28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



which converge posteriorly and usually meet in a short median groove 

 (mg) ; without setae except at lateral margins, which are slightly 

 raised and carinate, bearing 3 prominent blunt "teeth" (to), each 

 with a long bristle; transverse impression {trim) usually rather weak, 

 indefinite, and interrupted in middle, rarely continuing completely 

 across segment as a somewhat wavy line bulging anteriorly at middle. 

 Tergite {tg) continues uninterruptedly laterally and on posterior 

 ventral surface; usually with from 18 to 25 unpaired setae (some 

 small) on each side, some issuing from small, sclerotized tubercles ; 

 anteriorly on lateral aspect with a few small punctures, some with 

 minute hairs. Distance between posterior margin of pleural area and 

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

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

 {pi) large, consisting of transversely striated membrane except at 

 anterior end, where there is small ovate pleurite bearing several ex- 

 tremely minute setae. Sternum {st) of 2 sclerites, separated ante- 

 riorly by median suture and posteriorly by tenth abdominal segment ; 

 each sclerite with from 9 to 14 setae, mostly in row around tenth 

 abdominal segment ; posterior margin membranous and striate, articu- 

 lating with tenth segment. 



Urogomphi {ur, figs. 6, d ; 7, </, d ; fig. 7, h, c) separate, bifid, short 

 and stout; prongs short, robust, subequal. Inner prong {ipr) directed 

 caudad in horizontal plane, turning slightly mesad, with short, sharp 

 point turning upward and usually inward; prominent tubercle {tub) 

 on ventro-caudolateral surface from inner margin of which a large 

 bristle extends backward, another prominent seta issuing from just 

 above inner margin of tubercle or from upper part of tubercle ; 



1 long seta ventrally at base of prong or slightly farther anterad ; 

 sometimes i or 2 minute setae around distal part of prong. Outer 

 prong {opr) projected dorsad or caudodorsad with sharp, horny 

 point inclined backward; i prominent seta on anterolateral aspect 

 about halfway up prong; up to 10 short fine hairs around distal part 

 of prong; 2 large setae ventrally at base or near base of prong, 

 arising from upper margin of small tubercle. Undivided part of uro- 

 gomphus with i stout seta ventrally near base. An occasional speci- 

 men has more setae on prongs than described above. 



Caudal notch {en) large, U-shaped, usually wider than long, some- 

 what narrowed posteriorly by incurving tips of inner prongs. 



Tenth Abdominal Segment {10, figs. 6, d; 7, d) short, tubular, 

 directed caudoventrad ; terminal portion membranous, striate; with 



2 whorls of about 10 fine setae, the more proximal whorl varying 



