222 POTTSVILLE FAUNA OF OHIO 



half the length of the shell; also in its rounded posterior margins and 

 its less prominent umbonal ridge. N. ohioense, however, is very vari- 

 able and differences exist in the size and prominences of the anterior 

 lobe, the length of the hinge line, and the outline of the posterior por- 

 tion. Whether these points of difference are due to slight distortion 

 or natural variation among individuals, or whether more than one 

 species is really present, is a matter of question. But on account of 

 the variable nature of the genus itself, such differences are to be ex- 

 pected and are therefore particularly difficult to evaluate. After a 

 careful study of the material at hand, it seems best to the writer to 

 group under one species these forms with the long hinge line, as no 

 tangible basis for further subdivision is evident. 1 



Horizon and locality. Sharon ore: Scioto County, occurs in 

 nodules of iron ore in the John Alexander mine, Locality 3, aa. 



Naiadites sp. 



Remarks. Several crushed,, poorly preserved specimens of a very 

 large species of Naiadites were found associated with large numbers of 

 Lingula carbonaria in the black shales of the Anthony coal horizon. 

 They are, however, too poor for identification. 



Horizon and locality. Anthony coal horizon: Scioto County, Wm. 

 E. Dee mine, Locality 7, r. 



Genus Schizodus King 



Schizodus amplus Meek and Worthen 

 PL XII, fig. 18 



1870 Schizodus amplus. Meek and Worthen, Proc. Acad. Nat. Sci. Phil., p. 41. 



Coal Measures: Seville, Fulton County, Illinois. 

 1873 Schizodus amplus. Meek and Worthen, Geol. Surv. 111., Vol. 5., p. 579, PI. 27, 



Fig. 6. 



Coal Measures: Seville, Fulton County, Illinois. 



the above discussion was completed there has come to the attention of 

 the writer figures and a description of a species of Naiadites, designated by Price as 

 N. carbonaria Dawson, from the Pottsville series of West Virginia. (See W. Va. 

 Geol. Surv., Webster Co. Kept., p. 602, PI. XXXV, Figs. 1, 2.) Price states that 

 these fossils may represent immature forms of either N. elongata or N. carbonaria. 

 The writer is unable to find any essential differences between the Ohio and West 

 Virginia species, unless perhaps N. ohioense has a greater posterior extension as well 

 as a typically longer hinge line which equals the greatest diameter of the shell; 

 but these characters are very variable. The umbonal ridge and the sinus below are 

 more prominent on our specimens than the figures of the West Virginia form 

 seem to indicate, which may, however, be accounted for by the fact that the former 

 is unusual in being practically unaffected by pressure. Considering, then, the variable 

 character of the group it does not seem at all improbable that the Ohio and West 

 Virginia forms may belong to the same species. However, our form differs from typ- 

 ical N. carbonaria, as described and figured by Dawson, in the smaller size of mature 

 individuals and in the longer hinge line, and seems to constitute a distinct species. 



