SYRPHIDAE OF MAINE. 163 



The chalky-white median line of adipose tissue, which is scarcely a 

 third of a millimeter wide throughout the anterior segments, ends abrupt- 

 ly between segments 6 and 7 where the body is always quite blackish in 

 larvae of all stages. On the anterior part of segment 7, the white adipose 

 mass begins again, quite as abruptly, with two U-shaped loops opening cau- 

 dad, and separated by the black heart-line ; the white mass occupying per- 

 haps a third or fourth of the body width in segments 7 and 8. In segments 

 9 to 11, inclusive, the white masses expand in laterally-directed, angular 

 wings to occupy four-fifths or more of the width. The large mass is not 

 uniformly white, but is interrupted in each segment from 9 to 11 by the 

 , pulsating black heart-line and at the sides of this by large irregular pock- 

 ets and smaller areas of greenish gray where the body fluids are unob- 

 scured by the globular masses of white. In very young larvae, the whole 

 mass above described as white may be more or less tinged with tan. The 

 venter is maroon to black, the margins whitish. 



The transparent integument is uniformly papillose but without integ- 

 umental vestiture. The segmental spines are small, light in color, and only 

 moderately elevated, 0.045 to 0.075 mm. long, of two sub-equal, sub-cylin- 

 drical segments, the basal one 0.025 to 0.03 mm. in diameter, the distal one 

 half as broad. The body wrinkles are moderately prominent. The poste- 

 rior respiratory organ (Fig. 10, D, E) is very characteristic, being consid- 

 erably longer than in the described members of this genus. About two- 

 thirds the distance from the base is a prominent constriction, the tube be- 

 ing much depressed and somewhat compressed at this point. The basal 

 two-thirds is very rugose with rounded papillae and dark maroon or black 

 in color, while beyond the constriction the tube is smoother, polished and 

 light brown in color. The entire respiratory organ measured as follows: 

 length 0.702, 0.756, 0.756, 0.878, 0.918, 0.922 mm., the average 0.822 mm.; 

 widfh at base 0.41 to 0.54 mm., the average 0.485 mm. ; width at tip 0.325 

 to 0.35 mm., the average 0.334 mm. ; height at base 0.35 to 0.43 mm., the av- 

 erage 0.54 mm. ; height at tip 0.164 to 0.189 mm., the average 0.173 mm. 



The stigmal plates are somewhat divergent at the tip with a noticeable 

 emargination between them, the slit-like spiracles only moderately elevated 

 and short measuring 0.055 to 0.06 mm. in length by about 0.02 mm. wide. 



The rugose, black, dorsal spiracular spine is rather prominent, elon- 

 gate dorso-ventrad, somewhat crescent shaped and bending laterad some- 

 what over the circular plate. The latter is very inconspicuous and appears 

 to be elongate dorso-ventrad and narrower at the ventral end, rather than 

 round. In each inter-spiracular space is a slight ridge with a single, tiny, 

 whitish hair about 0.015 to 0.02 mm. long arising from a minute circular 

 crater. 



These larvae are aphidophagous, having been taken first in 

 early July, 1916 at Orono on a willow infested with Pterocomma 

 smithiae (Monell). In captivity one pupated July 28, the adult 

 emerging August 6. Another pupated a few days later and on 

 August 12 a puparium was found in the field, glued to a small 

 twig of willow near an infestation of this aphid; this specimen 



