34 AMERICAN BLACK FLIES OR BUFFALO GNATS. 



(;koup c. 



Scutum unstriped, at most the anterior margin with weak indica- 

 tion of a central, divided stripe, and anterior hiteral white spots. 



TABLE OF SPECIES. 



1. Tarsal claws with a distinct subbasal tooth in addition, and anterior, 



to the normal tuberculate or rounded base ' 2 



Tarsal claws without subbasal tooth, only the base tuberculate, rounded, 

 or produced thuniblike (as in PI. II, figs. 5 and 7) 6 



2. Thoracic pilosity arranged in irregular gi'oups, disk with upright black 



hairs, in addition to lalosity, which are most distinct on anterior 



angles mexicanum, p. 35. 



IMlosity not arranged in groups, regularly disposed 4 



4. Thoracic pilosity black or black-brown, fine and hairlike parnassum, p. 36. 



Thoracic pilosity lanceolate, scalelike, whitish or yellowish in color. 



arcticum, p. 37. 



5. Tarsal claws produced thumblike at base 6 



Tarsal claws not produced thuniblike at base 7 



U. Scutum with brassy, scalelike pilosity ; base of tibiae not blackened. 



bractcatuin, p. 38. 

 Scutum with yellowish hairlike pilosity; base of tibiae distinctly black- 

 ened ^ johannseni, p. 05. 



7. Pilosity on scutum arranged in puuctiform groups, the scales short and 



broad, small species exiguum, p. 39. 



Pilosity on scutum not arranged in punctiform groups, either regularly 

 or irregularly disposed 8 



8. Scutum with irregularly disposed golden yellow pilosity and upright 



brown hairs on disk clavipes, p. 40. 



Scutum with regularly disposed pilosity, discal hairs absent 



9. Small species (1-1.5 mm. in length) ; mid tarsi almost all pale; third 



joint of hind tarsi pale; scutum with pearlaceous pollinosity. 



jennincjsi, p. 11. 



Larger species (2-4 mm. in length) ; mid and hind tarsi black, except 



bases of first and second joints; scutum with whitish pollinosity 10 



10. Scutum more or less shining, the anterior margin at center with indica- 

 tions of a divided stripe; pilosity yellow venustuni, p. 43. 



Scutum not shining, no indications of a central stripe ; pilosity whitish. 



pincicidium, p. 45. 



Simul'mtn tarsale Williston belongs to this group, but from the 

 description I am unable to place it in the table. In all probability 

 it is distinct from any of those included in my table, but nothing is 

 said of the tarsal claws and certain other essential characters in 

 "Williston's description, so that it is impossible to decide its status. 

 The species belonging to this group are the most widely distributed 

 and most closely allied of the Simuliida:'. It is to this segregate that 

 reptans Linnaeus and several other European species belong. 



^ I have includef] johaiiiiseni hero as woll as in the proiip with vittato scutum, as it is 

 closely allied to Vracteafuin in the formation of the claws, but the coloration as given 

 above, though of alcoholic specimens, is quite distinct from that of hracteatum, as i-^ also 

 the vestiture of the thorax. For description see pp. 65-66. 



