ae PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
pogoninae, but they are, as a rule, less heavily built, have weaker 
legs, fewer bristles, and a differently shaped head; the eyes never 
bulge out conspicuously from the vertex and are usually contiguous 
in the males. The venation easily distinguishes the Therevidae from 
the Bombyliidae and the Apioceridae, the latter differing also in the 
form of the palpi. Most of the species are small or moderate in 
size, but usually over 5 mm. in length. The antennae are three- 
jointed and the radius is furcate; thus they belong to the first group 
of the Orthorrhapha Brachycera, the Tromoptera, or fourth super- 
family. The abdomen is usually more or less conical, the general 
color gray or brown, and in many species densely covered with pile. 
The males are usually more pilose than the females, and in some 
species they are silvery pollinose. There are no North American 
species with a metallic coloration. 
The head is usually hemispherical, the occiput distinct, the eyes 
large and in most genera the males have the facets on the upper 
portion noticeably larger, often with a more or less distinct line of 
division between the small and large facets. The eyes are bare and 
usually holoptic, or nearly so, in the male. In a few genera the 
eyes are separated in the male by the width of the ocelli, as in the 
foreign genera Neothereva, Platycarenum, and [etinorrhynchus, and 
the American genera Tabuda, Metaphragma, Henicomyia, and Nebri- 
tus. One species of Psilocephala described in this paper, latifrons, 
has the eyes thus widely separated, and might be placed by some 
dipterists in a new genus. The eyes of the female are always widely 
separated. Some species have the eyes colored or marked with a 
purple crossband. There are three ocelli on the small ocellar tubercle. 
Most of ‘he species have distinct orbital or post-ocular bristles. 
The writer has not followed Peterson in naming some of the 
sclerites of the head. The term ‘vertex’? as used by Peterson 
applies to the space between the eyes from the top of the head to 
the cheeks. It has been the custom of dipterists to limit the term 
“‘vertex’’ to the region of the occelli, the part from the vertex to 
the base of the antennae being called the front or frons, that from 
the base of the antennae to the genae the face. The frons in the 
Therevidae is usually flat or slightly convex, never excavated as in 
the Asilidae, and may be wholly pollinose, shining, or marked with _ 
characteristic spots and lines. The face is short and often receding 
and may be bare or pilose. The cheeks are usually quite narrow. 
The antennae are porrect, of medium or large size, situated in the 
middle of the head in profile, or a little below the middle, and are 
often on a protuberance; they are usually close together at the base. 
In most species the first antennal joint is cylindrical and rather long, 
but often greatly swollen; in Huphycus it is longer than the head. 
The second joint is shortest and usually rounded and with very short 
