78 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
recently been permitted to examine the types of Loew’s species and 
thus to make sure of the correctness of the determinations of the 
species in my collection. As far as I am aware, none of the species 
described and tabulated by Professor Williston in Biologia Cen- 
trali-American a, vol. 3, have yet been found in the United States. 
It is not unlikely that some of them will be found in our most south¬ 
ern states. I strongly suspect that P. reipublicae Walk, is the 
same as P. fusciis Lw. and that P. translatus Walk, is P. subvi- 
rescens Lw. Professor Williston’s description of P. aridus (Dipt, 
of Death Valley expedition, p. 255-256) applies exactly to P. 
subvirescens Lw., with which it is therefore probably synonymous. 
I shall arrange the species in accordance with the tables in Becker’s 
monograph. 
Division 1. Stigma wholly or partly colored; abdomen wholly 
opaque ; third antennal joint usually long acuminate. 
Division 2. Stigma wholly or partly colored; abdomen wholly 
or partly shining; third antennal joint usually obtuse. 
Division 3. Stigma not colored at all. 
Division 1. 
1. Fourth longitudinal vein without an appendix. 
2. Legs not wholly black, at least the knees yellow. 
3. Abdomen naked, at most with a few scattered, erect, fine hairs. 
5. Hypopygium (sixth abdominal segment) of varying size but 
not larger than two abdominal segments together. 
7. Stigma (subcostal cell) not colored its whole length. 
8. Males..9 
Females. .10 
9. Fourth longitudinal vein with a very distinct angle at its 
junction with the hind cross vein. 
a. Hypopygium without a cleft. 
Third antennal joint obtuse . . fasciatus Lw. 
Third antennal joint prolonged into a long white 
process ..... subopacas Lw. 
b. Hypopygium with a cleft. 
Hypopygium small, shiny, only thinly pollinose; cleft 
to the right of the median line . nigripes Lw. 
Hypopygium large, opaque, thickly gray pollinose 
except a spot near the cephalic border; cleft to left 
of median line . . . atlanticus sp. nov. 
P. fasciatus Lw. In the Loew collection there is a single male. 
