MALE. Vertical callosity reddish; below it an opaque black band, connected in the middle with a V-shaped spot about the base of the antennae; the front elsewhere, and the face for the greater part, light yellow, the sides of the latter with a broad silvery sheen. Cheeks black. Antennae red; the first joint a little shorter than the third joint; second joint about twice the length of the first; style short, thick. Thorax black, opaque; near the humeri and behind, as also on the scutellum, thickly golden pollinose; pleurae diffusely pollinose. Abdomen opaque black; the hind margin of the first three segments, and the remainder of the abdomen, save spots on the sides of the fourth and fifth segments, thickly light golden pollinose. Legs reddish brown, the base of the tibiae and the basal joints of the tarsi yellowish. The brown of the wings extends to the third vein and through the middle of the first posterior cell; costal and subcostal cells lighter colored. Length 11 millimeters. Two specimens, Chapada, H. H. Smith. 8. =Conops parvus, n. sp.= FEMALE. Closely allied to _C. sylvosus_ Williston, but differs in the lighter colored antennae and their more elongated third joint, which is as long as the first two joints together; in the wings being wholly grayish hyaline, save a quadrate brown spot in front a little beyond the middle; and in the lighter colored legs and abdomen. The proboscis is as long as the antennae; the legs are brown or brownish yellow. Length 8 millimeters. Two specimens, Chapada, H. H. Smith. Explanation of Plates. PLATE I. Skull of _Pteranodon_ sp., one-fifth natural size. PLATE II. Left front paddle of _Clidastes velox_ Marsh, two-thirds natural size. _C_, coracoid; _S_, scapula; _H_, humerus; _I_, first digit; _V_, fifth digit. PLATE III. Left hind paddle of _Clidastes velox_ Marsh, two-thirds natural size. _Il_, ilium; _P_, pubis; _Is_, ischium; _F_, femur; _T_, tibia; _Fb_, fibula; _I_, first metatarsal. PLATE IV. Right front paddle of _Clidastes Westii_ Williston, one-third natural size. _S_, scapula; _C_, coracoid; _H_, humerus; _R_, radius; _U_, ulna; _I_, _IV_, first, fourth digits. PLATE V. Right hind paddle of _Clidastes Westii_ Williston, one-half natural size. PLATE VI. Eighteenth dorsal vertebra of _Clidastes Westii_ Williston, natural size. Fig. 1, centrum from behind; fig. 2, from below. PLATE VII. Fig. 1, _Microdon megalogaster_ Snow; fig. 2, _Brachyopa cynops_ Snow; fig. 3, _Syrphus ruficauda_ Snow; fig. 4, _Callicera montensis_ Snow; fig. 5, _Tropidomyia bimaculata_ Williston; fig. 6, _Rhingiopsis rostrata_ Roeder; fig. 7, _Ancanthina hieroglyphica_ Wiedemann.