THE ROUGH-HEADED CORN STALK-BEETLE 27 
head is of a distinctly reddish color but, unlike Z. rugiceps, the head 
is smooth or at most but slightly rugulose, lacking almost entirely 
the deep punctures which are so conspicuous in the latter species. 
(Pl. Il, A and &.) Furthermore, in the larva of Z. gibbosus there 
is no trace of a median double row of modified bristles on the last 
ventral segment, such as occurs in £. 
rugiceps. (Pl. III, D and £.) 
PUPA 
The pupa of Z. gibbosus (Pl. IV, B) 
is distinguished from that of /. rugi- 
ceps by certain characters associated 
with the mouth parts, by the form and 
position of the postcoxal process of the : 
prosternum, and by the prominent bi- Fre. 13—ventral view of head re- 
costate elytral pads (PL IV, A and B, fin of pupal of Ligyrus ait, 
and figs. 4 and 13). The mandibles mouth parts. (Drawn by Henry 
: ‘ox from a photograph by J. H. 
(fig. 13) are much smaller and slen- Paine) 
derer than those of #. rugiceps, and are. 
further characterized by the truncate, not angulate, apex which lies 
in contact with the nearly straight sides ef the labrum. The maxil- 
lary palpi are also shorter and rather more rounded at the apex than 
in EL’, rugiceps. The postcoxal process of the prosternum is less nearly 
erect and the apex is rather more acuminate than in £’, rugiceps. 
ADULT 
In general form and size the adult of 
L. gibbosus (fig. 14) resembles that of 2. 
rugiceps, but is usually distinguishable 
at a glance by its reddish brown color 
and by the distinctly hirsute character of 
its ventral surface. Occasionally adults 
are found in which the color is so dark 
as to be almost black. The most reliable 
differential character is the presence 1n 
L. gibbosus of a median pit or depression 
close to the anterior margin of the pro- 
notum, which is entirely lacking in £. 
rugiceps. In front of this pit is a blunt 
spine or tubercle. Other distinguishing 
characters of L. gibbosus are the absence 
; of transverse rugule and the presence of 
ee faen tty Henny Foxy a continuous transverse ridge on the dor- 
sal surface of the head. 
The stridulating areas on the inner surface of the elytra are well 
developed in Z. gibbosus and are capable of producing a low but 
audible sound, which is usually heard whenever the beetles are han- 
dled. In Z. rugiceps the stridulating area is barely recognizable and 
is apparently functionless. 
