MOLLUSCA. 135 



(Alniis i7ica7ut), dwarf willows {Salix sp.). and, in wetter i)laces, patches 

 of the cat -tail flag (Typha latifolia), and the sweet flag (Acorus calamus). 

 During the month of August, which was the time of the year the party 

 was at Rush Lake, there is no water in most places along the marsh, but 

 the ground is very wet and is overflowed every season. For this reason, 

 both land and water snails were found in these places; however, in most 

 places, the latter were aestivating. (PI. VII a.) 



In the drier portion of this sedge marsh, a single specimen of Vertigo 

 ovota and many specimens of Succinea retusa were obtained under 

 planks, etc., and considerable numbers of Lijmnaea palustris, and two 

 specimens of Planorhis nautUeus were found aestivating. In the wetter 

 portions, Pla7iorbis trivolvis, Lymnaea palustris and the form zebra, and 

 Succinea retusa were found in some abundance. 



13. Marly bottom. One of the places where the bottom is covered 

 with cj[uite a firm deposit of marl was studied. This deposit is probably 

 due to Chara as there is quite a thick growth of it here, and Davis has 

 shown that this plant is a great producer of marl.* There is also, be- 

 sides the Chara, a wide zone of Scirpus americanus along the w^ater's 

 edge and outside of that a scattered belt of Scirpus validus. The water 

 deepens very gradually off shore which makes the zone of the first- 

 named sedge especially wide. 



In this habitat, out beyond the middle of the sedge zone, Anodonta 

 grandis gigantea was very abundant. A few small specimens of Lamp- 

 silis luteola were also obtained. 



14. Raymond's Point. This point is one of the few places in the lake 

 where the sand on the bottom is not covered with a deposit of marly 

 muck; here there is practically no peat present but the sand is some- 

 what intermixed with marl. The water is ciuite shallow for some dis- 

 tance off shore; the sand begins to become covered over with the peaty 

 muck about forty yards out from the shore. Along the sandy beach and 

 out into about two inches of water, Dulichium arundinaceum is the pre- 

 dominant plant. Beyond this for about ten yards is a zone of Scirpus 

 americanus, and beyond that a narrow zone of Scirpus validus. Thru- 

 out the second zone, there is a sod formed of a small Utricidarw that is 

 almost buried in the sand; so much so that it is hardly noticeable from 

 a boat. 



In this habitat, in about six inches of water, Pleurocera subulare in- 

 tensum and Amnicola limosa were very abundant. As the water be- 

 comes deeper farther out, first Sphaerium flavum and then S. sulcatum 

 and a form of Amnicola lustrica appeared, while the first species soon 

 began to diminish in numbers, until in about a foot and one-half of 

 water, near the middle of the inner sedge zone, the Sphaeridae were 



*C.eol. Surv. Mich., Vol. VIII, Part III, Chap. V. 



