236 DIPTERA OF NORTH AMERICA. [PART IV. 



The small number of Trichocerde which I have before me for 

 comparison, may be grouped thus : — 



I. Wings with two brown clouds, one near the origin of the 

 prsefurca, the other on the small cross-vein. 



1. Knob of the halteres not infuscated ; thorax with a 



yellowish-gray bloom above, and with rather dis- 

 tinct brown stripes ; the petiole of the first sub- 

 marginal cell is about three times the length of the 

 distance between the inner end of this cell and the 

 marginal cross-vein (Tab. II, fig. 13) ; the latter not 

 perceptibly clouded with brown ; wings compara- 

 tively narrow ; long. corp. about 0.25. Very com- 

 mon everywhere ..... bimacula Walk. ? 



2. Knob of the halteres distinctly infuscated ; wings much 



broader than in the preceding species ; the thorax 

 is of a paler yellowish-gray and the stripes less dis- 

 tinct, although visible ; the petiole of the first sub- 

 margiual cell is but little longer than the interval 

 between the inner end of this cell and the marginal 

 cross-vein ; the latter with a distinct brown cloud ; 

 long. Corp. 0.25. A single female specimen, from 

 Canada . . . maculipennis J/e?y., or nov. sp. ? 



II. Wings with a single faint brown cloud on the small cross- 

 vein. 



3. The petiole of the first submarginal cell is about twice 



the length of the distance between the inner end 

 of this cell and the marginal cross-vein ; the wings 

 are rather broad, almost hyaline ; the tliorax 

 brownish, with a yellowish-gray bloom ; stripes 

 almost obsolete, hardly visible ; knob of the 

 halteres brown ; the great cross-vein is a little 

 before the posterior end of the discal cell ; a single 

 male specimen ; long. corp. 0.18 . . . .Spec, nova? 



III. Wings unicolorous. 



4. Thorax brownish, with a yellowish-gray bloom, and 



with tolerably well marked brownish stripes ; 

 wings with a very faint yellowish tinge ; the 

 petiole of the first submarginal cell is equal in 

 length to the distance between the inner end of 

 this cell and the marginal cross-vein ; the great 

 cross-vein is at the posterior end of the discal cell, 

 or very near this end ; halteres with brownish 

 knobs; long. corp. 0.21 Spec, nova? 



