hungerford: aquatic hemiptera. 221 



well known, there exists throughout the group an extraordinary sexual 

 dimorphism, such that the uninitiated might be led to class males and 

 females of the same species in different families, so great is the dis- 

 similai'ity in structure. It is of interest to note that the larval stages 

 up to the last instar, with i-espect to those structures (palje, frontal fovea, 

 asymmetry of abdominal segments, etc.), that exhibit this dimorphism, 

 are entirely of the female type. The writer has dissected the much 

 larger Arctocoriva harrisii Uhl, during the last moults, and has found 

 the same thing to be true. A specimen in the fifth instar just ready to 

 moult may easily be 'shelled out' of its cuticle and, if a male, the 

 irregular arrangement of the abdominal segments \\'ill be found fully 

 developed, but entirely concealed by the regular and sjTumetrical ar- 

 rangement, characteristic of the females and larvae." 



Summary. Ramphocorixa acumitiata Uhl., known in literature and in 

 Van Duzee's checklist and catalogue as R. balanodis Abb., winters as 

 adult, places its eggs upon crayfish in such a manner that they receive 

 the maximum amount of fresh water. The species occurs in muddy 

 ponds in the middle west and its eggs are found in June and July. Each 

 instar requires about a week, adults being produced in some seven weeks 

 after the deposition of the eggs. 



Pahnacorixa huenoi Abbott. 



There have appeared life history notes on species of but two of the six 

 genera of the family Corixidae in this country. The first of these was 

 by Doctor Abbott, and dealt with the only species in the genus Rhampho- 

 cori:ca. The second was a report upon Arctocori.va alternata by the 

 writer. This present account considers the biology of a species of the 

 genus Palmacorixa. 



There are only two species reported for this genus, P. gillettii Abbott, 

 found in Colorado, and P. buenoi Abbott, reported for the eastern states. 

 This latter species came to the writer's attention while collecting water 

 bugs at the Field Station, Ithaca, N. Y., on January 19. 



The day was very cold and the net stiffened as soon as it came in 

 contact with the air. All still waters were frozen over solidly, but on the 

 south side of the station there was a cement walled ditch containing 

 about two feet of water supplied from a strong spring. Near the spring 

 there was but a thin coating of ice, easily broken. 



Amongst the dense tangles of Elodea many active Corixid adults of 

 several species were taken. This was to be expected, for all the water 

 bugs were supposed to pass the winter as adults. However, among this 

 afternoon's catch were many strikingly marked nymphs of some Corixid, 

 all in the same instar. This seemed so unusual that these n>Tnphs were 

 followed in nature and in the laboratory until the entire cycle was estab- 

 lished. 



So exceptional in its seasonal appearance is this form that no attempt 

 is made to follow the usual order in the discussion. 



Collecting throughout the remainder of the winter and early spring 

 established the presence of only the nymphal form of this species. These 

 nymphs were abundant in the pool above mentioned, in the slack waters 

 of Cascadilla creek, known as "Dwyer's" pond, and in the quiet strip of 

 water called "Bool's Backwater," which connects Bool's brook with Fall 



