204 Henry LesLie Oszorn, 
the kidney is equally accessible there, yet Cotylaspis has not been 
found in Chautauqua Lake in U. edentulus. 
Moreover in other localities this discrimination is not made by 
the fluke. Thus Keniry (1899) reports observations made in Penn- 
sylvania, Illinois, and Iowa, in all of which States he found Cotylaspis 
present in several different species of Unio, though he reports Ano- 
donta as being most frequented. 
Kertey also reports a much greater number of parasites per 
host than is found in the mussels of Lake Chautauqua. The maximum 
number which I found was twenty-four, and this is far in excess of 
the average number, while the maximum found by KELLEY is thirty- 
eight, and he cites a case of Anodonta corpulenta in which Kororp 
found ninety-two Cotylaspis in a single mussel. This far exceeds 
the numbers for the Chautauqua Anodonta, where however nearly 
every one is parasitized in some degree. In only two cases were 
the flukes entirely absent. In a few instances I found only one or 
two, but the number commonly ranges from four to eight or ten, 
though it varies somewhat with the kind of bottom inhabited by 
the host. 
A count made in three different situations gave the following 
results : 
Bottom of clean, hard | 32 Anodontas, 113 flukes, av. of 3.5 per host 
sand J 
BL \ 86 Anodontas, 432 flukes, av. of 5 per host 
Bottom of very soft, Vay 
thick oozy mud J Anodontas, 96 flukes, av. of 8.7 per host. 
The last situation was especially interesting, being at the mouth 
of a drain, where the mud was very soft and oozy and very fine 
grained, and the hosts of unusually large size. The epidermis of 
the host was gone and the shell externally white and pearly. There 
is apparently in this case a close correlation between the soft oozy 
mud bottom due to organic matter brought down by the drain and 
great number of the flukes, which throws light on the food of the 
fluke. The age of the host is not closely correlated with the number 
of Cotylaspis, if at all. To test this point fifty Anodontas from a 
stony, weedy bottom were taken and the length of the shell in 
millimetres taken, and the number of Cotylaspis counted. The results 
of this enumeration were as follows: 
