84 Journal New York Entomological Society. [Vol. xx. 



are very small and inconspicuous and do no harm further than to 

 walk on people. 



On the Southern Pacific cut-off west of Ogden the fly appears in 

 a new role. The train-men pass through the train a few minutes 

 before the lake is reached, shutting the windows " on account of 

 the salt-flies," as I heard one say. It appears that the suction of the 

 moving train raises the flies much above the usual level of their flight, 

 and they come into open car windows by myriads. Even with care in 

 closing the windows some will find their way in, where they become 

 a nuisance by walking on passengers and on the tables in the dining 

 cars. I had no difliculty in finding some of the flies in the latter situa- 

 tion as far west as Reno, Nevada, and I doubt not that they may be 

 found after the cars reach Oakland. Reno is approximately 500 

 miles west of Great Salt Lake. 



Nor is the story of gracilis yet completed. In the summer evenings 

 they congregate on the rails of the cut-off to such an extent as often 

 to stop the gasoline motors used by track-men, and even sometimes 

 to stall freight trains. PI. VIII, Fig. 10, shows as good a picture 

 as I could make with a regular kodak of flies on the rails ; it was taken 

 on the morning of July 12, 191 1, at Lakeside, on the western shore 

 of the lake. 



From Saltair bathing pavilion I walked ashore, and near the rail- 

 road in a little bay I found a place where the salt water had evapo- 

 rated down until it was full of salt crystals. Even here the larvae of 

 gracilis were active and unconcerned. I found none of them, how- 

 ever, in fresh water a short distance away from the lake, nor in that 

 which was tolerably brackish, although a few adults were present 

 sometimes at a little distance from the salt waters. Professor Voor- 

 hies at the University of Utah informed me that he had left larvae 

 of gracilis in water that had evaporated down until it was covered 

 with a crust of salt, and even in this condition the insects were active ; 

 also that he had on one occasion kept some of them in a histological 

 fixing solution over night and for several hours of the following 

 day, before they succumbed to the poison.^ 



' Wilcox, in Anat. Anzeiger, XII, 278, describes the remarkable resistance 

 of a dipterous larva from stagnant salt pools at Newport, R. I. He identified it 

 with doubt as a Helophilus, but I suspect it may have been an Ephydra. 



