54 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
These characters are therefore not of generic value (so used by Coquil- 
lett to place R. quadnsetosa as a species of Helicobia). The character 
of the bristles on the first and third veins is not even indicative of the 
two groups into which the four species described are separated since 
R. xauthopyga (Van der Wulp), which would belong to the first along 
with R. communis and R. peniculata, has both veins bristly, whereas 
the latter two have onl}' the third. R. quadnsetosa (Coquillett) and 
R. latisetosa, which compose the second group, have bristles on both 
veins. 
Characters of the second genital segment are particularly character- 
istic of the genus, especially the small anal area and the forceps. The 
wide spread forceps prongs with darkened tips are distinctive and do 
not occur in any other genus studied by the writer. (Sarcophaga 
haemorrhoidalis approaches this condition.) These characters are 
perhaps somewhat obscure unless one is familiar with the genera and 
species of this family, but the forceps is generally visible in part at 
least, often wholly so. The brown and light-yellow epaulets are sug- 
gestive, but occur in other genera as a specific character. The same 
applies to the arrangement of the frontal bristles and to the absence 
of scutellar apicals. 
The females, which show the same remarkably close resemblance 
of external genital characters as the males, can best be separated by 
the chaetotaxy of the thorax which corresponds to that given in the 
descriptions. The bristles on the first and third veins are very 
useful as eliminating characters. 
Table of Species. 
1. Fourth ventral plate with 'brushes' 2. 
Fourth ventral plate without 'brushes' 3. 
2. Four posterior dorsocentral bristles present communis, n. sp. 
Three posterior dorsocentral bristles present peniculata, n. sp. 
3. Lateral vertical bristles present; forceps prongs approximated basally for 
at least half their length, their tips not convergent latisetosa, n. sp. 
Lateral vertical bristles absent; forceps prongs separated from near the 
base, their tips convergent guadme^osa (Coquillett). 
(1, 2). — The first two species described, with several other American 
species not mentioned in this paper and R. haematodes (Meigen) 
(Europe and North Africa) form a natural group within the genus. 
The following characters are common to these species: medium-sized 
flies; breadth of front at narrowest part about one half eye width; 
