8 PROCEEDINGS OF THE NATIONAL MUSEUM. You. 62. 
they will be used more in the classification of the species, as they 
have been used in other groups of the diptera. 
The legs of most of the species are long and not very heavy, the 
hind legs longer than the others. The anterior coxae have two (or 
more) bristles in front near the tip, the hind coxae have one bristle 
outside near the middle and two similar or smaller ones in front near 
the tip. The femora may be bare or with one or several bristles; the 
hind femora usually have a row of anteroventral bristles. There is 
often long pile on the femora, especially in the male. The front 
tibiae usually have two or three rows of small bristles, the hind tibiae 
often as many as four rows, and there are about six bristles in the 
circlet at the apex of the tibiae. As a rule the tarsi are slender, with 
short apical spines, the posterior tarsi with short plantar bristles on 
the basal joint. There are two small pulvilli (absent in the foreign 
Caenophanomyia). The empodia are wanting, or represented by a 
bristle, thus distinguishing the species from the Rhagionidae. The 
arrangement of the bristles on the legs is not very constant but may, 
when studied carefully, furnish specific characters. 
There is a remarkable uniformity in the wing venation, the general 
plan being the same throughout the family, the new genus Caenotus 
showing the greatest departure from the normal type. In this paper 
the Comstock system will be used in place of the older Schinerian 
system, and the modification of it used by Williston and adopted by 
most of the dipterists in this country. In the Therevidae, R—4 and 
R-5 fork some distance from the end of the wing and the upper fork 
is noticeably curved in some of the genera, including Psilocephala and 
Thereva. . The vein R-5 always ends in the wing margin, except in 
Xestomyza, where the lower fork drops down to the vein M-1. In 
Metaphragma there is a spurious cross vein connecting R-5 and M-1 
beyond the fureation of Rs. The cell M-3 is open or closed, there 
being a certain amount of individual variation here, but the character 
usually holds for the species. The cell first A (anal cell) is always 
long and closed near or in the margin; cell R is longer than second 
M. Although the genera Henicomyia and Nebritus are quite aberrant 
in some respects they have a normal venation. In the genus Phero- 
cera M-2 does not reach the wing margin and Cu—1 and M-3 coalesce 
far before the wing margin and stop short of it; insome specimens M—2 
reaches the wing margin and in some it does not; also there seems to 
be a tendency for M—2 to branch near M-1 and for an extra cross vein 
to form. Abnormalities of venation are not infrequent. There is in 
many species a semicircular cloud at the outer side of cell first M-2 
(discal cell), called a ‘‘ Bogenwisch”’ by Kréber; an apical spot is also 
present in some, the cross veins are clouded in many, and there may 
be spots and bands on the wing, or a general infuscation. Meta- 
phragma is the only genus having a supernumerary cross vein between 
