AGROMYZID LEAF MINERS — FRICK 383 



prominent keel between the antennae, and the lunule is abruptly 

 narrowed immediately dorsad of the antenna (fig. 78). The eye is 

 not as smoothly romided anteriorly (fig. 79) as it is in P. angulata 

 (fig. 69). I have seen no reared specimens but in Europe this group 

 mine the leaves of species of Carex, Cyperus, and ScirpiLS. I have 

 identified only a few specimens as belonging to this species, all from 

 Illinois. Most of the specimens Malloch placed under Phytobia 

 subangvlata belong to P. angulata sens. str. 



5f. Subgenus Dizygomyza Hendel 



Dizygomyza Hendel, in Lindner, Die Fliegen der palaearktischen Region, fara. 

 59, p. 83, 1951. 



Of the six described species of this subgenus two are Nearctic and 

 four are Holarctic. The adults placed in this subgenus are char- 

 acterized by a very large lunule. The lunule is in the plane of the 

 frontal vitta and abruptly raised above the plane of the mesofacial 

 plate (fig. 83). This is in contrast to subgenus Poemyza where the 

 lunule is sunken somewhat below the frontal vitta and is in the plane 

 of the mesofacial plate (fig. 78). The height of the lunule is usually 

 less than one-half its width at the antennal bases. However, the 

 lunule may be higher (fig. 83), as it is in Phytobia (Dizygomyza) 

 thompsoni, but the lunule being in the plane of the frontal vitta sepa- 

 rates the latter species from species of the subgenus Poemyza. Sub- 

 genus Dizygomyza has the frontal triangle no larger than the ocellar 

 triangle (fig. 83), in contrast to the elongate frontal triangle found in 

 subgenus Icteromyza which reaches to the lunule (fig. 85). The third 

 antennal segment of the males is greatly enlarged. The larvae have 

 three bulbs on each posterior spiracle. One or more of these is usually 

 elongate, heavily sclerotized, acuminate, and variously curved. The 

 posterior spiracles of some species are quite similar to some found in 

 subgenus Poemyza. 



Key to the described species of Phytobia (Dizygomyza) 



1. Anterior half of mesonotum with acrostichal setae numerous, in six to eight 



irregular rows 2 



Anterior half of mesonotum with acrostichals relatively sparse, in four to five 

 irregular rows 4 



2. Legs with all femora distally light yellow for a distance subequal to the femoral 



diameter 3 



Legs with forefemur distally light yellow, others light brown iridis 



3. Head rounded in profile, genovertical plates at most barely extending beyond 



eye margin; tarsi dark brown; small species, two to 2.3 mm. in wing length. 



iracos 



Head subtriangular in profile, genovertical plates strongly extending beyond 



eye margin (fig. 82); tarsi yellowish; large species, 2.75 to 3.0 mm. in wing 



length thompsoni 



