28 Mr. C. II. T. Townsend on Diptera 



or blackish to base of antennae, the front border of the brown 

 being perfectly concave-semicircular, as limited by the poste- 

 rior edges of the pit or hollow in which antennae are inserted. 

 Each of the two joints of proboscis 2 millim. long ; base of 

 proboscis a little more broadly yellowish and with silvery- 

 white reflection. Mesoscutum shining blackish,, without 

 lighter lateral border, oidy humeri whitish, the black of 

 dorsum extending in a dilute fascia halfway to middle coxas, 

 the rest of sides of thorax being whitish. Scutellum blackish. 

 Abdomen without median vitta, but blackisli or brown, with 

 second and third segments more or less broadly whitish 

 yellow on bases, usually leaving on third segment a median 

 brown triangle and on second segment a triangle with a 

 median geminate or entire spot-like dilatation at anterior 

 angle. Fourth segment more or less yellowish laterally on 

 base, often in female almost wholly black, quite constantly in 

 male rather broadly yellowish ; the fifth segment with less 

 yellowish on base than fourth. Ovipositor of female blackish, 

 yellowish at base ; appendages yellowish and with the two 

 palj)us-like organs more elongate. Hind femora biannulate 

 with blackish. The pale yellowish of hind legs more or less 

 tinged with brownish, and especially on the tarsi and distal 

 half of tibite, which appear dusky. Tip of male abdomen 

 usually blackish, with the yellowish hair inconspicuous. The 

 brushes of long black hairs on underside of bases of hind 

 femora in male are comparatively better developed than in 

 S. stylosa, and the hind tibia3 are more distinctly bent. 



Tachiiiidae, sens. lat. 



14. Acaulona costata^ v. d. Wulp. 

 Acaulona costata, v. d. Wulp, Biol. Centr.-Ani., Dipt. ii. p, 4. 



Two specimens, male and female : the male, April 8, Paso 

 de Telaya; the female, July 12, San Rafael, on flowers of 

 the Cordia sp. 



Length of female 5 millim., of male fully 6 millim. 



After examining the genitalia of both of my specimens, I 

 believe that v. d. Wulp's specimens are the female. Tiie 

 front is the same width in both sexes. The male has the 

 claws and pulvilli elongate, about twice as long as in female. 

 The male has the elongate-oblong, somewhat flattened abdo- 

 men characteristic of the males of Trichopoda. It is not 

 widened in midtUe, but is of equal width except for the 

 gentle narrowing of last two segments and rounding off of 

 anal segment. It is but slightly narrowed at base. The 

 female abdomen is ovate, convex, more narrowed at base, an d 



