28 
ORIGIN OF LIFE IN AMERICA 
small carnivores and a variety of the black bear (Ursus 
americanus).* * * § 
The small mouse-like creatures belonging to the genus 
Synaptomys are aptly called £ ‘ lemming-voles ” because, ex¬ 
ternally like lemmings, their teeth approach those of voles. 
When Dr. Merriam undertook his revision of the species of 
Synaptomys,f seven kinds were known to him. A few more 
have since been discovered. The genus is entirely confined to 
the North American continent, and all the species except two 
have a limited range in the boreal region. One of the latter 
(Synaptomys cooperi) is found from Massachusetts westward 
to Minnesota and southward to North Carolina, the other is 
peculiar to Moimt Washington. Almost all the other species 
are confined to Canada and Alaska. It does not seem, there¬ 
fore, as if Synaptomys innuitus, which inhabits the coast of 
Labrador, were a recent immigrant from the south. On the 
contrary, the genus Synaptomys, being almost confined to the 
north, is probably of boreal American origin, one adaptable 
species having advanced far southward along the east coast 
of America. 
The next two species alluded to, Microtus enixus and M. 
pennsylvanicus, are true voles, though the last-named animal 
is generally known in the States by the name of “ meadow- 
mouse.” Both of them belong to a sub-genus which is 
very widely spread in Europe, Asia and boreal North 
America, i Some migrations across ancient land connections 
must have taken place, no matter whether we assume that the 
sub-genus is of Old World or New World origin. It only 
remains for us to determine whether Microtus crossed the 
North Atlantic land bridge or the one supposed to have been 
situated at Bering Strait, assuming that there was such a one. 
Professor Tullberg thought the members of the genus Microtus 
had travelled to America in Pliocene times by means of the 
first land bridge. § This view does not appear to me pro¬ 
bable, because the family is entirely absent from Ireland, 
* Bangs, 0., “ Mammals of Labrador.” 
t Merriam, C. H., “ Revision of Synaptomys.” 
\ Bailey, V., “ Revision of Microtus.” 
§ Tullberg, Tycho, “System der Nagetiere,” p. 499. 
