242 CALIFORNIA ACADEMY OF SCIENCES [P»oc. 4th See. 



as strongly built and the eyes do not protrude above the ver- 

 tex; the abdomen of most species is slender and the wings of 

 all the known American species have five posterior cells. 

 They have been recorded as preying on other diptera, but 

 must capture very small species as their mouth parts would 

 not permit them to kill the prey selected by their more robust 

 relatives, the robber flies. The larvae are long and slender, 

 with segments 1 to 6 so constructed that they appear to 

 have twenty segments. They live in mold, rotten wood, and 

 in the ground, and prey on other insects or their larvae. The 

 metamorphoses are not well known. 



233. Psilocephala aldrichii Coq. 



Burns, Mt. Jefferson, VIII- 14 (Lovett) ; Hood River, 

 VI-20 and Forest Grove, VI I- 12 (Cole). 



234. Psilocephala costalis Loew 



Hood River, VI 1-3 (Cole). A large number were taken 

 on the foliage of strawberry plants. 



235. Psilocephala munda Loew 

 Multnomah Falls, IX-30 (Cole). 



236. Psilocephala notata Wied. 



Hood River, VI-4 to VI-20 and Forest Grove, VI I- 12 

 (Cole). 



237. Thereva fucata Loew 

 Crook Co., VII-14 (Lovett) ; McDermitt, Malheur Co., 

 VIII-20 (J. R. Bunch). 



238. Thereva hirticeps Loew 

 Horse Lake, VII-25 (Lovett). 



239. Thereva johnsoni Coq. 

 Hood River, VI 1-5 (Cole) ; Forest Grove, V-20, bred 

 from rotting debris in stump. (Rockwood). 



240. Thereva vialis O. S. 

 Quite common in Hood River in June and early July; 



