GEOLOGICAL SURVEY OF THE TERRITORIES. 5G1 



Measurements. 



M. 



Depth ramus at penultimate molar 0. 00i=!0 



Length crowu of penultiniate molar ()040 



Elevation crown of penultimate molar (1025 



Width crown of penultimate molar 0033 



Found on Black's Fork of Green Eiver. An ally of Slypolophus and 

 Triacodon. 



This species appears to belong to the genus Viverravus of Marsh, 

 "which bears date July 22, 1872, consequently sixteen days earlier than 

 Miacis, -which thus becomes a synonym. The species is dili'erent from 

 those described by that author. 



UNGULATA. 



In no group of Mammalia have the determinations of paleontology 

 been more siguificant than in the Ungulata. Here, in an especial manner, 

 the anticipations of science have been realized, in the filling up of the 

 numerous gaps in the series of living forms. Here especially is it evi- 

 dent, that the existing fauna is but a fragment, and that the faunse of 

 the past, as we know them to-day, are but the precursors of what we may 

 bring to light to-morrow. 



The primary range of variation in t\e structure of the Ungulata has 

 been generally admitted by zoologists to be found in the structure of the 

 limbs and feet. Three most prominent types have been distinguished on 

 this basis, viz: the Ariiodactyla, Perissodactyla, and the Froboscidia ; 

 with some of lesser importance, those of the Toxodontia and Hyra- 

 coidea* If we direct our attention to the detailed structure of the feet, 

 or of the teeth, each division oifers its own range of variation ; witness 

 iu the Artiodaciyles the differences between the Buminantia and Omni- 

 vora, and in Perissodactyla, between Equus and Ehinoceros. In either 

 order canines and incisors may be present or absent, and molars assume 

 a great variety of patterns of enamel plication. The toes in the latter 

 order may vary from four to one. Nevertheless, the most diverse genera 

 are bound together by intermediate forms, often extinct. Connecting 

 Omnivora and Ruminantia come Oreodon, Merycopota^nus, Tragulus^ &c. 

 In Perissodactyla^ AncMtherut,ni, Falceosyops, &c,, connect the extremes. 



The Proboscidians have, on the other hand, remained until recently an 

 isolated group with but few representatives, hence its definition as an 

 order has been more or less obscured by characters of a special nature, 

 drawn from the dentition, trunk, &c., which it has been found necessary 

 to omit in characterizing the two orders above mentioned. These char- 

 acters are so striking in their appeanmce as to suggest greater systematic 

 importance than belongs to them. Thus the trunk is not more imjiortant 

 as a character of the Prohoscidia, than it is of the Ferissodactyla, where 

 the tapir alone possesses it. Nor are the complex molars and large tusks 

 to be regarded as a definition, for in the Fhacochcerus we have molars as 

 compound as in some mastodons, huge canine teeth, and no incisors 

 belovv^; characters very different from many Artiodactyles. Nor can we 

 regard the exclusive union of the astragalus with the navicular as a 

 final test, for in Perissodactyles the facet for union with the cuboid may 

 be considerable (Rhinocerus) to almost nothing, {Equus.) 



The occasion for this discussion is presented by the discovery by the 

 paleontologists of Hayden's geological surveys of 1871-'72, of the remark- 



*Vide(ji\\, Arrangement of the Families of Mammals, Smithson. Misc. Coll., 1872;, 

 Xo. 230; the best analysis of the AlainmaUa yet ijublished. 



36 G s 



