SOUTH-WESTERN INSECTIYORES 
201 
less active and less vigorous types must have remained in their 
ancient western habitats. 
Among the order Insectivora which is now on its way 
towards extinction, several peculiar mammals, such as 
Atophyrax, Notiosorex and Scapanus are entirely western 
in range. The most noteworthy is what has been called the 
mole-shrew (Neiirotrichus), on account of its shrew-like look 
combined with its digging habits. The single species Nefiro- 
trichus gibbsi is a western rather than a south-western 
animal, being confined to northern California and Washington 
State. It has no near relations in America. Its nearest akin 
inhabit eastern Asia and Europe, but it has not yet been 
satisfactorily established to which of its two Old World 
branches it has most affinity. The whole group to which all 
these insectivores belong is known from the European 
Eocene onward. Nowhere else have fossils been found. 
Palaeontological evidence would, therefore, point to Europe 
as the centre of evolution. Possibly the ancestors of Neuro- 
trichus may have originated somewhere in the Mediter¬ 
ranean region, have crossed the Atlantic by a mid-Atlantic 
land bridge to California, as I shall explain later on, and have 
then passed to Japan, where a closely related genus occurs. 
The mole-mice (Onychomys), which are typical rodents, 
constitute a section which has evidently originated in the 
south-west, and has since spread northward and eastward so 
as almost to reach the Mississippi, though none of them have 
crossed this river. The wood-rats, belonging to the genera 
Nelsonia, Xenomys, Neotomodon, Teanopus and Hodomys 
are all confined to small areas in the south-west. The four- 
toed and the five-toed kangaroo-rats (Dipodomys and Pero- 
dipus) are almost all peculiar to the south-western States. 
Among the carnivores with a similar range may be men¬ 
tioned the raccoon foxes (Bassariscus) and the western skunks 
(Conepatus). 
The most striking examples tenanting the ancient south¬ 
western land areas must be looked for, as I remarked, among 
the more sessile and slow-moving creatures. The reptiles and 
amphibians yield good instances. Among the former the most 
noteworthy is the so-called “ Gila monster,” a repulsive, stout, 
thick-tailed lizard. It has gained the unenviable notoriety 
