NOTES ON THE DISTRIBUTION OF MILLIPEDS IN SOUTH- 

 ERN TEXAS, WITH DESCRIPTIONS OF NEW GENERA 

 AND SPECIES FROM TEXAS, ARIZONA, MEXICO, AND 

 COSTA RICA. 



By O. F. Cook, 



Of the U. S. Department of Agriculture. 



DISTRIBUTION OF MILLIPEDS IN SOUTH TEXAS. 



The millipeds and other primitive types of humus-inhabiting 

 arthropoda constitute a living summary of the biological conditions 

 and history of the soil. The environmental limitations of the milli- 

 peds render this group of animals especially interesting from the 

 standpoint of geographical distribution. It is impossible for these 

 creatures to exist or to extend their distribution over areas where 

 there are no accumulations of humus or other vegetable debris that 

 can retain a permanent supply of moisture. As these animals are 

 unable to fly, or even to run with rapidity, and can not endure 

 exposure to extremes of light, heat, or drought, thc} r afford unusually 

 direct evidence regarding the earlier extension of forests or other 

 conditions that would determine their geographical distribution. 



Attention has been called in a previous publication to the persist- 

 ence of tropical types of humus-inhabiting organisms in certain 

 localities in south Texas, as an evidence of permanent moisture in 

 the soil. The existence of such oases of permanently moist humus in 

 regions where desert conditions otherwise appear so nearly universal 

 has been taken to indicate a much greater extension of forest growth 

 in south Texas in former times. Without assuming a previous 

 extension of forest conditions it is difficult to imagine how animals 

 that require permanently moist humus could have reached the isolated 

 localities where they now exist. 1 



Reference was made in a previous paper to a spot a little to the 

 northeast of the town of Falfurrias, Texas, as one of these oases where 

 the existence of permanent moisture had made possible the survival of 



i Change of Vegetation on the South Texas Prairies, Circular No. 14, Bureau of Plant Industry, TJ. S. 

 Department of Agriculture, 1908. 



Proceedings U. S. National Museum, Vol. 40— No. 1810. 



147 



