Beede.] Carboniferous Invertebrates. 145 



Pinna subspatulata. Plate XVII, fig. 2; plate XVIII, figs. 1, Id, and 3. 



Pinna subspatulata Worthen, Geo!. Surv. 111., vi, p. 524, pi. xxx, f. 4, 

 (1875). 



Shell very large, triangular in outline, cardinal and ventral 

 margins diverging at an angle of about twenty degrees ; com- 

 pressed laterally. Dorsal and ventral margins nearly straight, 

 the dorsal slightly convex. Surface ornamented by very fine 

 lines of growth with occasionally larger ones ; beginning at the 

 dorsal margin, which is ridged, the lines pass across the cen- 

 tral portion of the valve nearly transversely and curve rapidly 

 forward, finally reaching the ventral edge several centimeters 

 in front of their origin in the dorsal margin. The hinge fur- 

 row down the dorsal margin makes a corresponding ridge on 

 the outside of the shell. Length of specimen, incomplete at 

 both ends, 23 cm. ; from broken posterior edge to the beaks, or 

 apex of the angle formed by the sides, 27 cm. ; height at the 

 posterior end, b.o cm. ; convexity (both valves), in the central 

 portion of the shell, about three-sevenths the height at that 

 place. 



Range and distribution : Upper Coal Measures; Topeka. 



This species differs from P. peracuta Shumard in being much 

 more compressed, and the angle of the dorsal and ventral mar- 

 gins being about twice as large. If the concentric lines of 

 growth cross the shell and reach the ventral margin nearly as 

 directly as the figure indicates, and the angle at the anterior 

 end of the shell is as small as represented, they will sharply dis- 

 tinguish our species from P. subspatulata AVorthen. He makes 

 no statement concerning the convexity of the shell, but accord- 

 ing to the figure it appears nearly flat, even more so than our 

 specimen. 



Some large specimens from near Kansas City, all of which 

 are either incomplete or crushed, may belong to this species, 

 or may be exceedingly large specimens of P. pcraci'fa Shumard. 

 Near the anterior end they are very much more convex than 

 the Topeka specimens while they are nearly fiat at the poste- 

 rior end. The angle of divergence of the anterior end is about 

 the same as in /\ \>< r acuta. 



