HELEOMYZID FLIES NORTH OF MEXICO—GILL 595 
Typrs.—Holotype male and 1 paratype male, both from McKinley 
Park, Alaska, collected by F. Morand (no date); allotype from Cape 
Prince of Wales, Alaska, 27 June 1926. The holotype and allotype 
have been deposited in the U.S. National Museum (USNM 65449) 
and the paratype in the American Museum of Natural History. 
Disrrinution.—Alaska, Northwest Territories, Quebec, Labrador; 
June-August. (The Canadian specimens were examined and the 
additional distribution records added after the original description 
had been prepared and types designated.) 
Remarks.—A study of chaetotaxy alone would seem to ally this 
species with Trichochlamys borealis Czerny, because of the presence 
of mesopleural and pteropleural hairs. It is therefore surprising 
that the male terminalia are very similar to Heleomyza nebulosa 
(Coquillett), which in all other respects is a typical Heleomyza and 
has both the mesopleuron and pteropleuron bare. Because these 
terminalia are relatively complex in structure, it would be difficult 
to justify placing the two species in different genera on the theory 
that the similarity of terminalia was the result of convergent evolu- 
tion. It is more reasonable to assume that /Z. difficilis, new species, 
and H. nebulosa (Coquillett) are closely related and that the former 
evolved a distinct thoracic chaetotaxy while evolution of the ter- 
minalia lagged. Mesopleural hairs are already known to occur in 
several species of Heleomyza, and pteropleural hairs have been ob- 
served occasionally in specimens of a species in which that sclerite 
is ordinarily bare (see H. pleuralis (Becker), p. 592). Thus the differ- 
ences in pilosity of the pleural sclerites in this genus probably do 
not represent such wide evolutionary gaps as is indicated in certain 
other groups. 
Genus Trichochlamys Czerny 
Trichochlamys Czerny, 1924, p. 155; 1927a, p. 45. 
This genus is distinguished from Heleomyza by the presence of 
hairs on the dorsum of the scutellum and on the pteropleura (ptero- 
pleural hairs are also present in H. difficilis, new species). Heleomyza 
and Trichochlamys are distinguishable from other related genera by 
having 2 or more pairs of prosternal bristles and the anterior fronto- 
orbital bristles about equal in length to the posterior bristles. As 
discussed under ‘77. difficilis, new species,” (p. 594), the presence or 
absence of pteropleural hairs does not appear to be a character of 
generic rank in this group; likewise, the presence or absence of hairs 
on the dorsum of the scutellum is probably not a sound basis for 
splitting genera. However, I think it best to retain genus rank for 
Trichochlamys until male specimens are available for study; the 
question of its relation to Heleomyza may then be reconsidered. 
