CHIGGERS — FARRELL 221 



E. criceticola, E. californica, E. luteodema, and E. sciuricola. 

 The Mexican E. nunezi is omitted from the list. Also omitted is 

 E. trigenuala, since its locality is not known with certainty. 



The importance of geography in the "rubra" group with its 

 subspecies has already been discussed in the remarks accompany- 

 ing the group. Reference has been made to the combined char- 

 acters of morphology and geographic range in separating the 

 southern E. carolinensis from the northern E. ohioensis. Avail- 

 able information indicates that each species of Euschongastia 

 has a definite geographic range. The range when known becomes 

 a part of the species definition and a very useful systematic 

 character. 



Another phenomenon which follows from a study of the geo- 

 graphic distribution of a species is that of geographic variation. 

 This implies the variations which occur in the characters of a 

 species over its geographic range. Such variations were found 

 and noted for characters of E. pipistrelli, E. peromysci, and E. 

 diversa diversa. When the length of the palpal claw (fig. 5,6), 

 the number of setules on the galeal setae (table 6) , and the size 

 of the scutum (fig. 5,a) were charted for E, peromysci, the char- 

 acters were found to vary in each locality and between different 

 localities. The same result was had when the size of the scutum 

 of E. diversa diversa (fig. 5,c) was charted geographically. More- 

 over, when the variations of all these characters were arranged 

 in a continuous gradient, some correlation with geographic 

 direction became evident. In all cases the pattern of variability 

 was the same, generally continuing from west to east, or from 

 south and west to north and east. Huxley (1940) discussed such 

 geographically correlated character-gradients. He termed them 

 "clines" and pointed to their value in summarizing variations and 

 in studying subspecific groupings. In the present paper they 

 have been used only for their value in summarizing geographic 

 variations in the characters of the species. 



Information is not adequate for an evaluation of seasonal dis- 

 tribution of the species of Euschongastia with regard to their 

 systematics. From the records available it appears that different 

 distributional patterns may be represented. The charted record 

 of E. rubra (fig. 6,d) shows that it occurs on hosts only during 

 the winter and spring. The known record of all the "rubra" 

 gToup falls in this pattern. The record of E. peromysci (fig. 6,c) 

 shows that it has a peak incidence on hosts during winter and 

 spring, but it also occurs in smaller numbers during summer and 

 fall. E. luteodema, E. marmotae, and Euschongastia sp., which 



