26B PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



considered as indicating more than individual variation. The differ- 

 ences will be appreciated from a comparison of the original of our 

 plate 6, figure 2, with the complete specimen figured by Newberry. 

 As regards the nature of the inserted portion, however, the two stand 

 in substantial agreement, both bemg shallow and greatly elongated. 

 Interesting to observe is the fact that the anterior extremity of the 

 elongated base rises into a tumid "shoulder, " recalling the very simi- 

 lar appearance presented by spines of Stethacanthus. 



Formation and locality. — Kinderhook limestone (Mississippian) ; 

 Le Grand, Iowa. 



ORACANTHUS TRIANGULARIS, new species. 



Plate 5, figs. 5, 6. 



Spines attaining to a large size, of triangular cross-section in the 

 distal portion, lateral face broad and triangular, resembling in con- 

 formation and size the spines of XystracantTiys mirabilis from the 

 Coal Measures, except in being less arcuate, and in having more 

 strongly developed conical denticles along the posterior margin. 

 Superficial ornament consisting of large tubercles arranged in more or 

 less regular transverse series, many of them fused together, forming 

 discontinuous ridges. 



A few spines presenting the above characteristics are contained in 

 the Musemn collection, and, although incomplete, are sufficiently 

 well marked to warrant the estabhslunent of a distinct species to 

 receive them. No other spines are known from the American Lower 

 Carboniferous which exhibit the same broad triangular outline and 

 transversely ridged external surface, due to the coalescence of coarse 

 tubercles in fairly regular series. At the same time the distal ex- 

 tremity is triangular and less laterally compressed in cross-section 

 than is true of most species. The style of ornamentation somewhat 

 resembles that of the type-species, 0. milleri, and the long and taper- 

 ing PJiysonemus-like spines which Inostranzev has described from the 

 Russian Carboniferous in accompaniment with the teeth of Poly- 

 rliizodus. A small fragment from the Chester limestone of Ilhnois, 

 described by St. John and Worthen as Oracanthus rectus, shows a 

 tendency of the tubercles of the exserted portion to become fused 

 into irregular transverse series. The same authors also figure the 

 distal portion of a triangular spine, possibly belonging to the species 

 under discussion, which they erroneously refer to 0. vetustus.^ In 0. 

 milleri the series of ornamented ridges extend obUquely over the 

 sides of the exserted portion. 



Formation and locality. — St. Louis limestone, near St. Louis, 

 Missouri. (Cat. No. 8377, U.S.N.M.) 



1 Pal. Illinois, vol. 7, 1883, pi. 24, fig. 2. 



