258 S. W. WILLISTON, M. D. 



low and black ; the margin of the yellow runs obliquely inwards from the tip of 

 the auxiliary vein to the base of the anal angle, connected through the subcostal 

 cell with a broad band reaching as far as the end of the first vein and terminating 

 on the posterior side of the fourth vein in the second posterior cell ; the black is 

 of a deeper color in front, between the yellow. 



%. — Third joint of antennse narrower; front only a little constricted. Ab- 

 domen, except the base and hypopygium, red. Wings black, with a narrow yel- 

 low band from the tip of the first vein nearly through the first posterior cell. 



Two specimen, Chapada. 



4. i^Iicro<loii iiiei'inis n. sp. 



% . — Length 8 mm. Black, with green and violet reflections ; scutellum with- 

 out si>ines; fourth abdominal segment golden tomentose; hypopygium yellow. 

 Face shining green, white pilose; in profile not gibbose below ; rather narrow. 

 First two joints of antennpe reddish brown, the third wanting. Front black, 

 with slight purplish reflections and black pile ; constricted in the middle so that 

 its least width is less than half the distance from the foremost ocellus to the base 

 of the antennffi. Mesonotum deep black, opaque, with inconspicuous purplish 

 or coppery reflections, bare. Scutellum more distinctly coppery purple, rounded, 

 without spines, and with a scarcely noticeable emargination. Abdomen bare, 

 deep black, with faint green and purple reflections; fourth segment as long as 

 the two preceding together, on the posterior two-thirds or more shining yellowish 

 green, thickly covered with light orange yellow pile or tomentum ; hypopygium 

 yellow. Legs black, the tibiae in part, and all the tarsi deep brownish red ; hind 

 metatarsi not wider than the succeeding joints. Wings nearly uniformly tinged 

 with blackish. 



One specimen, Entre Rios, September. The species is evidently 

 closest allied to 31. violaceus Macq., but is at once distinguished by 

 the fourth abdominal segment. 



5. JfIicro«loii ? cyaiieiveiitris Macq. 



9 . — Length 11 mm. Deep steel-blue with purple and coppery reflections ; sou 

 tellum with spines; face with yellowish white })ile. Face shining green, in 

 profile parallel with the margin of the eyes. Front deep blue-black, with coppery 

 reflections and some black |)ile above. Antenna" black ; third joint a little longer 

 than the first, cylindrical. Mesonotum resplendent coppery purple blue black, 

 nearly bare. Scutellum strongly purple, with two remote spiniferous tubercles, 

 bare. Abdomen deep steel blue, with purple reflections ; the anterior angles of 

 the third, fourth and fifth segments with fine white jiubescence. Legs black 

 Wings nearly uniformly brownish. 



Two specimens, Chapada. It is })ossible, though not very probable, 

 that this is 3f. cyaneiventris, but the difficulty of distinguishing these 

 allied species when the differences are not pointed out, I'enders their 

 naming always a more or less doubtful procedure. 



6. Microdoii sp. 



Not unlike the species described by me as 31. avrifex Wied. (but 

 doubtfully the same — Synopsis of the N. A. Syrphidae, p. 9), except 



