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UNITED STATES NATIONAL MUSEUM BULLETIN 224 



26. Four posterior cells ; small, pollinose flies, usually with 



bare and polished areas Itolia Wilcox 



Five posterior cells 27 



27. Third antennal segment slender and much longer than the 



head and bearing 2 large, conspicuous microsegments ; 

 large flies usually with numerous, opaque, pollinose 



areas 28 



Third antennal segment never with expanded and swollen, 

 or lengthened microsegment ; microsegments always small 

 and reduced in size 29 



28. Second microsegment nearly as long as the third segment 



and longer than first and second segments combined ; this 

 microsegment densely short plumose. 



Ceratttbgus Wiedemann 

 Second microsegment short, plane above, expanded below 

 and distinctly wider than the third segment, its length 

 much less than the third segment. 



Ceraturgopsis Johnson 



29. Proboscis exceptionally short, stout, bluntly pointed and 



directed downward with the apex curved posteriorward ; 

 vertex not excavated, the ocellarium low or moderately 

 high ; bristles in general reduced but anterior basalare 

 with a patch of bristles or bristly hairs. 



Ancylorrhynchtjs Latreille 



Proboscis straight, long or short; apex usually more or less 



attenuate ; vertex generally distinctly excavated . . 30 



30. Head from the anterior aspect distinctly narrow, the whole 



presenting a nearly circular appearance ; face in conse- 

 quence narrow ; antenna elongate and comparatively slen- 

 der and but little flattened ; third segment with 1 or 2 

 microsegments, the second always attenuate and usually 

 longer than the first. Face usually with numerous, strong 

 bristles and very little ordinary pile. Gena well devel- 

 oped beneath the eye. Fourth posterior cell usually closed 

 and stalked, sometimes open and narrowed .... 31 

 Head from anterior aspect distinctly wider than high ; not 

 circular in aspect. Antenna generally less elongate and 

 slender 36 



31. Anterior femur having ventral surface with an extensive 



patch of dense, stout bristles ; base of femur sometimes 



swollen Gonioscelis Schiner 



Anterior femur with only the usual complement of 

 bristles 32 



32. Third antennal segment 2 or 3 times the combined length 



of the first 2 segments, with short, fused, spoonlike micro- 

 segment, or with the third segment widened and dilated 



through the middle Ospriocerus Loew 



Third antennal segment 1 or 2 times as long as first and 

 second segments combined; apex with cylindrical micro- 

 segment 33 



33. Face not at all gibbous ; that portion visible ventrally due 



to the posterior recession of the eyes ; second microsegment 

 of antenna attenuate to a fine point. 



Rhacolaemus Hermann 



Face distinctly prominent below, the extended portion plane 



or slightly curved, but reaching upward from one-half to 



three-fourths of the face 34 



34. Metapleuron without pile or bristles . . Stenopogon Loew 

 Metapleuron with bristles or pile, or both 35 



35. Eye strongly recessive posteroventrally ; 1 or 2 microseg- 



ments present, the second long and attenuate. Face gib- 

 bosity beginning above the middle of the face. 



Scxeropogon Loew 

 Eye not recessive posteroventrally ; 1 microsegment with 

 apical spine ; face gibbosity beginning at middle of face ; 

 upper part of face with stiff, abundant hairs. Upper pos- 

 terior mesopleuron densely pilose. Male terminalia al- 

 ways strongly rotate and always with a well developed, 

 elongate (dorsal) hypandrium ; posterior coxa with an 

 anterior process in both sexes . Neoscleropogon Malloch 



36. Fourth posterior cell closed and usually stalked, rarely closed 



in the margin or quite narrowly open 37 



Fourth posterior cell open and usually widely open ; never 

 closed 50 



37. Ventral surface of middle femur with an anterior patch of 



dense, short, stout bristles ; wings have fourth posterior 



cell narrowly closed with short petiole 38 



Ventral surface of middle femur with at most 1 or 2 rows 

 of regularly spaced bristles 39 



38. Antenna large, the third segment swollen through the mid- 



dle ; bristles of face strong ; palpus longer than face ; pro- 

 boscis with ventral bristles in the middle. Subcostal cell 

 with several supernumerary crossveins. 



Prolepsis Walker 



Antenna slender and of uniform width ; face bristles weak ; 



palpus shorter than face. Proboscis without bristles in 



the middle below. No supernumerary crossveins present. 



Sphageus Loew 



39. Face densely beset with bristles or with bristly hairs on at 



least the lower half and usually such bristles extend up- 

 ward nearly to the base of the antenna 41 



Face with bristles or pile or both confined to a narrow band 

 immediately above the epistoma, leaving the greater part 

 of the face conspicuously bare 40 



40. Face with a single bristle row above epistoma. Third an- 



tennal segment long, slender, without microsegment, spine- 

 tipped and often attenuate distally ; this segement with 

 conspicuous, dorsal bristles. Large or very large flies. 



Archilestris Loew 

 Face quite plane in profile; in addition to the epistomal 

 bristles there are sometimes a few, scattered bristles on 

 the lower part of face. Third antennal segment rather 

 short, plane above, without bristles, dilated or swollen 

 below. Small or medium size flies. 



Axyssomyia, new genus 



41. Face below antenna plane with eye for a short distance, then 



abruptly and greatly produced into a prominent gibbosity, 

 densely bristly and with abrupt, dorsal shelf or ledge. 

 Small, blue black flies, including the wings. Occiput and 

 vertex strongly developed ; proboscis not longer than 



face Teratomas Loew 



Face and occiput and vertex differently constructed; pro- 

 boscis longer than the head 42 



42. Third antennal segment quite long, distinctly longer than 



head, slender, without dorsal bristles, bearing an 

 oblique, apical, spoon-shaped microsegment enclosing a 



spine 43 



Third antennal segment shorter, as long as the head ; but if 

 longer than the head, never slender ; apex always with 

 cylindrical, attenuate, spine-tipped microsegment . . 45 



43. Aerostical bristles absent or reduced to minute setae. 



Proboscis without dorsal ridge, except near the base. Base 

 of third abdominal segment constricted. Male terminalia 

 dorsally with a medial process. Scutellum with 1 pair 

 of long bristles . . . Cylicomera Lynch Arribalzaga 

 Aerostical bristles well developed. Proboscis with medial 

 ridge. Abdomen nowhere constricted ; scutellum with 2 

 or more pairs of long bristles 44 



44. Abdomen stout basally, tapered to the apex. 



Tolmerolestes Lynch Arribalzaga 

 Abdomen cylindroid with parallel sides . Dizonias Loew 



45. Face gently convex, densely long pilose and third antennal 



segment elongate, distinctly wider than the second seg- 

 ment. Occiput tumid and well developed behind vertex. 

 Fourth posterior cell usually open, sometimes greatly 



narrowed, or closed Spanurcs Loew 



Antennal length and head length nearly equal. Third seg- 

 ment if swollen never greatly lengthened. Occiput reduced 

 dorsally and behind the vertex 46 



46. Face quite plane and, except for the supraepistomal mystax, 



very few bristles present. Third antennal segment rather 

 short, plane above, strongly swollen or widened below. 



Alyssomyia, new genus 

 Face short beneath the antenna, distinctly gibbous and pro- 

 duced below and beset with dense pile or bristles or both. 



