r.s NEW YOI;K STATI: MTSIMM 



The nymph. (P1.7. ligs.r, and T.I Length, apparently full 

 gn>\\ n. !i nun.; antenna. l..~ nun.. :iml setae, ! nun. addit ional. 



Body elongate, ^trough depressed, widest across the front of 

 ihr licad and the incus. .1 horax. ilirsr iM-ing of about equal width; 

 head widest an-oss the front well before the e\es, and strongly 

 narrowed posteriorly to tin- obtuse hind angles; infero lateral 

 margins of tin- head iliin and llaring a^ usual, and closely fringed 

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

 in ligs.lL'h. i::d and 1 hn. 



Itorsiini of the proihorax a liiile produced laterally, and angu- 



late obtusely in the middle of ihe *ides. Legs i lei-ale, tibiae 



and femora all with \\ell developed external fringes of hair; 

 femora \er\ moderately llaiieiied ami dilated, the fore femora 

 most so; tarsal da\\ peciinaie. there being t \\ o to four minute 

 teeth at its anterior border before the apex ili^.lb/i. The \\ in^ 

 cases reach the base of i he hh abdominal segment. 



Abdomen rejrularh tapering posteriorly, its se-ments increas- 

 ing in length lo ihe middle. Tun lateral s|>ines each side of 

 seu'iiieiiis L' i! and one on segment 7. all stout, triangular, and 

 directed outward. 



(lills represented on segments 1 7: on 1 a very largo, broadly 

 and obtusely triangular Hap of membrane shaped like the gill 

 scoop of a crawlish. attached by the middle of one of the sides. 

 its front end extending foruard and 1\ ing against the base of the 

 hind leg. its hind end o\erlapping the succeeding gill lamella. 

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

 tusely pointed membranous plates, each with regularly arcuate 

 front margin overlapping the hind margin of the one on the pre- 

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

 finger-liko 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 rr/f/r.s all tin ir,/,/ 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 



