VOL 54, NO. 1, JANUARY 1978 
23 
claws with 6-10 denticles. Abdominal terga may be uniformly pale to 
light or dark brown, or brown with a pale median longitudinal stripe 
and variable pale submedian spots on the posterior margins; postero¬ 
lateral projections on segments 4-9, lateral margins of projections 
pale; well developed paired abdominal tubercles absent, however 
slight paired projections or undulations sometimes may be present 
on posterior margin of any or all terga of abdominal segments 3-9; 
abdominal sterna light brown. Caudal filaments pale with brown 
transverse bands, whorls of spines on posterior margin of segments 
in basal two-thirds, heavily setaceous on distal one-third. 
Ephemerella inermis Eaton 
Mature larva. Body length 5-9 mm, terminal filaments 4-5 mm. Pale stripe across face at 
anterior medial margin of eyes; stripe often interrupted at center of frons. Posterior 
margins of femora with one or more rows of short spines, .02-.05 mm long, which may be 
inconspicuous or absent on forefemora; forefemora with sparse dorsal subapical band of 
spines, or subapical band absent or represented by only a few spines; claws sharply 
curved. 
Distribution: E. inermis is lower boreal and widely distributed in western North America 
from central British Columbia austrad to southern California, and central Arizona and 
New Mexico (Fig. 3). 
Ephemerella infrequens McDunnough 
Mature larva. Body length 5-11 mm, terminal filaments 4-6 mm; pale stripe across face 
usually interrupted at center of frons to form two pale spots or medially extending bars at 
the anterior medial margin of the eyes; posterior margins of femora with one or more rows 
of spines .07-.09 mm long, always present on forefemora; forefemora with distinct 
subapical band of spines on dorsal surface; claws gently curved. 
Distribution: E. infrequens is a mid-boreal species extending from central Alaska 
austrad to central California and northern New Mexico along the Cascade-Sierra and 
Rocky Mountain ranges (Fig. 3). 
Collections used to derive the ranges given by Allen and Edmunds 
(1965) and Allen (1968) probably consisted of composites of both 
species and do not accurately represent their distribution. My modifi¬ 
cation of the northward extent of the two species is based upon the 
identification of all available specimens from Northern British Colum¬ 
bia and Alaska as E. infrequens. Particular northern locality records 
which were originally identified as E. inermis and have been subse¬ 
quently identified as E. infrequens are as follows: Alaska: Anon Creek, 
S.E. Mainland, 25’, 26-IV-58, G.L. Miller; McMannus Creek, 60 mi. N.E. 
Fairbanks, 23-VI11-66, L. Boddis (Allen, 1968); British Columbia: 
Terrace, 12-VII-72, G.F. Edmunds, Jr. 
Biology 
Larvae of E. infrequens may be found in clear, fast-flowing streams 
with rocky substrates. They inhabit the underside of rocks in the 
riffles of a stream and seem to prefer rocks of medium size over small 
stones or pebbles. They range in elevation from sea level in Alaska 
