AQUATIC INSECTS IN THE ADIRONDACKS 417 



moniliform ; not close set cylindric and tapering as in the more typical 

 Perlidae. Median ocellus clearly double! 



Body slender, with sides nearly parallel. The prothorax narrower 

 than the head, regularly quadrangular, with straight sides and ends, and 

 with angles all a little rounded ; a faint ifiedian raised line and on either 

 side of it a faint raised circle covering nearly half of the prothoracic 

 dorsum. 



Color brown, becoming yellowish on legs and sutures. Wings smoky 

 hyaHne with brown veins {see pi. 15, fig. 12). 



On the dorsum of the abdomen in the male there is a conspicuous 

 prominence on the seventh segment 

 which rises to a hight equal to one 

 fifth of the thickness of the abdomen 

 (fig. 4^). 



Nymph. Fully grown, measures 

 12 mm in length of head and body; 

 abdomen alone 4.5 mm; antenna 

 4.5 mm; abdominal setae 4.5 mm. 

 Width of head .o mm. 



~rt -, .^1 -^1 11 1 -J Fig. 5 Wings of Leuctra tenella 



Eody with nearly parallel sides. 

 Head as wide as the prothorax; mesothorax a little wider; abdomen a 

 little narrower. 



Color nearly uniform yellowish fulvous, pale below and on sutures, 

 antennae and setae. Legs pale yellow. Eyes blackish; oceUi brownish, 

 with a faint wash of brown between the posterior pair. 



No tracheal gills. 



Little Clear creek at Saranac Inn N. Y. June 21, 24, 26, 28, July 31 

 and Aug. 2, 1900. Not common. 



The two stone flies discussed above fall in separate divisions of the 

 family, which I regard as subfamilies, distinguishable by the following 

 characteristics. 



1 Perlinae. Imago. The median vein hardly fused with the radius 

 at the base, but running close beside it, and bending away from it very 

 gradually, not forming a distinct arculus. 



Nymph. Flat body, flattened femora ciliate on the sharp and convex 

 margins, and with tapering abdomen. Tracheal gills, when developed, 

 consisting of tufts of filaments. 



This subfamily includes the two tribes, Pteronarcini and Perlini of 



Banks.i 



2 Nemourinae. Imago. The median vein fused with the radius at 

 the base, then bending sharply away from it to meet the cross vein, with 

 which it forms a distinct arculus. 



Nymph. More cylindric body ; femora not flattened or sharp edged ; 

 abdomen with nearly parallel sides. Tracheal gills \yhen developed 



1 Am. ent. soc. Trans. 1900, 24 : 210. 



