CPnCGERS — FARRELL 215 



ber of setules on either of these setae was charted for a species, 

 the distribution always appeared normal (tables 6, 12-15). The 

 taxonomic importance of these selected setae is shown most 

 clearly in the "rubra" group (fig. 6,a,6). In this group each of 

 the four related forms has a characteristic distribution of setules. 

 Determinations of distributions of these sorts must be made on a 

 group basis, but, having been made, the data may be used for the 

 identification of single specimens. Differences can be found in 

 the number of setae on the palpal tarsus, but these are associated 

 with chiggers which are distinct on other grounds. 



The feathered setae of the legs have not been considered as 

 systematic characters by most workers. Floch and Abonnenc 

 (1941) enumerated these setae by leg segments for E. guyanensis. 

 Wharton (1946) enumerated them by leg segments for Euschon- 

 gastia indica. His count coincides well with the number of setae 

 found in the "lacerta" group and on E. nunezi. These species have 

 eight feathered setae on the tibia of the first leg. All other North 

 American species have seven feathered setae on this segment. 

 Possibly the number of feathered setae on the first tibia will 

 prove diagnostic at the level of groups of species. In E. guntheri 

 the two setae on the coxa of the third leg are diagnostic at the 

 level of species. Differences occur in the number of feathered 

 setae on the tarsi of certain species; but accurate determination 

 of this is laborious and is not required at the present time. With 

 the exceptions mentioned, the number of feathered setae on the 

 leg segments of Euschongastia studied are the same. 



Acarologists have not used the structure of the feathered 

 setae of the legs of chiggers as a systematic character. Gunther 

 (1940) made brief descriptive statements concerning them in 

 describing new species. Later workers have used only a descrip- 

 tive term, if the setae were mentioned at all. In the present study 

 the structure of these setae was found to differ considerably be- 

 tween many species while remaining constant within a species. 

 This is in contrast to the general uniformity within the genus 

 of the number of the setae per segment. The structure of these 

 feathered setae is useful as a key character in separating the 

 "luteodema" group from the " criGeticola-californica" group. The 

 very similar E. criceticola and E, californica themselves can be 

 separated by this character, and it could be used elsewhere. 



The arrangement of the dorsal setae into rows is conspicuous 

 and lends itself well to counting. Consequently these setae have 

 been used by m.ost acarologists. Ewing (1937), in discussing the 

 setae, stated that their number probably did not vary within a 



