AMERICAN DIPTERA. 319 



3. Wings hyaline, the cross-veins and furcations alone sometimes 



clouded with brown 4 . 



Wings more or less brown, the apex never blackish ludius. 



Wings with the apical half blackish I plioenicurus. 



b ^ I macermus. 



4. Tibiae usually black, sometimes varying to reddish J JOlinsoni. 



J J & \ nigripes. 



Tibias always reddish 5. 



5. Bloom of abdomen extending on the base of the segments.. senilis. 

 Bloom of abdomen confined to the apices of the segments.. lautus. 



6. Wings nearly uniformly smoky-gray; head, first two segments of 



antennas, thorax and legs, obscure brown rubidus. 



Wings smoky-brown, darkest on the apical half; head, antenna? 

 and thorax, black patruelis. 



As I have never been able to get together all the species of 

 this genus, I have relied, for the most part, on Mr. Coquillett's 

 table of species published in Can. Ent., XXV, 20, which, so far 

 as I have used it, has proved satisfactory. However, I will 

 supplement this key with one to the males made almost 

 wholly from descriptions, but which I believe will be of con- 

 siderable help. It does not include vespoides, as its descrip- 

 tion does not describe the legs fully enough. 



SYNOPSIS OF MALES. 



1. Middle tibiae with a brush of black hair and bristles on the anterior 



side 2. 



Middle tibiae without such a brush, very pilose species.. jolmsoni. 



2. Front tarsal segments all densely clothed above with appressed 



""■*"•■•■ {!£: 



Front tarsal segments not all densely clothed above with appressed 

 white pile 3. 



3. Front metatarsi destitute of dense appressed white pile rubidus. 

 Front metatarsi clothed with dense appressed white pile 4. 



4. Distal half and extreme base of wings deep black, rest hyaline; 



abdomen black, the posterior margin of the fifth and the 



whole of the following segments reddish plioenicurus. 



Distal half of wing not deep black as above, abdomen black or 

 blackish, not as above 5. 



5. Wings pure hyaline, not at all clouded senilis. 



,-, 7 . , ,. , .,v . ail f inaceriiius. 



Wings more or less tinged with brown or black < . rne ij s 



TRANS. AM. ENT. SOC, XXXV. AUGUST, 1909 



