HELEOMYZID FLIES NORTH OF MEXICO—GILL 497 
whereas these structures are abbreviated in the Heleomyzidae. 
Aside from these characters, there seems to be no more differentiation 
between the Trixoscelidae and Heleomyzidae than between the sub- 
families Heleomyzinae and Suilliinae. Furthermore, the only known 
data on the biology of trixoscelids show them to be inhabitants of 
bird nests (Collin, 1943; Ryckman, 1953; Lee and Ryckman, 1954), 
a character which they have in common with many of the Heleo- 
myzinae. The question of separating the Trixoscelidae from the 
Heleomyzidae appears to be highly subjective at the present time. 
Because of this and the fact that there is a recent paper (Melander, 
1952) which deals with the species of Trixoscelidae in North America, 
it seems best to concur with those who would consider the family 
distinct and to exclude the Trixoscelidae from further consideration 
in the present work. 
I have followed Aldrich (1926), Sabrosky (1949), and James and 
Huckett (1952) in using the name Heleomyzidae, based upon the genus 
Heleomyza, erected by Fallén in 1810 to include serrata Linnaeus and 
three unnamed species. In 1820, Fallén included serrata Linnaeus 
in the genus Helomyza, without reference to the earlier spelling. 
Czerny (1924, p. 1) attempted to justify the emendation of Heleomyza 
to Helomyza, but because Fallén did not indicate in either case the 
intended derivation of the name, the original spelling should be 
retained. 
Czerny’s ‘‘Monographie der Helomyziden” (1924) and the subse- 
quent ‘‘Ergénzungen” (1926, 1927b, 1929-33, 1935, 1937) give a 
virtually complete resume of taxonomic work on the Heleomyzidae. 
However, certain shortcomings seriously limit the usefulness of 
Czerny’s monograph and supplements: For one thing, the species 
which have been described in 1940-60 were not treated by Czerny; 
furthermore, Czerny in many cases had to quote original descriptions 
without having the benefit of examining types or even specimens. 
Unfortunately, it is often impossible to identify the species from these 
original descriptions, and after examining the types of Loew, Aldrich, 
Garrett, and others, I find it necessary to correct several synonymies 
made by Czerny. It must be recognized, however, that Czerny’s 
treatment of the group has provided invaluable assistance in the 
present study. 
Brackets around question marks preceding items in synonymies 
indicate that the present author, not the previous user of the name, 
questions the synonymy. 
I wish to acknowledge the cooperation of the many institutions and 
private collectors who loaned material or allowed me to visit and 
examine their collections. I am especially indebted to several indi- 
viduals who made it possible for me to examine type material. These 
