DESCRIPTIONS AND DETERMINATIONS OF SPECIES 



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fornicus (Inverness, Marin county, Freestone and Cazadero, Sonoma 

 county, Gualala and Mendocino City, Mendocino county, Calif.), Micro- 

 tias sp. (South Yolla Bolly Mt., Tehama county, Calif.), Microtus mor- 

 dax (Tuolumne Meadows, Calif.), and Phenacomys sp., (Mendocino 

 City, Calif.). We also have specimens from Epimys rattus, taken in In- 

 dia, and Mus sp. from Java. Osborn records it from the domestic rat at 

 Ames, Iowa, and it has been recorded from various species of rats 

 throughout Europe and Africa. 



Comparison of the California specimens with those from India, to- 

 gether with reference to Fahrenholz's excellent paper upon this and other 

 closely related species, enable us to be reasonably certain of our deter- 

 minations. There are certain differences between the specimens from 

 the various species of Microtus and Phenacomys and those from the rats, 

 but these differences are on the whole so slight and so intangible, consist- 

 ing merely of very small modifications of the shape and relative propor- 

 tions of the head and sternal plate, that we do not feel justified in basing 

 even a new variety upon them. 



Polyplax auricularis n. sp. 



Plate I, fig. 4 ; plate IV, fig. 8 ; text fig. 2. 



One female, one male and two larvae from a single individual of 

 Peromyscus maniculatus rubidus, (Inverness, Marin county, Calif.), and 

 two females from Peromyscus sitchensis prevostensis (Forrester Island, 

 Alaska, coll. Dr. Harold Heath), all referable to this curious species. It 



-Polyplax auricularis n. sp. ; head and ventral side of terminal segments 



of female. 



