80 Journal New York Entomological Society. t^'°'- ''^^• 



black bristles for the genns, both on dorsum and sides ; scutellum some- 

 what elongated, convex, hairy and with four bristles ; sternopleural only one ; 

 several small bristles at posterior edge of mesopleura, one larger ; halteres 

 yellow. Abdomen rather uniformly gray pruinose with a little greenish tinge, 

 first segment short, next three of equal length, fifth a very little longer; 

 hypopygium small, narrow, blackish, with two yellowish stiff processes pro- 

 jecting forward as far as the middle of the fourth ventral ; the longest hairs 

 on the abdomen are about the apex and before the incisures near the sides, 

 but they are hardly bristle-like. Coxse and femora concolorous with thorax, 

 the trochanters and knees yellow ; tibiae varying from yellow to the color of 

 the femora, the front ones usually paler than the others ; tarsi mostly yellow, 

 variably infuscated at tip, longer than their tibiae, the three middle joints of 

 equal length, claws long, straight, black, no pulvilli. The hind femora have a 

 long shining streak on the inner side, and the hind tibiae have a short shining 

 streak at the tip behind. Wings of ordinary structure, yellowish at base, 

 especially the veins. 



Larva (PI. VII, Fig. 2).— Length in a full-grown, average specimen, of body, 

 10.6 mm.; of anal tube to the fork, 4.9 mm.; of each terminal fork, 1.6 mm.; 

 of each basal fork, 2 mm. Color white, somewhat transparent. Eight pairs 

 of rather long prolegs, the members in each pair united in a single tubercle in 

 the basal third, but entirely separate on the remainder of their length ; in 

 front of the segment bearing the first prolegs there are three apparent seg- 

 ments, the foremost retractile, containing the jaw-capsule; the jaws, as in 

 related forms, turn down in the form of hooks, and are not opposable. 

 Behind the last pair of prolegs the body narrows suddenly into a long anal 

 tube, which gives off close to the base on the under side a pair of long 

 filaments, and at its tip divides into a pair of somewhat shorter filaments. 

 The hindmost prolegs have a longer common tubercle and a shorter divided 

 portion than the rest. 



The anal tube is considerably retractile, and varies in length in different 

 preserved specimens. It contains two tracheae, which continue to the terminal 

 fork, where one leads into each branch and ends in a vestigial spiracle at the 

 tip. I doubt if these spiracles are ever put to the surface of the water ; I have 

 not yet seen it done, so I conclude that the whole structure has changed its 

 mode of functioning, and operates as a tracheal gill. 



Puparium (PI. VII, Figs. 3, 4). — Length of body in an average specimen, 

 to the last prolegs, 8 mm. ; anal tube so variable that it can hardly be esti- 

 mated, perhaps five or six mm. would be about the usual total length beyond 

 the last prolegs. The form of the insect is much changed from the larval 

 stage. The thickest part of the body is in the region of the third pair of 

 prolegs, and it tapers suddenly in front, more slowly behind, so as to be some- 

 what fusiform with the thickest portion well before the middle. The pro- 

 legs toward the anterior end are small ; the front pair are almost indis- 

 tinguishable and have no hooks ; the successive pairs are each a little larger, 

 but only the last three pairs have hooks and are of about the same size as in 

 the larva. The last pair, which in related species hold the insect attached 



