GO 



DIPTERA OF NORTH AMERICA. 



[PART III. 



The wings of Trypeta ocellata and obscura differ from the 

 usual shape of the wings of the Ortalidse by their narrowness, 

 the parallelism of their anterior and posterior margins, their 

 broad and rounded apex and their comparatively great length. 

 Macquart placed the first of these species in the genus Platy- 

 storna, and the second, still more oddly, in the genus Camplo- 

 neura. Rondani has had a better eye for the plastic peculiari- 

 ties of Trypeta ocellata and established the genus Pterocalla 

 for it. I have derived the name of the present group from this 

 well-founded genus of Rondani's, and not after Rob. Desvoidy's 

 Myennis, established for Scatophaga fasciata, because the latter 

 name, although much earlier in date, is a senseless malformation. 



Trypeta obscura is, as Wiedemann has correctly observed in 

 its description, a near relative of Pterocalla ocellata. As what 

 occupies us now is the systematic location of only a small num- 

 ber of species, we can, without any hesitation, unite both of these 

 species in the same genus, although the venation of T. obscura 

 differs from that of Pterocalla ocellata in the second longitudinal 

 vein being more arcuate than undulated, and in the fourth lon- 

 gitudinal vein being distinctly curved forward. 



A small North American species, which will be described 

 below, stands close enough to those two species in the shape of 

 its wings and its venation to be placed in the same genus. It 

 differs however in the second, third, and fourth longitudinal 

 veins being quite straight, and neither wavy nor arcuate. 



A most striking resemblance to this Pterocalla strigula is ex- 

 hibited by Trypeta ulula, a South African species, described by 

 me {Berl. Entom. Zeitschr.) after an incomplete specimen, with- 

 out head. Already in describing this species, I drew attention 

 to the fact that it differs from the ordinary venation of the Try- 

 petina in the great distance intervening between the tips of the 

 auxiliary and of the first longitudinal veins. I do not doubt 

 now that this species is a Pterocalla, and that I would have 

 recognized this earlier if I had had a complete specimen before 

 me. Both species agree very well in all their plastic characters, 

 especially in the shape of the wings and in the venation ; the 

 only difference which I notice in P. ulula is the position of the 

 posterior crossvein, which is much steeper. 



The genus Pterocalla, as I define it here, thus embraces all 

 those Pterocallina which, in the outline of their wings, resemble 



