218 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 106 



Wharton and Hardcastle (1946), who found the scuta of larger 

 specimens of their new species Neoschongastia eivingi were larger 

 than the scuta of unengorged specimens. The scuta also differed 

 in shape. The draAving of the scutum of E. setosa (pi. 8,c) was 

 made from a well engorged specimen which was flattened on the 

 slide. It measures 112 microns between the posterolateral setae. 

 This is the largest measurement recorded for a scutum of E. 

 setosa. A scutum obviously deformed as a result of preservation 

 on a slide was found in E. sciuricola. Wharton and Hardcastle 

 point out that it is clear that changes can occur in the character 

 of the scutum of an individual chigger, and mistakes may result 

 from placing too much emphasis on the standard data. This state- 

 ment is supported by present observations on the scuta of 

 Euschbngastia. Judged in this light, the clinal nature exhibited 

 by the size of the scutum of E. peromysci (fig. 5,a) and that of 

 E. diversa diversa (fig. 5,c) are not above suspicion. However, 

 the figures referred to (charting this feature for the two species) 

 are included on the basis of the presumed random selection of 

 the specimens represented. 



The presence or absence of punctae on the cheliceral base, the 

 palpal coxa and femur, the leg segments, and the scutum may be 

 of systematic value. Lawrence (1949) used the difference in size 

 of scutal punctae as a key character. Differences in size of punc- 

 tae occur in North American Euschongastia and have been used 

 as diagnostic aids. Usually, however, advantage is taken of the 

 differences in distribution of the punctae. Within certain species 

 the punctae characteristically are present on some parts and 

 absent on others. This aid has been of particular value among 

 certain species of the "blarinae" group. 



The eyes are of distinct, though limited, systematic value. 

 Most species have two pairs of eyes not held in ocular plates. In 

 E. pipistrelli, with its one small and indistinct pair of eyes, the 

 character is important. In E. trigenuala the eyes are reduced 

 apparently to one pair, but this species is quite distinct on other 

 criteria. E. lacerta and E. nunezi are the only species studied in 

 this work which have ocular plates. Occasionally, in an unen- 

 gorged specimen of one of the other species, the eyes may be 

 close together and appear to be in an ocular plate. 



Differences occur in the size of the teeth on the chelicerae. For 

 example, these are rather large in E. crateris and quite small in 

 E. blarinae. Usually the dorsal tooth cannot be detected in E. 

 blarinae. Differences in the shapes of leg segments occur between 



