404 MR. J. G. H. FREW : MORPHOLOGY OF THE HEAD CAPSULE 
it will be seen that the lateral vertical plates bave absolutely typical relation- 
ships as torma?. According to Peterson's view that the lateral plates and the 
superficial plate represent tormaj alone, the tormfe ol: the Cyclorrliapha are 
strikingly different in their relationships from the tormae of generalized 
insects or of the Orthorrhapha ; a difference which he hardly attempts to 
exi^lain. 
As in the remainder o£ this paper I shall have no cause to disagree with 
Peterson's views, it maybe useful to summarize here the points of difference. 
In Chlorops I consider that the tentorium clearly consists of the three typical 
arms ; this may, however, be a special case, as it certainly appears to be 
judging from Peterson's figures, and not general to all Oyclorrhapha. The 
following points, however, are almost certainly applicable to all Cyclor- 
rliapha : — 
1. The position of the arms of the epicranial suture is marked by the 
dorsal and lateral borders of the oral depression. 
2. All regions of the head lying dorsal and lateral to the oral depression 
are derived from the paired sclarites of the head, and the frons and 
clypeus must lie within the oral depression. 
3. The antennse arise on the vertex. 
4. The superficial plate of the fulcrum is the clypeus or fronto-clypeus. 
5. The tormse are the chitinized plates joining the sides of the clypeus 
to the sides of the chitinized basipharynx. 
It cannot be claimed that absolutely rigid proof of any one of the above 
statements has been given. The evidence in support of them seems to me, 
however, to be very strong, and their acceptance appeal's to afford a very 
much clearer explanation of the nature of the facial aspect of the Cyclor- 
rhaphous head capsule than does Peterson's homology, and, moreover, 
brings the Cyclorrhaphous head capsule more into line with that of the 
Orthorrhapha or of generalized insects. 
Ihe Ptilinum shows no mai'ked peculiarities. It lies within the head 
capsule close against its anterior wall. The frontal suture {f.s.) lies just 
dorsal to the antennal bases. 
The Labrum (figs. 1, 5, & 6) is a rather heavily chitinized ti-iangular 
sclerite lying along the dorsal surface of the mediproboscis, its base being- 
continuous with the dorsal membrane of the distal end of the basiproboscis, 
so that it is separated from the clypeus by a considerable extent of membrane 
— a condition which is usual, Init uot universal, in Diptera (Peterson, pp. 20- 
21). The ventral surface of the labrum is longitiuiiually grooved for the 
reception of the epipbarynx, which fits tightly within the groove and cannot 
be removed without damaging the labrum. The epipbarynx does not extend 
quite to the distal end of the labrum, and just beyond its termination the 
labral groove bears two small conical papilhe, one on each side, which have 
