321 



and but slightly tapered ; and the penultimate segment — sometimes 

 the antepenultimate also — bears 2 or 4 curved thorns on the posterior 

 margin of the ventral surface. 



HABITS OF I^ARVAK 



The larvae are aquatic, living in streams, particularly in those with 

 slow current and muddy bottom. Their food consists of algae, small 

 crustaceans, and decaying vegetable matter. 



HABITS OF IMAGINES 



The flies are commonly found on flowers along the margins or in 

 the immediate vicinity of streams. 



Key to Larvae 



1. Dorsum with 6 pale vittae, which are usually so close together as 

 to give the appearance of a single longitudinal band that tapers 



posteriorly ; large species, 20-30 mm. in length cincta. 



— Dorsum with 6 pale vittae which are rather widely separated and 

 do not form a longitudinal pale band ; smaller species, 12-15 mm. 

 in length vertehrata. 



Odontomyia CINCTA Olivier 



Odontomyia cincta Olivier, Encycl. Meth., Vol. 8, p. 432. (1811) 

 Odontomyia extremis Day, Proe. Acad. Nat. Sei. Phila., 1882, p. 80. 



The larva (PI. XLVII, Fig. 3) of this species has been described 

 by Mr. Hart*. I have dissected the head and find that the maxillae 

 and mandibles differ from those of Stratomyia norma as shown in 

 Figures 3 and 6 and 5 and 7, Plate XLVIII. The larvae may also 

 be distinguished from Stratiomyia as indicated in the key to genera. 



The species is represented in our collection by many larvae, mostly 

 obtained in the Illinois River. Most of the imagines were taken in 

 the vicinity of the Sangamon and Illinois rivers, but a few were ob- 

 tained at Muncie, near some small streams where the larvae were 

 found. 



Odontomyia vertebrata Say 



Odontomyia vertehrata Say, Appendix to Vol. 2 of Keating 's Narrative of an 

 Expedition to the Source of St. Peter's River, etc., p. 369. (1824) 



*BuU. 111. State Lab. Nat. Hist., Vol. 4, Art. VI, pp. 260-261. 



