24 NORTH AMERICAN DIPTERA. 



ow,s in the Rocky Mountains the writer has seen them rise at 

 nightfall in the most incredible numbers, producing a hum- 

 ming noise like that of a distant waterfall, and audible for a 

 considerable distance. While at rest they usually raise their 

 forelegs in the air and keep them constantly vibrating. 

 Aquatic larvae may be frequently met with in standing water, 

 often extremely delicate little creatures, so transparent as to 

 be hardly distinguishable; they have been dredged from 

 nearly one thousand feet below the surface of Lake Superior. 



Most of the species are inoffensive, or actually beneficial as 

 scavengers. There are some, however, belonging to the genus 

 Ceratopogon, and its allies, and known generally as midges, 

 or punkies, which have the power of sucking blood and are 

 extremely annoying. In the White Mountains, at the sea- 

 shore, along mountain streams generally, and in the West 

 Indies they are especially troublesome. The larvae live in the 

 flowing sap of trees, in decaying vegetation or under fallen 

 leaves. 



The following table, largely adopted from V. d. Wulp, 

 contains many genera heretofore known only as exotic, not a 

 few of which will doubtless be found in the United States 

 when the family has received more attention with us. 



TABLE OF GENERA. 



1. Antennae of the $ long-plumose or penicillate 2 



Antennae of the $ with short hairs. . . , . . 13 



2. Second posterior cell wanting and hence no second basal cell. . 3 

 Second posterior cell present, the second basal cell complete. . 12 



3. Fourth longitudinal vein furcate. . . . . . . 4 



Fourth longitudinal vein not furcate; antennae with an unequal num- 

 ber of joints in the two sexes ; antennal joints of the $ plumose to 

 the tip; thorax projecting in front over the head. ... 5 



4. "Palpi composed of three joints". . . TERSESTHES Townsend. 

 Palpi composed of four joints ; antennae of the male penicillate, 



the last joint bare ; dorsum of the thorax not produced over the 

 head ' . CERATOPOGON Meigen. 



