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the whole of Europe, as far nortli as Laplaiid, tlirongli the 

 nortliern and centrai Asia, beginning with Syria and Persia, 

 through China to Japan; in northern Africa (Algiers) and on 

 the islands surrounding Africa (Madeira, the Canary Islands, 

 and, on the eastern side, IVCadagascar and Bourbon). During 

 my twenty years of residence in North-America, spent in 

 coUecting diptera and receiving collections from many other 

 entomologists, I never met with a specimen of E. teìiax, until 

 Nov. 5*^' 1875, when, to my great astonishment, I found 

 one on a window in Dr. Hagen's house in Cambridge, 

 Mass. A year later (Oct, Nov. 1876), I observed several spe- 

 cimens on the fences of Newport, R. I. In June 1877, I sailed 

 for Europe, but I heard afterwards that during the same year 

 the fly had become so common, that « hundreds were caught. » 

 A few years later, the species was reported from nearly ali 

 the States of the Union, including California and Washington 

 Territory; also from Canada (Montreal, common, as stated by 

 Mr. Caulfìeld in Caìiad. Entom. 1884 p. 138). 



A communication made by the american Dipterologist 

 Dr. Williston proves that the invasion has gone, not from 

 the Atlantic border to the West, as one might have expected, 

 but on the contrary, from AVest to East. Dr. Williston had 

 seen a specimen of E. tenax hidden among a lot of duplicates 

 in Prof. Riley's coUectiou, hearing a label S. Louis, Au- 

 gust 1870. Upon drawing Prof. Riley's attention to the ily 

 (which the latter did not previously know by name), he was 

 assured that the species had long been familiar to Mr. Riley 

 in outhouses about S. Louis. The surprising rapidity, however, 

 with which the species spread along the Atlantic coast soon 

 after its first appearance renders it probable that it cannot 

 have existed in S. Louis very long before 1870, otherwise it 

 would have reached the Atlantic sooner. We are thus driven 

 to accept the following outline of its history: We know that 

 it exists in Japan and Eastern Siberia ; from there it must 

 have migrated to the North American Pacific Coast, perhaps 



