GEOLOGICAL SURVEY OF THE TERRITORIES. 561 



Measurements. 



M. 



Depth ramus at pennltimate molar. 0. 00.*iO 



Length Clown ofpcuultinKite mohsr , . 0040 



Elevation crown ot penultimate molar (.0^5 



Width crowu of penultimate molar 00;}'i 



Fouucl on Black's Fork of Greeu River. An ally of ^typolojjhns and 

 Triacodon. 



This s[)ecies ai)penrs to beloni;- to the genus Vircrravus of Marsh, 

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

 Miacis, \v])ich thus becomes a synonym. The species is dilierent from 

 those described by that author. 



u>;gulata. 



In no group of Mammalia have the determinations of paleontology 

 been more significant 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 faunae 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 f .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 ty])es have been distinguished on 

 this basis, viz: the Aiiiodactyla, FcHssodactyla, and the ProboscidUt ; 

 with some of lesser importance, those of the Toxodontia and E>jra- 

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

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

 in the Artiodaciijles the differences between the Uuminantia and Omni- 

 vorttj and in Pcrissodactyla, between Equus and Bhinoceros. In either 

 order canines and incisois 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 Uuminantia come Orcodon, Dlerycoijotamus^ Tra(j}dus^ &c. 

 In Perissfxlactyla, Andiitheriiim, Fahvosyops, ibc, 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 oiiiitwn characterizing the two orders above mentioned. These char- 

 acters are so striking in their api^earauce as to suggest greater systematic 

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

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

 the tapir alone possesses it. Kor are the complex molars and large tusks 

 to be regarded as a definition, lor in the Fhacocharus we have molars as 

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

 below; 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 {Bhinocerus) to almost nothing, [Equus.) , 



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

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



*V\deG\\\, Arrangement of the Families of Mammals, Smithsou. Misc. Coll., 1872,. 

 No. 230; the best analysis of the Mammalia yet published. 



36 G s 



