EASTMAN : CAEBONIFEKOUS SHARKS. 89 



Ctenacanthus varians St. John and Worthen. 

 1875. Ctenacanthus varians St. John and Worthen, Pal. Illinois, Vol. VI., p. 422, 



pi.^vi.. Fig. 2. ^y I \/ 



1875. Ctenacanthus speciosus St. John and Worthen, ibid., p. 424, PI. XIV., Figs. 

 3,4. 



Ti/pe. Fractured spine ; Museum of Comparative Zoology. 



Regarding the type-specimen of G. varians, now preserved in the 

 Cambridge Museum, Messrs. St. John and Worthen speak as follows 

 (Pal. Illinois, Vol. VI., p. 423) : " The solitary example which we have 

 examined of the present form represents a spine probably seven inches 

 in length, and though broken and parts are missing, sufficient remains, 

 together with the perfect condition of the external characters, to show 

 its distinctive features as contrasted with other forms. . . . Compared 

 with G. speciosus, with which it has in common the same general out- 

 line and similar style of ornamentation, its distinguishing peculiarities 

 consist in its more robust proportions and greater lateral thickness, the 

 double row of tubercles along the anterior ridges, and the more promi- 

 nent denticles arming the postero-lateral angles." 



The same authors, in describing G. speciosus, again call attention to 

 the close resemblance between the latter form, of which they possessed 

 several fragments besides the type, and the unique specimen of G. 

 varians. From comparisons of a large series of Selachian fin-spines, the 

 present writer has been led to the conclusion that the supposed differ- 

 ences between C. varians and C. speciosus are of too trifling nature to 

 be considered of specific importance ; hence the latter title had best be 

 abandoned. 



Formation and Locality. — Kinderhook Group ; Flint River, near 

 Burlington, Iowa. 



Ctenacanthus semicostatus St. John and Worthen. 



1875. Anaclitacanthus semicostatus St. John and Worthen, Pal. Illinois, Vol. VI.. 

 p. 443, Pi. XVI., Fig. 14. 



Type. Abraded and distorted spine ; Museum of Comparative Zool- 

 ogy- 



This species is founded on a much abraded and distorted spine which 

 is now preserved in the Museum of Comparative Zoology at Cambridge, 

 and whose relations are evidently with the genus Ctenacanthus instead of 

 Anaclitacanthus. Traces remain in some places of the original tuber- 



