ORIGIN OF THE GARTER SNAKES 
129 
from north Australia through the Malay Archipelago and 
northward to Japan. Westward it extends to India, Africa 
and Europe. In America the genus occurs principally 
in the eastern States, but there is also a species in Cuba 
and several in Central America. None have penetrated 
to South America. From Hr. Boulenger’s * catalogue and 
Dr. Stejneger’s description of Japanese forms,f it seems 
evident that the east Asiatic forms are not very closely 
related to the American ones. On the other hand, Tro¬ 
pidonotus validus, from Lower California, Arizona and 
Mexico, is nearly akin to the west European Tropidonotus 
viperinus, whose high antiquity is indicated by its occur¬ 
rence in Sardinia and Algeria. I may have another oppor¬ 
tunity later on of dealing with this interesting genus, but 
it must be conceded that although we possess no fossil 
evidence, the origin of Tropidonotus must date back at least 
to the commencement of the Tertiary Era. In another chapter 
I shall show how extraordinarily intimate is the relationship 
of the south-west American and the West European faunas. 
Evidence will then be given in support of the theory that 
southern Europe and the south-western parts of North 
America have been connected with one another by land, and 
that we probably owe the resemblance in the animals prnd 
plants of these two regions to that fact. The species of 
Tropidonotus, in America at any rate, are semii-aquatic. They 
are so much attached to water that they are popularly known 
as “ water-snakes,” whereas the garter-snakes are much less 
bound to the neighbourhood of water. The latter are not 
uncommonly found on higher ground and in drier situations, 
a change in the climatic conditions of the south-west may thus 
originally have given rise to the Thamnophis branch from the 
original Tropidonotus stock. The headquarters of Tropi¬ 
donotus now lie in the eastern States, where the conditions 
for its existence are more favourable than in the south-west. 
All the same, it seems probable that the original centre of dis¬ 
persal was in the south-west, for when Tropidonotus arrived 
* Boulenger, G. A., “ Catalogue of the Snakes in the British Museum,’. 
Vol. 1. 
t Stejneger, L., “ Herpetology of Japan,” pp. 264—294. 
L.A. 
K 
