204 
ORIGIN OF LIFE IN AMERICA 
Arizona, while a third, the rubber boa or silver snake actually 
passes into Washington State and central Nevada. 
The recent increase of dryness in the south-west has no 
doubt affected the original fauna considerably. Semi-aquatic 
forms and aquatic ones have either been destroyed or forced 
to take refuge in the neighbouring States where climatic con¬ 
ditions were more favourable. To this cause may be attri¬ 
buted the present scarcity of amphibians in most of the south¬ 
western districts, where many of them, we may presume, 
originally had their headquarters. The only American mem¬ 
ber of certain toads, which on account of the peculiar shape 
of their tongues have been called Discoglossidae, occurs in 
Washington State in western North America. This family 
has always been looked upon with particular interest, because 
to it belongs the solitary amphibian known from New Zealand. 
This toad (Liopelma) must have reached New Zealand, ac¬ 
cording to Dr. Stejneger,* before Cretaceous times by means 
of a very ancient land connection with the north. The same 
author expresses the opinion that the Himalayan Mountains, 
or rather the region to the south-west of them, was the ori¬ 
ginal home of these discoglossoid toads, and that they spread 
from there to New Zealand and North America. On the latter 
continent we still find, as I remarked, a single genus of the 
Discoglossidae (Ascaphus). The present centre of dispersal 
of these discoglossoid toads is southern Europe, since three 
genera are found there, viz., Discoglossus, Alytes and Bom- 
binator. The first two are strictly European, whereas a single 
species of Bombinator also inhabits northern China and Korea. 
Considering the fact that these toads do not occur in south¬ 
western Asia, and that both Discoglossus and Bombinator 
have been found in European Miocene beds, the Mediter¬ 
ranean Region seems more likely to have been the original 
centre of dispersal than south-western Asia. At any rate, 
that event leads us, no doubt, to the dim and distant past of 
the early part of the Mesozoic Era. 
The allied family Pelobatidae is likewise of great faunistic 
interest, as the two genera Scaphiopus of North America and 
Pelobates of Europe are only, distinguished by slight differ- 
* Stejneger, L., “Distribution of Discoglossoid Toads,” pp. 91 — 93. 
