464 
NORTH AMERICAN PLECOPTERA 
cross-veins, that is those which have more than a single cross- 
vein between radius and the radial sector. In color these stone- 
flies are dark brown with markings of yellow; the head is rela- 
tively large; the eyes are hemispherical; there are present three 
small ocelli arranged in an isosceles triangle, the base of which 
is greater than the sides; the tubercles are more or less conspicu- 
ous; the antennae and palpi are slender. The prothorax is 
broader than long, a median yellow stripe is usually present and 
the lateral fields are embossed. Legs are rather long; the three 
segments of the tarsi are of unequal length, the third being the 
longest, and greater than the first two taken together, the second 
segment is the shortest, it is half as great as the first. The wings 
are often shortened, especially in the males. An apical network 
of cross-veins is always present, its extent and regularity differing 
in the various genera; the accessory branches of the first cubital 
vein have a decided anterior flexure ; with the exception of 
Dictyogenusf phaleratus, in the fore-wing the first anal vein angled 
at the base, as it leaves the anal cell it runs forward to the second 
cubital vein, then it makes an abrupt posterior bend. Another 
useful venational character of generic importance in this tribe is 
the relation between the length of the inner inter-radial cell 
(1st Ri) and its base, measured to the point at which the arculus 
would meet radius if produced. Dr. Ris and Prof. Klapalek have 
used this character. 
Some of the members of this tribe are gill-bearing. In dried 
specimens the gills are very difficult to detect on account of their 
shrunken condition and small size. In alcoholics they appear as 
delicate, white, fleshy, finger-like, blind sacs. Their number 
varies in different species but is constant within a single species. 
Other species are without gills. 
In the males the ninth sternite is produced in a sub-genital 
plate; the tenth tergite is bifid in most genera (in all the genera 
that are known certainly to occur in this country) ; the sub-anal 
and supra-anal plates often modified as accessory copulatory 
organs. 
In the females the usual vulvar lamina is present. Klapdlek 
has used its form as a generic character, but his groupings contain 
such a wide range that they are not especially valuable. However, 
they s6rve as excellent specific characters. 
