238 POTTSVILLE FAUNA OF OHIO 



the margins contract strongly toward the anterior extremity. 1 The 

 basal margin is not sinuous, but very slightly convex, and the anterior 

 extremity is much less conspicuous than that of P. subcostatus. On 

 the latter species about three radiating costae are mentioned, while on 

 P. occidentalis five or six are present. As the figured specimens are 

 internal casts, more costae could probably have been observed on the 

 external shell; also other surface markings similar to those described 

 above may be assumed to have been present. 



Obviously the forms under discussion, which belong to the same 

 species cited by Herrick as P. subcostatus ?, resemble P. occidentalis more 

 closely than typical P. subcostatus', in fact there seems to be no essential 

 difference between the two forms. However, identification with P. 

 occidentalis seems rather doubtful as that species occurs in the upper 

 Pennsylvanian and Permian systems of a distant locality; so it is con- 

 sidered best for the present to retain a distinct species name for these 

 Pottsville forms from Ohio, especially in want of specimens of P. oc- 

 cidentalis to confirm the identification. 



Since Herrick's P. subcostatus? and P. immaturus are probably the 

 same species, and since that species is not P. subcostatus as originally 

 described, the name P. immaturus is here provisionally retained, but 

 in a larger sense than originally intended; however it is not unexpected 

 that this name will prove to be a synonym of P. occidentalis. 



Considerable variation exists in regard to the number and strength 

 of costae on the umbonal slope. Nine is the greatest number observed, 

 while some specimens, even from Herrick's type locality on Flint Ridge, 

 have the costae evanescent with only one clearly marked, although in- 

 dications of others, can generally be observed. Likewise the spinulose 

 structure is not evident on all specimens and is apparently lacking most 

 often on those which have the costae reduced in number. Allowance 

 must be made for variations in the development of costae and the 

 simultaneous loss of the costae with the spinules may be accounted for 

 by adverse conditions of preservation. After an examination of a 

 comparatively large number of these specimens, there is little doubt in 

 the mind of the writer that even those which show the number of costae 

 greatly reduced belong to the same species. 



Horizon and locality. Widely distributed throughout the Lower 

 Mercer and McArthur limestones, c. Black Flint: Jackson County, 

 Locality 87, r. 



Pleurophorus oblongus Meek 



1866 Clidophorus pattasi. Geinitz, Die Carb. und Dyas in Nebraska., p. 23, Tab. 2, 

 Fig. 4. (Non Modiola Pallasi de Vern., 1845.) 

 Nebraska City and Wyoming, Nebraska. 



Meek, F. B., U. S. Geol. Surv. Nebraska, Final Kept., PI. X, Fig. 12, 1872. 

 This figure is used instead of the original one which Meek states is inaccurate. 



