228 MAINE AGRICULTURAL LXPERIMe;nT STATION. I909. 



The type, from the District of Columbia, is now in the 

 museum at Cambridge, Mass. Another specimen of this beau- 

 tiful species is in the United States National Museum. 



4. Genus Symmerus Walker. 



Symmerus Walker, List Dipt. Brit. Mus. I. 88. 1848. 



Plesiastina Winnertz, Stett. Ent. Zeit. XIII. 55. 4. 1852. 



Head, antennae, palpi, abdomen and legs as with Ditomyia. 

 Eyes somewhat approximated on the vertex, ocelli 3 in number. 

 Fore tibise on inner side with several slender setse, the hind 

 pairs as with Ditomyia. Wing venation (fig. 81) as with 

 Ditomyia but differs primarily in having a shorter R2+3, the 

 base of which is somewhat distad of the fork of the media, and 

 the costa ends at the tip of R^+b. 



Table of species. 

 a. Thorax shining fuscous black; abdomen and halteres 

 mainly black, the basal half of peduncle of the latter, 

 yellow; length 5 mm. Eastern states. i. tristis. 



aa. Thorax and usually halteres also, mainly yellow. 

 b. Wings distinctly fasciate. 



c. Wing with a single slender fascia across the cross- 

 veins ; abdomen black, segments with yellow 

 posterior margins ; length 12 mm. Mexico. 



2. lenis n. n. 

 cc. Wing with two transverse fascia. 



d. Thorax with 3 shining black stripes ; legs 

 mainly yellow, hind femora, tip of hind 

 tibise, hind tarsi and tip of middle tibia, 

 black, 6^-y mm. Mexico. 3. bifasciata. 

 dd. Thorax yellow, reddish in the middle; legs 

 pale, tarsi fuscous ; length 10 mm. 

 Mexico. 4. mexicana. 



bb. Wings not distinctly fasciate. 



c. Thorax shining yellow, abdomen yellow, segments ' 

 with wide, black posterior margins ; length 

 y-y^ mm. Eastern States. 5. annulata. 



cc. Thorax yellow with blackish median fascia; 

 dorsum of abdomen black, the segments with 

 pale margins ; length 4.5-6 mm. New York. 



6. lauta. 



