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- 
similarity in structure.. It is of interest to note that the larval stages 
up to the last instar, with respect to those structures (pale, frontal fovea, 
asymmetry of abdominal segments, etc.), that exhibit this dimorphism, 
are entirely of the female type. The writer has dissected the much 
larger Arctocorixa 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 will be found fully 
developed, but entirely concealed by the regular and symmetrical ar- 
rangement, characteristic of the females and larve.”’ 
Summary. Ramphocorixa acuminata 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. 
Palmacorixa buenoi Abbott. 
There have appeared life history notes on species of but two of the six 
genera of the family Corixide in this country. The first of these was 
by Doctor Abbott, and dealt with the only species in the genus Rhampho- 
corixa. The second was a report upon Arctocorixa 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 nymphs 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 
