lo University of Michigan 



of Lower Lake, or the sand was covered with a relatively thin 

 layer of muck as along the north shore of Upper Lake. In 

 all other places around both lakes the inner zone was prac- 

 tically absent and the middle zone reached the swampy shore, 

 except along a few rods of the west shore of Upper Lake, 

 where the inner zone was quite wide, had a mucky bottom 

 and was covered with floating logs. 



Habitat j. Szvampy West Shore. Along the northern por- 

 tion of the west shore of Lower Lake and along the entire 

 west shore of Upper Lake there was a large bog w-ith a float- 

 ing marsh at its edge. Adjacent to this bog no inner zone 

 occurred, except for a short distance along its southern end 

 and near Habitat 5 ; here a large number of more or less water- 

 soaked logs were jammed together in shallow water. A few 

 scattered bunches of Riccia Hidtans, Spirodela polyrhica and 

 other small water-plants were fastened to logs and floating 

 amongst them. The molluscan fauna of this area was poor 

 and resembled that of a pond (Table I). 



Habitat 4. North Shore. Along a short portion of the north 

 shore of Upper Lake the bank is high and sandy. Off this 

 region the bottom is also sandy, but is covered with a thin 

 layer of marly muck ; the latter varies in depth from one inch 

 near shore to about six inches in a foot of water. The muck 

 is mostly made up of decaying bark and other vegetable mate- 

 rials. The line of distinction between this zone and the inner 

 plant zone was not so well defined as in the other two habitats, 

 and scattered groups of plants, mostly Chara, encroached upon 

 it. Amnicola limosa was most abundant near these patches. 



Habitat 5. Sandy West Shore. In places where the west 

 shore is high and sandy only a very slight layer of marly muck 

 covers the bottom. In these localities the inner zone could 



