146 HYMENOPTERA OF AMERICA. [PART I 



perhaps nearly double this number, for there is no region of the 

 globe which does not offer an abundance of these insects. 



Therefore the prospect of the future leads us to see riches 

 which by their very abundance will bring the entomologist to 

 desperation in keeping the genus Odynerus out of a general chaos. 



Among the so various forms of this group,. some are charac- 

 teristic of general zoological groups, which form natural subdivi- 

 sions of the genus. These forms present themselves on several 

 continents and are not peculiar to all the species of one continent. 

 Other forms are, on the contrary, so to speak, mere geographical 

 impressions, which belong to particular regions of the globe, 

 which stamp their character upon all the species of those locali- 

 ties, through all the genera, but are not to be found in other 

 countries. 



Examples of modification in the first way. — (General zoologi- 

 cal modification, special to one or several genera, but not peculiar 

 to one country.) 



a. The modification of the first segment of the abdomen, taking 

 a transverse suture (subgenus Ancistrocerus and Symmorphus) 

 is to be found on the whole globe. It forms quite a zoological 

 group, repeated in Odynerus and in Alastor. 



b. The modification of the antenna? of the males simple, not 

 taking a terminal hook. This is to be found amid the Odyneri 

 with a sutural first segment, in Symmorphus. The Symmorphus 

 are spread over the northern hemisphere, mixed up with Odyneri 

 having hooked antennae. 



c. This same character of the % antennas destitute of a hook 

 appears also in the true Odyneri, where it forms the division 

 Pachodynerus, but in those insects it is already a more geogra- 

 phical character, for the Pachodynerus is a special American type 

 spread over the new continent, and is particularly abundant in 

 the central parts. But, though quite American, it is not exclu- 

 sively a geographical group, for in America it is mixed with 

 Odyneri of other groups. 



This same character also presents itself and much in the same 

 way in the genus Eumenes where it forms the Division Omicron, 

 resuming the species with simple % antennae and has just the 

 same geographical type as Pachodynerus, being only American, 

 but also mingled in America with the- hooked Eumenes. This 



