NO. 1935. MU8C0ID FLIES FROM SOUTH AMERICA— T0WN8END. 353 



A third female of this genus, taken indoors at Piura, December fs, 

 1911, measures only 6 mm. in length. The apical cell is absolutely 

 closed, the tip of wing slightly more rounded, and the two costal cells 

 wholly clear. The discal row of bristles of anal segment is prac- 

 tically wanting, and the small discal scutellar bristles are more 

 approximated. There are three sternopleural bristles on one side, 

 but the middle one of opposite side is atrophied. It remains to be 

 seen whether this specimen represents a distinct form. These flies 

 are so rarely met with that sufiiciently large series for study do not 

 yet exist in collections. 



Deposits isopodiform maggots with dorsal and lateral chitinized 

 segmental plates, which evidently have often to endure long exposure 

 before reaching their hosts. 



As throwing possible light on the host habit of this genus, it may 

 be mentioned that Trixa has been reared in Europe from certain 

 coprophagous scarabs. On external characters Phasiopteryx, Oestro- 

 phasia, and their immediate allies seem more or less nearly related to 

 Trixa. A certain small coprophagous scarab allied to OnthopTiagus 

 is common in Piura, where it feeds and breeds in dung of horses and 

 burros, evidently burying dung-pellets with its eggs. It may be that 

 the present species of Phasiopteryx is parasitic in its larva. The 

 structure of the first-stage Phasiopteryx maggot seems very weU 

 adapted for attachment to the legs or ventral surface of the female 

 scarab, awaiting the formation by latter of the dung-pellet which it 

 afterwards roUs away for burial. The maggot may easily transfer its 

 attachment from the scarab to the peUet during the rolling process. 

 The maggot is evidently adapted, in a greater degree than is any 

 other first-stage maggot so far known in the Muscoidea, not only 

 for exposure in the open but also for external attachment to heavily 

 chitinized surfaces during such exposure. Its hard highly chitinized 

 and polished segmental plates afford it protection from air, light, 

 and external contacts, while its soft unchitinized and sucker-like 

 ventral surface affords it means of external attachment. The pecuHar 

 cephaUc bunches of talon-like spines possessed by the first-stage 

 maggot of Phasiopteryx hilimelci (TD 1791a from Vera Cruz) may well 

 be a further special adaptation for external attachment. It is thus 

 possible if not probable that the female Phasiopteryx deposits her 

 maggots on or at the edge of fresh dung, where they would have 

 excellent opportunities for attaching themselves to the arriving 

 scarabs. The fecundity of Phasiopteryx is apparently very moderate, 

 in the neighborhood of only 500 or 600, and this indicates a larvipo- 

 sition habit that would make reasonably sure of the maggot encoun- 

 tering the host. 



48702°— Proc.N.M.vol.43— 12 23 



