319 



Imago. — Robust, black species, with conspicuous yellow, greenish, 

 or whitish markings. Abdomen with 5 or 6 visible segments ; third 

 antennal joint without a differentiated arista ; 4 posterior veins pres- 

 ent on wing, 3 of which arise from discal cell; third vein forked; 

 scutellum spinose; basal joint of antennae at least 3 times as long as 

 second. 



HABITS OF I^ARVAE 



The larvae are aquatic, occurring in ponds and slow-flowing 

 streams. Their food consists of decaying vegetation and minute 

 organisms — such as algae, diatoms, and crustaceans. Species that I 

 have kept in the laboratory fed upon decaying leaves, eating all but 

 the veins and main ribs. The skin of the larvae is very tough and, 

 except just after molting, covered with a sedimentary deposit which 

 serves to conceal the species on the mud bottoms where they occur. 

 They become conspicuous, however, when they crawl out of the water 

 on the muddy banks, as their skins dry out rapidly and become gray- 

 ish, so that they are readily seen against the darker ground. The 

 larvae stand drying out remarkably, some of those I had recovering 

 upon being placed in water even after they appeared to be hard and 

 lifeless. This faculty of recovery must prove of great value to the 

 species which occur in shallow ponds or in streams which dry up dur- 

 ing periods of summer drought. 



HABITS OF IMAGINES 



The flies are usually found on flowers of various plants, and are 

 particularly common upon wild parsnip and wild carrot. 



Key to Larvae and Puparia 



1. Prothorax with slender hairs on its anterior margin ; apical segment 



about 6 times as long as its basal width norma. 



— Prothorax with a number of short, stout processes on its anterior 

 margin in addition to the slender hairs; apical segment about 3 

 times as long as its basal width meigeni. 



Stratiomyia NORMA Wiedemann 



Straiiomyia norma Wiedemann, Ausserenr. Zweifl. Ins., Vol. 1, p. 62. (1828) 



Larva (PI. XLVII, Fig. i). — Length, 30-40 mm.; greatest 

 diameter, 5.6 mm. Dorsum with 6 indistinct pale vittae and pale spots 

 at bases of the slender surface hairs, lateral margins pale. 



