A Systematic Study of the Anthomyiinae of New York 53 



weaker and hair-like. Apical tufts occur in Hydrophoria uniformis, Pego- 

 niyia luteola, and Anthomyia phwialis In Hylemyia innocua the marginal 

 bristles are exceptionally long, and describe a delicate curl toward the tips. 

 In what may be termed the " true " Pegomyia group, ^ the bristles are 

 invariably weak- and sparsely distributed. 



The genital styles (gonostyli) 



The genital styles (gonostyli) represent a part of the paired appendages 

 of the ninth abdominal segment. Each genital style is composed of two 

 segments: the basistylus, or proximal segment (the tenth sternites of Met- 

 calf , the pleural plates of Snodgrass) ; and the dististylus, or distal segment 

 (forceps inferiores, styles). According to Crampton (1923), the tergal 

 position of the genital styles in the h'gher Diptera, as compared with their 

 sternal relationship in the lower Diptera, is due to a migration dorsad. 

 The dististyli thus become fused with the caudoventral angles of the ninth 

 tergum, immediately laterad of the cerci, and project typically as two 

 bisymmetrical rami beyond the apex of the cerci. In Pegomyia hyoscyami, 

 the dististyli are asymmetrical, the left process being longer than the right. 

 Besides being adjusted to the movements of the cerci, the dististyli articu- 

 late, through the medium of a basal process, with the caudal extremity 

 of their respective basistyli. 



The dististyli vary considerably in form and appearance among the 

 genera and among the species. The innumerable shapes can best be 

 described and compared by referring to the illustrations Only in Hydro- 

 phoria might such a character be called generic in distinction. In the 

 species represented in New York, as Hydrophoria amhigua, H. uniformis, 

 H. divisa, and H. flavohalterata, the dististyli are elbowed at the middle 

 in a caudal (posterior) direction. In the " true " Pegomyia group (except- 

 ing hyos.yami), the dististyli are short and stout, with the inner surface 

 considerably notched and irregular in outline. In a group in which the 

 species closely resemble one another, as Hy'emyia inornata, H. setigera, 

 H. piloseta, H. marginella, and H. marginata (Malloch, 1918 d, plate 17), 

 the delicate excisions of the inner surface are of considerable taxonomic 

 importance in differentiating species. 



The surface of the dististyli may be expanded, contracted, furrowed, 

 excavated, or ridged in different ways. The integument may possess 

 minute or longish hairs, tubercles, or teeth, frequently bunched and 

 arranged in a significant manner, as, for example, in Pegomyia juvenilis and 

 Hylemyia depressa. 



The basistyli occur typically as two lateral chitinous strips situated 

 on the membrane of the genital pouch, mesad of the lateral borders of 

 the ninth tergum. Their direction may be modified so that they tend 



3 Comprising the species rubivora, vanduzeei, hyoscyami, fuscofasciata, ccdyptrata, bicolor, and winthemi 

 of the genus Pegomyia, and trivittata of the genus Hylemyia. 



