A Systematic Study of the Anthomyiinae of New York 57 



in P. ruhivora the blunt, stiff bristle is borne on a pronounced basal process. 

 (Plate I, B and e.) 



The cephalic pair of internal lobes also arise from the membrane of 

 the genital pouch. Like the caudal pair, they vary enormously in specific 

 shape and size. The lateral (outer) extremities of the appendages fre- 

 quently articulate with the distal margin of the penis sheath. Each append- 

 age, or lobe, is typically furrowed on the inner surface so as to form a 

 distinct fold or ridge. Usually this division becomes more marked toward 

 the apex. In Pegomyia connexa, P. geniculata, P. ruhivora, Hammomyia 

 spp., and other species, the division is so marked as almost to divide the 

 appendage into two parts. In Pegomyia winthemi and P. fuscofasciata, 

 the caudal margin bears a well-developed fold. In Hylemyia trivittata, 

 H. inornata, H. setigera, and H. betarum, the two cephalic internal lobes 

 are reduced to inconspicuous appendages. Typically each appendage 

 bears two bristles on the apical region. In Paregle cinerella these bristles 

 are borne on a small prominence on the inner surface ; in Hylemyia inornata 

 and H. setigera, the bristles are represented by long, flexible lashes. (Plate I, 

 B and D.) 



The membrane, which coordinates the positions of the parts forming 

 the penis, and occupies the ventral surface, or floor, of segments 8 and 9, 

 is mostly hyaline and flexible. Occasionally, as in Hylemyia cilicrura, 

 there arise on each side what seem to be cushion-like swellings. In the 

 mid line, dorsocaudad of the ejaculatory hood, the membrane may become 

 more densely chitinized and extend on the surface as a thinly chitinized 

 lamella. (Plate I, a and h.) 



The processes of the fifth sternum 



The processes of the fifth sternum represent paired chitinous plates 

 modified to aid in the act of copulation. The outer surface is heavily 

 chitinized; the inner surface is Ijned with a delicate membrane which, in 

 certain species, is modified into swellings and chitinous folds covered with 

 minute setulae or spinules, as in Hylemyia arnolitra, H. variata, Pegomyia 

 calyptrata, P. fuscofasciata, P. winthemi, and Hydrophoria ambigua. 

 Typically the processes assume the position and the form of two lateral 

 ensheathing plates or guides, possessing many sensory hairs and bristles. 

 The specific shapes of the processes, and the arrangement and appearance 

 of the bristles and hairs, afford characters of considerable taxonomic 

 importance. A knowledge of these can best be conveyed by illustrations, 

 for example, Hylemyia pluvialis, Pegomyia vanduzeei, Hydrophoria ambigua, 

 and H. uniformis. In many species (for example, Paregle cinerella, 

 Hylemyia coenosiaeformis, H. innocua, H. curvipes, and H. setitarsata) 

 each process may bear, near the apex, spines or stiff, stout setulae; or 

 this region may be significantly devoid of any bristles or hairs, as in 

 Pegomyia bicolor, P. hyoscyami, and P. geniculata. Stout basal spines 



