550 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Measurements. 



M. 



Length deutal line 0. 0148 



Length of last molar 0030 



Length of ante-penult 0025 



Width of ante-penult 0020 



Length of three molars preserved 0070 



From the Briclger Beds of the uj^per valley of Green Eiver. 



CAElSriVORA. 

 MESONYX, Cope. 



This genus was described by the writer in the Proceedings of the 

 American Philoso]3hical Society for 1872, p, 460, and published in an 

 advance edition of the same paper on July 29, 1872. It was there 

 refeiTed to the Carnivora, and stated to resemble Hycenodon in some 

 respects. I propose on the present occasion to attempt a more exact 

 determination of its structure and relationships. The only species yet 

 certainly referable to it is Mesonyx oMusidens, Cope, 1. c, which is repre- 

 sented by a fragmentary skeleton. There are preserved portions of 

 the skull with the teeth, chiefly mandibular ; numerous vertebree from 

 all parts of the column ; ]3arts of scapula, ulna and fore feet ; portions 

 of pelvis, femora, tibias, tarsals, metatarsals, and phalanges. 



The numerous nuguiculate digits, the sectorial character of the molar 

 teeth, and the characteristic form of the astragalus demonstrate this 

 genus to belong to the Carnivora fisi^ipedia. It becomes interesting, then, 

 to determine the relations of an Eocene type of the order to the families 

 now living. 



The cervical vertehrm are damaged. The dorsals are strikingly smaller 

 than the lumbars, being less than half their bulk. They are opistho- 

 coelian with shallow cups, and the centra are quite concave laterally 

 and inferiorly. The centra of the lumbars are more truncate, with a 

 trace of the opisthcelian structure, and are quite depressed in form. 

 The median part of the series is more elongate than in the correspond- 

 ing vertebras of the genus Ganis. They exhibit an obtuse median longi- 

 tudinal angle, on each side of which, at a little distance, a nutritious ar- 

 tery entered by a foramen. The zygapophyses of the posterior lumbars 

 have interlocking articulations, the posterior with a convex exterior ar- 

 ticular face, the anterior with a concave anterior one. The sacrum is 

 not completely ijreserved ; three co-ossified centra remain. These are 

 more elongate and the diapophyses have less expansion than in Felis, 

 JEyoena, Ganis, orUrsus. They are much flattened, and the middle one 

 has two slight median longitudinal angles. The caudal vertebr£B indicate 

 a long tail, with stout base, Its proximal vertebrse are depressed, and 

 with broad anteriorly-directed diapophyses. The more distal vertebrse 

 have sub-cylindric centra ; the terminal ones are very small. 



The glenoid cavity of the scapula is shallow ,• the coracoid process is a 

 short hook separated by a strong groove from the edge of the former. 

 The spine is well developed. In the character of the- coracoid, this 

 genus resembles Felts more than Ganis or Ursus. The ulna exh.ibits 

 little trace of articular face for the radius, less than in Felis or Ganis. 

 Its humeral glenoid face is more convex transversely in its anterior or 

 vertical portion than in those genera, and a little more than in Ursus. 

 In the hind limb the femur resembles that of other Carnivora in all 



