118 
Psyche 
[Ssptember 
the time of maximum oviposition in June (Graphs 5 and 6) . 
This fact suggests that at least some females die after ovi- 
position and that their bodies may remain in the supra- 
branchial chambers for several months. 
Nymphs of N. ingens occurred in small numbers in all 
but 4 of the 13 months (December, January, May, and 
September) with no significant seasonal variation. 
The total number of mites recovered from the 1147 A. 
cataracta was 1400 (with monthly extremes of 17-207), 
comprising 893 males (11-137) and 507 females (6-74). 
This gave an average of mites of either sex per parasitized 
clam of 1.58 (1.22-1.85). During the 13 months neither the 
average number of mites per parasitized clam nor the per- 
centage of males and females changed significantly. The 
average monthly percentage of males in the total of 1400 
mites was 63.8 per cent (52.4-67.2), while that of females 
was 36.2 per cent (32.7-47.6). The sex ratio of males to 
females was 1.76:1. 
The distribution of adult mites among the four supra- 
branchial chambers of A. cataracta did not vary signifi- 
cantly throughout the 13 months. The most frequently 
occupied position was the outer suprabranchial chambers 
(in 865 or 97.6 per cent of the 886 parasitized clams). In 
a few clams mites occurred in the inner suprabranchial 
chambers (7 or 0.8 per cent) and in both outer and inner 
chambers (14 or 1.6 per cent). 
Summary 
1. Monthly collections from December, 1949, to Decem- 
ber, 1950, inclusive, in Wash Pond, New Hampshire, showed 
Najadicola ingens to occur most commonly in Anodonta 
cataracta and occasionally in Elliptio complanatus. The 
mite did not occur in Lampsiiis radiata. The monthly in- 
cidence of adult male and female mites showed no signifi- 
cant seasonal changes. 
2. The gills of A. cataracta were gravid from September 
to May inclusive. In gills with mites or papillae the 
glochidia usually only partly filled the gills, even early in 
