74 Rev. T. A. Marshall's Monograph of 



the 2nd recurrent nervure (an essential and invariable 

 character of that family), and by the insertion of the 

 abdomen somewhat above the hind coxae : from the 

 Evaniidss, by almost every character available for classi- 

 fication, except the insertion of the abdomen, which 

 character however is but feebly represented : from the 

 Braconidx, by the neuration, nothing similar to which is 

 found in the entire family, and by the structure of the 

 abdomen, in which the 2nd suture is diarthrodial or 

 penetrating, as in the Ichneumonidm. Lastly, the insects 

 composing the genus Pachylomma are parasites of ants, in 

 which habit there is nothing to show an affinity to one 

 more than another of the above-mentioned families, — 

 except only the case of Elasmosoma among the Braconidie, 

 also parasitic upon ants, but totally different in external 

 structure. 



It is not worth while to multiply objections, which it 

 would be easy to do ; enough has been stated to show 

 that Pachylomma represents a very small isolated group, 

 having no near relation to any other parasitic Hymen- 

 optera. The connecting links have been lost in long 

 ages, through some obscure causes which oppose un- 

 favourable conditions to the propagation of certain forms. 

 Several of these abortive offshoots from the primitive 

 type are well known in other orders of insects, and 

 among the Hymenoptera occur some of the most con- 

 spicuous ; such are * Stephanus, Monomachus, Pelecinus, 

 Elasmosoma, etc., whose position in any artificial system 

 has always been, and must continue to be, based upon 

 fanciful analogies, or altogether indeterminate. 



Two species only of the Pachylomma-gvoup are at pre- 

 sent known in Europe, one of which occurs in the British 

 islands. In America three more have been made known 

 by Provancher and Ashmead, viz. Eupachylomma rileyi, 

 Ashm., E. flavocinda, Ashm., and Rop)ronia pediculata, 



* Nees V. Esenbeck commences his monograph of the Bracoinden 

 with the genus Stephanus. This genus is now regarded as a separate 

 family. Stephunidse, to which Schletterer has lately added Ste/iu- 

 phasnms, Westw., a genus taken from the Braconidec, and allied to 

 Spathnis, of which it has all the forms, with exaggeration, and a 

 neuration absolutely identical, but widely different from that of 

 Stephanus. The resiilt of this is that the group of Spathius enjoys 

 a double representation, figuring among the Braconida3 as Spathius, 

 and among the Stephanidee. as Stenophasmus. 



