During the last seven years the writer has taken advantage of every opportunity to study the stoneflies, or Plecoptera, of Illinois. The desire to have this investigation rest upon an understanding of the bionomic and taxonomic relationships of this order in North America as a whole has led to the collection by myself of material in other geographical regions and the examination of specimens collected hy others in various localities.

The present paper is the result of an attempt to segregate the species confused in collections under the name Dolopius lateralis Esch. and to determine the characters of the genus Dalopius Esch. (Dolopius auct.). It is based on material in the Canadian National Collection supplemented by specimens from the collections of Messrs. Ralph Hopping, G. Stace Smith, J. B. Wallis, F. S. Carr, L. J. Milne, and E. H. Strickland. More than one thousand specimens of Dalopius, mostly from Canadian localities, have been available for study. I have recognized forty-two species in this material.

An excellent way to present generic revision is to show the names arranged in annotated check list style. This method stresses classificational position. I believe entomologists in general are becoming more concept-minded and realize the need of improved lower categorical systems and better Code Rules governing the arrangement of their names. In lepidoptera this need is felt strongest. (See note under No. (15) in this article and also the Entomological News for July, Nov. and Dec., 1932, for further discussion.)