CHIGGERS — FARRELL 175 



forms become apparent. Morphologically the group is split in two 

 by the shape of the scutum and the form and number of the body 

 setae. The split is emphasized by the variation in the number of 

 setules on the galeal setae (fig. Q,a) and the lateral seta on the 

 palpal tibiae (fig. 6,b). Thus, E. rubra and E. magna go together 

 and are distinctly set off from E. diversa. Evidence that this 

 cleavage represents a real difference at the specific level and 

 not a geographical variation at the subspecific level is obtained 

 in the collections from Union County, Pa. Here the ranges of the 

 morphologically distinct E. diversa and E, magna coincide. 



The collections from Union County are meager ; and, since they 

 are pivotal in determining the number of species in the "rub^-a" 

 group, some consideration should be taken concerning the possi- 

 bility that the two forms are variants of the same species. Of 

 the eight specimens from Union County, six have been placed in 

 E. diversa and tv/o in E. magna. The E. diversa specimens rep- 

 resent four collections of two host species. The E. magna speci- 

 mens represent two collections of the same two host species. 

 Both forms v/ere taken once from the same host animal. Although 

 the sampling of the chigger population is small, it is well dis- 

 persed; and it seems unlikely that a minor group of genetic 

 variants would comprise as m.uch as 25 percent of such a sample. 

 The occurrence of both forms on a single host is evidence that 

 they are not ecophenotypes. The morphological distinctness of 

 the two forms with the absence of intergrades indicates they are 

 not variants. 



Within the basic pattern of E. diversa two populations are 

 separable geographically. The known geographic ranges of the 

 two populations are separated by only one county in Pennsylvania. 

 Based on the combination of morphology and range, the best 

 explanation of the relationship between the two populations seems 

 to be that they are geographic races of the same species. Two 

 subspecies have been erected for them in E. diversa. 



The relationship between those forms here named E. rubra 

 and E. magna is by no means clear. The difference in size of scuta 

 is not great when the geography is considered. However, at the 

 present time the two forms can be separated by the size of the 

 scutum. The extra rows of dorsal setae in the northern form 

 separate it from the southern form. There are no collections 

 between North Carolina and Union County, Pa., to indicate trends 

 of variations or extent of ranges. Future collections may show 

 that the two forms are distinct or that they fall within the limits 

 of a single species. In the present state of knowledge of the genus 

 It seems best to recognize forms that are clearly separable. In this 



