144 University Geological Survey of Kansas. 



A. americana. Surface ornamented with concentric lines paral- 

 lel to the posterior end of the shell. They are directed from 

 the hinge line obliquely backward until they pass the central 

 part of the valve, where they curve rapidly forward, finally be- 

 coming nearly parallel to the ventral margin before reaching 

 it. These lines are sharp, thread-like elevations or lamellae, 

 abruptly elevated from the surface of the shell and separated 

 by broad, shallow spaces of several times their width. Length 

 of specimen ( the posterior portion is shortened by compres- 

 sion) , 55 mm.; height, at the posterior end, 19 mm.; con- 

 vexity, 9 mm. 



Range and distribution : Upper Coal Measures ; Kansas City, 

 head of Deer creek ( western portion of Douglas county ) . 



This specimen agrees with Worthen's description and figures, 



except that the angle formed by the dorsal and ventral margins 



is a little smaller. It differs from A. americana in being a little 



more convex, larger, in having the lines farther apart and 



larger. 



PINNA. 



Linnaeus, Syst. Nat., 10th ed., (1758). 



Pinna peracuta. Plate XVII, figs. 3, 3b. 



Pinna per acuta Shumard, Trans. St. L. Acad. Sci., i, p. 214, (1858) ; Meek, 

 Fin. Rep. U. S. Geol. Surv. Neb., p. 198. pi. vi, ff. 11a, b, (1872); White, 

 U. S. Geog. Surv. West 100 Mer., iv, p. 151, pi. xi, f. 5a, (1877); etc. 

 See Weller, Bull. 153 U. S. Geol. Surv., p. 429, (1898). 



Pinna adamsi, McChesney, New Pal. Foss., p. 74, (1860). 



Meek's description: "Shell thin, very narrow, elongated, 

 and tapering gradually and regularly from the larger to the 

 smaller extremity ; convex or almost subcylindrical, excepting 

 toward the posterior extremity, which is compressed and ob- 

 liquely rounded, or subtruncated. Hinge margin very long, 

 and almost perfectly straight — carinated in consequence of the 

 sudden erection of the dorsal edges of the valves ; ventral mar- 

 gin equally as straight as the dorsal, and ranging at an angle of 

 about 12° with the latter. Surface nearly smooth, or showing 

 very obscure lines of growth." 



Range and distribution : Upper Coal Measures ; Kansas Citj^, 

 Lawrence, Topeka. 



