AKT. 18 NEW GE15TEEA OF MILLIPEDS COOK AFD LOOMIS 6 



are represented from six separate districts. Only one genus in 

 California is shared with the Eastern States.^ 



A genus HypozoniuTn, closely related to Pol'j/Boniwm, was de- 

 scribed in 1904 from Seattle, Wash, One of the new genera described 

 on a later page was found by the writers in the fall of 1919, on 

 Mount Tamalpais, near San Francisco, Calif. Three other genera 

 were distinguished in a remarkable collection of millipeds from a 

 small area in Plumas County, Calif., obtained in the winter of 

 1922-23, by H. S. Barber, of the Bureau of Entomology. Although 

 this collection included only five species, four of them belonged to 

 the Colobognatha. Three of the species had to be treated as distinct 

 genera, while the fourth is referable to the genus Brachycybe, known 

 also from the Eastern States. In October, 1924, another member of 

 this order was collected in the Pinal Mountains of southern Arizona, 

 the first specimen being secured by L. K. Lytton and others from 

 the same locality by the writers. This animal belongs to a distinctly 

 tropical family, Siphonophoridae, not previously known to exist in 

 the United States.^ 



The species from Mount Tamalpais was found in loose stony soil 

 under a layer of oak leaves on the western slope of the mountain not 

 far from the redwood forest known as Muir Woods. Equable condi- 

 tions are maintained in the coast districts by the breezes and fogs 

 from the ocean. The survival of the redwood and giant sequoias 

 in the coast belt of California show that climatic conditions have 

 remained nearly the same for long periods, though the trees are 

 reckoned as survivals of a former age of wider extension of forests, 

 when the vegetation generally was more luxuriant if not more tropical 

 in character. The forest fires and the periodical burnings of brush- 

 land and grasslands undoubtedly have been the chief restricting fac- 

 tor during the period of human occupation. Changes of climate 

 have been alleged, but changes of vegetation may have been 

 sufficient to localize such types as redwood trees and millipeds in the 

 few places that have afforded continuous protection through the 

 centuries. 



Whether the humus fauna in California was derived from tropical 

 America or from other land masses of the ancient world is hardly to 

 be conjectured at present, but it is worthy of note that the nearest 

 relatives of the milliped from Mount Tamalpais are in the Mediter- 

 ranean region, not in other parts of America. 



A southern origin or alliance may be claimed for the milliped froni 

 Arizona, which belongs to a family widely distributed in the Tropics 



'- An additional genus, Gosodesmus Chamberlin, related to Brachycybe, was described in 

 1922 from southern California. Its characters are given at the end of this paper.. 



^ Another member of this family was found still farther north in California, in Novem- 

 ber, 1926, while the paper was awaiting publication, so that two new genera ol 

 Siphonophoridae are included. 



