XXX BULLETIX 31, UNITED STATES NATIONAL ML'SEUM. 



51. — Hind femora thickened, with a hifid spnr below on outerond, (phitc xi, fig. 1). 



Senogaster, 238 



Hind femora not with a bifid si)nr beh)w • 52 



52. — Slender specie.s, abdomen narrowed oil basal portion Baccha, 116 



Abdomen iu no wi.se elub-shaped or narrowed basally 53 



53 — Thorax with distinct yellow markiug.s other than on the humeri ... 62 



Tiiorax not with distinct yellow markings other than rarely on the humeri 54 



54. — Face transversely arched or carinate, not produced, not tubereulate ; abdomen 



more or le.ss elongate and nearly bare 55 



More or less thickly j)ilo.se spj'cies, often large 57 



55. — Hind femora extraordinarily thickened ; anterior cross-vein rectangular (plate 



xii, fig. 1) Syritta, '2:i'J 



Hind femora more or less thickened ; cross-vein oblique 56 



56.— Face sharply carinate (plate ix, fig. 2) Tropidia, 20(1 



Face transversely arched (plate ix, figs, 5-b) Xylota, 224 



57. — Scutellum, margin of the thorax, and the pleura; with bristly hairs (plate xi, fig. 



5) ChrysocWamys, 240 



Thorax wholly without bristles 58 



58.— Face short, not produced, concave from antenn;eto tip, not tubercuhite ; hind 



femora thickened ' 59 



Face produced, longer than the front 60 



59.— Abdomen elongate Brachypalpus, 221 



Abdomen A^ery broad, thorax densely ))ilo.se, very large species (plate x, fig. 7) 



Pocota, 220 



60.— Face produced forward, pointed, concave from antennie to tip, not tubereulate, 



sub-carinate ; hind femora thickened (plate x, figs. 4-6) . Crioprora, 217 



Face not evenly concave, tubereulate or convex 61 



6i. — Third joint of antenna; produced above into a conical process, terminating iu 



the thickened arista (plate xi, fig. 2) Merapioidus, 243 



Third joint of antennie obliciuely oval : liind femora rarely thickened* (plates 



ix, x) Criorhina, 209 



62.— Hind femora with a conical, tooth-like protuberance below, near the end (plate 



xii, figs. 3-.^) Spilomyia, 224 



Hind femora without such protuberance 63 



63. — Antenna} inserted low down, near the middle of the head in profile; face not 



longer than the front (plate xii, figs. 6-7) Temnostoma, 249 



Antcnnaj situated high up, on a conical i)roce8S, front .short, face much produced 

 downward ; antennas long or short (plate xii, fig. 8) . Sphecomyia, 2.'3B 



* If thinly pilo.se, with the abdomen nearly bare, and the hind femora thickened, 

 see Xj/lota tuherans, p. 225. 



