J. H. MERRILL 125 



4. Projections along groove of the sternal plate nearer the base of each seg- 

 ment than its apex Megarhyssa 



Projections on sternal plate situated about mid-way between base and 

 apex of each segment Rhyssa 



Males 



1. Propodeum areolated: head without a carina between the antennae 



Pseudorhyssa 



Propodeum not areolated 2 



2. Pleura and sternum of second abdominal segment fused for a short dis- 



tance Megarhyssa 



Pleura and sternum of second abdominal segment not fused Rhyssa 



Genus MEGARHYSSA Ashmead 



Thalessa Holmgren, Ofvers. Svensk. Vet.-Akad. Forh., xvi, 1859, p. 132. 



Megarhyssa Ashmead, Can. Ent., xxxii, 1900, p. 369. 



Megarhyssa Dalla Torre, Cat. Hym., iii, 1901-2, p. 479. 



Thalessa Schmiedeknecht, Gen. Ins. Fasc. 62, 1907, p. 63. 



Genotype: {Ichneumon clavator Fahricms) . [Sic]= (Ichneumon) Megarhyssa 

 clavatus (Fabricius) = (7c/mewmori) Megarhyssa Superbus (Schrank). (Vide 

 Viereck, Proc. U. S. Nat. Mus., Bull. S3, p. 144, (1914).) 



In Megarhyssa the clypeus is usually anteriorly truncate, the 

 abdominal segments in the male are smooth, with segments 

 3 to 7 at the apex emarginate or deeplj^ excavated. The sternal 

 plate of the second abdominal segment is for a greater or lesser 

 distance fused with the pleura at its anterior end. The amount 

 of fusion varies with the species. The sternal plate of this 

 segment is largely membranous, the chitin being apparently 

 degenerated. Between the seventh and eighth segments, issues 

 the membrane used by the female in ovipositing, as already 

 described. The projections of the sternal plates of segments 

 3 to 6, on either side of the mid-ventral groove are longer than 

 in Rhyssa, and are situated nearer the base than the apex of 

 each segment. 



Table to Females 



1. Insects black or fnostly black 2 



Insects yellow or yellowish red 4 



2. Black with white spots on the abdomen humida (Sa}-) (p. 126) 



Black without white spots on the abdomen 3 



3. Ovipositor at least twice as long as the body atrata (Fabr.) (p. 128) 



Ovipositor not twice as long as the body canadensis (Cress.) (p. 129) 



4. Areolet in fore-wings absent mesdcana (Cress.) (p. 131) 



Areolet in fore-wings present 5 



TRANS. AM. ENT. SOC, XLI. 



