Wishing to obtain a series of males of our common ground wasps, I paid a visit on the afternoon of October 21st to a larqe nest of Vespa occidentalis, Cresson, that I had noted some time previously, near my house. The day was dull and the wasps sluggish, but quite a number of males and perfect females were crawling about the entrance to the nest. Among the wasps were some specimens of a conspicuous yellow and black Hymenopteron unlike anything that I had seen before. I secured nine specimens, all males, and on my return home easily made out by the help of Cresson's Synopsis that the insects belonged to the genus Trigonalys. The next step was to turn to Harrington's paper in the Can. Ent., XXVIII., page 108, and compare my specimens with the description of the unique Trigonalys canadensis. unfortunately, all my specimens were males, while Harrington's type was a female. Consequently the description did not quite fit, but on the following day I took three females and satisfied myself that the species I had found was the genuine T. canadensis.