TICHOLEPTUS 



189 



auditory meatus is peculiar in that the long, straight tube is directed markedly upward and not so 

 much outward as is normal for the genus. It is also directed slightly backward. The bullse are 

 decidedly large. The glenoid surface is gently concave, and the glenoid process is short and stocky. 

 The paroccipital process is moderately expanded laterally and thickened anteroposteriorly behind 

 the bulla, while inferiorly it terminates in a blunt point. Index: 0.54. 



Mandible: The symphysiodental angle is about 44°, and the symphysis ends inferiorly in a 

 small knob. The horizontal ramus is moderately deep and approximately uniform in height from 



Fig. 138. — Tickoleptus brachymelis Douglass. Skull and jaw. HT. 



(After Douglass, 1907.) 



Cat. No. 9731 A.M.N.H. 2/5 nat. size. 



P 3 to M 3 . The angle of the ascending ramus is large and regularly convex but does not extend 

 much below the line of the straight inferior border of the horizontal ramus. The masseteric fossa is 

 deep but small in extent. The coronoid process is short and thin, with the sigmoid notch wide open 

 and shallow and the condyle gently convex. 



Foramina: The infraorbitals lie above the anterior of P\ 



Dentition: Premolars neither long nor high. The superior ones are not crowded, but the 

 inferior Pi and P 2 overlap slightly. The molars are subhypsodont, with hypsodonty more marked 

 in M 2 and M 3 . Molar-premolar index 0.80. 



Skeleton: Limbs and feet short. 



Discussion: In comparison with other species of the genus, Douglass made the following 

 observations : 



From the type of the genus, Ticholeftus zygomaticus Cope, this species differs in the greater length of the 

 skull in proportion to the height, in the more nearly straight upper contour of the skull, in the less thickened and 

 rugose squamosal portion of the zygomatic arch, and in the less hypsodont teeth. 



From Tickoleptus breviceps Douglass, from Divide Creek, Montana, it differs in the following respects: 

 Skull larger, longer, and proportionally narrower; brain case proportionally smaller; paroccipital processes thicker 

 antero-posteriorly; pillar of the occiput narrower and less flattened; occipital condyles less compressed antero- 

 posteriorly; tympanic bullae smaller; malars heavier and more ascending; form of squamosal process of zygoma 

 different; teeth less hypsodont; metapodials, and probably limbs, slightly more robust. 



It is distinguished from Tickoleptus bamiackensis Douglass from Grasshopper Creek above Bannack in Mon- 

 tana, by its smaller size, smaller premolar teeth, less, but more uniform, depth of the horizontal ramus of the 

 mandible, and its shorter and proportionally heavier limbs and feet. 



