^4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



impressions, 2 laterally and a paramedial pair which converge pos- 

 teriorly sometimes meeting in a median groove ; without setae except 

 at lateral margins, which are slightly raised and carinate, bearing 3 

 small, sharp "teeth" (to) (the most anterior very small, most posterior 

 largest), each with i long bristle; a fourth "tooth" is situated farther 

 caudad and ventrad ; transverse impression wanting. Tergite con- 

 tinues uninterruptedly laterally and on posterior ventral surface; 

 usually with from 16 to 28 setae on each side, some issuing from 

 small sclerotized tubercles; lateral aspect usually moderately densely 

 punctulate. Distance between posterior margin of pleural area and 

 anterior margin of caudal notch approximates one-fifth to one-fourth 

 total length of segment (exclusive of urogomphi). Pleural area large, 

 consisting of transversely striated membrane except at anterior ends 

 where small ovate pleurites. Sternum of 2 sclerites, separated an- 

 teriorly by median longitudinal suture and posteriorly by tenth ab- 

 dominal segment; each sclerite with from 8 to 14 setae, mostly in row 

 around tenth abdominal segment. 



Urogomphi (ur, fig. 16, a; fig. 13, /) well developed, separate, bifid ; 

 directed dorsocaudad; prongs well developed, subequal; urogomphi 

 and prongs long and relatively slender. Inner prong (ipr) directed 

 mesocaudad and slightly dorsad, terminating in sharp, upturned horny 

 point; prominent, sharp, toothlike tubercule (tub) on ventro-caudo- 

 lateral aspect, halfway along prong; sometimes an additional small 

 tubercle ventrally near base of prong; 3 large setae, one ventrally at 

 base of prong, i from inner aspect and i from upper aspect of base 

 of prominent tubercle ; usually 2 or 3 smaller setae issuing from prong 

 near base of large tubercle. Outer prong (opr) somewhat corniform; 

 directed dorsad, and usually slightly caudad with sharp tip turned 

 posteriorly; large, horny tubercle (tiib) with sharp upturned point 

 situated laterally just below base of prong; usually with 3 large setae, 

 I from anterolateral aspect, about halfway along prong, 2 from near 

 upper aspect of base of tubercle; several small, fine setae scattered 

 over distal half of prong, most abundant on posterior surface at point 

 where prong distinctly becomes narrower. Undivided part of uro- 

 gomphus about as long as divided portion; without setae except as 

 noted above. Caudal notch (en) large, shape variable, but usually 

 subcircular ; about as broad as long, somewhat narrowed posteriorly. 



Tenth abdominal segment with i whorl (sometimes 2 whorls) of 

 10 fine setae; anal aperture linear and median. 



Material used in study. — Twenty-two specimens were examined, 

 3 from Alberta and 19 (U. S. National Museum collection) from the 

 State of Washington. The latter were received through the courtesy 



