PLECOPTERA NYMPHS OF NORTH AMERICA 59 
ments very short, sub-equal, and the two together about one- 
fourth as long as the third segment. Abdomen somewhat flat- 
tened. Cerei quite short, usually not much more than one-fourth 
the length of the body; stout at base and tapering to a slen- 
der tip; thirteen to fifteen, or possibly up to eighteen segments, 
which are hairy and bear on the posterior margin a whorl of long 
hairs. 
Gills absent. 
Mouth parts. Labrum very short and about four times as wide 
as long, clothed with long hairs; front margin with long hairs. 
Mandibles rather narrow; asymmetrical; left one with five more 
or less distinct unequal teeth; right one with six unequal teeth 
grouped by threes; following the teeth, on the inner margin of 
each mandible, a series of long stiff hairs; a second row of hairs 
on the ventral surface extends from the base of the teeth diago- 
nally rearward to the inner base of the mandible. Maxillae: lacinia 
broad at base, gradually tapering and ending in a single incurved 
apical tooth, sometimes with an indication of a second short tooth ; 
inner margin with a row of long stout hairs; galea slender, cy- 
lindrie, shorter than the lacinia, and at the tip with a small 
buneh of hairs; maxillary palpus with the first two segments 
wider than long, subequal; third segment about three times as 
long as second; fourth segment longer than third and slightly 
produced on the inner apex, which bears a group of hairs; fifth 
segment very slender and not more than half as long as fourth. 
Labium. Glossae minute, triangular; paraglossae large, directed 
inwards at tip and covered with hairs. First segment of palpus 
not more than half as long as second; apical segment shorter than 
second and not more than half as wide. Mentum a narrow, trans- 
verse, broadly triangular band; submentum very large, wider 
than long, hairy. Hypopharynx rounded, closely beset with hairs, 
and normally extending to, or nearly to, the tip of the para- 
olossae. 
The sexes in this genus are not readily distinguishable. 
Inasmuch as the coloration of the nymphs of this genus is 
rather uniformly brown it is quite difficult to identify the dif- 
ferent species. Identification of the following species has been 
possible only through rearing records or by adult-genitalia char- 
acters which could be detected in mature nymphs. Little is known 
of the biology or life cycle of the nymphs of this genus, but the 
life cycle appears to occupy one year. 
Alloperla is generally distributed over the entire North Ameri- 
can continent. 
