LIBRARY

PLECOPTERA 153
temperate, the arctic, and the antarctic regions. There are approximately 100
genera and 1,260 species described.
Handlirsch (1925) groups all the members into a single family, PERLIDlE, and
six subfamilies: T JENIOPTERYGINlE, NEMOURINlE, PERLINJE, PTER­
ONARCINlE, GRIPOPTERYGINlE, and CAPNIINJE. Ordinarily, however,
five or seven families are recognized as follows: PTERONARCIDlE,
NEMOURIDlE, PERLIDJE, CAPNIIDlE, AUSTROPERLIDJE, EUS­
THENIIDlE, and LEPTOPERLIDLE. The last three Australasian families
are often combined in the single family GRIPOPTERYGIDJE. The TlENI­
OPTERYGIDlE may also be set apart from the NEMOURID.tE as a separate
family.
KEY TO FAMILIES OF NORTHERN HEMISPHERE 1
ADULTS
1. Anal area of fore wing with two or more full rows of cross veins
PTERONARCIDlE p. 154
Anal area of fore wing either with no cross veins or, if they are present,
with but one row . 2
2. Cerci one-segmented or much reduced . NEMOURIDlE p. 156
Cerci many-segmented and well developed 3
3. Fore wings with a series of median and cubital cross veins; radius and
media are incompletely fused and separate gradually at the base except
in small greenish-colored forms . PERLIDlE p. 156
4. Fore wings with only one or two median and one cubital cross vein;
radius and media are completely fused at base and separate at a
rather sharp angle. . CAPNIIDlE p. 157
NAIADS OR NYMPHS 2
1. Gills visible . 2
Gills invisible. 4
2. Gills under the thorax and first two or three abdominal segments (prosternum
wider than head, ligula four-lobed; mostly large dark-brown
nymphs; herbivorous) .PTERONARClDlE p.154
Gills only on the thorax. 3
3. Gills on the underside of the prothorax (a pair p.ither at the throat or as
single filaments at the base of each coxa; hind wing pads diverge outward
from the body except in Leuctra, where they are long and narrow
and lie parallel to the body; and labial palpi extend far beyond tip of
ligula) (in part) . . NEMOURIDlE p. 156
Gills on all three thoracic segments arranged as filamentous tufts on the
sides; legs densely fringed with long hairs (first and second tarsal segments
very short, subequal. together less than half as long as third;
labrum three to four times as wide as long; labial paJpi slender and
extend far beyond tip of the labium, which is two-lobed; mandibles
1 After Needham and Claassen (1925, p. 31).
2 After Qaassen (1931) and other sources.