6 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
buccal cavity (see fig. 1B) consists of the hypopharynx, the epi- 
pharynx, a membraneous area in posterior continuation of and rising 
above the epipharynx, and a small salivary bulb behind and fastened 
to the hypopharynx. Almost at right angles to the hypopharynx 
is the frontoclypeus, and leading back to the esophagal pump is the 
heavily chitinized basipharynx. At the top of the basipharynx on 
each side is a small appendage called the cornu. In none of the 
North American genera do we find the proboscis noticeably protruding 
(the foreign Acupalpa has needlelike mouthparts). The palpi are 
longer haired in Psilocephala than in most of the other genera and 
in Henicomyia are very peculiar in shape. 
The thorax is of moderate size, the dorsum long oval and with 
hairs and bristles; the bristles are quite uniform in general arrange- 
ment, but are apparently of no systematic importance, owing to the 
variation being mostly individual and not specific. There are from 
two to six praesutural, usually two supraalar, one postalar and one 
or two pairs of praescutellar bristles. In the new genus Caenotus 
there are no distinct thoracic bristles. ‘The mesonotum is usually 
more or less pollinose and often with longitudinal vittae; in the 
males the mesonotum is usually densely pilose, but in some forms 
almost bare in both sexes. The scutellum is medium sized and 
usually semicircular, with two to four apical bristles; it is like the 
thorax in color as arule. The squamae are small and the halteres 
are quite large; in Furcifera the squamae are hairy. 
The abdomen varies somewhat in general form, but is usually 
conical, especially in the male; in some of the foreign genera the 
abdomen is more or less modified in shape. The males of some 
genera have a silvery shimmer to the pollen on the tergites and the 
females often have silvery spots or bands. The abdomen in the 
male is usually much more pilose than in the female. As in many 
of the Asilidae, the female has a terminal circlet of spines on the 
last segment; this is lacking in the new genus Pherocera and in the 
foreign Oldenbergia. The male hypopygium is not very large in the 
majority of species and the genitalia have not been made use of in 
the past in the classification of the group, but they possess specific 
differences which are of great importance. The typical genitalia are 
shown in text figures 2 and 3. Crampton in a recent article* has 
worked out the homology of the genitalia of several orders of insects, 
including the diptera, and the writer has followed this interpretation 
of the different parts. In the Therevidae there are two plates 
forming the hypandrium, which is usually smaller than the upper 
covering of the genitalia; this upper portion is composed of the ninth 
and tenth segments combined and is called the epiproct. The gen- 
eral form of the genitalia is alike in ail the North American genera. 
3 Psyche, vol. 27, pp. 34 to 44. 
