This report is based on the examination of 256 specimens representing the entire known geographic range of the species. I am indebted to H. E. Anthony, Remington Kellogg, C. C. Sanborn, and Stanley P. Young for the privilege of examining specimens in their charge. The study here reported upon was aided by a contract between the Office of Naval Research, department of the Navy, and the University of Kansas (NR 161-791). The specimens in the University of Kansas Museum of Natural History were obtained by field work supported by the Kansas University Endowment Association. _Transmitted December 6, 1951._ 24-2174