148 MOLLUSCA. 



lubrica, C. I. morseana, Pyramidula cronkhitei anthonyi, P. alternata, 

 Succinea avara and Polygyra thyroides. 



37. Wooded flats. On the wooded flats, most of which are con- 

 siderably above the level of low water, the trees keep the ground quite 

 moist. A habitat is thus formed which is more moist than the dry 

 meadows, less so than the swampy ones, and more stable than either. 

 Also, in addition to the river deposit, there is considerable leaf mould; 

 the ground in the higher places is carpeted with fallen leaves, and in the 

 lower and damper places has a thick undergrowth of nettles. 



The trees of these woods are mostl}" deciduous, consisting of swamp 

 maples, black ashes, poplars, cottonwoods, and elms, the first two being 

 the most abundant. It is under fallen logs and driftwood that the 

 majority of the shells are to be found. 



Wooded flats were studied both along the Pigeon and Pinnebog 

 Rivers, but the former was a much more favorable collecting ground. 

 Along the Pigeon River, Helicodiscus parallelus, Zojiitoides arhorea, 

 Pyramidula alternata, P. cronkhitei anthonyi, Cochlicopa lubrica, C. I. 

 morseana, Agriolimax agrestis, Succinea avara, and juvenile specimens 

 of some Polygyra were collected in considerable numbers, while Zoni- 

 toides minuscula, Z. nitida, Carychium exile, C. exiguujn, Euconulus 

 chersinus polygyratus, Bifidaria tappaniana, Vitrea hammonis, V. in- 

 dentata, V . hinneyana, Polygyra albolahris, P. thyroides, P. fraterna, and 

 Succinea ovalis optima were also obtained, but in lesser numbers. Along 

 the Pinnebog River, Pyramidida alternata, Succinea avara, S. ovalis, 

 Polygyra albolahris maratima, P. fraterna, Cochlicopa lubrica, Helicod- 

 iscus parallelus, and Zonitoides arborea were found in small numbers. 



Habitats of the Clay Soil. — Behind the narrow sand region along the 

 shores of the Bay lies a flat region of clay soil, the old lake bottom. In 

 Huron County, the latter region is much larger than the former. l)ut 

 most of the work of the party was done in the sand dune region, so that 

 the only portions of the clay region that were studied are those along 

 the inner border of the sandy region. These records, then, cannot be 

 taken as characteristic of the region farther in towards the center of the 

 county. 



38. Swampy woods. The land around Rush Lake is so low and flat 

 that the majority of the woods near the lake are low and swampy. 

 These woods are made up in large part of deciduous trees, consisting 

 mostly of ashes, swamp maples and elms, with a sprinkling of sugar 

 maples, common and blue beeches and poplars; the arbor vitae, how- 

 ever, is quite abundant and the hemlocks and balsam firs are also present 

 in small numbers. (PI. XV.) 



In damp swamps, under logs and among leaves, a large number of 

 shells were collected. The species were: Euconulus fulvus, Succinea 



