EASTMAN: CARBONIFEROUS SHARKS. 87 



surface ornamentation have been figured by St. John ami Worthen^ aa 

 Drepanacanthus reversus, and by Newberry ^ as Physonemus stellatus. 



The theoretical association of Physonemus, including Xystracanthiis, Dre- 

 panacanthus, and Batacanthus, with the teeth of various species of Petalodonts, 

 as proposed by Jaekel (loc. 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. 



1883. Ctenncanthus coxianus St. John and Wortlien, Pal. lUinois, Vol. VII., p. 233, 

 PI. XXI., 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 Zoology, and was derived from the Kinderhook lime- 

 stone of Iowa. Considerable resemblance is to be observed between 

 this species and G. furcicarinatus from the Waverly sandstone of 

 Kentucky. 



Formation and Locality. — Kinderhook and Keokuk Groups ; Iowa. 



Ctenacanthus spectabiiis St. John and Worthen. 



Plate 5, Fig. 1. 



1875. Ctenacanthus spectabiiis St. John and Worthen, Pal. Illinois, Vol. VI., p. 

 420, PI. 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 costse, 



1 Pal. 111., Vol. VI. (1875), p. 456, Plate XIX., Figure 5 {non Figure 6). — Ibid., 

 Vol. VII. (1883), p. 253, Plate XXIV., Figure 6. 



2 Monogr. U. S Geol. Surv., Vol. XVI. (1889), p. 200, Plate XXI., Figure 12. 



