No. 2317. FIVE TRIBES OF ICHNEUMONINAE—ROHWER. 417 



biological habits they seem to be more closely allied to the Xoridini. 

 In the classifications used by Ashmead and others it is impossible to 

 satisfactorily place a Rhyssine in the tribe Ichnemnonini because the 

 tergites lack the impressions and strong punctures. 



All of the species which have been reared are parasitic on wood- 

 boring larvae and most of the records indicate that they prefer the 

 larvae of homtails. A few observers have recorded the hosts as some 

 wood-boring Coleopterous larvae but all of these are without positive 

 proof and in case of the records from Monohammus it seems that they 

 can be discarded. The records of Serropalpus can not be so easily dis- 

 credited because the larvae of members of this genus are usually 

 associated with the larvae of horntails. 



Tribal characters. — Head large, transverse, well developed behind 

 the eyes; the posterior orbits margined at least below, the occiput 

 immargined; clypeus transverse, well-defined above; malar space 

 present; malar furrow wanting; mandibles bidentate, the upper tooth 

 broad; eyes slightly converging below; pronotum vertical; scutum 

 prominent, transversely rugose; notauli wanting or incompletely 

 defined; scutellum transversely rugulose; propodeum rather short, 

 the spiracle well removed from base; legs rather long and slender; 

 claws simple; areolet variable; nervellus strongly reclivous and broken 

 far above the middle; abdomen long, often parallel sided in the male; 

 first tergite without prominent carinae, shorter than the second and 

 with the spiracle well before the middle; ovipositor long; apical tergite 

 of female prominent, triangular in outline; hypopygidium small, not 

 prominent. 



The shape of anterior margin of the clypeus, the character of the 

 frons, the areolation of the propodeum, the size and position of the 

 propodeal spiracle, the position of the first tergal spiracle, the fusion 

 of the first sternite with the tergite, the emargination of the apical 

 tergites and the position of the nervulus offer the best generic char- 

 acters. The presence or absence of the areolet has often been used 

 as a primary generic character but that this can not be used as such 

 is abundantly proven by the fact that in some specimens it is com- 

 pletely wanting on one wing while on the other wing it is well defined. 

 The following table is based on the Nearctic genera but the genus 

 EpirJiyssa Cresson is included as it has often been misinterpreted and 

 has never been well characterized. 



TABLE TO THE GENERA. 



1. Clypexis with a median tooth; first sternite completely separated from the first 

 tergite; second sternite of female with two median tubercules near the middle; 

 nervulus postfurcal; tergites not at all emarginate posteriorly 



Rhyssa GraverJiorst. 



Clypeus truncate; first sternite fused with the first tergite basally; second sternite of 



female with the median tubercules close to the base; apical tergites at least in 



the male more or less emarginate posteriorly 2 . 



144382— 20— ProcN.M. vol.57 27 



