CHIGGERS — ^FARRELL 179 



AW 59-63, mean 61.3; PW 79-82, mean 80.5; AP 15-19, mean 17 

 SB 21-27, mean 24.8; ASB 22-22, mean 22; PSB 13-16, mean 13.8 

 AL 32-41, mean 86.3; AM 29-31, mean 30; PL 44-46, mean 45.3 

 S 31-35, mean 32.7. Width of head of sensilla in two specimens, 

 14 and 16. 



Eyes: Two pairs lateral to the posterolateral setae. Diameter 

 of anteriors, 10 to 13, mean 12; of posteriors, 10 to 12, mean 

 10.7. 



Dorsal setae : Uniformly covered with short setules on side op- 

 posite body, any on edges closer to body appear heavier ; all setae 

 of the same general pattern. Length of hiimerals, 48 to 57; of 

 setae near the middle of the first posthumeral row, 42 to 48; of 

 setae in the posterior group, 32 to 34. 



Dorsal formulae for four specimens from Beaverhead County, 

 Mont. : 



Ventral setae : Poststernals generally similar to dorsals in form. 

 Number of first sternals, 2 ; of second sternals, 2 ; of poststernals, 

 41 to 54. Length of first sternals, 42 to 48 ; of second sternals, 28 

 to 35 ; of setae near the middle of the first poststernal row, 25 to 

 32 ; of setae in the posterior group, 30 to 32. 



Material: Two of the paratypes in the Rocky Mountain Lab- 

 oratory, the other two in the U. S. National Museum. Specimens 

 from host : 



Peromyscus 



Beaverhead County, Mont., Sept. 3, 1945, 4. 



Seasonal DISTRIBUTION : Brennan (1948) reported collections 

 in February, June, and September. 



Geographic distribution: Brennan (1948) lists collections 

 from Ravalli and Beaverhead Counties, Mont., and from Elmore 

 County, Idaho (fig. 7,b). 



Diagnosis : E. criceticolo. can be distinguished by the following 

 combination of characters: No tibiala III; palpal claw usually 

 with three prongs; scutum with two strong, horseshoe-shaped 

 ridges, each inclosing a pseudostigma in a deep depression; and 

 a thin lateral seta, nude or with one or two thin setules, on the 

 palpal tibia. E. criceticola is quite similar morphologically to 

 E. californica. On E. criceticola the lateral seta on the palpal 

 tibia is slender with one or two thin setules or nude. This seta 

 is strongly branched on E. californica. The character of the non- 

 specialized leg setae differs in the two species. The nonspecialized 



