34 PALEOZOIC FISHES OF NORTH AMERICA. 
of the triangular ones seem to have resembled in form and functions the 
dermal spines of Climatius, Parexus, ete., and it is possible that they were 
set in greater or less number on the body. Some are quite spine-like in 
character, narrow, compressed and acute, but toward the bases of the cones 
they form the walls are crushed together, and it is evident that they were 
thin, bony, and enameled shells attached to the surface of the body or 
head, where composed of soft tissues, and were not planted in the integu- 
ments like the spines of Elasmobranchs. There is probably much hetero- 
geneous material included in the genus Oracanthus, for some of the spines 
assigned to it are solid, symmetrical, roughened, and pointed at the base, 
and are plainly the dorsal spines of Sharks; others are unsymmetrical, 
the sides being of unequal breadth, and these, I suspect, were the pectoral 
spines of Elasmobranch fishes. 
Mr. J. W. Davis, in his work on the fishes of the Mountain limestone, 
recognizes their paired character, but locates them back on the body. Dr. 
Traquair suggests that a spine of this kind, which he has called Oracanthus 
armigerus, was the defense of the angle of the head. This seems highly 
probable, and it may be true of the triangular spines of Acantholepis as 
well as of the spines called by St. John and Worthen Pnigeacanthus. 
ACANTHOLEPIS PUSTULOSUS. 
Plate XX XI, Figs. 5, 5*, 5°. 
Cranial or body scutes having a somewhat spatulate form, and attain- 
ing in some cases a length of seven or eight inches and a breadth of two 
inches. These scutes were set contiguous to each other, forming a defense 
to the body or head; the more elongated ones becoming curved spines, 
similar in general character to those of Acanthaspis, but differing in this, that 
they are not united by sutures with flat bones or plates, but are the extrem- 
ities of such plates drawn out into spines, which must have projected from the 
general surface. The broader plates are quite thin, and seem to have been 
applied to flat or arched surfaces, while those which form spines have their 
remote extremities narrowed and thickened till they become prominent and 
effective defensive organs. In some instances the plates are triangular in 
