114 
Psyche 
[September 
bottom temperature had dropped to 19.5 degrees C. At 
that time many clams were gravid (19.1 per cent of all 
A. cataracta of both sexes, both parasitized and unpara- 
sitized, collected in September). 
In unparasitized A. cataracta without papillae gravid 
gills tended to be filled completely with glochidia in Sep- 
tember and through the winter months (Graph 3). No 
gravid clams were found in the small February sample. 
The reference lines to February are not connected to the 
rest of the graph because of the inadequate sampling. As 
spring approached, the glochidia were gradually shed, and 
the percentage of clams with partially filled gills increased, 
reaching a high point in March. By May all gravid clams 
contained only a relatively few glochidia, usually in the 
central part of the gills. During this time the percentage 
of clams with completely filled unparasitized gills became 
smaller. 
In parasitized gills or those with papillae the glochidia 
completely filled the gills in only a relatively few cases, 
and then only during September to December inclusive 
(Graph 4). No gravid clams were found in the small 
February and March collections. As in Graph 3, the refer- 
ence lines to these months are not connected to the rest of 
the graph. Most gills with mites or papillae were in- 
completely filled with glochidia even early in the gravid 
period. For example, in September 46.3 per cent of all the 
gravid gills with mites or papillae were partially filled, 
while only 3.7 per cent were completely filled. On the other 
hand, in the same month all unparasitized gravid gills were 
completely filled. 
Glochidia were found in the gills of E. complanatus from 
May to July inclusive (Graph 2). These clams were first 
found gravid in the middle of May, when the water tem- 
perature had risen to 20 degrees C., and were shed by the 
middle of August, when the temperature was 25.5 degrees 
C. No significant data on the seasonal distribution of the 
mites in this species were collected, since so few clams were 
parasitized (Table 1). 
Living egg masses of N. ingens were present in A. 
cataracta only in June, July, and August (Graph 5) , coincid- 
