22 PROC. ENT. SOC. WASH., VOL. 24, NO. 1, JAN., 1922 



two visible sternites is subequal except for the intrusion of the 

 metathoracic coxae; the last sternite is about one-third longer 

 than each preceding pair. A narrow membrane connects the 

 last two visible sternites. The fifth visible sternite in different 

 species exhibits some variation in the degree of its convexity 

 and in the nature of its punctuation. 



The number and character of the retractile segments of the 

 abdomen vary with the sex and the species (figs. 23, 24, 25 

 and 26). They are most easily seen in specimens which have 

 been prepared in dilute acetic acid. 



Retractile segments of the male (described from communis 

 Gyll., figs. 23, 24 & 25). The eighth tergite is about as long as 

 the seventh, and about as wide. It is slightly longer than 

 broad; its sides are subparallel and broadly rounded on the 

 apical third, and fimbriate on its posterior margin; it is very 

 nearly flat and of the same degree of chitinization as the 

 seventh tergite. The ninth tergite is subquadrate; its poster- 

 ior margin is deeply emarginate, the outer third on either side 

 being free, while the inner third is fused with the tenth tergite. 

 The tenth tergite at its base is about two-thirds as wide as 

 the posterior margin of the ninth, and is subtriangular in out- 

 line. The ninth and tenth tergites are subequal in length, 

 together a little shorter than the eighth. They are less heavily 

 chitinized and more flexible than the eighth. 



The eighth sternite is subquadrate, slightly wider at the 

 base and a little longer than wide; it is nearly flat, and along its 

 outer margins about as heavily chitinized as the corresponding 

 tergite. The ninth sternite is slender and bullet-shaped, about 

 two and one-half times as long as its basal width. It is narrowly 

 rounded and on the sides is flexed sharply upward. Its base is 

 membranous, but towards its apex it becomes well chitinized. 

 The tenth sternite is ovate and flat; it is flexible and about one- 

 third the length of the ninth sternite. 



The pleurites are entirely membranous (fig. 24). A small 

 prominently-borne spiracle (Sp8, fig. 24) is present on the eighth 

 pleurite about halfway from the base of the eighth tergite; in 

 dried specimens it is usually completely hidden by the collapse 

 of the pleural region and the consequent approximation of the 

 tergite and sternite. 



The anus (An, fig. 24) lies just beneath the tip of the tenth 

 tergite, and may be strongly everted. 



Retractile segments of the female (described from communis 

 Gyll., fig. 26). The eighth tergite is subogival in outline, with 

 the sides almost parallel along their basal half; it is membranous 

 at the base but well chitinized apically; it is about two-thirds 

 the length of the seventh tergite. Its sides are flexed downward 

 along their basal third to partially enclose the pleurite, and just 

 beneath the flexed edge at about the point where it curves 



