692 Hans Gapow, 
satisfied with sorting them roughly into six groups. Those which 
are found only in the cool or cold regions; those found in these 
and in the temporate zone; in the cool, temporate and hot zones; 
in the temporate zone only; in the temporate and hot; and an 
in the hot zone only. 
The lines of demarcation are quite arbitrary. The Hotlands 
extend, according to the practical usage of the Mexicans up to about 
3000 ft., while everything beyond 7000 ft. or 2000 m can safely 
be considered within the cool zone. 2000 m of altitude corresponds 
with a lowering of the annual mean temperature of 10° Centigrade, 
a difference equal to that prevailing between London and Algeria, 
or New York and New Orleans. 
For the present paper I have endeavoured to compile a list ot 
those species of which the range of altitude may be considered as 
tolerably well ascertained, say within 1000 feet or 300 meters. 
In addition to my previous journeys I have since spent six months 
from April to September 1008 in the State of Chihuahua, visiting the 
Western Sierra Madre of the Tarakumare, and chiefly in the State 
Michoacan with such attractive and varied features as the hot 
depression of the Balsas basin with the wonderful Jorullo volcano, 
the delta of the Balsas, and the mountain of Tancitaro which rises 
to 13000 feet above the level of the sea. — It was not easy to 
collect the data and the total member of species falls short of 100. 
It could have been rounded up to 100 by the addition of the Crocodile, 
Caiman, and a few species of Cinosternum which had been omitted 
accidentally, but frankly I felt uneasy that such a round number 
might look suspieious and after the endless collations and calculations 
had been made and began to yield such unexpectedly good, reason- 
able results, I feared that additions might not be free from bias. 
Although my own personally collected material comprises about 
150 species, I do not feel sure about the range of more than 56 to 
60 of these, less than half! SumicHrast (in: Arch. Sc. nat., 1873, 
p. 233—250) has published a paper on the distribution of snakes in 
South Eastern Mexico and he is the only one who has paid special 
attention to this matter. I had therefore to resort to the localities as 
reported in the literature, in many cases not at all a safe guide, 
fairly reliable only when the species had been reported from many 
localities, or by such careful eolleetors as the veteran Ducks of 
Guanajuato or Dr. Merk of Chicago. Far too many species are known 
from a few localities only and had therefore ‘to be left out, also 
