THE UNIVERSITY SCIENCE BULLETIN. 351 
the drawings on plate XXXI. In the genus Buenoa we find 
the beginnings of asymmetrical development in that the right 
and left claspers are unlike. (A faint suggestion of this is 
to be found in Pelocoris and Plea.) See the drawings on 
plate XXXI, figures 1, 2 and 4. 
In the families Gelastocoridze and Corixide are found 
marked asymmetry, not only of the genital capsule and its 
parts, but of the abdominal segments themselves as well. The 
elaspers of Gelastocoris are profoundly unlike—the ventral one 
(the right one) is large, stout, and equipped with short, blunt 
pegs or processes; the other one is small and not greatly modi- 
fied in shape. See plate XXXII, figure 5, R. C. and L.C. The 
Corixid capsule and its parts are more complicated and per- 
plexing than the forms above mentioned, but have been used 
by the writer with success as an aid to the separation of 
difficult species. 
There are figured, herewith, the male genital segments of 
nine species in the genus Notonecta*—two in Buenoa, one in 
Plea, two species of Ambrysus, two Saldids, and two Gelas- 
tocorids. The reading of the discussion which follows should 
be accompanied by an examination of plates XXXI and 
XXXII. 
* The figures of Notonecta raleighi Bueno, Notonecta shooteri, Uhl., Notonecta whleri 
Kirk., Notonecta montezuma Kirk., and Notonecta lutea Mull. are not figured. Notonecta 
lutea from British Columbia, identified as such by Bueno, has a genital bulb much like 
N. irrorata. The ventral process is shorter and located farther cephalad. The fold of the 
lobe in front of the clasper extends to the ventral margin. These two species, N. trrorata 
and the so-called lutea, are quite related. .The genital bulb of Notonecta shooteri re- 
sembles figure five very closely, and the bulb of Notonecta raleighi is very like that of 
Notonecta variabilis. 
