MAY FLIES AND IMIDGES OF NEW YORK 61 



The subimago stage lasts 24 hours, and when the final emergence 

 takes place the subimago alights on some object near the edge 

 of the stream, where it transforms in less than a minute. The 

 skin of the subimago remains attached to the bases of the setae 

 of the imago and in this manner is carried out over the stream by 

 the flying insect, where it is finally released after some minutes. 



The adult of this species is briefly described in Eaton's Mono- 

 graph, p.47. The habitat given there is Passaic river, Belle- 

 ville, N. J. (Williamson); Winnipeg river (Say); Red river of 

 the north and New York (Hagen). This seems to indicate a 

 rather wide distribution for P . a 1 b u s in the eastern and 

 northern United States, but during the summer of 1903 I made 

 collections from several of the boulder and limestone streams 

 tributary to the Wabash in Indiana without obtaining a single 

 specimen. 



The nymph. Leng-th, 14-16 mm.; an-tennae, 3.5-4 mm., and 

 setae, 7-8 mm. Body depressed, widest across prothorax where 

 the thin lateral margins project; eyes prominent and lateral; 

 three somewhat crescent-shaped ocelli arranged in the form of a 

 broad-based triangle; antennae many-jointed, bearing a whorl of 

 minute bristles at the apical ends of the joints, the first two 

 joints much stouter and the joints 4-8 decidedly shorter than the 

 others, projecting beyond the mandibular tusks by a little less 

 than half the length of the latter; mandibular tusks about 2.5 

 mm. long, stout at base, narrowing rather abruptly near the mid- 

 dle, the slender distal half tapering gradually to the acute, 

 slightly out-curved tip; the basal half of tusk is thickly set with 

 stout, acute spines, being less numerous on the slender distal 

 portion, and entirely disappearing at about one third the distance 

 from the tip; a few long hairs are borne on the outer side near 

 the base; mandible stout, bearing two prominent tridentate fangs 

 on its anterior surface nearly parallel with the distal half of the 

 tusk, the middle tooth of each the longest ; the endopodite arising 

 from the base of the inner fang is inclined toward the molar 

 surface, and bears a brush of long hairs on its inner side near 

 the tip; the laibrum is about half as long as broad, slightly 

 emarginate in front, and thickly covered with fine hairs; maxillae 

 somewhat slender, the outer basal portion fringed with stiff hairs; 

 the maxillary palpi three-jointed besides the short pedicel, the 

 second joint the shortest, the third joint about as long as the 

 first and second together; outer side of third joint bearing a few 

 long hairs, the stoutest ones being near the distal extremity, the 



