A New Genus and Species in the Diplopod Family Nearctodesmidae from Illinois (Polydesmida)

Abstract

Ectopodesmus remingtoni, a new genus and species in the diplopod family Nearctodesmidae, is described from a cave in western Illinois. Heretofore the family has been known only from three genera in northwestern North America, a fact which lends particular impor- tance to the discovery of the new genus. Ectopodesmus resembles the known genera in external appearance, but differs in that the gonopod is provided with only one prefemoral process instead of two, presumably reflective of a more primitive condition. Additional points of difference are given between the families Poly- desmidae and Nearctodesmidae, and a key for separation of the four genera of the latter group is included. Ectopodesmus is considered to be a relict survivor from a much wider nearctodesmid distribution in the middle Tertiary. This earlier range has presumably been destroyed largely by the increasing aridity of central North America, and perhaps also to some extent by later glaciation. A collection of millipeds kindly entrusted to me for study by Dr. Charles L. Remington contains a single male which is clearly refer- able to the polydesmoid family Nearctodesmidae. Since this specimen differs in various ways from all three of the established genera in that family, I regard it as the type of a previously undefined generic category. The discovery of new genera of diplopods is in itself not particu- larly noteworthy, and scarcely warrants individual publication. The present instance, however, is of interest from the standpoint of zo- ogeography, since the specimen under consideration was collected in a cave in western Illinois, more than 1200 miles from the previously- known family range in northwestern United States and adjacen,t Canada! For this reason I venture to publish the names and diagnoses in advance of a badly needed, but not immediately foreseeable, revision of the family. I wish to express my appreciation to Dr. Remington for the oppor- tunity to examine the millipeds accumulated by him during the collec- tion of arthropods in other groups.