136 University Geological Survey of Kansas. 



very thin shell. It also agrees very well in these respects with 

 Paracyclas, but that genus is not at present known from the 

 Carboniferous. 



Posidonomya ? pertenuis. Plate XIX, fig. 5. 



Posidonomyaf pertenuisBeede, Kans. Univ. Quart., vin, p. 127, pi. xxxn, 

 f. 5, (1899). 



Shell a little larger than in the. previous species and less 

 oblique. Transversely ovate in outline, very thin, quite com- 

 pressed. Hinge line is nearly straight, about equaling half the 

 length of the shell. The posterior? margin is somewhat trun- 

 cate and nearly straight ; anterior extension of the hinge longer 

 than the posterior, rather flat, not separated from the shell by 

 well-defined depression. The front and ventral margins regu- 

 larly rounded. The shell is compressed, probably most convex 

 near the middle ; beak obtuse, not very prominent, protruding 

 above the hinge line. The surface is marked by concentric un- 

 dulations of growth, and fine, close, concentric striae. Height, 

 40 mm. ; length, 36 mm. ; convexity of single valve, 4 or 5 mm. 



Range and distribution : Upper Coal Measures ; Lawrence. 



This species belongs to the same genus as the preceding. It 

 has some resemblance to the figure of Keyes, 10 which he refers 

 to Placunopsis carbonaria, though it is very difficult to see why 

 it should be referred to that genus or species ; his species may 

 be the same as the one here described. 



MODIOLA. 



Lamarck, Hist. Nat. les Anim. sans Vert., (1801). 



Modiola subelliptica. 



Clidophorus (Pleurophorus) occidentalis Geinitz, Carb. u. Dvas in 



Neb., p. 23, pi. ii, f. 6, (1866). 

 Modiola f subelliptica Meek, Fin. Rep. U. S. Geol. Surv Neb., 211, pi. 



x, f. 5, (1872;. 



Meek's description : " Shell narrow, subelliptical, rather con- 

 vex, extremely thin, usually a little more than twice as long as 

 high ; basal margin nearly straight, or sometimes very slightly 

 convex or sinuous near the middle, rounding up at each ex- 



10. Geol. Surv. Mo.,V, p. 108, pi. xliii, fig. 9. 



