136 MOLLUSCA. 



more numerous than the Pleurocera, and Aynnicola lustrica had almost 

 entirely supplanted A. limosa. Thruout these depths, the living and 

 dead shells were present in such large numbers as to almost entirely 

 cover the bottom. In about two feet of water, the Sphaeridae reached 

 the climax of their abundance ; in deeper water they diminished in num- 

 bers even faster than the Pleurocera, until in nearly four feet of water, 

 some distance beyond the limits of the vegetation, both the Sphaeridae 

 and the Pleurocera were rare, but were present in almost equal numbers, 

 while Amnicola lustrica had about disappeared. Here, however, the 

 Pleurocera apparently dropped out, leaving only the Sphaeridae in deep- 

 er water. Planorhis parvus was quite abundant from the shallow water 

 out into the deep places, while Anodonta grandis gigantea, a form of 

 Lymnaea ohrussa, and Valvata tricarinata simplex were present in con- 

 siderable numbers in water about a foot and a half deep. 



15. Dune Point. This locality resembles the preceding, but there 

 is a layer of peaty marl, not quite an inch thick, covering the sandy 

 bottom; and in places w^here there are clumps of Chara this layer is 

 much thicker, reaching a depth of over a foot. Along the shore there 

 is a zone of Scirpus americanus only about two yards wide ; the bottom 

 in this zone is mucky, and is carpeted with decaying leaves from the 

 trees along the shore. East of this habitat the layer of mucky deposit 

 becomes much deeper, until it reaches a depth of two or three feet. 

 (PI. X a.) 



Off this point, Sphaerium sulcatum, Amnicola limosa, a ventricose 

 form of Amnicola lustrica, and Pisidium medianum w'ere found in great 

 abundance; Lymnaea ohrussa and forms connecting it with the variety 

 decampi, Anodonta grandis gigantea, A. marginata, Planorhis parvus, 

 Valvata tricarinata unicarinata, V. t. simplex, and variations connecting 

 the last two forms, were also obtained but in lesser numbers. In ad- 

 dition, a few specimens of Planorhis hirsutus, Pisidium splendidulum, 

 P. vesiculare, P. strengi, P. variahile, and Musculium truncatum, single 

 individuals of Lymnaea haldemani, Pisidium compressum and the variety 

 rostratum, and Lampsilis luteola, and a few, indeterminate, juvenile 

 specimens of Lymnaea and Pisidium were collected. Amnicola limosa 

 was only abundant in the mucky strip along the shore, and A. lustrica 

 and Sphaerium sulcatum, only in the deeper water out beyond this 

 strip; the remainder of the shells occurred in both localities, or their 

 distribution was not satisfactorily determined on account of the small 

 numbers of specimens that were obtained. 



16. Fourth Point. Off Fourth Point, as in the two preceding habi- 

 tats, there is little or no peaty marl covering the firmer, and in this case 

 gravelly Ijottom. There is a narrow border of Scirpus americanus along 



