72 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



but do not meet ; without setae except at lateral margins, which are 

 slightly raised and carinate, and bear 3 prominent blunt "teeth," each 

 with a long bristle; transverse impression (trim) continues com- 

 pletely across segment. Tergite continues uninterruptedly laterally 

 and on posterior ventral surface; usually with from 10 to 16 un- 

 paired setae on each side, some issuing from small sclerotized tuber- 

 cles ; anteriorly on lateral aspects with a few small punctures. Distance 

 between posterior margin of pleural area and anterior margin of caudal 

 notch approximates one-sixth of total length of segment (exclusive 

 of urogomphi). Pleural area large, consisting of transversely striated 

 membrane except at anterior ends where small ovate pleurite. Sternum 

 of 2 sclerites, separated anteriorly by median longitudinal suture, 

 and posteriorly by tenth abdominal segment; each sclerite with from 

 6 to 9 setae, mostly in row around tenth abdominal segment. 



Urogomphi (ur, fig. 17, a; fig. 17, c) separate, bifid; projecting 

 caudad or dorsocaudad; inner prong usually about one-half size of 

 outer prong. Inner prong (ipr) short, projected caudad and usually 

 slightly dorsomediad, with sharp upturned tip; less than twice as 

 long as wide ; 2 large setae, i on caudolateral aspect, other ventrally 

 at base of prong; usually a few minute hairs scattered on prong. 

 Outer prong (opr) usually well developed; projecting caudodorsad, 

 sometimes slightly laterad, terminating in sharp, horny point usually 

 curving forward at tip; 2 large setae, i from anterolateral surface 

 (usually in distal half of prong), other from lateral aspect of base 

 of prong ; several minute setae scattered over prong, the most notice- 

 able usually on anteromesal surface near tip of prong. Undivided 

 part of urogomphus with i to 3 setae on ventral aspect, usually i or 2 

 large. 



Caudal notch (en) large, U-shaped, sometimes with anterior margin 

 slightly notched; longer than wide; usually only slightly narrowed 

 posteriorly. 



Tenth abdominal segment with whorl of 10 fine setae; sometimes 

 additional minute setae in complete or partial whorl farther proximad ; 

 anal aperture linear and median. 



Material used in study. — Examination was made of 15 specimens, 

 including the larval exuviae of 2 specimens reared to maturity. Reared 

 adults were identified by W. J. Brown, Ottawa. All specimens were 

 collected in Saskatchewan at the following points: Saskatoon (4), 

 Katepwa (i), Emma Lake (3), Round Lake (7). Unfortunately no 

 whole larvae were collected at the same time and place as the speci- 

 mens that were reared, but some were collected on different dates 



