f. Fore femur as long as or longer than the hind femur; first segment of the beak much shorter than the second. _Z. audax_, in the north eastern states; other species south and west. _Zelus_ Fabr. ff. Fore femur shorter than the hind femur, rarely of equal length, in this case the first segment of the beak as long or longer than the second. g. First segment of the beak shorter than the second; fore femur a little shorter than the hind femur; the first segment of the beak distinctly longer than the head before the eyes. _P. cinctus_ a widely distributed species (fig. 160). _P. punctipes_, _P. spinicollis_, Cal., Mex. (= _Milyas_) _Pselliopus_ Berg. gg. First segment of the beak as long or longer than the second. h. Pronotum armed with spines on the disc. i. Juga distinctly prominent at the apex and often acute or subacute; fore femur distinctly thickened; hemelytra usually not reaching the apex of the abdomen. _Fitchia aptera_, N. Y., south and west; _F. spinosula_, South; _Rocconata annulicornis_, Texas, etc. ii. Juga when prominent, obtuse at apex; eyes full width of the head; fore femur not thickened; pronotum with four spines on posterior lobe. _R. taurus_, Pa., south and west. _Repipta_ Stäl. hh. Pronotum unarmed on the disc. i. Spines on each apical angle of the penultimate abdominal segment. _A. cinereus_, Pa., and south. _Atrachelus_ A. et S. ii. Apical angle of the penultimate abdominal segment unarmed. _Fitchia_ (in part); _Castolus ferox_, Arizona. ee. Sides of the mesosternum with a tubercle or fold in front at the hind angles of the prosternum; first segment of the beak longer than the part of the head cephalad of the eyes. f. Fore femur thickened, densely granulated; hind femur unarmed. [Illustration: 161. Taxonomic details of Diptera. (_a_) Ventral aspect of abdomen of Cynomyia; (_b_) antenna of Tabanus; (_c_) ventral aspect of abdomen of Chortophila; (_d_) ventral aspect of abdomen of Stomoxys; (_e_) claw of Aedes (Culex) sylvestris, male; (_f_) claw of Hippoboscid; (_g_) foot of dipterous insect showing empodium developed pulvilliform; (_h_) hind tarsal segment of Simulium vittatum, female; (_i_) foot of dipterous insect showing bristle-like empodium.]