414 



Anax Junius Drury. 



A single specimen Aug. 12. 

 Sympetrum vicinum Hagen. 



Two specimens talien 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 larvae either had never been in this pond befoi-e 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 numloers. Their numbers have not appreciably 

 decreased since. The reappearance of the laiwte 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, larvse 3 mm. long were present that had been hatched from 

 the eggs of that year. It is not likely that larvae 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 tlxeir migration was 

 partially passive. 

 Chirouomus sp. 



Larvae occurred rarely. 



MOLLUSCA. 



Gastropoda — 

 Succinea retusa Lea. 



The most common mollusc 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. 



