. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. EASTMAN : CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 179 1872. Peripristis xemicircitlaris 0. H. St. John, Hayden's Final Kept. U. S. Gcol. Surv. Nebraska, p. 242, PI. III., Figs. 3, 4, PI. IV., Fig. 20. 1875. Ctenoj)ti/ckius semicirculnris J. S. Newberry, Hept. Geol. Surv. Ohio, Vol. II., p. 52, PI. LVIIL. Fig. 14. 1902. Periprislis semicircularis C. R. Eastman, Geol. Mag. (IV.), Vol. IX., p. 389, Text-fig. 1. It is evident from marks of contact that the relations between the supposed upper and lower teeth of this s
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. EASTMAN : CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 179 1872. Peripristis xemicircitlaris 0. H. St. John, Hayden's Final Kept. U. S. Gcol. Surv. Nebraska, p. 242, PI. III., Figs. 3, 4, PI. IV., Fig. 20. 1875. Ctenoj)ti/ckius semicirculnris J. S. Newberry, Hept. Geol. Surv. Ohio, Vol. II., p. 52, PI. LVIIL. Fig. 14. 1902. Periprislis semicircularis C. R. Eastman, Geol. Mag. (IV.), Vol. IX., p. 389, Text-fig. 1. It is evident from marks of contact that the relations between the supposed upper and lower teeth of this species are identical with those known to obtain in , a specimen of the latter having been found which dispU\ys the Fig. 7. Peripristis semicircularis (N. & W.). Chester Group, Kentucky. Lower tootli, in profile and front view, X I- dental plates of both jaws in natural association. The tooth which may be provisionally referred to the lower jaw in all these forms is the one which fitted inside that of the opposite jaw when the mouth was closed, this condition having been ascertained to hold in the case of Janassa, and being true among sharks generally. The lower tooth of P. semicircularis differs from the upper. Fig. 8. Peripristis semicircularis (N. & W.). Chester Group, Kentucky. Upper tooth, in profile and front view, X x- in having the serrations of the cutting-edge obsolete, or nearly so, and the basal border deflected downward in the median line in front, as shown in Text- figure 7. It also has a longer root than the upper tooth. The coronal margin of the latter is always strongly serrated in the unworn condition (Text-fig. 8), there being usually four denticulations on one side of the median line and five on the other. The coronal* cavity of the upper tooth exhibits a deep pit in the median line at the junction of tiie horizontal and vertical portions of the posterior face, but there is no groove extending from it on either side as in P. falcatus. In one
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