AQUATIC INSECTS IN THE ADIRONDACKS 579 



thoracic three times as long as the prothoracic segment, smooth except 

 for a single piliferous tubercle each side. 



Abdominal segments 1-7 similar, and of nearly equal length, each 

 bearing three rings of tubercles, a median ring of tubercles of moderate 

 size, and at each end close beside the suture separating the segments a 

 ring of minute tubercles; median ring, with the pair of tubercles beside 

 the middorsal line (pi. ^6, fig. 3^) very mobile, transversely elongated, 

 bearing a stiff brush of recurved or hooked bristles, well adapted for crawl- 

 ing beneath the surface film ; on the ventral side, two pairs of prominent 

 rounded tubercles ; between the dorsal and the ventral there are on either 

 side four or five lesser tubercles, mostly unisetigerous, sometimes not very 

 distinct, the third of them, counting from above, a little out of line, in 

 advance of the others. There is a broad median ventral lobe on the eighth 

 abdominal segment, liplike, rounded, covered with very minute re- 

 curved prickles. 



Apex of the abdomen (pi. ;^6, fig. ;^d) upturned, flattened, tipuloid, 

 fashioned into a disk which surrounds the frmged respiratory apertures. 

 There are two pairs of long processes on the ventral half of the margin of the 

 disk and three pairs of lov,^ tubercles on the dorsal half of it. The two 

 submedian ventral processes are long, triangular, almost lanceolate, simple; 

 those of the pair external to these are two-jointed, the joint midway 

 their length ; both pairs are pilose, and about equal in length to the 

 diameter of the disk. Respiratory apertures in two groups of three 

 each, sHtlike, radiating in arrangement. From the notches between the 

 apertures and at their sides arise tufts of black, floating filaments 

 arranged in a flat whorl, well adapted to holding the breathing apertures 

 up to the surface of the water; these filaments are black, dichotomously 

 (often irregularly) four or five times branched, about 10 or 12 in number, 

 and extending almost to the margin of the disk. 



The larva when undisturbed lies quietly at the surface of the water 



amid a tangle of vegetation. It can swim when disturbed, and its 



swimming is most curious. It pulls itself below the surface, turns over on 



its back, and then progresses by bending and straightening its body, 



striking the water sharply with the flat face of its caudal disk. 



Puparium. (PI 14, fig. 3-5)- Length 6 mm; greatest horizontal 

 diameter 3 mm; vertical diameter 2.5 mm. 



Color reddish brown, closely marked with yellowish on the ventral side. 

 Body shaped like an undetermined seed, which was not uncommon, float- 

 ing on the surface of the creek. I first mistook the pupae for seeds, and 

 afterward occasionally mistook seeds for pupae, so good was the 

 resemblance. 



Body ovate, dorsally flattened and ventrally rounded, broadly canoe- 

 shaped, but suddenly contracted anteriorly into a flat, truncate, rostral 

 prominence .5 mm wide and .9 mm long. There is a black, middorsal 

 curved mark (concave anteriorly) just behind the base of this beak. 

 (When the imago emerges, this beak splits down its sharp lateral margins, 

 and across the dorsum of the body near to the aboved mentioned black 

 mark, and comes oft' as one half of the cap.) 



The posterior end is suddenly, and strongly contracted into a cylindric 

 tail, which is directed upward at an angle of 75° with the axis of the 

 body. The float of the larva persists on the summit of this tail, and 



