716 The American Naturalist. [August, 
frenulum (i. e., frenulum in which the hairs are not united 
into one single strong spine) of the lepidopterous wing. This 
- trichopterous frenulum is, however, much shorter than the 
lepidopterous frenulum and does not fit into a frenulum hook | 
on the under surface of the fore wing, but merely rests against 
the jugum of the fore:wing. The jugum is fairly well devel- 
oped but can hardly overlap the base of the hind wing much, 
The series of tying hooks extends along the costal margin 
from near the base of the wing for 
about one-third the length of the 
margin. I have figured the method 
of wing tying for another species 
(see Fig. 9) which, however, illus- 
trates the method and the function- 
ing structures quite as truly for Hal- 
lesus sp. In the species figured, the 
hooks method, combined with the 
overlapping of the opposed margins 
of the wings, is the only means of 
union, the small, jugum-like structure at the base of the fore 
wing being practically functionless. When the wings are ex- 
tended a narrow space along the inner margin of the fore 
wing, roughened on its under surface by many short, strong, 
sharp-pointed bristles, and with the membrane greatly strength- 
ened and made less yielding by these bristles, is underlain by 
the costal margin of the hind wing for a distance of more than 
half the length of the margin. Along the extreme costal bor- 
der of this underlying space, which is slightly expanded cos- 
tal-wards, there is a regular series of strong, hooked hairs or 
bristles, each of which bears on the concave surface of the 
curved or hooked portion many fine teeth (see c, Fig. 9). 
These toothed hooks are applied to and firmly grasp a strong, 
roughened, chitinous line or ridge running along the under 
side of the fore wing. ‘This chitinous line is roughened by 
the presence of fine ridges for the firmer grasping of the hooks. 
By the overlapping and hooking there is formed an effective 
tying together of the two wings. 
Fic. 8. Base of hind wing of 
Hallesus sp.; f, frenulum hairs. 
