162 PROCEEDINGS OF THE NATIONAL MUSEUM vOL. 106 



Dorsal setae: Shafts of setae moderately heavy; rather short 

 setules cover shaft well but not densely; anteriorly, the side 

 adjacent to body is nude; posteriorly, setules distributed around 

 the shaft; posteriors end bluntly or with V-clefts. Length of 

 humerals, 43 to 50; of setae near the middle of the first post- 

 humeral row, 38 to 44 ; of setae in the posterior group, 33 to 38. 

 Dorsal formulae of the five specimens studied from Ravalli 

 County, Oreg.: 



2 . . 10 . . 13 . . . . 15 . . 8 . . 6 . . 2 



2 . . 10 . . 13 . . . . 11 . . 8 . . 8 . . 7 



2 . , 10 . . 12 . . . . 14 . . 9 . . 7 . . 5 



2 .. 10 .. 12 .. .. 12 .. 8 .. 6 .. 5 



2 . . 10 . . 10 . . 2 . . 10 . . 10 . . 7 . . 5 



Ventral setae: Poststernals similar to dorsals. Number of 

 first sternals, 2; of second sternals, 4; of poststernals, 57 to 71. 

 Length of first sternals, 35 to 42; of second sternals, 25 to 32; 

 of setae near the middle of the first poststernal row, 21 to 24; of 

 setae in the posterior group, 32 to 42. 



Material: Five paratypes studied. The four collected Oct. 

 16, 1945, are in the U. S. National Museum; the one collected 

 Feb. 6, 1946, was borrowed from Rocky Mountain Laboratory. 

 Specimens from hosts, all in Montana : 



Peromyscus m. arteviisiae 



Ravalli County: Oct. 16, 1945, 4. 



Peromyscus 



Ravalli County: Feb. 6, 1946, 1. 



Seasonal DISTRIBUTION : Brennan (1948) reported collections 

 in February, May, and October. 



Geographical distribution : E. cordiremus has been collected 

 only in Ravalli County, Mont. (fig. 4,a). 



Diagnosis: E. cordiremus is the only species with four setae 

 in the second sternal row. It is quite similar to E. Tjeromysci. 

 In E. cordiremus the enlarged portion of the sensilla is less 

 sharply distinct from the pedicel than it is in E. peromysci. The 

 galeal seta of E. cordiremus lacks the bristlelike appearance 

 which characterizes the galeal seta of E. 'peromysci. 



Remarks: Advantage has been taken of the similarity of E. 

 cordiremus to E. peromysci in the description of the former. 

 The two might easily be considered to form a group. 



The **ruhrd!* group 



The "rubra" group, as it is now known, is composed of three 

 new species, with one of these divided into two subspecies. Diag- 

 nostic features of the group include: Tibiala III present, two 

 genualae I, subterminala and parasubterminala I present, papal 

 claw with three prongs, galeal seta usually branched, two pairs 



