216 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 106 



species. This statement does not hold in Euschongastia. A series 

 of dorsal formulae for any species shows a range of variation in 

 the number of setae. However, Ewing's observation that the 

 positions of the setae change with engorgement is true within 

 this genus. Varying degrees of engorgement doubtless account 

 for certain variations in the dorsal formulae determined for a 

 species. The effect is most noticeable on the posterior portion of 

 the body which undergoes greatest change during engorgement. 

 The anterior rows are quite distinct in all engorgements. Also, 

 this factor may in part be responsible for the lateral setae. These 

 setae apparently are lateral extensions of the dorsal rows. Their 

 appearance out of line may be the combined result of displacement 

 by engorgement and a flattening of the specimen on the slide. 

 During a large portion of this study, an effort was made to as- 

 sign the laterals to the rows of dorsals. It can be questioned 

 whether this is the better procedure, since including the setae 

 in the formulae as laterals conforms more closely with the dis- 

 tribution observed on a specimen. Usually the dorsal setae are 

 clearly arranged in rows; and the length of each row conforms 

 somewhat to the diameter of the body where it is found. In some 

 species there are extra setae which may occur out of line. This 

 condition is found in the "luteodema" group. It is most strongly 

 developed in E. guntheri. In E. magna the extra setae occur as 

 short rows between the longer rows. Each species of Euschon- 

 gastia has a characteristic pattern to its dorsal formula which is 

 a valuable systematic aid. 



Differences in structure of the dorsal setae have been recog- 

 nized by several systematists. Earliest instances occurred when 

 the setae assumed a leaf like shape. On this basis Gunther (1940) 

 and Womersley (1944) used the shape of dorsal setae to distin- 

 guish new species. However, Lawrence (1949) determined dif- 

 ferences in the more normally shaped body setae of African 

 Euschongastia. He figured both dorsal and ventral body setae 

 for his new species and used the relative thicknesses of dorsal 

 setae as key characters. In the present study these setae have 

 been found to have similar systematic value for North American 

 Euschongastia. The flat, leaflike shape and the distribution of 

 the posterior body setae are diagnostic in E. carolinensis and E. 

 ohioensis. Within the "rubra" group the character is important. 

 Here the setae have normally round shafts, and the difference 

 involves the setules of the posterior setae. The relative size of 

 the setules on the dorsal setae is useful in distinguishing between 

 E. setosa and E. blarinae. Potentially the structure of the dorsal 



