Art. 4. REVISION OF THE FAMILY THEREVIDAE—COLE. 9 
R-5 and M-1 (in the first posterior cell). There is usually a well- 
developed stigma, often quite thick and very prominent when the 
wing is hyaline. In the new genus Caenotus there is a great coa- 
lescence of veins; in C. minutus there is no m—cu cross vein or cell M-3 
and Cu merges with M-3 in one vein, forming the bottom of cell first 
M-2 (discal cell); thus there are four veins from the cell. In the 
Therevidae only the alar pair of squamae are more or less developed, 
and these are folded so as to give the appearance of two pairs. 
HABITS OF THE ADULT THEREVIDAE. 
The habits of the adults are not well known. Some of the species 
have been reported as predaceous. Many years ago Schiner spoke of 
the adults as ‘‘robber flies’ which have a somewhat cunning and 
uneasy catlike demeanor, lurking between the leaves of low shrubs 
and being able to conceal themselves quickly. Verrall never observed 
them preying on other insects in England, and Professor Poulton was 
not able to obtain any records for his paper on the predatory diptera. 
The writer has observed several species carefully and has never seen 
them catch other insects. Williston stated that the adults fed on 
small diptera, lying in wait for them on the ground or upon the leaves 
of trees and bushes. If they are predators they are feebly organized 
for such a mode of life. They are usually less active than the Asilidae, 
this being especially true of the females, and the proboscis has a fleshy 
labella which would make it impossible for them to kill any of the 
larger or more heavily chitinized insects. As a rule one does not have 
to watch a predaceous insect very long before seeing some evidence 
of its habits. 
The imagines have been reported in large numbers around certain 
plants and many species are said to seek certain blossoms, the flowers 
of Rubus and Crataegus furnishing good collecting in parts of England. 
The writer has taken species of Pstlocephala and Thereva while sweep- 
ing alfalfa plants during the summer months and large numbers of a 
new species of Psilocephala were taken about strawberry plants in 
June, in the Hood River Valley of Oregon. 
The flight of some species of Therevidae is quite quick, but for only 
short distances and in some species hoplike. Thereva pygmaea is 
very quick on the wing. Undoubtedly the weather has a great deal 
to do with the activity of the flies, and specimens taken toward even- 
ing are apt to be slow in their movements, but the imagines of Meta- 
phragma planiceps appeared to be sluggish when observed about 
midday. Some species taken along stream banks appear to keep 
rather close to the water, crawling about among grass stems, over 
drift trash, or sunning themselves on rocks and patches of sand. 
Many species are found not far from running streams, but others occur 
