28 THOMAS SAY FOUNDATION 
being a little closer to each other than to the eyes; on either side 
of the ocellar triangle a rounded reddish spot, and a reddish V- 
or M-shaped mark in front of the ocellar triangle; occiput with 
longitudinal reticulations; supra-antennal plates well developed. 
Prothorax about twice as wide as long with flaring sides and 
with its angles more or less produced; surface of pronotum with 
embossed markings; meso- and metanotum with coloration simi- 
lar to that of pronotum but less rugose ; in some species the lateral 
margins of pronotum and wing pads are lighter. Legs stout, 
brown; femora usually with a narrow median lighter line above; 
outer margin of femora and tibia fringed with hairs; first two 
segments of tarsus short, the first about twice as long as the 
second, the third at least twice as long as one and two together ; 
two tarsal claws, each with a blunt tooth at the inner base. 
Abdomen cylindric, segments either smooth or with lateral 
teeth. In the female the tenth abdominal tergite is medially 
produced into a sharp triangular conical process, while in the 
male it is variously modified; cerci rather short, containing up 
to forty or more segments. 
The thirteen pairs of gills on the ventral side copious and long, 
and arranged as follows: prothorax with five pairs, three pairs 
in front of the prothoracic legs arranged as a transverse collar 
along the neck, and two pairs just posterior to the front pair 
of legs; three pairs on the mesothorax; three pairs on the meta- 
thorax and one pair on each of the first two abdominal segments. 
Mandibles asymmetrical, the dentation of the left and right 
mandibles being different. The left mandible has the following 
five sharp teeth: first, second, and fourth longest, largest, and 
most pronounced; third and fifth teeth small, and, in some eases, 
fifth rather inconspicuous. These five teeth followed by a large 
molar, and beyond this the mandible bears a buneh of long 
hairs. The right mandible has four teeth, the first two of which 
are largest; following the fourth tooth which is the smallest, a 
large quadrangular molar, and this is likewise followed by a 
brush of hairs. 
Labrum almost exactly twice as wide as long, with long hairs 
on the front margin, which is concave in the center; hind margin 
somewhat sinuate; posterior angles sharp; chitinous prolonga- 
tion for muscle attachment about one-third as long as width of 
labrum. 
Maxillae: maxillary palpus composed of five rather stout seg- 
ments; segment one a trifle longer than wide, segment two about 
one-fifth longer than wide, segment three half again as long as 
wide, segment four slightly less than twice as long as wide, seg- 
