EASTMAN: CARBONIFEROUS SHARKS. 89 
Ctenacanthus varians St. John and Worthen. 
1875. Ctenacanthus varians St. John and Worthen, Pal. Illinois, Vol. VI., p. 422, 
PANE) Bigs. 2. 
1875. Ctenacanthus speciosus St. John and Worthen, ibid., p. 424, Pl. XIV., Figs. 
3, 4. 
Type. Fractured spine; Museum of Comparative Zodlogy. 
Regarding the type-specimen of C. 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 C. 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 C. 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 C. 
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, Pl. XVI, Fig. 14. 
Type. Abraded and distorted spine; Museum of Comparative Zodl- 
ogy. 
This species is founded on a much abraded and distorted spine which 
is now preserved in the Museum of Comparative Zoédlogy at Cambridge, 
and whose relations are evidently with the genus Ctenacanthus instead of 
Anaclitacanthus. Traces remain in some places of the original tuber- 
