ORTALID^S — SYSTEMATIC DISTRIBUTION. 37 



stoma lunulata belongs, unless the figure of the head is entirely 

 incorrect, to the Trypetidse and not to the Ortalidae. The same 

 may be said of Platystoma latipennis, of which Macquart does 

 not give the habitat, but which is American. 



In the same way as those species of Macquart, Walker's 

 Platystoma australis, from Australia, does not belong to this 

 genus. It seems even that not one of the Australian Platystomse 

 hitherto described is a real Platystoma, and that this genus is 

 confined to the three old continents. 



Should we even confine, as we must necessarily do, the genus 

 Platystoma to those species only which agree with the European 

 species in the formation of the head, in the venation, and in the 

 peculiar picture of the wings, we will find species in it which 

 show some, and not unimportant, plastic differences. To the 

 European species, the arista of which has only a short pubescence, 

 may be opposed African species, some of which have the arista 

 perfectly bare, and the scutellum very much swollen, with only 

 four bristles upon it (for instance, Platystoma asphaltin a W ied.); 

 others, on the contrary, with a feathery arista. The latter are 

 again divided in species, in which, as in the European species, 

 the scutellum has six bristles, and the femora are unarmed (for 

 instance, Platystoma nigronotata Lw.) ; and in such the scutel- 

 lum of which has four bristles, and the front femora of which, on 

 the under side, towards the tip, are armed with a few little 

 spines. The latter, and among them P. pectoralis Lw., differ 

 moreover from the former in the usually more metallic coloring 

 of the conspicuously broad abdomen, the upper half segments of 

 which have a much harder consistency than in the other species; 

 and besides, in such species, the two parts of the first abdominal 

 segment, which represent the first two abdominal segments of 

 other diptera, are not completely coalescent. It results from the 

 foregoing that Platystoma may easily be subdivided in four 

 smaller genera, which can be distinguished by the following 

 characters : — 



1. Arista bare ; femora unarmed ; scutellum swollen, with 

 four bristles ; type : P. asphaltina Wied. 



2. Arista with a very short pubescence ; femora unarmed ; 

 scutellum moderately convex, with six bristles ; type : P. umbra- 

 rum Lw. 



