HISTORY OF THE CARNIVORA 535 



and was not overlapped and concealed by the great carnassial ; 

 the sabre-like tusk had not attained such great proportions. 

 The skull of ^Machairodus, the only part of the skeleton which 

 is definitely known, was hke that of ^Smilodon on a much 

 smaller scale, but more primitive in several respects. It was 

 longer and had a less capacious brain-case and less prominent 

 sagittal and occipital crests. The large tympanic bullae were 

 conspicuous in the side-view of the skull, as the processes for 

 the attachment of the neck-muscles had no such development 

 as in ^Smilodon. The descending flanges of the lower jaw 

 were larger than in the latter. 



The upper Oligocene (John Day) contained a large variety 

 of cat-like forms, of which no less than five genera have been 

 described ; one of them {\Pogonodon), nearly as large as a Lion, 

 would seem to have died out here without descendants, and 

 two others, to which we shall return later, so combined the 

 characters of true felines and fmachairodonts as to be of un- 

 certain reference. Two other genera, which are much com- 

 moner and better known, from the White River, will be described 

 from specimens of that stage. 



The White River, or lower Oligocene, had three highly 

 interesting genera of fmachairodonts, two of them known from 

 nearly or quite complete skeletons. One of these {^Hoylo- 

 phoneus), which was, it can hardly be doubted, the direct an- 

 cestor of the later typical fmachairodonts, had several species, 

 which are found in the various levels of the White River beds. 

 The largest of these species was considerably smaller than 

 \Machairodus, and the smallest and most ancient was inferior 

 to the modern Wild Cat. The number of teeth was variable, 

 but normally greater than in the genera above described, being 

 i\, c\, pf^f, mY,X2 =28-32. The foremost premolar in each 

 jaw was very small and often absent. The upper canine was 

 a long and curved, but very thin, scimitar, finely serrate on 

 both edges, while the lower canine was but little larger than 

 the incisors. The carnassial teeth had a significant Ukeness 



