ZETHUS. ] 5 



form of the two first segments recalls specially that of Icaria 

 (Social Wasps). 



In general with Zethus, above all among the small species, the 

 head and thorax are cribrose with coarse punctures. These some- 

 times extend upon the petiole, but commonly the inctathorax is 

 less punctured and the abdomen very smooth. 



Most of these insects are colored black and yellow; but the 

 yellow markings are often wanting, and the variations are very 

 numerous. 1 



The genus Zethus is particularly interesting in view of its 

 zoological affinities. In fact, here the head becomes large and 

 excavated posteriorly, as in the Vespinse; the mandibles are short 

 as among them ; and one remarks a certain relationship in the 

 appearance or some resemblances which seem to establish an 

 affinity with the Social Wasps ; 2 while in the construction of the 

 parts of the thorax, one recognizes some traces of the forms of 

 the Odynerinse sessiliventres. 



Zethus seems also to establish a lien between the Odynerinse 

 and the Social Wasps by their habits ; for the Zethus, although 

 certainly solitary insects, construct nests composed of irregular 

 cells, few in number but agglomerated, which is probably a pre- 

 liminary step in the series toward the construction of numerous 

 serried and regular cells. (See Zethus Bomandinus.) 



Even with all the gradations of form which we observe in 

 passing from one to another in this genus, we do not think that 

 one can divide the Zethus into more genera. Even the Asiatic 

 type Catligaster seems so intimately attached to Zethus that we 

 can scarcely keep it separated now that more numerous Asiatic 

 species are known. 



In conclusion, the genus Zethus is a very numerous American 

 group, peculiarly abundant in the intertropical parts of this con- 

 tinent. In the United States it is represented by but one known 

 species; while in Mexico we find a very great number, which 

 seem to be but an indication of a very much greater number which 

 must exist in the other parts of tropical America. 



' From my ignorance of this fact. I regret having published in my Mono- 

 graphic des (Tnepes Solitaires, descriptions of a certain number of species 

 of Zethus, the distinctions of whioh arc founded especially on the distribu- 

 tion of colors. 



2 See below, the division Zethus* 



