MOLLUSC A. 147 



probably restored both by migration from inland as mentioned under 

 the preceding habitat, and by shells being washed ashore on driftwood 

 as suggested under the discussion of habitat twenty-five. 



These conditions were much better represented on North Island than 

 they were on Stony Island. On the former, considerable numbers of 

 Succinea return, S. avara, S. a. vermeta, Pyramidula cronkhitei anthonyi, 

 P. alternata, Polygyra albolabris, P. monodon, P. thyroides, Zonitoides 

 minuscula, Z. arborea, Vertigo ovata, Bifidaria contracta, B. tappaniana 

 and Agriolimax agrestis were obtained, while on the latter, lesser num- 

 bers of Polygyra albolabi'is, P. monodon, Pyramidula aUernata, all of 

 them large shells, were all that were collected. 



Habitats of the Creek Flats. — ^The flats of the Pigeon River form a 

 series of closely alUed habitats unlike any others in this region. The\' 

 are formed, primarily, by the meandering of the stream, which deposits 

 soil and debris on the side where there is little current, but there may 

 also be included under this head the other low ground on which the 

 stream is depositing soil during floods, as of course the soil will be prac- 

 tically the same. This is necessarily deposited below the level of 

 floods, so that these habitats are flooded nearly every spring. In the 

 district studied, these flats may be di\'ided into three groups: swampy 

 meadows, dry meadows and woode(,l flats. 



35. Swampy meadows. Under this habitat are included all of those 

 treeless flats which have pools of water on them even in the summer. 

 They are grassy, except around the pools, where the vegetation con- 

 sists mainly of the common blue flag with scattered sedges and marsh 

 ferns {Aspidium thelypteris) . Most of the shells obtained were found 

 under drift logs, etc.. but also in lesser numbers in the wet grass. 



In such localities, Cochlicopa lubrica, Carychium exile, Zonitoides 

 nitida, Z. arborea, Succinea retusa, S. avara, Vitrea hammonis and Heli- 

 codiscus parallelus were present in considerable num1:)ers. and Zoni- 

 toides minuscula, Punctum pygmaeum. Pyramidula cronkhitei anthonyi, 

 Bifidaria tappaniana. Vertigo ovata, Vallonia pulchella, and Agriolimax 

 agrestis, were also obtained, but in lesser numbers. In addition, a few 

 specimens of Vertigo, too young to l3e identified, were collected. 



36. Dry meadows. Most of the meadow flats along the Pigeon are 

 high enough above the level of the river so that they are well-drained 

 and relatively dry during most of the year. They are covered with 

 grass which is quite green, even in August, and which, in the places 

 studied, had been kept short by grazing. Under driftwood, etc.. in 

 these places, as in the preceding habitat, many species and individuals 

 of shells are to V^e found. 



Here were found considerable numV)ers of Bifidaria contracta. B. 

 tappaniana, Zonitoides arborea, Z. nitida, Vitrea hammonis. Cochlicopa 



