EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 179 
1872. Peripristis semicircularis O. H. St. John, Hayden’s Final Rept. U. S. Geol. 
Surv. Nebraska, p. 242, Pl. IIL, Figs. 3, 4, Pl. IV., Fig. 20. 
1875. Ctenoptychius semicircularis J. S. Newberry, Rept. Geol. Surv. Ohio, Vol. IL., 
p. 52, Pl. LVIII., Fig. 14. 
1902. Peripristis semicircularis C. R. Eastman, Geol. Mag. (IV.), Vol. IX., p. 889, 
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 P. falcatus, a specimen of the latter having been found which displays the 
Fig:.7:; 
Peripristis semicircularis (N. & W.). Chester Group, Kentucky. Lower tooth, in 
profile and front view, X }. 
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. semacircularis differs from the upper 
Fie. 8. 
Peripristis semicircularis (N. & W.). Chester Group, Kentucky. Upper tooth, in 
profile and front view, X 1. 
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 the 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 specimen, that shown in Plate 2, Fig. 7, the pit is de- 
