112 
Psyche 
[September 
less meaning than for the other months because of the 
small numbers of clams collected. 
The temperature on the bottom of the pond at a depth 
of about 24 inches varied from 0.5 degrees C. in March to 
26.5 degrees C. in July (Graph 1). The pond was covered 
with ice in January, February, and March. 
Throughout the 13 months A. cataracta was very fre- 
quently either parasitized by mites or had papillae in the 
suprabranchial chambers (which is evidence of having 
been parasitized) (Table 1). Mites were found in 886 
or 77.2 per cent of the 1147 A. cataracta (a figure lower 
than the 87.3 per cent given by Humes and Jamnback, 1950, 
which was based upon a single November collection) and 
papillae only in 160 or 13.9 per cent. The total number of 
A. cataracta parasitized or with papillae was 1046 or 91.2 
per cent, leaving 101 or 8.8 per cent unparasitized and 
without papillae. 
E. complanatus was parasitized or had papillae much 
less frequently than A. cataracta (Table 1). N. ingens oc- 
curred in 19 or 1.8 per cent of the 1038 E. complanatus. 
No papillae were observed in the suprabranchial chambers 
of this species. 
No N. ingens were found in L. radiata. 
Adult male and female N. ingens occurred throughout 
the 13 months. The frequencies of clams with one male and 
one female adult mite, with males only, or with females 
only, showed no seasonal trends. Four hundred and fifty- 
five, or an average of 35 or 51.4 per cent per month (ex- 
tremes of 5-64 or 41.6-66.6 per cent) of the parasitized A. 
cataracta, had at least one male and one female mite. 
Three hundred and twenty, or an average of 24.6 or 36.1 
per cent (3-62 or 25.0-50.0 per cent), had male mites only. 
One hundred and eleven, or an average of 8.5 or 12.5 per 
cent (1-22 or 5.2-27.6 per cent), had female mites only. 
A. cataracta with glochidia in the gills was found from 
September to April inclusive (Graph 2). All glochidia 
were shed by the middle of May, when the bottom temper- 
ature had risen to 20 degrees C. The gills were not found 
gravid again until the middle of September, when the 
