316 Annals Entomological Society of America [Vol. XV, 



At the apical margin of each postgena is a distinct acetabulum, a coila, 

 known as a postcoila (ptl) in which the caudo-proximal portion of each 

 mandible is articulated. The postgense in all the species of Mecoptera 

 studied extend mesad and fuse on the meson, forming a bridge, known 

 as the genaponta (gn), which limits the ventral extent of the occipital 

 foramen. The genaponta in Boreus (Fig. 26) is a large area, whereas 

 it is very narrow in the other genera. 



In Blatta and other Orthoptera, the tentorium consists of the 

 following parts: metatentoria, carpotentorium, pretentoria, lami- 

 natentorium and supratentoria. The tentorium in the Mecoptera 

 (Figs. 37, 38, 39, 40) is not as well developed as in the Orthoptera. 

 All of the typical parts of the tentoriirm mentioned above, except the 

 laminatentorium, are present in the Mecoptera. The metatentoria 

 (mt) support the lateral margins of the occipital foramen and are pro- 

 longed mesad, fusing into a strongly chitinized bridge known as the 

 carpotentorium (ct) or body of the tentorium, and which, as has been 

 stated previously, divides the occipital foramen into two portions. 

 The points where the metatentoria are invaginated are the metaten- 

 torinse (mn); as a rule they are not very distinct in the species of 

 Mecoptera studied. The pretentoria (pt) or anterior arms of the 

 tentorium connect the caudal and the cephalic aspects of the head. 

 The places of invagination of the pretentoria are the pretentorinas (pn) , 

 which have been described elsewhere. Arising from each pretentorium 

 and connecting the latter with the ental portion of each lateral margin 

 of an antennaria is a supratentorium (st). The supratentorium are 

 best developed in BiUacus and Apterobittacus and are hardly dis- 

 tinguishable in Panorpa and Panorpodes where they are thread-like. 



MOVABLE PARTS OF THE HEAD. 



The antennas are usually long, setiferous and multiarticulated in 

 the Mecoptera. The antenna of Boreus (Fig. 35) is filiform and consists 

 of twenty-three segments. Those of Panorpodes and Panorpa, like those 

 of Boreus, are filiform and consist of a larger number of segments. 

 Bittacus (Fig. 33) has a setaceous antenna consisting of about twenty 

 segments. The antennas of Merope (Fig. 34) are very different, monili- 

 form, there being twenty-nine segments. 



The mandibles of all the species studied are decussating. Those 

 of Panorpodes oregonensis (Figs. 20, 21) are triangular and are provided 

 with two distadentes (dd), the distal one being more prominent. The 

 mesal margin is irregularly serrated. The mandibles of Panorpodes 

 carolenensis (Figs. 15, 23) differ somewhat in shape and the distadentes 

 are not as prominent. The mesal serration is more regular than that 

 of oregonensis. Those of Merope (Figs. 9, 18), Panorpa (Figs. 11, 12), 

 and Boreus (Figs. 4, 11) do not differ very much in shape from those 

 of the two species of Panorpodes. Unlike those of Panorpodes, they are 

 not serrated along the mesal margins. The mandibles of Merope and 

 Panorpa are each provided with three distadentes, the lateral one being 

 the most prominent and is especially well developed in Merope, and the 

 mesal tooth the smallest. Hine (1901) gave as one of the characteristics 



