418 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 57, 



2. Spiracles of the first tergite at about the basal third, the distance between them less 



than the distance from one to the anterior margin of tergite ; second tergite with- 

 out distinct lunulae; nervnlus instertital; areolet wanting; abdomen of male 

 slightly widening posteriorly a little more than twice as long as head and thorax. 



Epirhyssa Cresson. 



Spiracles of the first tergite close to the base, the distance between them greater 



than the distance from one to the anterior margin of the tergite; second tergite 



with distinct lunulae; nervulus postfurcal; abdomen of the male practically 



parallel-sided and three or more times as long as the head and thorax 3. 



3. Propodeal spiracle about two and one-half times as long as wide and about three 



times its length from the base of the propodeum; tergites three to five not or 

 but slightly emarginate posteriorly; small or medium size black species. 



Rhyssella Rohwer. 

 Propodeal spiracle three or more times as long as wide and about twice its length 

 from the base of the propodeum; tergites three to six deeply angulately 

 emarginate posteriorly; large or medium size usually yellowish species. 



Megarhyssa Ashmead. 

 Genus RHYSSA Gravenhorst. 



Rhyssa Gravenhorst, Ichn. Eur., vol. 3, 1829, p. 260. Genotype. — Ichneumon 

 persuasorius Linnaeus. 



Cryptocentrum Kirby, W. Kirby, Fauna Bor. Amer., vol. 4, 1837, p. 260. Geno- 

 type.- — Cryptocentrum lineolatum Kirby. 



Pararhyssa Walsh, Trans. St. Louis Acad. Sci., vol. 3, 1873, p. 109. Geno- 

 type. — Rhyssa persuasoria (Linnaeus.) 



As originally described the genus Rhyssa included ail of the 

 Palaearctic Rhyssini but since the time of Holmgren European 

 authors have restricted the genus much as it is in the present paper. 

 American authors have not, however, been as careful and, with the 

 exception of Viereck and Merrill, have included species now placed 

 in Rhysella in the genus Rhyssa. While Holmgren was the fu'st to 

 point out the clypeal character which separates the genus Rhyssa 

 from its allies Merrill was the first to point out the decided difference 

 in the fu'st sternite. 



Although there is a superficial resemblance between Rhyssa and 

 Rhyssella, the genus Rhyssa is remarkably distinct from the other 

 genera of this tribe. As far as has definitely been proven the species 

 are parasitic on horntail larvae belonging to the subfamily Snicinae, 

 all of wliich live in coniferous trees. There are some records of 

 Rhyssa being parasitic on the larvae of the Cerambycid genus 

 Monohammus but considering the habits of the Monohammus larva 

 it seems that these records are open to question. There are other 

 records of Rhyssa being parasitic on the Coleopterous genus Serro- 

 palpus but none of these have been definitely proven and should be 

 verified before accepted. 



Generic characters. — Clypeus with a medium projection; nervulus 

 postfurcal; areolet normally present; propodeum with two raised 

 median, longitudinal ridges; the propodeal spiracle fully three times 

 as long as wide and about twice its length from the base of the pro- 



