[September 
82 Psyche 
ity that mites in certain localities may have been overlooked because 
of the small sampling. 
Commonly 1 male and 1 female mite were found in each par- 
asitized A. cataract a and E. complanatus. Single males and single 
females were frequently found in these clams, but very rarely two 
of the same sex. This was not the case in L. radiata, where at least 
two of each sex were present, one clam having 4 males and 8 females. 
The average number of mites per clam was 1.7 in E. complanatus 
and 1.8 in A. cataracta. 
The smaller and presumably younger individuals of E. complan- 
atus and A. cataracta were more frequently parasitized, as shown in 
Figs. 2 and 3. The arithmetical mean length for unparasitized E. 
complanatus was 6.9 cm. and for parasitized individuals 5.6 cm. 
The arithmetical mean length for unparasitized A. cataracta was 
7.1 cm. and for parasitized individuals 6.2 cm. The largest par- 
asitized clam was an A. cataracta 11.2 cm. in length. The smallest 
was an E. complanatus 2.7 cm. in length. 
The position of N. ingens in the host clams varied with the host 
species. Almost invariably when there was a male and a female 
present they occurred in the same suprabranchial chamber, usually 
in the anterior half of the gill area. Immature mites or single males 
were generally located distally between the gill lamellae. The mites 
occurred in any of the four suprabranchial chambers, but there was 
noticed a distinct difference in location in E. complanatus and A. 
cataracta. In A. cataracta the mites occurred with about equal fre- 
quency in the right and left outer suprabranchial chambers. In 
only 4 individuals were mites found in the inner gill chambers. In 
E. complanatus the mites occurred nearly equally in the right and 
left inner suprabranchial chambers. In only 6 individuals were 
mites found in the outer gill chambers. Since mites were found in 
the outer chambers of E. complanatus and in the inner chambers of 
A. cataracta , they are probably not mechanically prevented from 
entering those chambers. The position of the mites seems to have 
little relation to the use of the gill as a marsupium, since in A. 
cataracta mites were found in both gravid and non-gravid gills. 
According to Baker (1928) the specialized long-term breeding clams 
like Anodonta have the gills modified to provide better water circula- 
tion than in the short-term breeders like Elliptio. This may have 
some bearing on the difference in location of the mites in the two 
clam genera. It is of interest to note that both these genera use the 
