158 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



6. Caudal fin diphycercal. 



7. Two anal fins, 



8. A large denticulated spine attached to occipital region of 



cranium. 



9. Teeth with two divergent cusps springing from a broad, flat 



base, and with one or more small median denticles. 



Pleuracanthus quadriseriatus (Cope). ( Plate 26, figs. 3-3^. ) 



1877. Orthacanthus quadriseriatus Cope, Proc. Amer. Philos. Soc, p. 192. 



1889. Pleuracanthus quadriseriatus (Cope), Woodward, Cat. Fos. Fishes, i, p. 9. 



1900. Pleuracanthus {Orthacanthus) quadriseriatus Cope, Case, Journ. Geol., vin, 



p. 700, pi. 1, figs. 3a-3J. 

 1902. Pleuracanthus quadriseriatus (Cope), Hay, Bull. U. S. Geol. Surv., No. 179, 



p. 264. 



Type: Small fragment of a head spine, 7 mm. long, from near the distal 

 end of the spine. No. 6502 Gurley Collection, University of Chicago; 

 Vermilion County, Illinois (plate 26, figs. 3-3^). 



Referred specimen: A small fragment of a head-spine associated with 

 the type specimen (plate 26, fig. 3'). 



The fragment upon which this species is based is from the distal portion 

 of a spine — the part which shows less of the peculiarities of the spine than 

 any other, since it is generally smoother and rounder than the proximal 

 portion. But since the species has been described, the name must be 

 retained, provisionally at least. Cope's diagnosis of it is as follows: 



Original description: "The spine is wider than deep, and the series of 

 denticles are widely separated. The surface between them is gently convex 

 and smooth. The anterior face is strongly convex, and presents at each 

 side two shallow furrows. The external groove is divided by a series of 

 thin longitudinal denticles which are smaller than those of the principal 

 row and which are sometimes confluent at the base. The principal denticles 

 are closely placed, stout, acute, and recurved. 



"Transverse diameter of shaft 0.0035 "^-j anteroposterior diameter 

 0.0025 J^- j the portion of the shaft preserved is straight." 



Pleuracanthus gracilis (Newberry). (Plate 26, figs. 4-4J.) 



1875. Orthacanthus gracilis Newberry, Paleont. Ohio, 11, p. 56, pi. lix, fig. 7. 

 1881. Orthacanthus gracilis Newb., Cope, Am. Nat., xv, p. 163. 

 1889. Orthacanthus gracilis Newb., A. S. Woodward, Cat. Fos. Fishes, i, p. 9. 

 1900. Pleuracanthus (Orthacanthus) gracilis Newb., Case, Journ. Geol., viii, p. 701, 

 pi. I, fig. 4. 



This species is represented by a number of fragments of head-spines 

 preserved in the University of Chicago collection (No. 6503), from the Red 

 Beds in Vermilion County, Illinois. They may be distinguished at a glance 

 from the preceding species by their circular cross-section and larger, more 

 widely-spaced denticles. In the proximal portion of the spine the denticles 

 of the two rows are placed opposite one another, while in the more distal 

 portion they alternate, though not regularly. Newberry's definition of the 

 species applies word for word to the fragments in hand and may here be 

 appended : 



Original description: " Spine small and straight, about three inches long, 

 very slender and acute; section circular at base, posterior face and sides 

 flattened above; the angle inclosed by them set with acute, recurved, com- 



