DIZ Ittinois NATURAL His'orY SURVEY BULLETIN 
cerning the ramifications of this variation. 
However, it seems desirable to illustrate 
a form which is commonly encountered in 
the Great Smoky Mountains National 
Park near Gatlinburg, Tenn., because its 
identity might be overlooked. “The nymph 
of this variant is shown in fig. 37. 
Fig. 384 is a dorsal view of the head 
and pronotum of this variant, and fig. 386 
Fig. 38.—Perlesta placida: A from Great 
Smoky Mountains National Park, 
B from lower altitudes. 
is the same view of more nearly typical 
specimens taken at lower elevations. ‘The 
difference in color pattern is quite notice- 
able even in old pinned specimens. “he 
nymph of this variant, fig. 37, differs from 
typical specimens from elsewhere in its 
generally lighter color and in the com- 
parative absence of numerous short, stout 
setae which usually give the nymphs a 
freckled appearance (Frison 1935a, figs. 
307 and 308). 
Acroneuria arida (Hagen) 
Perla arida Hagen (1861, p. 18). Original 
description, ¢, @. 
Perla valida Banks (1906a, p. 32). Orig- 
inal description, @. Previously correctly syn- 
onymized by Needham & Claassen (1922). 
Acroneuria arida Needham & Claassen 
€1925,.p2 185) 4p part. 
Acroneuria arida Claassen (1940, p. 172). 
Catalogue—in part. 
Through the courtesy of Dr. Nathan 
Banks, I have had the privilege of study- 
ing in considerable detail the types of 
Perla arida Hagen (1 female, No. 14,386) 
and P. valida Banks (1 female, No. 11, 
315), both in the collection of the Mu- 
seum of Comparative Zoology. Because 
of the importance of establishing the pres- 
ence or absence of anal gill remnants on 
the subanal lobes, the apical abdominal 
segments of the typic female of arida from 
“Philadelphia—Winthem” were clipped 
Vol. 22, Art. 2 
from the abdomen, softened in potassium 
hydroxide and studied in fluid. The typic 
female of valida is from “Waynesville, N. 
C., July, 1901, F. Shermans 
Needham & Claassen (1922) were cox- 
rect in placing valida as a synonym of 
arida, but in 1925 they confused another 
species with arida which led me (1935a) 
to an erroneous assignment of certain IIli- 
nois specimens to this species. These Illi- 
nois specimens belong to a species which 
was described later by Claassen (19370), 
on the basis of a single adult female, as 
prolonga, which in turn is a synonym of 
evoluta Klapalek, as I am now using this 
name. 
Studies of the types involved, the rear- 
ing of evoluta (= arida Frison 1935a) 
and comparisons of extensive material in 
the Illinois Natural History Survey col- 
lection all have established that evoluta is 
a species with anal abdominal gills in the 
nymph and subanal gill remnants in the 
adult, and that arida (== valida) lacks 
such structures in the adult, and, of course, 
this means that the nymph when discoy- 
ered will not possess anal abdominal gills. 
A fundamental character for the sepa- 
ration of arida from evoluta, as now recog- 
nized, having been established, the differ- 
ences previously observed in the shape of 
the subgenital plate of the females become 
understandable as specific differences. In 
arida, the subgenital plate is much con- 
stricted at its base, fig. 39, so that the end 
portion is much broader than its base, 
whereas in evoluta the base is not, or but 
slightly, constricted (Frison 1935a, figs. 
242-3). 
Although Klapalek (1909) records 
three males and one female of valida from 
“North Carol. Morr.” in the Selys Long- 
champs collection, no description or illus- 
tration is given of the male, and it 1s 
possible that these specimens, particularly 
the males, are not arida. Klapalek failed 
to recognize arida as a valid species and 
erroneously placed it in the synonymy of 
arenosa (Pictet). 
Since the male of arida has not been 
previously described (Needham & Claas- 
sen 1925 description is undoubtedly male 
of evoluta), I present fig. 39 and the fol- 
lowing brief description. a 
Mave.—General habitus the same as 
for other species of Acroneuria from 
North America. Dorsum of head yellow 
