110 Bulletin of the Brooklyn Entomological Society Vol. XI 



11. Hind tibia slightly prolonged into a blunt apical process on ventral 



surface; mid femora without long bristles on basal half of ventral 



surface; hind tibia with 2-3 ventral bristles dentipes Fabricius, 



Hind tibia normal at apex ; mid femora with 6-7 long bristles on basal 

 half of postero-ventral surface ; hind tibia with i ventral bristle or 

 with only ventral setulse 12 



12. Mid tibia with a continuous series of very short upright hairs from 



base to apex on anterior surface; mesonotum distinctly shining and 



vittate houghi n. sp. 



Mid tibia without short upright hairs; mesonotum dull velvety black, 

 not vittate meteorica Linne. 



Hydrotsa houghi, n. sp.— Male.— Black, distinctly shining, slightly bluish 

 on dorsum of thorax and abdomen. Head black ; ocellar triangle shining ; 

 interfrontalia opaque; orbits, face, and cheeks with silvery pile. Thorax 

 vittate, the vittas consisting of whitish pruinose stripes covering the regions 

 occupied iby the acrostichal and dorso-central bristles, the intervening 

 spaces showing as narrow black lines. Abdomen with whitish pruinescence, 

 which gives the surface a slightly tessellate appearance; dorso-central 

 stripe slender, most distinct at base. Legs black. Wings clear or slightly 

 grayish. Squamae whitish. Halteres brown, knobs black. 



Eyes narrowly separated, almost entirely bare; arista tapering, pubes- 

 cent. Thorax with 3 pairs of strong presutural acrostichals. Thorns on 

 fore femora of unequal strength, the posterior one much more acute than 

 the anterior; 4 long blunt bristles on basal half of postero-ventral surface, 

 a series of short stout bristles on basal half of ventral surface, and 4 or 5 

 similar bristles on same surface just basad of the thorns distinguish the 

 femora. Mid femora with a series of very long curled bristles on basal 

 half of anterior surface and another one of straighter bristles on same 

 portion of postero-ventral surface. Mid tibiae with their anterior sur- 

 faces covered with tiny upright hairs; posterior surfaces with 2 bristles, 

 one above and the other below middle. Hind femora with a series of 

 stout bristles on the apical half of their antero-ventral surfaces and 2 

 complete series of long fine hairs on their ventral. Hind tibiae with short 

 hairs, distinct from which are 3-4 antero-ventral setulae, one weak antero- 

 dorsal bristle, a very strong dorsal bristle, and the usual preapical bristle. 

 Third ■ and fourth wing-veins convergent apically. 



Female. — Agrees in color with the male except for the more distinct 

 pruinescence of the dorsum. 



The eyes are separated by one third the head-width. The fore femora 

 have no characters that distinguish the species from dentipes. The mid 

 tibiae have one bristle one third from apex on anterior surface in addition 

 to the 2 on the posterior surface. The antero-ventral setulse on hind 

 tibiae are stronger than in the male. In other respects except as to the 

 femoral bristles the female is similar to the male. 



Length, 7-8.5 mm. 



