414 
Anax junius Drury. 
A single specimen Aug. 12. 
Sympetrum vicinum Hagen. 
Two specimens taken June 18. 
Libellula pulchella Drury. 
June 18, July 16, Aug. 12. Emerged from nymphs in aquaria during 
June and July. Nymphs of this form were the most numerous of the 
group. 
Libellula lydia Drury. 
Flying over pond Aug. 12. 
Corethra. 
Corethra larve either had never been in this pond before 1909, or had 
been exterminated by the drying up of the pond in the autumn of 1908. 
The latter proposition seems to be the correct one. 
As stated previously, no collections were taken during the summer of 
1909. In the autumn when observations were resumed, corethra larva: 
were present in enormous numbers. Their numbers have not appreciably 
decreased since. The reappearance of the larvee may be accounted for 
either (1) by eggs having lain dormant during the dry period and winter, 
and then hatching as the temperature increased the following spring, or 
(2) adult imagoes may have migrated to the pond during the spring and 
summer of 1909. I think that the first proposition is untenable because on 
May 25, 1910, larvee 3 mm. long were present that had been hatched from 
the eggs of that year. It is not likely that larvee of that size could have 
escaped observation the previous spring. If the species was re-introduced 
into the pond by the imago, it necessitated a migration of over a mile. 
Wind doubtless influences these flying forms, so that their migration was 
partially passive. 
Chironomus sp. 
Larve occurred rarely. 
MOLLUSCA. 
Gastropoda— 
Succinea retusa Lea. 
The most common molluse of the pond. Eggs laid in April, May and 
June. Hatched in about 15 days. This period probably varies with tem- 
perature. At 12°-14° C., eggs laid April 8 hatched April 23. 
