jj. Anterior inner dorsocentrals and the setæ; on the extensor surface of the hind tibia wanting. _M. micans_, etc. Europe and North America. _Morellia_ R. D. ff. Squamula thoracalis not broadened mesad and caudad, not reaching the margin of the scutellum; macrochætæ on extensor surface of the hind tibia wanting. g. Eyes pubescent. _M. meditabunda._ Europe and America. _Myiospila_ Rdi. gg. Eyes bare; R_1 ends before the middle of the wing. A number of species from the tropics of both hemispheres. _Clinopera_ V. d. W. bb. Hypopleuræ with a vertical row of macrochætæ. c. Eyes pubescent. d. R_1 ends about opposite the r-m crossvein; basal section of R_{4+5} bristly nearly to the crossvein; _S. enigmatica_. Africa. _Somalia_ Hough dd. R_1 ends distad of the r-m crossvein. e. Eastern hemisphere. Australasia. _N. ochracea_, _dasypthalma_. _Neocalliphora_ Br. ee. Western Hemisphere. _T. muscinum._ Mexico. _Tyreomma_ V. d. W. cc. Eyes bare. d. The vibrissal angle situated at a noticeable distance above the level of the margin of the mouth. e. Sternopleural macrochætæ arranged in the order 1:1. f. Genæ with microchætæ. g. Body grayish, with depressed yellow woolly hair among the macrochætæ; wings folded longitudinally over the body when at rest. Cluster flies. _P. rudis_ and related species, widely distributed. _Pollenia_ R. D.[N] gg. Body metallic blue or green. Eastern Hemisphere. h. Vibrissal angle placed very high above the oral margin; a carina between the antennæ; outer posthumeral wanting; anterior intraalar present. _T. viridaurea_. Java. _Thelychæta_ Br. [Illustration: 167. Horn fly. (_a_) egg; (_b_) larva; (_c_) puparium; (_d_) adult. (×4). Bureau of Entomology] hh. Vibrissal angle moderately high above the oral margin; carina small or wanting; no post humeral macrochæta; lower squamæ hairy above. (= _Paracompsomyia_ Hough) (fig. 166). _Pycnosoma_ Br. ff. Genæ bare. _S. terminata_. Eastern Hemisphere _Strongyloneura_ Bigot ee. Sternopleurals arranged 2:1. f. Body metallic green or blue, with gray stripes; genæ hairy to the lower margin; post humerals often wanting; lower squamæ bare above. (= _Compsomyia_ Rdi.). CHRYSOMYIA R. D. g. With one or two orbitals; height of bucca less than half the height of the eye. South and east U. S. (fig. 107). C. MARCELLARIA