AMERICAN DIPTERA. 219 



the structural characters render it almost, if not quite, im- 

 possible to collate them. Observation in the field will be 

 necessary for this purpose." I have found this true. 



The males resemble somewhat those of Ospriocerus in that 

 they are dark in general color, have broad blackish wings 

 and an elongate third antennal segment without a terminal 

 style. They differ chiefly, however, in the decidedly broader 

 head, the cylindrical, not tapering, abdomen, and in the 

 arrangement of the male genitalia, also in the possession, in 

 good specimens, of the abdominal white bands. 



Dizonias tristis (PI. VIII, fig. 3.) 



Dasypogon tristis Walker, Dipt. Saund., 93, 1856. 



Dasypogon quadrimaculatus Bellardi, Saggio, II, 80, pi. I, f. 8, 

 1861. 



? Dizonias phcenicurus Loew, Cent., VII, 53, 1866. 



Dizonias bicinctus Loew, Cent., VII, 54, 1866. 



Dizonias bicinctus Osten Sacken, Cat., 230, note 103, 1878. 



Dizonias phcenicurus Van der Wulp, Tijdschr. V. Ent., XXV, 

 96; oc. in Argentina. 



? Dizonias phcenicurus Williston, Biologia, Dipt., I, 304, 1901. 



Dizonias tristis Howard, Insect Book, 1902; PI. XIX, fig. 6 <$", 

 fig. 13, 9- 



Ospriocerus albifasciatus Back, Can. Ent. XXXVI, 292, 1904. 

 $ 9- — Length 16-23 mm. — £ .—Wholly black, the second segment 

 of the antennae, the dorsum of the thorax occasionally, and the distal 

 portion of the abdomen quite frequently reddish; the abdomen with 

 two white pruinose fasciae near the base; bristles of entire body black, 

 hypopygium chiefly with white pile. 9- — -Quite different, see below. 

 $. — Wholly black, legs and wings of the same color; abdomen with 

 two white pruinose fasciae; bristles of the entire body black; hypo- 

 pygium chiefly with white pile. Head black; front, sides of face and 

 occipital orbits whitish pruinose; bristles of the front and occiput, 

 the mystax, beard and pile of palpi black. Antennae black; the 

 second segment and the base of the third slightly reddish, the second 

 and third segments, each in certain lights, grayish-white pruinose. 

 Dorsum of thorax black, lateral margins whitish pruinose, pile short 

 and all the bristles black. Abdomen black, not polished; the basal 

 cross-bands of the second and third segments whitish pruinose, very 

 broad on the sides, narrowed above, sometimes interrupted. Pile of 

 the abdomen short, black, the side of the first, and the anterior angles 

 of the second, clothed with longer pile; the posterior margin of the 

 last segment and the hypopygium with white pile. Venter black. 



TRANS. AM. ENT. SOC-, XXXV. JUNE, 1909. 



