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which the collector had kindly permitted. On my previous discussion of nigrotroch. I had evidently forgotten to make a note of the matter, so I had nothing to remind me. 23/3 I had to interrupt the writing yesterday. As you remark, there is a difference in stigma colour between mensurator & nigrotrochanterata, but it seems to be the only difference beside the abdominal colour. In the north the races differ slowly because of the want of heat, in the south the proceeding is quicker, & for that I think the race of the Alps, where the sun burns strongly in summer, to be a step farther differentiated by the dark stigma. This is, of course, a theoretical speculation, but to my experience it has a strong probability. Something similar is the case with Rhyssa persuasoria L. It is well known to occur in all the Holarctic zone, & everywhere, with one exception, it [[end page]] [[start page]] looks about the same. The exception is its southernmost occurrence, the Himalayas. A few years ago I received for inspection from the Brit. Museum a couple of specimens which puzzled them. After all comparison I could effectuate, I gave the opinion that it was a well-marked race of persuasoria, but no separate species. The hymenopterists of the Br. Mus. took the same side, & the form is now known as Rh. pers. himalayensis Wilkes. Now you have my opinion on nigro-trochanterata, but so far it is not found in Sweden, & mensurator also is rare here. You say both & their intermediates are not rare in Ireland, & that you care give me specimens of them. I thank you for this offer & shall be very glad to have them. If I can give you something in return, please let me know it. Expressing once more my sympathy