TICHOLEPTUS 197 



Pro?iomotherium laticefs is considerably larger than Merycochaerus ( ? ) rustlcus, the anterior palatine 

 foramina are smaller; the shelf at the bottom of the facial concavity — the top of the malo-maxillary ridge — 

 is flatter and more horizontal; the malo-maxillary ridge is narrower and more angulate, not broadly and evenly 

 convex as in Merycochaerus ( ? ) rustlcus. Premolars one and two do not incline backward and become much 

 more worn on the posterior edges as in Merychyus. The fourth premolar has a larger inner cingulum, and molars 

 one and two have more prominent buttresses. . 



It may be that Merycochaerus rustlcus belongs in the same genus as Prono?notherium laticefs, but it is still 

 very doubtful, as the type of the former is so incomplete. 



On the evidence of good skull and skeletal material from the Pawnee Creek beds, Loomis 

 (1920) referred this species to Ticholeptus and compared it chiefly with T. brachymelis and 

 T. breviceps. While there are several rather marked deviations from the norm of the species now 

 included in Ticholeptus, yet this species falls more truly within the distinguishing Ticholeptus char- 

 acters than into any of the allied or contemporaneous groups of merycoidodonts. 



Ticholeptus smithi (Douglass) 1903 

 Fig. 144 



Original Reference: New vertebrates from the Montana Tertiary. Ann. Carnegie Mus., II, pp. 1 79- 

 180, fig. 19 {Merychyus smithi). 



Type Locality: Near New Chicago, Montana. 



Geologic Horizon: Upper Miocene (Flint Creek). 



Type: Holotype, Cat. No. 766 CM., lower portion of right side of skull with parts of mandible. Upper 

 molar-premolar series present, as is lower series back of P 2 . The jaws have not been separated, and the grinding 

 faces of most of the molars are still hidden. The specific name was given in honor of Professor F. D. Smith. 



Specific Characters and Discussion: In the comparable parts this species resembles 

 T. zygomaticus very closely, except in a few characters. Douglass says that it resembles Poatrephes 

 paludicola in some respects. It is unfortunate that the holotypes of both T. zygomaticus and T. smithi 

 still have the lower jaws attached by matrix, thus obscuring the tooth patterns to a major extent. 



The following are the characters that are in close accord with those of T. zygomaticus. The 

 skull in T. smithi is somewhat shorter, but the proportion of the face to total skull length is approxi- 

 mately the same in both. The infraorbital foramen is over P 3 . The malar is deep beneath the 

 orbit, and its anterior origin is above M 2 . The ridge is carried forward on the face. The zygo- 

 matic process has an abrupt upward turn nearly above the posterior termination of the malar, which 

 lies just in advance of the glenoid surface. The inferior border of the zygomatic process is rugose, 

 with one or two rounded angles. The orbits are proportionally of the size in Merycoidodon culbert- 

 sonii and were closed by a slender postorbital bar. The external auditory meatus is directed back- 

 ward, outward, and upward. Externally it has a short but large tube which internally becomes 

 more wedge-shaped. This is a character somewhat like that found in Poatrephes, though resembling 

 the T. zygomaticus form much more closely. The tympanic bulla is lost but undoubtedly was 

 present. The glenoid articular surface is nearly flat. The paroccipital processes are approximately 

 the same in size and shape in both species of Ticholeptus. 



Mandible: In so far as preserved the mandible resembles that of T. zygomaticus, except that 

 the condyle is set inward more abruptly in Cope's species. 



Dentition: In the main the teeth are proportionally somewhat smaller in T. smithi and perhaps 

 slightly shorter crowned, but the animal is an old individual, with the teeth much more worn than in 

 T. zygomaticus. The molar-premolar index is the same in both, 0.85. The anterior part of P 4 is 

 bifurcated. The chief distinction is that in T. smithi the anteroposterior diameter of P 1 is about a 



