CAMBAI.OID MILLIPEDS LOOMIS 29 



]ated localities from a common and widespread ancient fauna, as in 

 the eastern region. That the climatic and other changes that sepa- 

 rated and restricted different parts of the western fauna occurred 

 very long ago is shown by the many closely related species that 

 have been found, for evolutionary changes sufficient to establish 

 species undoubtedly take places more slowly in animals living under 

 uniform conditions, as do the millipeds, than in animals whose en- 

 vironment is less stable. The relatively large number of generally 

 small but closely related genera among the western millipeds is still 

 better proof of the long isolation that has existed between parts of 

 the fauna, for a still greater length of time is required for the ac- 

 complishment of changes of such magnitude as require generic 

 recognition. 



The 20 species of millipeds of the suborder Cambaloidea found 

 in the United States are arranged in 12 genera, of which 9 are mono- 

 typic and 3 each contain three or four species. Of these 12 genera, 

 9, containing 11 species, are strictly Callfornian; another genus of 

 four species has three of them in California and one in Utah; one 

 monotypic genus is confined to Tennessee; and last is the genus 

 Cainbala, most widely distributed of the American group, with its 

 four species scattered through many of the Eastern States, Texas, 

 and Arkansas. Thus, approximately three-fourths of the members 

 of this suborder are limited to the relatively very small area of Cali- 

 fornia, while all the rest of the United States contributes only one- 

 fourth to the population of the suborder. 



The material examined in the preparation of the present paper 

 Avas collected principally by Dr. O. F. Cook, with a lesser amount 

 collected by the writer and several of his friends. Most of the ma- 

 terial plainly belonged to the family Cambalidae, but also included 

 were four species, apparently new, that it has been necessary to re- 

 fer to the Cambalopsidae, a family associated with India and the 

 Malayan region and hitherto unknown in the Western Hemisphere. 

 The wide removal of the American from the Asiatic branch of this 

 family is, at present, lacking definite proof for explanation, but in- 

 creased knowledge of the millipecl faunas of China, Japan, Siberia, 

 and northwestern North America may indicate past connections, 

 although such evidence may no longer be found except in fossil 

 forms. 



Separation of the Cambalopsidae from the older Cambalidae has 

 been made principally on the basis of the species in the former group 

 having an entire or undivided mentum, while the latter group is 

 characterized by species in which the mentum is transversely di- 



