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THe BroLtocy oF EpHypRA SUBOPACA LOEW 605 
irrigating ditch; Nevada, Hazen, in overflow from irrigating ditch; 
Winnemucca Lake, in alkaline environment; Walker Lake, in alkaline 
environment; California, Mono Lake, in near-by seepage; Washington, 
Soap Lake, Grand Coulee, in alkaline environment. 
Aldrich states that the density of the water (salt or alkaline) in which 
this particular species lives is subject to great fluctuations. 
From the experiments described herein, proving that larvae of Ephydra 
subopaca can live in salt solutions of different strengths, varying from 
1 to 9 per cent, it follows that there is an ample chance for this species 
to surv.ve in pools or lakes the salinity of which falls within such limits. 
SEASONAL APPEARANCE AND METEOROLOGIC CONDITIONS 
To temperature and humidity is largely due the seasonal appearance 
of this species. Warm weather in late spring causes the adults to appear 
early, and high humidity in summer causes all stages to appear in great 
numbers throughout the season. The weather records of the two seasons 
1916 and 1917 are different in this respect. In the year 1916 the species 
appeared much earlier than in the year following, while in 1917 there was a 
greater abundance of both the adult and the immature stages than in the 
year before. These differences were due mainly to the temperature and 
the rainfall in the spring and summer of the two years. 
According to the report of the United States Weather Bureau at Ithaca, 
New York, the average temperature for May, 1916, was 57.6° F., while 
that for 1917 was 48.4°. The work of the writer began in June, 1916. 
Although the first appearance in the preceding month was unfortunately 
lacking in the field record, the field observations convinced the writer 
that they must have appeared three or four weeks before the work started. 
During June, adults were found in the salt pools and even in the one the 
water of which had almost lost its briny character; and the mass of the 
flies that every day assembled over the water surface did not seem to 
indicate that they were the ones that appeared first in the season. The 
writer- was informed by Dr. O. A. Johannsen that he had caught many 
adults in May. The first appearance of the adults is usually in the latter 
part of this month. In 1917, on the other hand, the appearance was 
evidently delayed on account of low temperature. Beginning on May 1, 
the writer frequently visited the pools, looking for adults, but none were 
found until June 21, when they appeared in large numbers, In June, 
