198 



THE MERYCOIDODONTIDA? 



quarter greater. There is a certain resemblance in the crown pattern to that found in Poatrephes 

 paludicola, but in the latter the molar and premolar series are almost equal in length, a feature not 

 seen in any form of Tichole-ptus. 



In addition to the few differences pointed out above between T. zygomaticus and T. smithi, 

 there are certain others in the latter which I consider to be of specific value. These are, first, that 

 the zygomatic portion of the squamosal is somewhat heavier and is extended farther forward, that is, 

 to a point under the posterior quarter of the orbit, whereas in the former species it probably did not 

 extend forward of the postorbital bar; second, that the paroccipital process did not adhere so closely 



Fie. 144. — Ticholeptus smithi (Douglass). 



Fragmentary skull and jaw. HT. Cat. No. 766 CM. 1/2 nat. size. 

 (After Douglass, 1903.) 



to the external auditory meatus in T. smithi; third, that the occipital condyles are situated nearer to 

 a transverse line across the paroccipital processes than they are in Cope's specimen. 



Finally, we can be certain that this specimen of Douglass' is a true Ticholeptus. Furthermore, 

 it is very close to T. zygomaticus in many essential characters but differs sufficiently to be entitled to 

 specific rank of its own. Further cleaning may help to determine controversial points, but a more 

 complete skull, as well as limb bones and feet, would definitely settle the position of this species. 



Ticholeptus zygomaticus Cope 1878 

 PL XXIX, figs. 1-2 



Original Reference: A new genus of Oreodontid.-e. Amer. Nat., XII, p. 129 (preliminary notice); 

 Descriptions of new extinct Vertebrata from the Upper Tertiary and Dakota formations. Bull. U. S. Geol. Geog. 

 Surv. Terr., 1878, IV, pp. 380-382 (amplified description). 



Type Locality: Smith River Valley, Montana. 



Geologic Horizon: Upper Miocene (Deep River). 



Type: Genoholotype, Cat. No. 8112 A.M.N.H., skull and jaws, joined by matrix and considerably crushed 

 laterally, as well as damaged in nasal region. Collected by J. C. Isaac. 



Specific Characters: The skull is about the size of that of Eporeodon major. The pre- 

 maxillaries are fused. The zygomata reach their maximum expansion about opposite the postorbital 

 constriction, and anteriorly they turn abruptly outward above the fourth premolar. The squamosal 

 part is expanded horizontally rather than vertically, rises slightly aft, and terminates in an obliquely 



