T^ASTMAN : CAKBONIFEROUS FISHES FROM THE CENTRAL WEST. 215 



Stethacanthus productus Newberry. 



(Text-flRure 14.) 



1875. Physonemus gigas (errore) St. John and Worthen, Pal. Illinois, Vol. VI., I'l. 



•> XVII., Figs. 7-9. 

 1897. Stethacanthus productus J. S. Newberry, Trans. N. Y. Acad. Sci., Vol. XVI,, 



p. 291, PI. XXIII.,Figs. 2, 2. 

 1897. Stethacanthus compressus J. S. Newberry, Ibid., p. 292, PI. XXIIL, Figs. 3, 4. 



Tyjje. — Imperfect spine ; Mu- 

 seum of Chicago University. 



The spines referred to this 

 species are characterized by hav- 

 ing the concave margin ver}' 

 gently curved, in consec^uence of 

 which the apex is much inclined 

 backwards. The smaller 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 Mes.srs. St. John and 

 Worthen as Physonemus depressus, 

 P. carmatus, and P. gigns (in 

 part) are distinguished from one 

 another and from S. productus in 

 only minor details, and the types 

 are extremely fragmentary. Nev- - 

 ertheless, it is 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- 

 hibit a marked increase in size, 

 and in the next succeeding for- 



FiG. 14. 



Stethacanthus productus Newb. Keokuk lime- 

 stone, Keokuk, Iowa. Lateral aspect of spine, 

 with cross-sections of sunimital portion, X \ 

 (approximately). 



mation, the Keokuk, the maximum appears to have been attained by spines 

 such as the one represented in the accompanying Text-figure. 



