490 0. E. Osten-Sacken on facts concerning the 



Corsica, and Malta; in Algiers (Loew, Sudafr. Dipt., p. 

 318) ; in Gibraltar and Madeira (Scliiner, Novara, 360) ; in 

 Cairo and round Mount Sinai (Walker, Entom., v., 274); 

 in the Canary Islands, Madagascar, and Bourbon (Macq., 

 Dipt. Exot., ii., 2, p. 30) ; in China (Schiner, Dipt. 

 Austriaca, Syrphidse, p. 114) ; in Siberia and Japan 

 (Loew., Wien. Ent. Monatschr., ii., p. 101) ; in Northern 

 Persia (Kondani, Ann. Mus. Civ. Gen., iv., p. 295); it is 

 also common in Syria (Schiner, I. c). For the occur- 

 rence at the Cape I do not find any authority, except the 

 passage in Schiner, I. c, p. 10, where it seems to be a 

 laj^sus calami, as the statement is not repeated under the 

 head of E. tenax on p. 114. 



During my twenty years' collecting in North America 

 I had never met with this species, until November 5th, 

 1875, when I found a specimen, to my great astonish- 

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

 Mass. A year later, October and November, 1876, I 

 observed several specimens on fences in Newport, Ehode 

 Island. In June, 1877, I left America, but, as I ascer- 

 tained afterwards, during that year the fly had become 

 so common that, according to Dr. Hagen's statement, 

 '-hundreds were caught " (see his Lecture before the 

 Soc. of Nat. History in Boston, Dec. 18, 1877). Between 

 1876 and 1878 many specimens were taken in the 

 vicinity of Boston, in Galena, Illinois (compare Psyche, 

 ii., p. 260), and even in Georgia (Psyche, ii., p. 188). 

 Mr. WiUiston (Can. Ent., 1881, p. 176) says that it had 

 become very common in New Haven, Conn. ; he also 

 had received specimens from beyond the Piocky Moun- 

 tains (Washington Territory). Von Boeder's collection 

 in Hoym (Anhalt) contains specimens taken about 

 1876^ — 77, in Georgia and Missouri, by the well-known 

 collector Mr. Morrison. 



This sudden appearance of E. tenax in all parts of 

 the United States, in localities thousands of miles apart, 

 and within a short period of three or four years, is a 

 verj^ extraordinary phenomenon, and requires an ex- 

 planation. Two hypotheses as to its mode of introduction 

 are possible. 



E. tenax may have been imported from Europe in 

 ships to one of the harbours on the Atlantic. But if 

 this importation happened long ago it would have been 

 noticed earlier ; if it has taken place recently it leaves 

 unexplained the almost simultaneous appearance of the 



