Among the Tenthredinidæ captured by me during the past season was a good series of Tenthredo delta Prov, consisting of 12 females and 26 males. In pinning them I was frequently struck by the evident irregularity of the venation of the wings, and on a more careful examination of the specimens I find these irregularities to be both numerous and remarkable. No other species represented in my cabinet show any such divergencies from the typical form, except in rare instances. Provancher describes the female (page 210, “Petite Faune Entomologique du Canada”) as having two discoidal cells in under wings, and Cresson (“Trans. Am. Ent. Soc.,” vol. viii., page 44) as having one or two middle cells. One middle cell appears to be the rule, and any deviation therefrom to be an exception. Of my 12 specimens, 10 have one middle cell each, one has two middle cells, and the other none. The males are more uniform apparently in their venation, as none of my 26 specimens have middle cells in the under wings, thus agreeing with the description given by Cresson (loc. cit). Apart from the varying number of middle cells, the under wing of the females have the cells varying much in shape, especially the middle one, which ranges from a small triangular form to a large foursided (square or irregular) one. There are also occasionally small additional cells on the posterior margin.