TICHOLEPTUS 199 



truncate extremity just behind the postglenoid process. The malar is deep below the orbit. The 

 facial vacuities are large, although from the type there is no way of determining just how large they 

 were in life. Cope said that they had "a greater vertical than longitudinal extent." Scott's drawing 

 (1895, pi. V) indicates that he thought the anteroposterior diameter greater than the vertical, and 

 this condition is what we should expect to find. The vacuity, it seems reasonably certain, was 

 bounded by the lacrimal and maxillary bones, and probably by the frontals and nasals as well. The 

 nasal bones are missing, but, since this form had a short face and since the nasomaxillary suture is 

 short, they must have been reduced in length and rather narrow in width. The lacrimal bone 

 extends onto the face and bears a fundus, which was apparently rather shallow and not extensive. 

 The frontals are very convex transversely and descend anteriorly. They are moderately wide. The 

 orbits are proportionally as large as in Merycoidodon culbertsonii, oval in shape, with the longer 

 diameter extending upward and backward, and undoubtedly closed behind, although the narrow 

 postorbital border is incomplete in the type. They are located about halfway between the alveolar 

 parapet and the summit of the skull. The temporal ridges unite just back of the postorbital con- 

 striction to form a prominent and moderately long sagittal crest. The supraoccipital crest is missing. 

 The brain case is relatively full. The external auditory meatus is large and is directed outward and 

 upward, somewhat like that in some of the Suidre. The glenoid surface is fairly flat. The post- 

 glenoid process is small and confined to the inner half of the zygomatic portion of the squamosal 

 bone. Index: 0.51. 



Mandible: The symphysis is not coossified and forms an angle of about 44° with the tooth 

 row. It is very slightly concave vertically and convex transversely. The ramus descends vertically 

 in a straight line from a point slightly aft of the condyle, then convexly at the angle, and nearly 

 straight beneath the teeth. 



Foramina: The infraorbitals cannot be clearly defined but probably were not far from a posi- 

 tion above the anterior of P 4 or the posterior of P 3 . 



Dentition: The dental series are complete with 44 teeth. P 2 and P 3 are longer than P 4 , with 

 their external apices in advance of the mid-line. The superior molars are subhypsodont and are 

 characterized by very prominent external vertical ribs, producing deep fossa; between them. Accord- 

 ing to Cope, there is a third (posterior) column on M 3 "which forms a small heel on section." The 

 outer ribs of the inferior molars are also decidedly prominent, and M 3 has a prominent fifth lobe, the 

 metastylid. The incisors are small in both series, as are also the inferior canines, which have lost 

 their typical shape. The molar-premolar index is 0.85. 



Ticholeptus species Merriam 1911 



Original Reference: Tertiary mammal beds of Virgin Valley and Thousand Creek in northwestern 

 Nevada. Pt. II: Vertebrate faunas. Bull. Dept. Geol. Univ. Calif., VI, pp. 276-277, figs. 48-49 (Merychyus 

 ? sp.). 



Type Locality: Virgin Valley, Nevada. 



Geologic Horizon: Upper Miocene (Virgin Valley). 



Discussion: Two molar teeth, a left M 2 and M 3 , afford the only evidence of merycoidodonts 

 in this area and are therefore very interesting. The M 2 is Cat. No. 12606 U.C.M., and the M 3 is 

 Cat. No. 11825 U.C.M. 



I consider these teeth typical of the genus Ticholeptus. They are less hypsodont than those of 

 Merychyus of comparable geologic age. The styles on M 2 are somewhat heavier, and the tooth 

 proportions are different from those normal to Merychyus. In dimensions and construction the teeth 

 are nearer to those of T. zygomaticus than to those of any other species in the genus, but on such 

 scanty evidence I hesitate to assign them definitely to that species. 



