ICHNEUMON-FLIES, PART 2 '. EPHIALTINAE 417 



Keys to the Nearctic species of Megarhyssa 



MALES 



1. Front wing marked with brown, at least with a brown spot in base of radial 



cell (fig. 319,d); median apical membranous area of tergites 3-5 extending 

 about 0.5 their length; apicolateral angle of tergites 3-5 usually about 60°. 



4. macrurus (Linnaeus) 



Front wing hyaline or subhyaline, without a definite brown mark though its 



apex may be faintly infuscate; median apical membranous area of tergites 



3-5 extending about 0.2 to 0.4 their length; apicolateral angle of tergites 



3-5 usuaUy about 75° to 90° 2 



2. Mesopleurum blackish brown, the subtegular ridge yellow; general color of 



thorax darker than that of abdomen; cheek about as long as apical width 



of mandible 1- nortoni (Cresson) 



Mesopleurum partly yellowish brown, the subtegular ridge yellow; general 

 color of thorax not darker than that of abdomen; cheek about 0.8 as long as 

 apical width of mandible 3 



3. Hind femur entirely light brown; abdomen light brown; hind edge of first 



sternite far beyond spiracle of first tergite .... 2. greenei Viereck 



Hind femur partly blackish, at least its hind face mostly blackish; abdomen 



dark brown; hind edge of first sternite a little beyond spiracle of first tergite. 



3. atrata (Fabricius) 



FEMALES 



1. Thorax and abdomen almost or quite entirely black (fig. 318,e). 



3. atrata (Fabricius) 

 Thorax and abdomen light brown to blackish, with conspicuous yellow mark- 

 ings (figs. 318,c,d,f,g) 2 



2. Tergites 4-6 each with a sharply defined, round yellow spot on each side 



(fig. 318,c) ; cheek about 1.4 as long as apical width of mandible; front wing 



with a uniform yellowish brown tinge 1. nortoni (Cresson) 



Tergites 4-6 with an angulated subapical yellowish band on each side, or with 

 a large irregular yellow blotch, or most of the tergite yellow (figs. 318,d,f,g) ; 

 cheek about 1.0 as long as apical width of mandible 3 



3. Front wing entirely clear along basal vein (fig. 319,b) or in a Florida subspecies 



the entire wing dark brown (fig. 319, c); fourth tergite with dense punctures 

 on less than half its surface, the rest almost impunctate; middle of hind 

 margin of first sternite usually beyond hind margin of spiracle of first ter- 

 gite; ovipositor sheath about 1.4 as long as head and body. 



2. greenei Viereck 



Front wing more or less brown or brownish along basal vein (figs. 319,e,f,g); 



fourth tergite with dense punctures on more than half its surface; middle of 



hind margin of first sternite in front of hind margin of spiracle of first tergite; 



ovipositor sheath about 1.9 as long as head and body. 



4. macrurus (Linnaeus) 



1. Megarhyssa nortoni (Cresson) 



Male: Front wing 9.5 to 20 mm. long; cheek about 1.0 as long as 

 apical width of mandible; median part of apical edge of first sternite 

 at or a little beyond hind edge of spiracle of first tergite; median 

 apical membranous streak of third through fifth tergites extending 



