CHIGGERS — FARRELL 211 



Dorsal setal formulae for five specimens from Ravalli County, 

 Mont. : 



2 .. 13 .. 12 . 



2 .. 14 .. 16 . 

 2 . . 14 . . 12 . 

 2 .. 12 .. 13 . 



2 



. 16 . . 8 



. 14 .. 8 



. 12 .. 10 



. 12 .. 7 



. 12 . . 9 



. 6 



. 8 .. 4 



. 6 



. 6 .. 3 



. 6 



1 .. 11 .. 12 



Note : It could not be determined if the final specimen of the 

 series was anomalous by lacking a humeral seta or if the seta 

 had been lost. 



Ventral setae: Similar to those of E. setosa. Data from five 

 specimens : Number of first sternals, 2 ; of second sternals, 2 ; of 

 poststernals, 43 to 50. Length of first sternals, 48 to 57 ; of second 

 sternals, 38 to 50; of setae near the middle of the first poststernal 

 row, 31 to 36 ; of setae in the posterior group, 40 to 48. 



Material: All specimens from the Rocky Mountain Labora- 

 tory. Specimens from hosts, all from Montana : 



Marmota f. nosophora 



Ravalli County: May 2, 1945, 2; 

 May 10, 1945, 2. 



Marmota flaviventer 



Ravalli County: Apr. 18, 1943, 1 



Seasonal distribution : Euschongastia sp. has been collected 

 in the spring months of April and May. 



Geographic distribution: The only known collections of 

 Euschongastia sp. have been made in Ravalli County, Mont. (fig. 

 8,a). 



Diagnosis : Because of uncertainty concerning the position of 

 Euschongastia sp., no diagnosis is given. 



Remarks: The five specimens described here appear to be 

 morphologically distinct. Apparently the form they represent 

 has a host preference for marmots, which further differentiates 

 them. At the same time they exhibit great similarity to E. sciuri- 

 cola, found on squirrels in the same geographic range. Collections 

 of the two forms have been made at different seasons. The his- 

 tory of the five specimens has not been determined. It is not 

 known whether they constitute the total collections of the form 

 from marmots or if they are a sample from larger collections. 



Characters by which the five specimens differ from E. sciuri- 

 cola include the number of dorsal setae and the number of prongs 

 on the palpal claw. However, the data for both characters of the 

 two forms can be put together to make continuous series. The 

 highest dorsal setal count of E. sciuricola slightly overlaps the 

 lowest count for Euschongastia sp. But when the data for the 

 total number of dorsal setae are put together in this way, the 



