378 Prof. H. G. Seeley on the Deniition of the 



reputed incisors of Trttylodon are canine teeth, tlie incisors 

 being lost earlier than the niicldle incisors of Gomphognathus 

 r>olfphagus. Professor H. F. Osborn states, in the ' Ameri- 

 can Naturalist' for May 1898, that I figured a portion of the 

 \ovit\ ^&.w oi Tritylodon', but no generic determination was 

 made of that fossil. 



The specimen belongs to a larger animal than Tritylodon 

 Jongcevus. The intractable matrix which obscured the alveolar 

 border in the mandible has now been removed, and the jaw is 

 referable to a species or subgenus of Gomphognathus near to 

 G. polyphagus. 



This mandibular fragment is 2\ inches long from the 

 incisor teeth to the first molar tooth. It is separated from 

 the missing left ramus by fracture, but the rami were united 

 by close bony union, and the socket of the first incisor of the 

 left ramus remains with this specimen. The crown of that 

 tooth n)ay have perished during the life of the animal, though 

 the larger part of the root remains, shown in a vertical 

 fracture. The symphysial surface, about 1^ inch long, 1 inch 

 deep in front, and f inch deep posteriorly, was of long ovate 

 form. 



The inferior external surface of the jaw is convex from front 

 to back, and from side to side slightly convex in front but 

 somewhat flattened. This convex chin surface makes an angle 

 with tlie relatively vertical external lateral surface, which is 

 gently convex from above downward. The lateral surface is 

 I inch deep at the canine tooth and increases in deptii as it 

 extends backward. The internal surface of the jaw above the 

 symphysis is a channel, nearly straight from front to back, 

 sunk well below the level of the canine and the anterior half 

 of the diastema. 



The three incisor teeth are close-set. They occupy a widtii 

 of half an inch. The crowns are broken, but they are nearly 

 uniform in size, nearly circular, with a slight transverse 

 natural compression. The third incisor is in front of the 

 canine. The second and first incisor teeth are further forward 

 successively, so as to make a curved external contour, much 

 in the manner of G omphognathus kannemeycri, which is the 

 only si)eeies with the mandible separated from the skull. 



The canine tooth is directed upward and Ibrwuid, and not 

 outward as in G. kannemeyeri, so that there is no appreciable 

 lateral bulbous expansion of the extremity of the mandible as 

 in that species. The tooth is strong, laterally compressed, 

 ovate in transverse section on the broken surface, /^y inch 

 from front to back at the fracture, and \ inch wide, but 

 slightly wider anterioily. Wiiat remains of the external 



