THE ROUGH-HEADED COEN STALK-BEETLE 



27 



head is of a distinctly reddish color but, unlike E. rugiceps, the head 

 is smooth or at most but slightly rugulose, lacking almost entirely 

 the deep pimctures which are so conspicuous in the latter species. 

 (PI. Ill, A and B.) Furthermore, in the larva of L. gibbosus there 

 is no trace of a median double row of modified bristles on the last 

 ventral segment, such as occurs in E. 

 rugiceps. (PL III, D and E.) 



Fig. 13. — Ventral view of head re- 

 gion of pupa of Ligyrus gib- 

 bosus, showing structure of 

 mouth parts. (Drawn by Henry 

 Fox from, a photograph by J. H. 

 Paine) 



The pupa of L. gibbosus (PI. IV, B) 

 is distinguished from that of E. rugi- 

 ceps by certain . characters associated 

 with the mouth parts, by the form and 

 position of the postcoxal process of the 

 presternum, and by the prominent bi- 

 costate elytral pads (PL IV, A and Z?, 

 and figs. 4 and 13). The mandibles 

 (fig. 13) are much smaller and slen- 

 derer than those of E. rugiceps, and are 

 further characterized by the truncate, not angulate, apex which lies 

 in contact with the nearly straight sides of the labrum. The maxil- 

 lary palpi are also shorter and rather more rounded at the apex than 

 in E. rugiceps. The postcoxal process of the presternum is less nearly 

 erect and the apex is rather more acuminate than in E. rugiceps. 



In general form and size the adult of 

 L. gibbosus (fig. 14) resembles that of E. 

 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 in 

 L. gibbosus of a median pit or depression 

 close to the anterior margin of the pro- 

 notum, which is entirely lacking in E. 

 rugiceps. In front of this pit is a blunt 

 spine or tubercle. Other distinguishing 

 characters of L. gibbosus are the absence 

 of transverse rugulse and the presence of 

 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 L. gibbosus and are capable of producing a low but 

 audible sound, which is usually heard whenever the beetles are han- 

 dled. In E. rugiceps the stridulal ing area is barely recognizable and 

 is apparently functionless. 



Fig. 14. — Ugyrua gibbosus: Adult. 

 (Drawn by Henry Pox) 



