1922] Otanes: Head and Mouth-Parts of Mecoptera 315 



The ventral margin is distinctly emarginate. That of Bittacus (Fig. 3) 

 is elongated, narrows gradually ventrad and is slightly rounded at the 

 apex. Its ventral half is fringed along the lateral margin with setae, 

 those toward the apex being rather prominent. The dorsal half of 

 the lateral margin is thin and folded mesad (Fig. 52). The ventral 

 portion of each lateral fold is also fringed with rather small setae. The 

 labmm of Apterobittacus (Fig. 5) is very similar to that of Bittacus. 

 That of Panorpa (Fig. 10) is reduced on account of the great elongation 

 of the fronto-clypeus. It is chordate in shape and its apical margin 

 is emarginate. Each lateral margin is fringed with setae, which are 

 more prominent and are present in larger numbers than in Bittacus. 

 Boreus (Fig. 14) has Hkewise a reduced labmm, which is rounded, 

 fleshy and densely setiferous at the apical margin. The setae of the 

 distal margin are minute. The labrum of Merope (Fig. 7) has a bluntly 

 pointed apex and its free margins are densely fringed with rather long 

 setae. The cephalic surface is also clothed with short setcC, an oblique 

 row of such setae being recognizable along each side of the meson. 



In all the genera studied, the occipital foramen (of. Figs. 17, 19, 22), 

 24, 25, 26) is of considerable size and is divided into two parts by a 

 strongly chitinized bridge designated as the corpotentorium (ct) , 

 or body of the tentorium. The dorsal or upper portion of the occipital 

 foramen is larger than the ventral, with the exception of Bittacus, 

 where they are almost of the same size. At each ventro-lateral margin 

 of the dorsal portion of the occipital foramen is a strongly chitinized 

 triangular projection known as an odontoidea (od), which serves as a 

 point of articulation for a cervepisternum (ccs), a chitinized lateral 

 sclerite of the cervix or neck which connects the head and the thorax. 

 The membrane connecting the neck and the head is the cervicoria (cc). 

 The odontoidea are more prominent in Panorpa and Panorpodes 

 than in Bittacus, Apterobittacus and Boreus. They can hardly be 

 identified in Merope. 



That part of the head adjacent to the occipital foramen and dorsad 

 of the odontoideae is known as the occiput (oc). In sorne insects, as 

 in the grasshopper {Melanoplus differentialis) the occiput can be 

 differentiated because of the partial presence of the occipital suture. 

 It is divided along the meson by the epicranial stem. In all the mecop- 

 terous insects studied, the occiput is merged with the vertex owing to 

 the obsolescence of the occipital suture. , 



In the Orthoptera, as in the grasshopper, there are two distmct 

 sclerites, known as the postgenae (pa), ventrad of the occiput, one on 

 each side of the occipital foramen. In the same insect, there is a trans- 

 verse suture which separates the occiput and a postgena. The suture 

 in question is designated as the occipito-postgenal suture. In the 

 mecopterous heads studied, the postgenae are continuous with the vertex 

 and occiput. In the absence of the occipito-postgenal suture, the 

 odontoidea3 may be used as landmarks in determining the point of 

 division between the occiput and each postgena. In all the species 

 treated in this paper, the postgenae are of considerable size and m 

 Boreus and Panorpa, they are prolonged ventrad as a narrow area. 



