MILLIPEDS OF THE OKDEK COLOBOGNATHA, WITH 

 DESCRIPTIONS OF SIX NEW GENERA AND TYPE 

 SPECIES, FROM ARIZONA AND CALIFORNIA 



By O. F. Cook and H. F. Loomis 

 Of the Bureau of Plant Industry, United States Department of Agriculture 



INTRODUCTION 



A special interest may be claimed for millipeds of the order Colo- 

 bognatha as examples of interrupted or residual distribution, in 

 widely separated regions which could not be reached by any method 

 of transportation now at the disposal of these animals. The expla- 

 nation for such facts of distribution is to be found by tracing back to 

 former ages of the world when vegetation and surface conditions 

 must have been widely different from those of the present time. The 

 Oolobognatha have greater environmental limitations than the mem- 

 bers of most of the other orders, though the habits and living 

 requirements are remarkably uniform through the whole class of 

 millipeds. 



From the general uniformity of habits at the present time it may 

 be inferred that a similar uniformity existed in the past, and that 

 the requirements for existence and survival have been much the same 

 during the whole period of biological history of the group, or since 

 their world-wide distribution was attained. 



In comparison with most of the other millipeds, the Colobognatha 

 are delicate, fragile, slow-moving creatures, unable to burrow in the 

 soil or to withstand surface exposure. The legs and other appen- 

 dages are very short and unspecialized, and restricted food habits are 

 indicated by minute, rudimentary mouth parts. 



The outstanding requirement for the existence of delicate humus 

 animals is a continuous supply of moisture, not necessarily a regular 

 supply, but one that is never completely interrupted, or the creatures 

 at that place are exterminated. Thus the existence of humus fauna 

 is an evidence of the moisture continuity of any locality, and may 

 afford a better assurance regarding local conditions in the humus 

 layer than is obtainable in any other way.^ 



1 Cook, O. F. Notes on the distribution of millipeds in southern Texas, etc. Proc. 

 U. S. Nat. Mus., vol. 40, pp. 147-167, 1911. 



No. 2714.— Proceedings U. S. National Museum, Vol. 72, Art. 18 



58237—28 1 1 



