ee I 
EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 177 
A large series of this exclusively Upper Carboniferous species have come 
under the writer’s observation, a study of which shows a wide range of varia- 
tion to exist between the large, symmetrically formed, symphysial teeth, such 
as is represented in Pl. 2, Fig. 17, and the low-crowned, short-rooted, often 
quite asymmetrical teeth belonging to the outermost of the lateral series. The 
form of the root is even more variable than that of the crown, as one may 
satisfy himself by comparison of Figs. 17 and 18 of Plate 2, or the other figures 
of this species contained in the literature. Dr. O. P. Hay has commented on 
the fact that in Newberry and Worthen’s figures of P. destructor the lateral 
angles of the crown are acutely terminated, and notes that in the specimen 
named by him P. securiger they are rounded off, at which point th° enamel 
folds become flexed upward. This appears to be the normal conditiov mani- 
fested by all perfectly preserved teeth, but the root being extremely attenuated 
close to the lateral angles, the edges are rarely found entire. And it is perfectly 
evident from Newberry and Worthen’s Figs. 1-3 that none of the lateral angles 
in their specimens have escaped injury. 
The imbricated enamel folds at the base of the crown are sometimes distinctly 
raised on both faces, and usually appear smoother on the anterior than on the 
posterior face, as if from contact with adjacent older teeth of the same series. 
The extent to which the teeth of a single series overlapped one another seems 
to have been greater than in Janassa, and equals that in Petalorhynchus! 
and Ctenoptychius.?_ Marks of wear also seem to show that the upper and 
lower dentition interlocked by a comparatively small margin. 
Besides the single tooth of this species described by St. John from the Mis- 
sourian of Rock Bluff, Nebraska, numerous examples have been obtained by 
Professor Barbour from the same formation at Richfield and Table Rock, and 
from the Permo-Carboniferous of Roca, Nebraska. 
Formation and Locality. —Coal Measures; Pennsylvania, Ohio, Illinois,, 
Iowa, Nebraska, Arkansas. Permo-Carboniferous; Nebraska. e 
Petalodus (Chomatodus) arcuatus (Sr. Jonny). 
1870. Chomatodus arcuatus O. H. St. John, Proc. Amer. Phil. Soc., Vol. XI., p. 435. 
1872. Chomatodus arcuatus O. H. St. John, Hayden’s Final Rept. U. S. Geol. Surv. 
Nebraska, p. 248, Pl. VI., Fig. 14. 
1875. Chomatodus arcuatus St. John and Worthen, Pal. Illinois, Vol. VI., Pl. X., 
Fig. 23. 
Low-crowned teeth of the form commonly ascribed to Chomatodus (pars) in 
all probability represent the postero-lateral series of Petalodus, and it would 
seem that this genus possessed a larger number of tranverse series than Janassa, 
as well as a more elongated mouth-cleft. The narrow, ray-like mouth-cleft in 
Janassa is regarded by Jaekel as evidence of specialization. 
1 Cf. J. W. Davis, On the fossil Fishes of the Carboniferous Iimestone Series, 
Trans. Roy. Dublin Soe. (2), Vol. I, 1883, p. 426, Pl. LXI., Fig. 16. 
2 Cf. St. John and Worthen, Pal. Illinois, Vol. VI., 1875, Pl. XIL., Fig. 9. 
VOL. XXXKIX. — NO. 7 2 
