40 BRITISH ICHNEUMONS. 



genus Ctenichneumon. Thomson, who sub-divided the genus Ichneumon 

 as it remained after Wesmael's various capital parturitions, erected genera 

 which are most undoubtedly quite natural groups, and it is by no means 

 difficult to tell at a glance to which of them a specimen, seen for the first 

 time, should be ascribed. It is, however, a very different matter to specify 

 points of distinction in a table such as the following, and the characters 

 there enumerated must be accepted in their broadest sense. Thomson 

 indicates a variety of structural features for his genera, some for one and 

 some for another, but there is no hard and fast line drawn between them, 

 and the points indicated in one genus are very often omitted in some or 

 all of the others, e.g., the genal costa of his genus Ichneumon is said to be 

 infle.xed, but one is left to pre-suppose that that of all the other genera is 

 entire since no reference is made to it. Ashmead helps one not at all, 

 since he relies mainly upon the shape of the areola which, so far from 

 being constant, usually differs more or less widely in the sexes of the same 

 species ; and I am not prepared to vouch for the stability of the juxta- 

 pleural carina. Dr. Schmiedeknecht in 1902, presents a table of these 

 genera in which Stenichneumon differs from the remainder in its posteriorly 

 narrowed head ; Barichneumon from Ichneumon in its pentagonal areola 

 whose costulae are emitted from behind the centre ; the remaining charac- 

 ters, excepting the stronger costulae in Melanichneumon than in Cratich- 

 neumon, are not original and the aciculation of the post-petiole cannot be 

 of the least use in characterising the genus Ichneumon. Nevertheless, 

 no doubt remains that these genera are good ones, and it is now only 

 necessary to discover their peculiarities. 



Table of Genera. 



Clypeus truncate or slightly and evenly rounded, not apically emargi- 



nate. 

 Basal segment not dorsally intume- 



scent in the centre. 

 Gastrocaeli often large ; terebra and 



eighth dorsal segment rarely ex- 



serted. 

 Base of second segment narrowly 



margined ; post -petiole broad 



and sub-glabrous 3. EUPALAMUS, IVcsvt. 



Base of second segment immar- 



ginate ; post- petiole centrally 



normal and sculptured. 

 Juxta-coxal and pleural areae con- 

 fluent ; areola usually quadrate i. Stenichneumon, Thorns. 

 Juxta-coxal and pleural areae 



usually discreted by a distinct 



carina. 

 Face usually convex ; body small 



or slender ; areola semi-circular 



or transverse. 

 Post-petiole centrally aciculate or 



shagreened ; antennae of ? 



filiform 2. Cratichneumon, Thorns. 



Post -petiole centrally punctate ; 



antennae usually attenuate 5. Barichneumon, Thorns. 



