94 THOMAS SAY FOUNDATION 
found to pass through twenty-two instars, and the life eycle oc- 
cupied one year. 
Key to the known Nymphs of Nemoura 
Je No gillsin cervicalreciony. «2 ater N. vallicularia (p. 95) 
Gills present’. 02. 0.4053 0s ene stereos er 2 
2. Gills consisting of four single filaments. .Nemouwra sp. (p. 96) 
Gills consisting of four groups of filaments >. oe 3 
3. Inner group of gills composed of about 17 filaments, outer 
Proups Ol BOUL Tote ee eee N. sinwata (p. 94) 
All groups of gills with about an equal number of filaments 4 
4. Each group composed of 6-7 filaments...... N. venosa (p. 95) 
Hach group composed of 8-9 filaments. NV. coloradensis (p. 96) 
Nemoura sinuata Wu 
(Plate 28, fig. 209; plate 32, fig. 226.) 
Length of body up to 6.5 mm.; antennae up to 4 mm.; cerei 
up to 4.5 mm. 
General color yellow to yellowish brown. 
Head about as wide as pronotum; surface covered with fine 
hairs; basal stem of epicranial suture more than half as long 
as the lateral arms; hind ocelli (showing in mature nymphs) a 
little closer to eyes than to each other; antennae of about forty- 
five segments. 
Pronotum narrowed posteriorly; front margin somewhat con- 
vex or nearly straight; angles rounded; surface dirty brown; 
margin fringed with short blunt spinules. Meso- and metanotum 
with some long hairs and with short spinules on the lateral mar- 
gins, especially at the antero-lateral angles; front wing pads nar- 
rower and longer than the hind ones, which diverge greatly from 
the body. Legs stout, the femora and tibiae covered with many 
stout spine-like hairs. 
Abdominal segments with a fringe of hairs on the posterior 
margin. Cerei long and slender, of about thirty-two segments, 
each segment terminating in a whorl of long hairs. In the male 
the tenth abdominal tergite is produced into a short broad supra- 
anal protuberance, which is absent in the female; eighth sternite 
of female with a depressed area in the center of the posterior 
margin, denoting the developing genital opening. 
Four groups of gills in the cervical region just anterior to the 
prosternum ; two outer groups contain seven gill filaments each, 
and the inner ones about seventeen. 
