Xc'ic Species of Fo.ssils from Ohio. 239 



valve flat, discoidal, circular iu outline, or perceptibly elongated in some 

 cases ; the apex a little more than one-third the length of the shell from the 

 posterior margin. Foramen small, elongate-elliptical, narrow, not extend- 

 ing more than one-fourth of the distance from the apex toward the margin, 

 and the depression somewhat further. Sui-face marked as in the other valve. 



This shell would appear to be identical with the one described 

 and figured by Messrs. Meek and Worthen as D. oiitida? under 

 the supposition that it was the same as that figured by Prof. 

 Phillips, in the Geol. Yorkshire Coast, Vol. II, pi. 11, filgs. 

 10 — 13 ; but it differs very much in outline fi'om those figures, 

 as well as those given by other authors, in its circular form ; 

 those being ovate, narrowed behind and widened in front; also, 

 in having the apex much more distant from the margin. They 

 also cite D. Missouriensis, Shumard, as a synonym of the Eu- 

 ropean sj)ecics. That author indicates his shell as parabolic in 

 outline; from which statement I should consider it as distinct 

 from the present species. 



Formation and Locality. — In the Coal-measures at Carbon 

 Hill and Flint Eidge, Ohio ; also in Illinois and Iowa. 



Crania carbonaria, u. sp. 



Pal. O., Vol. Ill, Plate 11, Figs. 11 and 12. 



Shell small, none of the specimens observed exceeding three-eighths of an 

 inch in diameter; sub-circular iu outline, or varied in form by the outline 

 of the object to which they are attached. Free valve depressed convex, 

 marked by a few concentric lines of growth ; attached valve thin, but with 

 a slightly thickened margin. Posterior muscular impressions large and 

 sub-marginal, the others being nearly central and forming a small eleva- 

 tion just posterior to the middle of the valve. 



The shells of this species are found attached to the spines of 

 Zeacrinus and other bodies, one of those figured being upon the 

 operculum of Naticopsis. They are very thin, and not easily 

 detected in the roughened condition caused by the adhering 

 material in which most of the fossils from these beds are found. 

 Species of this genus are rather rare in the Coal-measures, but 

 very few having been described. Crania Permiana, Shumard, 

 from the white limestones of the Guadalupe Mts., Texas, is a 

 large form, and probably not a Crania, according to the descrip- 

 tion given. C. modesta, White and St. John, from the Coal- 



