EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 215 
Stethacanthus productus Newserry. 
(Text-figure 14.) 
1875. Physonemus gigas (errore) St. John and Worthen, Pal. Illinois, Vol. VI., Pl. 
XVII. Figs. 7-9. 
1897. Stethacanthus productus J. S. Newberry, Trans. N. Y. Acad. Sci., Vol. XVI, 
p. oul, Ply XML, Figs..2,-2. 
1897. Stethacanthus compressus J. S. Newberry, Jbid., p. 292, Pl. XXIIL., Figs. 3, 4. 
Type. — Imperfect spine; Mu- 
seum of Chicago University. 
The spines referred to this 
species are characterized by hav- 
ing the concave margin very 
gently curved, in consequence of 
which the apex is much inclined 
backwards. The sinaller spines 
described by Newberry as S. com- 
pressus appear to be the young 
of the species under discussion, 
and it need scarcely be remarked 
that their correlation by this au- 
thor with the pectoral and pelvic 
fins is entirely fanciful. Spines 
having the same form as S. pro- 
ductus, but of much smaller size, 
occur in the Kinderhook lime- 
stone of Iowa. The species de- 
scribed by Messrs. St. John and 
Worthen as Physonemus depressus, 
P. carinatus, and P. gigas (in 
part) are distinguished from one 
another and from S. productus in 
only minor details, and the types 
are extremely fragmentary. Nev- 
ertheless, it 1s convenient to re- 
gard the Kinderhook species as 
distinct from the Burlington, 
provisionally at least, and as rep- 
resenting the earliest and most 
primitive expressions of the ge- 
nus. The Burlington species ex- 
Fig. 14. 
Stethacanthus productus Newb. Keokuk lime- 
stone, Keokuk, Iowa. Lateral aspect of spine, 
cp ‘ eae with cross-sections of summital portion, X 4 
hibit a marked increase in size, (approximately). 
and in the next succeeding for- 
mation, the Keokuk, the maximum appears to have been attained by spines 
such as the one represented in the accompanying Text-figure. 
