Dec, 1921 Bulletin of tJic Brooklyn Entomological Society 127 



2. Hairs of arista retrosse ; males dichoptic (Tropical; included 



in Willistoin's Manual) Megametopon. 



Hairs of arista not retrosse ; males holoptic Volucella. 



ERISTALIN^. 



The characters given in the table of subfamilies sharply sepa- 

 rate the Eristalinse from the Xylotinse; two groups which for- 

 merly were not considered separable because of such genera as 

 Tropidia, Syritta, Pterallastes and Teiichocnemis which were 

 thought to be intermediate. The long pile on the face and frons 

 is characteristic of the Eristalinas, while typical genera of the 

 Xylotinse have the face bare, except for some scattered hairs 

 along the eye margins. Further, in the males of Xylotinse the 

 frons is bare while the females have a broad bare space above 

 the antennae. 



The genera included in this subfamily are easily distinguished 

 except in the Helophilini. However even in this tribe there are 

 several good characters that can be used to divide them into 

 several groups and an attempt has been made here to split the 

 group. This arrangement is by no- means final. 



Polydontomyia {^Triodonta) has been considered congeneric 

 with Pterallastes (Xylotinae). The distribution of the pile on 

 the head and the dichoptic male easily locates it in the Helo- 

 philini. 



A discussion of the squamae and the first tergite is given in 

 the remarks under Volucellinae. 



Table of Genera of Eristalin^. 



1. Marginal cell closed 2. 



Marginal cell open 3. 



2. The bright yellow markings on the occiput, thorax and ab- 



domen formed by tomentum ; all the femora spinose be- 

 neath ; f acq rather evenly hollowed, somewhat of the 



Xylota type Meromacrus, 



Pile thin and normal in structure ; fore femora, at- least, 

 without spines ; face hollowed beneath antennae then 

 raised to a prominence Eristalis. 



3. Densely pilose species of bumble-bee appearance 4. 



Thinly pilose, not bumble-bee-like; males dichoptic {Helo- 

 philini) 5- 



