EASTMAN: CARBONIFEROUS SHARKS. 87 
surface ornamentation have been figured by St. John and Worthen! as 
Drepanacanthus reversus, and by Newberry? as Physonemus stellatus. 
The theoretical association of Physonemus, including Xystracanthus, Dre- 
panacanthus, and Batacanthus, with the teeth of various species of Petalodonts, 
as proposed by Jaekel (Joc. cit., p. 285), may be considered as negatived by 
the discordant distribution in the Mississippian series of these two classes of 
remains. 
Formation and Locality.—St. Louis limestone; Missouri, Illinois, 
Indiana, and Michigan. 
SPECIES FOUNDED ON SPINES BELONGING TO THE POSTERIOR 
DORSAL FIN. 
Ctenacanthus coxianus St. John and Worthen. 
1888. Ctenacanthus coxianus St. John and Worthen, Pal. Illinois, Vol. VII., p. 238, 
Pl. XXL, Fig. 1. 
This species was founded on a unique but fragmentary and abraded 
spine from the Keokuk limestone of Iowa, and no further examples 
have been recorded from this or from other horizons. An imperfect 
spine, denuded of most of its ornamentation, but apparently referable 
to this species, is preserved in the Worthen, Collection in the Museum 
of Comparative Zodlogy, and was derived from the Kinderhook lime- 
stone of Iowa. Considerable resemblance is to be observed between 
this species and C. furcicarinatus from the Waverly sandstone of 
Kentucky. 
Formation and Locality. — Kinderhook and Keokuk Groups ; Iowa. 
Ctenacanthus spectabilis St. John and Worthen. 
Plate 5, Fig. 1. 
1875. Ctenacanthus spectabilis St. John and Worthen, Pal. Illinois, Vol. VI., p. 
420, Pl. XV., Figs. la-le. 
This species was founded on a unique spine from the Kinderhook 
limestone of Legrande, Iowa, the more salient characters of which were 
stated to consist in its “great breadth along the oblique line of inser- 
tion and the abrupt posterior deflection in the curvature of the coste, 
1 Pal. Ill., Vol. VI. (1875), p. 456, Plate XIX., Figure 5 (non Figure 6). — Ibid., 
Vol. VII. (1883), p. 253, Plate XXIV., Figure 5. 
2 Monogr. U. S, Geol. Surv., Vol. XVI. (1889), p. 200, Plate XXI., Figure 12. 
