to 



120 Annals Entomological Society of America [Vol. XII, 



Erax pernicis Coquillett. 



Total length 15 to 20 millimeters. Known from Candidas by being 

 less distinctly white pollinose, the male is devoid of long hair on the 

 abdomen. The species averages smaller and the hypopygium is 

 different. See Figure 12. 



Specimens from Arizona and California. 



The aestuans Group. 



The species of this group have been divided into two parts for the 

 purpose of the present paper. So far only one species has been found 

 to be common to both the North American continent and to the West 

 Indies. This being the case the two faunas are separated and a key 

 given for each in order to facilitate determination. 



The species falling in the group are recognized at once by the 

 peculiar posterior branch of the third vein which, instead of curving 

 forward at its apex, as in other groups, curves backward and reaches 

 the costa near or beyond the apex of the wing. The branching of the 

 third vein occurs beyond the base of the second posterior cell. The 

 following key is offered as an aid in separating the species of the North 

 American Continent. 



1. Legs entirely shining black , 2 



At least the tibiae distinctly red 4 



2. Wings hyaline, male costa normal -. . .slossonae n. sp. 



Wings distinctly pale brownish, more pronounced on apical half; male costa 



plainly expanded 3 



3. Total length, 20 milHmeters or over, hypopygium longer than abdominal 



segments five, six and seven loewii Bellardi 



Total length not over 15 millimeters, hypopygium tumid. . . .mexicanus n. sp. 



4. Hypopygium from side view, most prominent apically on upper half, small 



species 5 



Hypopygium most prominent at middle apically, medium to large species. . .6 



5. Mystax yellow aurimystaceus n. sp. 



Mystax black with gray hairs intermixed belfragei n. sp. 



G. Femora red apically afiinis Bellardi 



Femora black 7 



7. Costa more or less dilated in the male, usually large robust species. Mystax 



black, intermixed with white hairs S 



Costa not at all dilated, medium sized slender species. Mystax with black 

 bristles above and pale yellow hairs below. Three species difficult to 



separate. Refer to figures of hypopygiums 10 



S. Hypopygium unusually large, conspicuously pilose below (Cuban species, 



one record from Florida), mystax with a few black bristles, .stylatus Fabr. 



Hypopygium of normal size. Mystax composed mostly of black bristles. . . .9 



9. Total length 25 millimeters or more, the largest species of the aestuans 



group femoratus Macquart 



Total length 23 millimeters or less, tibiae dark brown, general body color 

 blacker than usual aestuans Linn. 



10. Hypopygium with a tuft of dense pile below at apex. . .tabescens Banks, n. sp. 

 Hypopygium without such a tuft 11 



11. Apical part of hypopygium narrowed and curved downward, with a tooth- 



like prominence above apicalis Wiedemann 



Apical part of hypopygium nearly as wide as the preceding part, 



kansensis n. sp. 



