20 Unk'crsity of Michigan 



racks, spruces and balsam firs had been killed, but were still 

 standing. A large portion of the pond was covered with float- 

 ing duckweeds and floating logs, overgrown with fresh-water 

 sponge, even formed small sedge-covered islands. Smartweeds 

 were the main plants growing in the pond itself. 



In addition to the living specimens obtained from driftwood, 

 etc., a large number of dead and chalky specimens were col- 

 lected from the mud which the beavers had brought up from 

 the bottom and built into their lodges. Besides the living spe- 

 cies listed in Table III, the following forms were found only 

 in this subfossil condition. 



Flanorbis campaiiulatus Quite common 



Amnicola limosa Very abundant 



Valvata tricarinata and var. confusa Abundant 



Pisidium variahilc and var. brcviiim Abundant 



Valvata sincere Very common 



Planorbis deflcctus Very common 



Lymnaa obrussa dccampi Very common 



Pisidium comprcssum Infrequent 



Valvata tricarinata imicarinata Rare 



Valvata tricarinata simplex Rare 



Pisidium affine Rare 



Pisidium mcdianum Rare 



Habitat 28. Sivampy Cut-off. Several hundred yards below 

 the beaver pond Hancock Creek had formed a swampy cut-off, 

 which was filled with water only when the creek was in flood. 

 11iis ditch was about six feet wide and two deep, and was 

 partially choked by logs from a collapsed corduroy road at 

 the place studied. The soft bottom was composed of organic 

 material and was very damp, although the ditch contained no 

 standing water. Marchantia and some sedges were growing 

 here along with a few j^lants of the blue flag {Iris versicolor), 

 but most of the shells collected were from a large, bare patch 

 about six feet from the creek proper. This is the type locality 

 for Mv.scuUuni pusillum Sterki. 



