Diptera 69 c 
order to make clear the generic relations of these I have drawn up an abridged 
key to genera which is presented herewith. 
Key to Genera in Collection and the Genera most closely allied thereto. 
1 . Eyes hairy 2 
Eyes bare 3 
2. Abdomen broadly ovate, little longer than broad; eyes in male distinctly separated; in 
female the width of frons is very little more than that of male. . . .AUiopsis S. and D. 
Abdomen narrow, almost parallel-sided, much longer than broad; eyes in male contiguous, 
in female separated by at least one-third the width of head Lasiops Meigen. 
3. Calyptra decidedly unequal in size, the under one projecting beyond upper 4 
Calyptra not as above, the lower one not projecting 5 
4. Lower calypter very much longer than upper; arista plumose Hydrophoria R.-D. 
Lower calypter not much longer than upper; arista almost bare Egle R.-D. 
5. I^egs black; arista pubescent or bare Phorbia R.-D. 
Legs black, or with tibiae pale; arista hairy or plumose Hylemyia Meigen. 
Legs with at least the tibiae pale; arista pubescent or bare Pegomyia R.-D. 
The last three genera are poorly defined and overlap considerably, but my 
studies of the family have not been brought to the point where I am prepared to 
publish reliable characters for their differentiation, so I use the generally accepted 
characters. I have in preparation a generic synopsis of this and other sub- 
families which I hope to publish shortly. 
Hydrophoria Robineau-Desvoidy. 
The only species of this genus on which I possess information concerning the 
early stages is aquatic. The flies are always foimd in the vicinity of rivers or 
ponds. 
There is only one species in the present collection, which is described as new. 
Hydrophoria arctica, n. sp. 
Male. — Black. Frontal triangle opacjue black, orbits, cheeks, and face 
white pilose. Legs black, tibiae slightly brownish. Wings greyish, veins black. 
Squamse white, with yellow margins. Halteres brownish yellow. 
Interfrontalia obliterated below ocelli, the orbits at this point linear; thirtl 
antennal joint about 1-5 as long as second; arista tapered on basal half, long- 
haired to middle, bare apically; orbit in profile extending beyond eye as far as 
width of third antennal joint; cheek 1 • 5 as high as width of orbit; vibrissa long, 
marginal bristles on cheek long and strong. Presutural acrostichals weak, 
hardly distinguishable among the irregularly f oin* rowed hairs, prescutellars hair- 
like; prealar bristle about one-fourth as long as the bristle behind it; sternop- 
leurals two: two, the lower anterior one weak; upper margin of hypopleiu'se 
hairy proximad of spiracle. Abdomen short and broad, cylindrical, segments 
with long bristles on posterior margins; hypopygium with basal segment polished, 
the apical, recurved one slightly prominent, armed with many long strong bristles; 
fifth ventral segment densely covered with setulose hairs. Fore tibiae with two 
bristles; mid tibia with two to three antero-ventral, three to four antero-dorsal, 
two to three postero-dorsal, and three to four postero-ventral bristles; almost the 
entire length of mid-femora with long bristles on the antero and postero-ventral 
surfaces; hind tibia with five to six short bristles on antero-ventral surface, 
seven to eight irregular ones on antero-dorsal, seven to eight on postero-dorsal 
surface, one beyond middle being very long. Costal thorn at least as long as inner 
cross-vein; outer cross-vein v6ry much flexed; last section of fourth vein about 
1-5 as long as preceding section. 
Female. — Similar in colour to the male. 
Frons opaque black, densely brown pruinescent, nearly half as broad as head; 
orbits broad, each at broadest part nearly as broad as orbit at same part; cruciate 
bristles strong; supra-orbital bristles four in nimiber, the lower one directed 
