88 Journal New York Entomological Society. t^'o'- ^^^ 



modified so that they work vertically, as in all this group; in hia)is they are 

 provided with a transverse row of teeth. 



As in the case of other cycloraphous dipterous larvae, distinct stages sepa- 

 rated by moulting are not found. I have numerous newly-hatched larvae, and 

 a few of intermediate sizes. The youngest sizes differ from the full-grown in 

 several minor features, especially in the absence of dorsal pigmentation and 

 of the black plate on the ventral side of the (apparent) second segment ; also 

 in the presence of a large number of hooks in the mouth, almost like those 

 of a pair of prolegs. These last are retractile, and not visible in some small 

 specimens : I am unable to determine at what stage they are lost. They are 

 well developed in larvae 2.5 mm. long, and in smaller ones. 



Egg (Fig. 11). — Length .8 mm.; width, greatest, one-third the length, least, 

 one-fourth the length. Slightly curved ; white in color. Without any hairs 

 or appendages, (luite unlike those figured by Jones for £. niillbrcc. Not at- 

 tached to anything, as far as my observations go. 



Habits. 



The adult flies are abundant at the edge of the water of many 

 we.stern salt and alkaline lakes and ponds, as indicated to some extent 

 under distribution. I first observed them in July 31, 1908, near (iar- 

 field, Utah, on the shore of Great Salt Lake. \N\\\\q gracilis occupied 

 all the water's edge and extended out en the surface of the lake for 

 some distance, Iiiaiis occurred in numbers a little farther up the lake 

 beach, where there were windrows of rotting material that had been 

 washed up at a higher stage of water not very long before. The two 

 species seemed not to mix much, and my impression at the time was 

 that hians bred in the rotting Nostoc, etc., of the windrow. On visit- 

 ing the lake at several points in 191 1, at a season when gracilis was 

 not so overwhelming in numbers of adtilts, I found liiaiis occasionally 

 abtindant close to the margin of the water and walking out on the 

 surface for a few feet. Neither of these two species appears to live 

 in water of slight alkalinity or saltness, except when it is very close 

 to more dense water. To illustrate, at Promontory Point I was taken 

 to inspect a spring a mile and a half up the east side of the ridge; 

 it was abottt half a mile from the lake, and several hundred feet above 

 it. The water was only brackish to the taste, but both gracilis and 

 h'ans were abundant. The small outflow was lost in the dry earth 

 in a short distance but probably sometimes did reach the shore, giv- 

 ing the flies a chance to follow it up. Again, Pyramid Lake is nearly 

 fresh water, somewhat alkaline to the taste, but probably passable to 



