18 
NEW YORK ZOOLOGICAL SOCIETY. 
the type genus Felis are nearly all closely related, and vary in 
size and color rather than in structure. 
The sabre-toothed tigers were in North America in the Plio- 
cene, and entered South America in numbers at that time. 
Recent discoveries indicate an American line of sabre-tooths 
back to the Lower Oligocene and perhaps earlier, and one genus, 
Smilodon , existed until comparatively recent times, even as late 
as the Middle Pleistocene. 
The type genus, Felis, occurs doubtfully in the Upper Miocene, 
and certainly in the Pleistocene, but this genus undoubtedly 
achieved its development in Asia, and thence spread throughout 
the world. 
To the puma is probably to be assigned a rather more recent 
development, as, while it ranges from Canada to Patagonia, the 
local races which have arisen are all of doubtful value. Closely 
related fossil forms, however, suggest a possible American origin 
of great antiquity on this continent. 
In America, the genus Lynx, which is a thoroughly northern, 
possibly boreal, type, contains three well-marked species, L. can- 
adensis, L. rufus, L. baileyi, the last a western form, together 
with ten or more subspecies. All are closely related to European 
forms. 
RODENTS. 
Of the great order of Rodents, two interesting families are 
confined to North America. The curious sewellel, or mountain 
beaver, Haplodon, is surely of American origin. It has no near 
relatives outside of North America, and can probably be traced 
back, through Lower Miocene forms, as far as the Oligocene. 
The Geomyidae or pouched rats are also peculiar to America. 
Of the true Mnridae, the genus Fiber, the muskrat, goes back to 
the Lower Pleistocene. Since it is closely related to the voles, 
Arvicola, it also is probably of Eurasian origin. 
As has been already mentioned, the porcupines represent a 
peculiar group of South American rodents, which has now at- 
tained a world-wide distribution, and is interesting as the sole 
contribution of South America to the fauna of Eurasia and 
Africa. The genus Erithizon may have been developed in North 
America, but the ancestral type unquestionably came from the 
south. 
