58 NEW YORK STATE MUSEUM 



The nymph. (P1.7, figs.6 and 7.) Length, apparently full 

 grown, 9 mm.; antenna, 1.5 mm., and setae, 9 mm. additional. 



Body elongate, strongly depressed, widest across the front of 

 the head and the meosothorax, these being of about equal width ; 

 head widest across the front well before the eyes, and strongly 

 narrowed posteriorly to the obtuse hind angles; infero-lateral 

 margins of the head thin and flaring as usual, and closely fringed 

 with hairs; antennae short, slender, pale. Mouth parts as shown 

 in figs.l2h, 13d and 14m. 



Dorsum of the j)rothorax a little produced laterally, and angu- 

 late obtusely in the middle of the sides. I^gs moderate, tibiae 

 and femora all with well developed external fringes of hair; 

 femora very moderately flattened and dilated, the fore femora 

 most so; tarsal claw jjectinate, there being two to four mimite 

 teeth at its anterior border before the apex (flg.ll?/). The wing 

 cases reach the base of the 4th abdominal segment. 



Abdomen regularly tapering posteriorly, its segments increas- 

 ing in length to the middle. Two lateral spines each side of 

 segments 2-6 and one on segment 7, all stout, triangular, and 

 directed outward. 



Gills represented on segments 1-7 ; on 1 a very large, broadly 

 and obtusely triangular flap of membrane shaped like the gill 

 scoop of a crawfish, attached by the middle of one of the sides, 

 its front end extending forward and lying against the base of the 

 hind leg, its hind end overhipping the succeeding gill lamella. 

 On segments 2-7 the lamellae are ovoid, dorsally carinate, ob- 

 tusely pointed membranous plates, each with regularly arcuate 

 front margin overla])ping the hind margin of the one on the pre- 

 ceding segment, and each bearing at its base a tuft of 7-15 short, 

 finger-like gill filaments. The lamellae diminish in breadth pos- 

 teriorly, and 'become less divaricate in pairs, and the tips of the 

 7th pair are curved beneath the abdomen. 



Setae 2, rather short and stout, the median seta being repre- 

 sented by a minute triangular rudiment. The tips of the develop- 

 ing male forceps project beyond the apex to the 10th segment. 



This remarkable nymph dwells in the swiftest parts of the 

 stream, and its whole organization exhibits the most wonderful 

 adaptation to life in such a place; the extra grappling armature 

 appended to its claws and especially its flattened form with 

 thin edges nU the van around closely applicable to the supporting 

 surface, and admirably adapted to divert the flow of the water. 

 Probably the oval enclosure of the gill lamellae of the ventral side 

 of the abdomen acts as a sort of sucker, and holds the animal 



