g. Fore tibiæ each with three long spines on the ventral side. _S. diadema_ (fig. 159e), a widely distributed species; and several southwestern species. _Sinea_ A. et S. gg. Fore tibiæ unarmed. _A. multispinosa_, widely distributed; _A. tabida_, Cal. _Acholla_ Stäl. ff. Fore femur unarmed, rarely a little thickened, a little granulated. g. Pronotum produced caudad over the scutellum, with a high mesal tuberculate ridge (fig. 19e). A. CRISTATUS. N. Y. to Cal. and south. ARILUS Hahn. gg. Caudal lobe of the pronotum six sided, neither elevated nor produced caudad. _H. americanus_, Southwest; also several W. I. and Mexican genera. HARPACTOR Lap. DIPTERA (Mosquitoes, Midges, Flies) a. Integument leathery, abdominal segments indistinct; wings often wanting; parasitic forms. PUPIPARA b. Head folding back on the dorsum of the thorax; wingless flies parasitic on bats. Genus _Nycteribia_. NYCTERIBIIDÆ bb. Head not folding back upon the dorsum of the thorax; flies either winged or wingless; parasitic on birds and on bats and other mammals. c. Antennæ reduced, wings when present, with distinct parallel veins and outer crossveins; claws simple; palpi leaf-like, projecting in front of the head. Flies chiefly found on bats. Several genera occur in North America. STREBLIDÆ [Illustration: 162. Hippobosca equina, ×4. After Osborn.] cc. Antennæ more elongate, segments more or less distinctly separated; head sunk into an emargination of the thorax; wings when present with the veins crowded toward the anterior margin; palpi not leaf-like. HIPPOBOSCIDÆ d. Wings absent or reduced and not adapted for flight. e. Wings and halteres (balancers) absent. _M. ovinus_, the sheep tick. _Melophagus_ Latr. ee. Wing reduced (or cast off), halteres present. f. Claw bidentate; ocelli present. On deer after the wings are cast off. _L. depressa_. _Lipoptena_ Nitsch ff. Claw tridentate (fig. 161 f). On _Macropis_. _B. femorata._ _Brachypteromyia_ Will. dd. Wings present and adapted for flight. e. Claws bidentate. f. Ocelli present; head flat; wings frequently cast off. On birds before casting of the wing. _Lipoptena_ Nitsch. ff. Ocelli absent; head round; wings present. The horse tick H. EQUINA may attack man (fig. 162). HIPPOBOSCA L. ee. Claws tridentate (fig. 161 f.). f. Anal cell closed at apical margin by the anal crossvein. g. Ocelli absent. _Stilbometopa_ Coq. gg. Ocelli present.