ODYNKRUS. 149 



common to most parts of the globe. The evil is much less if 

 the fauna of one continent only is considered. 



The only groups which can be well defined arc the four 

 subgenera which Wesmael has indicated and which we have 

 adopted in our Etudes sur la Famille clcs Vespides. 1 These sub- 

 genera we are obliged to subdivide again to justify the arrange- 

 ment of the species, but it is prudent to say that these subdivisions 

 are very artificial, and that one must not trust too much to the 

 definitions of them, because of the difficulty of involving in them 

 all the exceptional forms, as well as of giving a true description 

 of the details of the forms. 



Definition rf the subgenera. 



A. First abdominal segment parted by a transverse suture. 



a. First abdominal segment rather funnel-shaped, parted by a deep 

 longitudinal groove; antenna? of the males simple, that is, without 

 a terminal hook. Symmorphus. 



h. First abdominal segment truncate at base, not parted by a deep 

 longitudinal groove; antennae of the males terminated by a hook. 



Ancistrocerus. 



B. First abdominal segment with no transverse suture. 



c. Thorax more or less square anteriorly ; abdomen conical, oval-conical 

 or spindle-shaped. OdynerUs. 



d. Thorax more globular or oval, rounded posteriorly, not very square 

 anteriorly. Abdomen oval, subsessile, more or less depressed, having 

 the same form as in Pterochilus (sublenticular). Epiponus. 



The last two sections rather overlap each other: those precede 

 ing are more defined and easier to distinguish. All of the four 

 subgenera are .represented in North America. The 4th is the 

 only one which has not yet been discovered in South America. 

 Although these groups are not sharply defined, their respective 

 'representatives can be easily distinguished by the eye, if one is 

 thoroughly familiar with their facies. The only very embar- 

 rassing types are those which unite Odynerus with Epiponus,but 

 they are not American. 



Determination of the species. 



We must here say, that, the most important specific characters 

 of the Odyneri being in the metathorax, the insects must be pre- 

 pared with the abdomen bent downward, so as to leave the hinder 



» Comp. this work, vol. I, p. 118-121. 



