striae. Dorsal valve distinctively concave, following 

 nearly the curvature of the other valve, its greatest convexity 

 being in the central region, while its ears are nearly flat ; sur- 

 face with concentric wrinkles and radiating striae as in the 

 other valve, but apparently without spines, though a series of 

 rather distinct pits are arranged over it in the same order as in 

 the other valve." Length, 8 mm. ; width, 11 mm. ; convexity, 

 5 mm. 



Range and distribution : Upper Coal Measures ; Kansas City, 

 Eudora, Lawrence, Lecompton, Topeka. 



This species differs from the preceding ones of the genus in 



the absence of the mesial sinus, thin shell, very small size and 



semicircular outline, as well as being much less gibbous. It is 



1 ikely to be confounded with no other shell of the Coal Measures 



of Kansas. 



Productus nebrascensis. Plate IX, figs. 7-7f. 



JProduetus nebrascensis Owen, Geol. Rep. Wis., Iowa, and Minn.-, p. 584, 



pi. v, f. 4, (1852); Meek, Fin. Rep. U. S. Geol. Surv. Neb., p. 165, pi. n, 



f. 2, pi. iv, f. 6, pi. v, ff. lla-c, (1872); etc. 

 Productus rogersl Norwood and Pratten, Jour. Acad. Nat. Sci. Phil., 



2d ser., in, p. 9, pi. i, f. 3, (1854); etc. 

 Productus asperus McChesney, New Pal. Foss.,p. 34, (1860); etc. 

 Productus ivilberanus McChesney, ibid., p. 36; etc. 

 Stropholosia horreseens Geinitz (non Murchison, etc.), Carb. u. Dyas in 



Neb., p. 49, (1866). 



Meek's description (in part) : " Shell of about medium size y 

 approaching subhemispherical ; length most usually a little 

 less than the breadth ; hinge line nearly or quite equaling the 

 greatest transverse diameter ; anterior outline nearly straight, 

 or a little sinuous near the middle, rounding into the lateral 

 margins, which are generally straight posteriorly, and ranging 

 at an angle of from 90 to about 100 degrees with the hinge ; 

 ears nearly rectangular or a little rounded in outline at the 

 immediate extremities. Ventral valve rather convex, most 

 gibbous behind the middle, thence rounding regularly to the 



