497 



Metriocnkmus Van der Wnlp 



\^ery few species of this genus are represented in the collections of 

 this Laboratory, and no attempt is here made to revise the North 

 American species. One species, hindhecki Johannsen, has been reared 

 by the writer, and full descriptions of its stages are published in the 

 Proceedings of the Entomological Society of Washington.* In the 

 present paper only brief descriptions of the stages are included. 



Kieffer has based the separation of several species from those of 

 Metriocncinits on the structure of the apical portion of the lateral arm 

 of the hypopygium and the presence of well-developed pulvilli. Spe- 

 cies which have the above portion of the hypopygium simple are re- 

 tained in Mctriocncnuis, while those that have this process bifid are 

 placed in his new genus Brillia, I have seen a single species which is 

 referable to Brillia, but as the genus does not occur in Illinois, as far 

 as I am aware, I shall not include it in this paper. 



When Johannsen wrote his 1905 paper on this family, the larva 

 and pupa of only one North American species of Mctriocncnuis were 

 known, and they possess characters which, although used by Johann- 

 sen in his generic keys to these stages, the larva and pupa of lundbecki 

 lack, and consequently in using the said keys to locate larvae and pupae 

 it is evident that those of lundbecki at least could not possibly be 

 placed in Mctriocncnuis. I have avoided the use of generic keys for 

 larvae and pupae because, with our present very imperfect knowledge of 

 the Chirononiidcr, mistakes in generic identification and classification 

 are almost certain to occur, and little good could now be accomplished 

 by adopting as a basis of generic separation characters possessed by the 

 few known species, which may be of specific and not real generic 

 value. 



The imagines of Mctriocncmus may be distinguished from those of 

 any other genus in the Cliirononuncr by the following characters: an- 

 tennae of male 15-jointed (2+13), those of female 8-jointed (2-I-6) ; 

 wings hairy; basal joint of fore tarsi shorter than fore tibiae; pulvilli 

 small or nearly wanting; hypopygium with apical portion of lateral 

 arm simple, armed with a small thorn at apex. 



Although but two species have been taken by the writer in Illinois, 

 one of them being liitherto undescribed, it is highly probable that 

 many species occur in the state and will be discovered later. 



*Vol. 16, 1914, p. 132. 



