VERTEBRATE REMAINS FROM THE DOCKUM TERRANE. 15 



PAL^OCTONUS, Cope. 

 Proceedings Amer. Philos. Society, 1877, p. 182. 



This genus embraces the largest known carnivorous Dinosauria of the 

 Triassic age. Up to the present time the only remains referable to it 

 consist of teeth. These are of two kinds, the one less compressed and 

 more elongate, and the other more compressed and less elongate. The 

 former I have supposed to occupy the more anterior position in the series 

 in accordance with the characters of the Megalosaurid genera of the Ju- 

 rassic and Cretaceous ages. This supposition is sustained by the fact 

 that the two forms of teeth are generally found together. In Zanclodon 

 Myr. , the Megalosaurid of the European Trias, the teeth are of equal size. 

 The only species known hitherto is the P. appalachianus, Cope (1. c), from 

 the Keuper Trias of Pennsylvania. The explorations of the Geological Sur- 

 vey of Texas, conducted by Mr. W. F. Cummins, in the northwestern part 

 of the State, demonstrate the existence of two species in the Triassic beds 

 which outcrop at the base of the eastern escarpment of the Staked Plains. 



PALiEOCTONUS ORTHODON, Cope. 



Sp. nov. Plate II, Figure 1. 



Represented by a single anterior tooth of large size. The axis of the 

 crown is straight, being curved neither inward nor posteriorly. The in- 

 ternal face is nearly flat transversely at the base, and is moderately convex 

 from the middle to the apex. The posterior cutting edge is denticulate to 

 the base of the crown; but the anterior edge is denticulate for the distal 

 three-fifths of the length only, although it is continued to the base of the 

 crown as a not very prominent ridge and a little within the anterior con- 

 vex outline of the crown. The convex anteroexternal side is marked on 

 the middle of .its length by parallel ridges or folds of the surface, which 

 are separated by shallow grooves wider than themselves. Their direc- 

 tion is inwards and upwards, and they are separated by a space from the 

 anterior cutting edge. This space is marked by transverse concentric 

 ridges, each of which is a continuation of a longitudinal ridge, and which 

 curves upwards and then downwards to the anterior cutting edge. More 

 than half the ridges which lie external to those which are thus recurved 

 simply disappear at both extremities, and successively becoming indis- 

 tinct, disappear entirely on the middle of the external face of the crown. 

 No longitudinal grooves on the inner face of the crown, except a short 

 one at the middle of the anterior cutting edge. Enameled surface min- 

 utely wrinkled. 



Measurements, 



Mm. 



Length of enamel covered crown 55 



Piameters of base of crown \ anteroposterior 25 



( transverse 20 



