Mexican Amphibians and Reptiles. 113 
The vertebrate fauna of the high Mexican mountains comprises 
no species which are dereliets of an Arctic or Boreal fauna, such as 
is supposed to exist elsewhere on high mountains within the tropies. 
The limit of glaciation remained about 20 degrees to the North off 
the Mexican peaks, a distance like that from London to the Sahara 
or New York from Cuba. Glaciation absolutely exceludes Reptilian 
and Amphibian life. No doubt there was a cool belt bordering the 
elaciation of North America, giving the creatures a lead onto the 
Mexican plateau, or onto and along the Sierras madres which at 
that time may have had a cooler climate than at the present time. 
At an altitude of 10000 feet, on Mexican mountains, the annual 
mean temperature works out at 11—12° Centigrade (with a January 
mean of 8° C) like the mean of the coast of California, and taking 
into account the rather limited fluctuation of summer and winter, 
and the prevailing moıst climate, the Mexican 10000 ft. level resembles 
muen that of the coast between San Francisco to Vancouver. At 
this level on the Mexican mountains snow is common enough, sometimes 
Iying for weeks, and only during this time reptilian life is suspended 
in the dominant pineforests mixed with evergreens and some deciduous 
trees like Oaks, Alder and Arbutus. 
Our fauna at and above this level consists of the following. 
Hylodes rhodopis 
Thorius pennatulus 
Spelerpes orizabensis 
Spelerpes leprosus 
Spelerpes chiropterus 
Gerrhonotus imbricatus 
Sceloporus microlepidotus 
Sceloporus scalaris 
Sceloporus aeneus 
Tropidonotus scalaris 
Tropidonotus ordinatus 
Crotalus triseriatus. 
Hylodes, as a Southerner, does not count, and we will sink the 
supposed difference between the five Sonorans and the five Nearctic 
species. Every one of the five genera has some species living in the 
United States, but only one of the 10 species occurs also in the 
States, and this species, Tropidonotus ordinatus has such an enormous 
range, from Canada to Guatemala and from sealevel to 12000 feet, 
that it is of no value in our question. Further, species which also 
