16 NORTH AMERICAN DIPTERA. 



this family, and, hence there are doubtless not a few geneva 

 that have hitherto escaped detection. The following table has 

 been mostly compiled from V. d. Wulp, Winnertz and Schiner, 

 and compared with representatives of most of the genera. 



E2nda2n(s scabies has recently been shown by Hopkins to be 

 a cause of the potato scab. Various species of Sciara have 

 also been bred from potatoes and other vegetables. The lar- 

 vpe of Sciai-a mall " destroy the interior of apples by burrow- 

 ing through them, while the fair exterior shows no indication 

 of concealed attack." The larvae of a species of Exechia have 

 been found by Lintner very destructive to miishrooms. 



TABLE OF GENERA. 



1. Coxae moderately long ; anterior cross- vein in the same right line with 



the second section of tlie tiiird vein; furcation of the fifth and sixtli 



veins near the base of the wing. . .,, . . vSriAKix.i;. 



Coxa; much elongated; anterior cross- vem not m the same right hne 



with the second section of the third vein. .... 2 



2. Origin of the fourth vein near the base of the wing; seventh vein more 



or less incomplete. ......... '-^ 



Origin of the fourth vein at or near the middle of the wing; seventh 

 vein usually complete. ........ 4 



3. Third longitudinal vein furcate, the anterior branch usually so near the 



origin and so transverse in position tiiat it resembles a supernume- 

 rary cross- vein ; three ocelli present . . . Scioimiilix.T':. 

 Tliird longitudinal vein not furcate; two or three ocelli present. 



MvcETorHiLiN.i:. 



4. Anterior branch of the third vein very long, terminating in the costa 



and arising very close to or at the beginning of the second section of 



the third vein Mvcktoiuixve. 



Anterior branch of the third vein short, more transverse, usually ending 

 in the first vein. .........-> 



5. The prefurca of the fourth vein arises from the third vein beyond the 



apparent cross-vein, i. e. tlie cross-vein is really wanting and the 



third and fourth veins are coaleseent for a short distance. . <! 



The fourth vein continues in the same line before the cross-vein to its 



origin from the fifth. . {HolitopltiUnd) \Io\a-yoviiu.\ Meigen. 



0. Antennse short and thick-set, often flattened. . . Ckp.oplatinmc. 



Antenna' long and slender, longer than the l)ody. 



{Marrorvriwt) Maci{oci-:I!A .Meigiii. 



