— - ee 
——————— 
May, 1953 
member and a lower, filamentous tuft, fig. 
225. These characteristics may be contrasted 
with those of the members of the Siphlon- 
urinae, as given on page 98 above. 
28. ISONYCHIA 
Isonychia Eaton (1871: 134). 
Chirotonetes Eaton (1881:21). 
unnecessarily proposed. 
Jolia Eaton (1881:192). 
Chirotenetes Needham (1905: 
Misspelling. 
Eaton 
New name, 
Za) re 
In Isonychia, the adult males have large 
compound eyes that are contiguous on the 
dorsal meson; each of these eyes is composed 
of an upper portion of large facets and an 
indistinctly separated lower portion of 
smaller facets. The outer surface of each 
eye is crossed by a pair of oblique, contrast- 
ingly colored stripes. Each compound eye in 
the adult females is approximately one-half 
the size of that of the males, and usually it 
has a single, broad, light-colored stripe ex- 
tending across the outer surface. 
In both sexes of all the species of [sonychia 
occurring in eastern North America, the 
fore leg is mostly or entirely red-brown, 
and the middle and hind legs are light yel- 
low or white. The fore tarsus in the males 
is approximately equal in length to the fore 
tibia, and is only one and one-third to one 
and one-half times as long as the fore tarsus 
in the females. The hind tarsus in both 
sexes has four clearly differentiated seg- 
ments. The wings, fig. 217, are relatively 
broader and shorter than in the members 
of the subfamily Siphlonurinae. The fore 
wing has the stigmal crossveins sometimes 
anastomosed, and the cubital intercalaries 
extend from vein Cu, to the anal wing mar- 
gin as a series of sinuate, branched veins. 
The hind wing lacks an angulate or acute, 
basal costal projection, and vein M is forked 
very near the outer wing margin. Rudi- 
mentary gills persist on the fore coxa in the 
adults of both sexes. There is a large, 
blunt, median projection on the meso- 
sternum, between the mid-coxae. 
The male genitalia are composed of a 
pair of short penis lobes and a pair of four- 
segmented forceps, the first segment of each 
arm being very obscurely set off. The for- 
ceps base is medianly excavated to form a 
more or less U-shaped cavity, and the char- 
acteristically short, stubby penes lie over or 
within this cavity, figs. 248-253. In this 
Burks: THe Mayr ties oF ILLINOIS 
109 
genus, there are four types of penis lobes: 
the sicca, fig. 252, the bicolor, fig. 253, the 
diversa, fig. 249, and the sayi, fig. 248. The 
terminal abdominal sternite in the adult 
females is usually emarginate on the meson 
of the posterior margin. The median caudal 
filament in both sexes is represented by a 
minute vestige. 
The nymphs, fig. 254, are streamlined, 
vigorously swimming forms which invari- 
ably develop in the rapidly flowing water of 
creeks and smaller rivers. They are known 
to be in part predaceous (Morgan 1913 :386; 
Clemens 1917:23); their food is principally 
vegetable detritus and algae, especially dia- 
toms. Each maxilla and fore ccxa bears 
tufts of filamentous gills. Each tarsal claw 
is single, acutely pointed, and short, being 
only one-fourth to one-third as long as the 
tibia. Each fore leg has a dense comb of 
long, stout setae on the inner margin, fiz. 
254. This comb of setae is used in gathering 
food. Each fore tibia bears an apical spur 
which is nearly one-half as long zs the fore 
tarsus. Each abdominal segment has small, 
flat, lateral expansions at the lateral mar- 
gins; the posterolateral angles of these ex- 
pansions are produced as large, spinelike 
projections on segments 8 and 9. Abdominal 
segments 1-7 bear each a pair of gills, the 
individual gill being composed of a dorsal, 
platelike member and a ventral, filamentous 
tuft, fig. 225. There are three well-devel- 
oped caudal filaments, and each cercus has 
a dense fringe of setae on the inner side 
only. 
Reliable characteristics for the separation 
to species of nymphs and females of this 
genus have not yet been found. 
KEY TO' SPECIES 
Avuttr Mates 
1. Forceps base with only a shallow, median 
excavation so that penis lobes are al- 
most completely hidden when viewed 
from ventral side; penis lobes with acute 
lateral teeth, fig. 248....-... 1. sayi 
Forceps base with a deep caudal excava- 
tion so that penis lobes are exposed 
when viewed from ventral side; penis 
lobes without lateral teeth, figs. 249- 
DISS UE ian MR octctmen ee en rad ee RS. ue 2 
2. Penis lobes relatively long, mushroom 
shaped at apexes, fig. 249...2. diversa 
Fenis lobes not mushroom shaped at 
ANEKES mC S 4625) DO Or eet kn acre 3 
3. Fore tibia white, shaded with brown at 
baserandeaiacapex meni. serene: 3. arida 
