Bkede.] Carboniferous Invertebrates. 161 



PLEUROPHORUS. 



King, Ann. Mag. Nat. Hist., XIV, p. 313, (1844). 



Pleurophorus subcostatus. Plate XX. figs. 11-llb. 



Ph urophorus subcostatus Meek and Worthen, Proc. Acad. Nat. Sci. 



Phil., p. 246, (1865). 

 Pleurophorus subcostatus Meek and Worthen, Geol. Surv. 111., n, pp. 



347, 348, pi. xxvn, IT. 2, 2a, (1866). 



Meek and Worthen's description: " Shell elongate-oblong, 

 moderately convex ; umbonal ridges the most convex part of 

 the valves, and extending obliquely from the beaks toward the 

 postero-basal margin ; anterior ventral region somewhat com- 

 pressed ; basal and cardinal margins very nearly straight and 

 subparallel, the former being usually somewhat sinuous or ar- 

 cuate along the middle ; extremities rather narrowly rounded, 

 the posterior being generally a little wider than the other, and 

 sometimes faintly subtruncate obliquely. Hinge line long and 

 nearly straight ; posterior lateral tooth of each valve elongated 

 parallel to the hinge margin, very remote from the cardinal 

 teeth, and extending back a little beyond the posterior muscular 

 impression. Beaks depressed upon a line with the dorsal mar- 

 gin, small, somewhat compressed, and placed about one-ninth 

 the entire length of the shell behind the anterior margin. Hear 

 of the anterior adductor muscle deep, trigonal-subovate, pointed 

 above, and strongly defined by the prominent vertical ridge 

 just behind it; those of the pedal muscles small, nearly mar- 

 ginal, and located directly over the anterior adductors ; posterior 

 adductor scars larger and more shallow than the anterior, sub- 

 quadrate in outline, and placed close up* under the posterior 

 hinge teeth. Pallial impression well defined. Surface of casts 

 showing traces of a few obscure concentric markings, crossed* 

 on the postero-dorsal region by traces of about three equal ob- 

 scure radiating costse. Exterior surface and cardinal teeth un- 

 known. Length of a medium-sized specimen (internal cast), 

 0.88 inch ; height of same, 0.37 inch ; convexity, 0.26 inch. 

 Some larger specimens, of same proportions, measure 1.33 

 inches in length." 



Range and distribution: Upper Coal Measures; Kansas 

 City. Mo. 



