EASTMAN: CARBONIFEROUS 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. arcuatus the 
spines were curved in the normal direction, that is to say, posteriorly. In 
P. gemmatus, P. stellatus, and P. gigas, 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 
vetustus.+ 
Formation and Locality. — St. Louis limestone; Illinois, Missouri, and Indi- 
ana. Lower Carboniferous Limestone ; Great Britain. 
Physonemus gemmatus (Newserry and WorrHEn). 
1866. Drepanacanthus gemmatus Newberry and Worthen, Pal. Illinois, Vol. IL, 
p. 123, Pl AIL; 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. gigas and some other forms. 
We are inclined to think that Newberry was correct in this view, but mis- 
taken in supposing that P. arcwatus 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. Asin 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 (Newsrerry and WortuHey). 
1866. Drepanacanthus (2?) stellatus Newberry and Worthen, Pal. Illinois, Vol. IL, 
pel267 PL XIE, Fig. 7: 
1875. Batacanthus stellatus St. John and Worthen, /bid., Vol. VI., p. 470, Pl. XXL, 
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 Newberry, J. S., Trans. N. Y. Acad. Sci., Vol. XVI.., 1897, p. 285, Pl. XXII, 
Fig. 5. 
VOL, XXXIX. — NO. 7 4 
