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XIII. Genus PACHYNEMATUS Konow. 
Pachynematus Konow. Deutsche Entom. Zeits., xxxiv, 1890, p. 238. 
Body short, rather stout; clypeus emarginate at apex; inner tooth of claw gen- 
erally minute and at right angles to outer; antennae of the male long, more or less 
compressed; female shorter, suhsetaceous, usually "black; pentagonal area of vertex 
distinct; eighth dorsal segment of the male broad, wide at tip; hypopygium sub- 
triangular, produced at apex; sheath of female short, stout. — Konow. 
This genus is characterized chiefly by the short inner tooth of claw 
projecting nearly at right angles with the claw and the emarginate 
clypeus, together with the distinctly developed ridges to the ocellar 
basin (pentagonal area). Its American representatives maybe readily 
divided into three well-marked groups. The first is the smaller of the 
three groups and is characterized by the large, greatly projecting, 
and rounded, flattened sheath of the female. The rest of the species 
are separated into two well-marked groups by the characters of the 
head and antennae. In one the head is very strongly developed and 
widens notably back of the compound eyes, particularly in the case of the 
females, and with the males the antenme are very long, cylindrical, and 
not at all or scarcely compressed. In the other group the head nar- 
rows in both sexes back of the compound eyes, and the antenme in the 
males are comparatively short, usually robust, and very strongly com- 
pressed. The first of these latter subdivisions, or the second group of 
species, has a typical representative in the wheat and grass sawfly 
(Pachynematus extensicornis Norton), the habits of which are described 
and illustrated in Insect Life, iv, pp. 174-177, fig. 14. The species was 
then referred to marylandicus, but it now appears that Norton's earlier 
description of extensicornis was of the male of this species. The close 
similarity of the species in this group in structural characters suggests 
a like similarity in habits, and we may therefore expect most of them 
to be grass feeders. They represent all sections of the country, from 
Maine to California. The third group approaches very closely in char- 
acters the following genus {Lygceonematus) in that the clypeus is often 
only slightly emarginate, and the separation and reference is therefore 
not entirely satisfactory in all cases. 
TABLE OF SPECIES. 
Females. 
I. Sheath very large, projecting free at least one-half its length, not or scarcely taper- 
ing, rounded at apex. 
Second recurrent usually interstitial; prevailing color black or dark brown. 
Lobes of clypeus triangular ; clypeus and labrum very hairy ; venter infus- 
cated 1. dimmockii Cresson. 
Lobes broad, rounded; clypeus and labrum nearly smooth; venter pallid. 
2. ruralis Cresson. 
Second recurrent not interstitial; prevailing colors yellow or resinous. 
3. oereatus Harrington. 
