EASTMAN : CAEBONIFEROUS FISHES FROM THE CENTRAL WEST. 209 



can be no question that the spines belonging to this species are homologous 

 with the compressed posterior branch of Erismacanthus, and reasoning from 

 analogy, it is natural to suppose that in the group typified by P. arctiattis the 

 spines were curved in the normal direction, that is to say, posteriorly. In 

 P. gemmatus, P. stellatus, and P. giyas, on the other hand, appearances are 

 in favor of Newberry's conclusion that the usual curvature was reversed, the 

 anterior margin being concave, and the posterior convex. Enlightenment as 

 to how this reversal may have been accomplished is furnished by a study of 

 the conditions in Stethacanthus and the Kinderhook specimens of Oracanthus 

 vet list us^- 



Formation and Locality. — St. Louis limestone; Illinois, Missouri, and Indi- 

 ana. Lower Carboniferous Limestone ; Great Britain. 



Physonemus gemmatus (Newberry and Worthen). 



1866. Drepanacanthus gemmatus Newberry and Worthen, Pal. Illinois, Vol. II., 



p. 123, PI. XIII, Fig. 1. 

 1889. Drepanacanthus gemmatus J. S. Newberry, Monogr. U. S. Geol. Surv., Vol. 



XVI., p. 195. 



A spine as perfect as the type of this species is preserved in the United 

 States National Museum, and agrees with it in the form of the inserted portion. 

 This, according to Newberry, affords proof that the spine was curved forwards 

 with the concave margin toward the front, as in P. (/zV/asand some other forms. 

 We are inclined to think that Newberry was correct in this view, but mis- 

 taken in supposing that P. arcuatus was curved in the same direction. The 

 propriety of including these two species in the same genus has already been 

 suggested by Newberry and Smith Woodward. 



Spines of the present species are not altogether uncommon in the Keokuk 

 limestone, and good examples may be seen in the Cambridge and Iowa State 

 Museums. Apparently the tubercles along the concave margin never attained 

 a size sufficient to be called denticles. As in P. stellatus Newb. and Worth., 

 the pulp-cavity is not central in position, but placed slightly nearer the convex 

 margin. 



Formation and Locality. — Keokuk limestone ; Iowa. 



Physonemus stellatus (Newberry and Worthen). 



1866. Drepanacanthus (?) stellatus Newberry and Worthen, Pal. Illinois, Vol. II., 



p. 125, Pi. XII., Fig. 7. 

 1875. Batacanthus stellatus St. John and Worthen, Ibid., Vol. VI., p. 470, PI. XXI., 



Figs. 1-3. 



Complete spines of this species have never been figured. Newberry and 

 Worthen were acquainted with but a single fragment of the distal portion, but 



1 Neicheny, J. S., Trans. N. Y. Acad. Sci., Vol. XVI.., 1897, p. 285, PI. XXII., 

 Fig 3. 



VOL. XXXIX. — NO. 7 4 



