ODONTOCERIDZ. 
the front margin. The pleure are contiguous behind the small, 
triangular gula. 
The Thorax.—The pronotum is extended in a thorn-like point 
at each cephalic corner. 
The mesonotum is completely chitinized. 
The metathorax bears two broad chitinous plates transversely 
across the dorsal surface, and a single plate on each side. 
PSILOTRETA FRONTALIS. 
Hasirat.—Psilotreta larve inhabit almost all of the larger 
streams of the uplands, but are never found near Cayuga Lake’s 
level. They are especially abundant in Mud Creek, near Free- 
ville. 
In the upland streams the larve are confined to the riffles, 
and the portions of the streams with stony bottoms. 
Hasits.—During their early life the larve are free moving, 
crawling over the stream’s bottom. At this time they show no 
evidence of social instinct, coming together only by chance in 
their wanderings. 
In the early spring, just before pupation, the larve develop 
a remarkable gregarious habit. Almost all of the larve within 
certain areas of the stream congregate on the sides of a few se- 
lected stones in such numbers that their cases are sometimes piled 
one on top of another to a depth of an inch or more, while other 
stones of the region are entirely uninhabited. The cases are al- 
ways placed parallel to each other, with their cephalic ends directed 
toward the surface of the water. Such congregations of cases 
may often be removed entire from the supporting stone, when the 
mass has much the form of a cord of neatly cut wood. 
Periop oF Emercinc.—Adults emerge during the latter week 
of May and the first week of June. 
DEscripTION oF LarvA.—Color in life deep blue-green. 
Head —On the dorsal surface the head is flattened. In color 
it is deep mahogany-brown, with a light line commencing at each 
eye and extending back to the caudal margin, and a narrow light 
cephalic border to the labrum, figure 162. On the ventral surface 
the head has a light-brown median mark, which shades into deep 
mahogany-brown toward the lateral margins. 
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