AND MOl'TH-PARTS OF CHLOROPS T^NIOPUS. 403 
.represents the fronto-clypeus. If it only represents the clypeus, the frons is 
represented by the intervening membrane uniting it to the dorsal edge of the 
oral depression. 
Only in Mycetoplnla among the Dipterous types studied by Peterson is the 
stem of the epicranial suture complete. Some forms {Rhahdoplmga, Mycetohia, 
Tahanus) " show depressions or thickenings along the meson. These marks 
may have no significance'' (p. 15). In Chlorops there is a very distinct 
internal ridge running along the meson from the median ocellus to the 
median point of the dorsal edge of the frontal suture. 
TORM^ AND FrONTO-CLYPBUS. 
In the base of the rostrum there is a somewhat complex chitinous structure 
usually termed the fulcrum (fig. 4), part of which is internal and is formed 
by the chitinized basipharynx, and part of which is superficial and is, as 
stated above, the clypeus or fronto-clypeus. The interniil portion will be 
Fig. 4. 
05 mm 
Ventro-lateral view of basiphaiynx, tornife, and clvpeus. 
considered later ; it consists of dorsal and ventral plates enclosing between 
them the pharyngeal cavity. A vertical chitinous plate (i) on each side unites 
one side of the superficial plate (clypeus) to the corresponding side of the 
basipharynx. Peterson regards these, together with the superficial plate 
which I consider to be the clypeus (or fronto-clypeus), as the Tormre. 
"The tormse in generalized insects are chitinized pieces which belong to 
the lateral portions of the epipharynx in the region of' the clypeo-labral 
suture and connect with the clypeus or labrum at the lateral ends of the 
suture. . . . The tormse of generalized Diptera also connect with the inner 
surface of the ventral portion of the fronto-clypeus " (Peterson, p. 19). The 
basipharynx is composed of united epipharynx and hypopharynx. Thus, by 
accepting the view that the superficial plate is the clypeus or fronto-clypeus, 
