364 THE SONORAN REGION. [CHAP. 



systems already mentioned [Alleghanies, Rocky Mountains, and 

 Cascade and Sierra Nevada ranges] ; while to the southward it 

 occupies the great interior basin of Mexico, and extends into the 

 tropics along the highlands of the interior. It covers also the 

 peninsula of lower California, the southern part of which seems 

 entitled to rank as an independent subdivision." 



Later it is stated that the region "may be divided by tempe- 

 rature into two principal transcontinental zones, Upper Sonoran 

 and Lower Sonoran ; and each of these in turn may be subdivided 

 into arid and humid divisions." 



The proposal to form a separate region for such an insignifi- 

 cant area as the southern extremity of California seems unnecessary, 

 although its fauna may differ considerably from that of the typical 

 Sonoran. 



Omitting mention of the bats, the mammalian genera charac- 



Characteris teristic of the Sonoran region may now be taken into 



tics of Mam- consideration. Commencing with the Insectivora, 



tnalian Fauna. , , .. 



the Sonadcz are represented by the peculiar genus 

 Notiosorex, which is closely allied to the Oriental Soriculus, 

 but has only 28 in place of 30 teeth. Of this genus the two 

 species do not range north of this region, although they also 

 enter Central America 1 . The short -tailed, or earless shrews 

 (Blarina), with either 32 or 30 teeth, are also mainly Sonoran, 

 although ranging northwards into the Holarctic, and southwards 

 into Guatemala. In the Talpida the three species of the mole-like 

 genus Scalops, characterised by having 36 teeth, webbed hind feet, 

 and a short and nearly naked tail, are mainly Sonoran, although 

 passing into the Transition zone. On the other hand, the two 

 species of Scapanus, distinguished by the possession of 40 teeth, 

 and the hairy tail, have a distribution very similar to Blarina, 

 although they do not enter Central America. 



In the Carnivora the raccoon-family (Procyonidce) is very 

 strongly represented, although none of the genera are absolutely 

 peculiar to the region. The genus Bassariscus a near ally of the 

 true raccoons, and possessing two species is nevertheless mainly 

 Sonoran, although it ranges into the Transition zone of the 



1 Teste Dobson. 



