HEAD, MOUTH-PARTS, ORTHOPTEIL\ EUPLEXOPTER.\ 261 



The clypeolabral suture (els) is distinct and complete in all, 

 except Orchelimum, where it is represented by a transverse 

 fold; in Stenopelmatus the mesal portion and in Diapheromera 

 the lateral portions are obsolete. The suture in IMelanoplus is 

 irregular, the clypeus is emarginate on the meson. 



The laterocaudal angles of the clypeus are produced into small 

 lobes which are emarginate on the cephalic and ventral aspects. 

 These emarginations form the precoilae in which the preartes of 

 the mandibles articulate. The precoilae (pr) are distinct and 

 practically similar in all. They are conspicuous in Mantis, 

 Diapheromera, and Stenopelmatus (fig. 6). 



The small chitinized structures at the lateral ends of the cly- 

 peolabral suture are the dorsal parts of the tormae (tm). They 

 extend on to the ventral aspect and are the landmarks indicating 

 the boundary between the clypeus and labrum. Tormae are 

 present in all the genera studied. 



The labrum (/) in Blatta is flexible, its lateral margins are 

 rounded, and its cephalic margin is emarginate. The emargi- 

 nation is marked on each side by an oblique blackish thickening 

 and bears spinulae. The labrum, although varying in size and 

 shape, is distinct and well developed in all. 



The tentorium is the endoskeleton of the head and is always 

 well developed. Its form is closely related with and to a large 

 extent influenced by the development and direction of the mouth- 

 parts. It is expanded and comparatively thin in Blatta (fig. 36) ; 

 thick and heavily chitinized in Mantis (fig. 41), Gryllus (fig. 37), 

 Stenopelmatus (fig. 43), IMelanoplus (fig. 39), and Anisolabis 

 (figs. 32 and 42). The cephalic portion is reduced in Diaphero- 

 mera (fig. 38) and elongated and enlarged in Anisolabis. The 

 location of the external markings or invaginations of the arms of 

 the tentorium have been described elsewhere. The tentorium in 

 Blatta (figs. 36 and 45) is composed of the typical parts, namely, 

 the metatentoria (mt), corpotentorium (d), pretentoria (pt), 1am- 

 inatentorium (It), and supratentoria (st). The corpotentorium 

 is the cuticular plate connecting the postgenae within the head; 

 it is formed by the fusion of the mesal portions of the meta- 

 tentoria. The ental plate surrounding the lateral and caudal 



