134 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



AA. Metatarsal article II with an apicral spine much exceeding segment ITT and 



often III and IV together. 

 B. Vertex and front very unusually bristled, with several rows of supernumerary 



bristles terrilnlk 



BB. Vertex and front with no more than the normal number of bristles. 

 C. Metatarsal article V with but four pairs of lateral spines on the mai'gins, tlie 



normal basal pair strongly dislocated toward the 

 median line and directed straight distad. 

 D. Eye vestigial; metathoracic notum fused with epimerum, and sternum with 

 episternum. 



¥.. Lal)ial paljii extending beyond trochanters divhus 



EE. Lal)ial palpi shorter than coxje , terinvs 



DD. Eyes distinct; metathoracic notum and sternum not fused with other parts. 



E. Metatarsal article I about equaling II, III, and IV together; bristles of 



metatarsus abnormally lengthened; labial palpi 



extending beyond trochanters tdcJiinum 



EE. Metatarsal article T equaling the three succeeding segments and three- 

 fourths of V together; bristles of metatarsi not 

 normally lengthened; metatarsal article I with 

 seven groups of spines on dorsal margin and five 

 on ventral; labial palpi shorter than the coxse. 



coloradensis 

 CC. Metatarsal article V with the spines all inserted in line on the margins, the 



first pair sometimes slightly bent inward. 



D. Eyes vestigial; second genal row with five bristles ujnoius 



DD. Eyes present; second genal row with one to three bristles. 

 E. Labial jialpi equaling coxae; one bristle in the second genal row., pet iolatus 

 EE. Labial palpi always extending to the femur and often nearly its whole 

 length. 



F. Hind tarsal article I equaling IT, ITT, and IV together Jxiccld 



FF. Metatarsal article I al)out e(iualing II and III together or less. 



G. Abdominal tergites with three rows of bristles hirsvfus 



GG. Abdominal tergites witli two rows of bristles. 



H. Claspers of male with ventral margin bearing three stout teeth and 



twoljristles pteantis 



HIT. Claspers of male with only bristles on ventral margin. 

 I. Claspers of male of a very short small, hemispherical type. 

 J. Claspers with bristles scattered along entire ventral margin. 

 K. Frontal notch very large, its lip projecting in the form of a 



tubercle tuheradatns 



KTv. Frontal notch small, its lip not projecting in the form of 

 a tubercle. 

 L. Labial paljii reaching at most to one-half of the anterior 

 femora. 

 M. Gena below eye pointed posteriori)'; on metatarsal 

 artidcle I with groups of spines 6-6; upper male 

 claspers distally obliquely truncate away from the 



body arizonensis 



MM. Genae below eye posteriorly subtruncate. 



N. Metatarsal article I with groups of spines 5-6; clas- 

 pers of male distally obliquely truncate away from 



body arctomys 



NN. Metatarsal article I with groups of spines 5-5; clas- 

 pers of niale distally gradually narrowed to a 

 jioint idahoensis 



