SOUTH-WESTEBN INSECTIVOEES 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 (Neurotrichus), on account of its shrew-like look 

 combined with its digging habits. The single species Neuro- 

 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 

 tranches 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 



