The Relation of Mollusks to Fish in Oneida Lake 221 
growth, a stony or sandy bottom subject to wave action for 
the aeration of the water. As Isely so aptly remarks (1911, 
p. 79) * This kind of environment gives a constant supply of 
oxygen and suflicient food; is free from shifting sand and 
silt accumulation. Those mussels that drop from the fish 
in these favorable situations develop in large numbers, while 
the less fortunate, that drop in shifting sand and silt, die 
early.” 
Two major types of glochidia occur, one with a simple 
rounded shell, the other with a toothed or hooked shell. A 
third type, with modified hooks, called the axe-head type, is’ 
known but is confined to a few species. (See Lefevre and 
Curtis, 1912, plate VIII.) The importance of these types 
is recognized when we learn that the hooked type attach 
themselves to the fins and external parts of fishes while the 
hookless type become encysted upon the gill filaments. Of 
the Oneida Lake clams the following genera represent the 
two types. 
Hooked. Hookless. 
Anodonta. Lampsilis. 
Strophitus. Elliptio. 
It has been quite conclusively demonstrated (Lefevre and 
Curtis, 1912, p. 153) that the fixation of the hookless type 
of glochidium upon the delicate gill membrane is induced 
chemically by the fluid excluded from the gill, which is 
irritated by the shells of the glochidia taken in through the 
mouth or gill cavity. 
It has also been ascertained that there is a long and short 
period of gravidity or reproduction. Of these breeding 
stages in the long period the eggs are fertilized from the 
middle of July to the middle of August, and the glochidia 
are carried in the marsupium until the following spring or 
early summer. In the short period the entire breeding season 
is confined to about four months, extending from the end of 
April to the middle of August, and the glochidia are dis- 
charged as soon as they are fully developed. The clams of 
Oneida Lake represent both long and short periods ( Winter 
