54 LAND MAMMALS IN THE WESTERN HEMISPHERE 



termination -idee, while that for the subfamily is -inoe. To 

 take an example, all the genera of cats, living and extinct, are 

 assembled in the family Felidse (from the genus Felis) which 

 falls naturally into two subfamilies. One of these, the Felinse, 

 includes the true cats, a very homogeneous group, both the 

 existing and the extinct genera ; the other subfamily, that of 

 the highly interesting series of the "Sabre-tooth Tigers," 

 called the fMachairodontinse, comprises only extinct forms. 



The fourth principal rank or grade is the order, distin- 

 guished by some fundamental peculiarity of structure and 

 usually including a large number of families. Some of the 

 orders, however, contain but a single family, a single genus, 

 or even, it may be, a single species, because that species is in 

 important structural characters so unlike any other that it 

 cannot properly be put into the same order with anything else. 

 Such isolation invariably implies that the species or genus in 

 question is the sole survivor of what was once an extensive 

 series. As in the case of the family and the genus, it is often 

 necessary to recognize the degrees of closer and more remote 

 affinity by the use of suborders. Existing Artiodactyla, or 

 even-toed hoofed animals, an enormous assemblage, may con- 

 veniently be divided into four suborders : (1) Suina, swine and 

 the Hippopotamus ; (2) Tylopoda, the 'Camel and Llama ; 

 (3) Tragulina, "mouse-deer," or chevro tains; (4) Pecora, or 

 true ruminants, deer, giraffes, antelopes, sheep, goats, oxen, 

 etc. In nearly all of the orders such subordinal divisions are 

 desirable and it is frequently useful to employ still further 

 subdivisions, like superfamilies, which are groups of allied 

 families within the suborder, sections and the like. 



In the Linnsean scheme, the next group in ascending rank 

 is the class, which includes all mammals whatsoever, but the 

 advance of knowledge has made it necessary to interpolate 

 several intermediate grades between the class and the order, 

 which, in the descending scale, are subclass, infraclass, cohort, 



t Extinct. 



