Entomology of the lllinou River. 241 



iace; rima nearly straight in its outer half, inwardly curv- 

 ing strongly forward, and ending in a conspicuous hook; 

 free margin of tubercle rounded at tip. [See Fig. 53.] 



First abdominal with two distinct setae each side above 

 the Hpiracles; abdominal spiracular tubercles rounded, 

 broad behind, low-subhemispherical, rima long, following 

 posterior border of tubercle, slightly curved at middle, 

 more strongly curved forwards at each end; on anterior 

 surface a transverse groove extending across the tubercle, 

 but not as long as the rima. [See Fig. 52.] Fringes of 

 unequal spines, often tipped with blackish, all but two of 

 the long spines wanting in a broad space above on seventh 

 segment. Terminal teeth nearly equal, tipped with black- 

 ish, their points marking the angles of a hexagon, slight- 

 ly wider than high. [See Fig. 54.] Ventral fringe of last 

 segment not webbed together; lateral tufts high— on a 

 level with upper lateral line. 



Tahanus sp. (b). [Fig. 49.] 



In collecting the larvae of Limnophila and Bittaco- 

 morpha in the swampy slough of Station I, many small 

 tabanid larvae were found in the mud and dead trash, 

 and among them occurred, on April 15, two examples 

 of a distinct very white form with faint markings like 

 those of the preceding species, but laterally striate more 

 like atratus, and with a conspicuous isolated smooth 

 spot in the lateral striated area of the prothorax. 



Lai^a [Fig. 49].— Length 22—23 mm., width 2.5 mm. 

 Very pale whitish, markings like those of stygius^ but 

 pale yellowish fuscous and inconspicuous. Head pale 

 brownish. 



Lateral prothoracic areas not more than half as long 

 as the dorsal, striation scarcely visible, microscopically 

 fine and opaque, much finer than that of the middle and 

 lower lateral areas of the mesothorax, which are some- 

 what shining; a rather large smooth spot included in 

 the striated lateral area of the prothorax, not far from 

 the shining ventral area but entirely isolated from it; re- 

 —1(5 



