754 THE AMERICAN NATURALIST [Vol. LI 



Brine shrimp, Artemia fertUisXevriU, occurred at this point in 

 enormous numbers and adults and larvfB of alkali flies, Ephydra 

 gracilis Packard and E. hiam Say, were abundant. E. siihopaca 

 Loew was less common. The brine shrimp were gathered in 

 great masses, and took advantage of the slightest depressions in 

 the mud as shelters against the ever-fluctuating currents. 

 Thousands frequently gathered in the lee of the boat during 

 periods of observation by the writer. 



In May and June adult i^p^t^m were found on mud, laid bare 

 by water receding from the high spring levels, in which alkalis 

 were rising through surface evaporation. On these areas the 

 flies formed dense masses several feet square. The insects were 

 busily probing or kneading the mud with their proboscides so 

 that the surface was heavily pitted or stippled with small de- 

 pressions that were visible at a distance of several feet. The 

 greater part of these insects were Ephydra gracilis. 



The statement made by Dr. Vorhies (p. 498) that "enemies 

 play no part in keeping down the numbers of Artemia, or of 

 Ephydra in the larval stage ' ' is not corroborated by observa- 

 tions of the present writer. After the first of September each 

 year shovelers, Spatula clypeata (Linn^us), began to congregate 

 in the bay below the mouth of Bear River, and by October 1 

 thousands of these ducks were present. The birds lay in great 

 banks on the open water, and it was not unusual to see such 

 flocks that were at least two miles long and from one quarter to 

 one half a mile broad. The shovelers were feeding almost en- 

 tirely upon Artemia fertilis and larvae and pupje of Ephydra, 

 and were crammed with them constantly. Usually this species 

 of duck is not a good table bird but individuals shot here were 

 all exceedingly fat, and the writer found them excellent eating. 

 These ducks remained in fall until the fresh water bays were 

 covered with ice. Another species of duck, the lesser scaup, 

 Marila affinis (Eyton), came into this region from the north be- 

 tween October 2 and 12 each year, and by October 20, was abun- 

 dant. These lesser scaups also frequented the lower bay, and, 

 like the shovelers, fed to a large extent upon the brine shrimp 

 and the immature stages of the alkali flies. At dusk on October 

 14, 1914, flocks of these ducks were observed from Promontory 

 Point passing from Bear River Bay southwest past Fremont 

 Island in the open lake. As there is no fresh water feeding 

 ground in that direction it was assumed that they were going out 



