140 MOLLUSCA. 



the shores beds of yellow and white water-lilies (Nymphaea advena and 

 Castalia odorata), and marshes of Sparganium euryearpum and Scirpus 

 validus are already making inroads on the channel. In addition, the 

 upper end of the pond is covered over with duckweeds and Riccia; this, 

 however, is probably largely washed out during the high water in the 

 spring, when the river partially overflows into its old channel. (PI. 

 XI a.) 



On the west side of this pond there is a high bank of sand which by 

 caving in has destroyed most of the plant life for some distance along 

 the shore. In these bare spots, partially hidden by large masses of 

 algae, numerous specimens of Campeloma integrum, Lampsilis luteola, 

 Anodontoides ferussacianus modestus, A. f. subcylindraceus, and Ano- 

 donta grandis were found. From boards floating among the sedges 

 along the edges of the pond, considerable numbers of Planorbis parvus, 

 P. exacuous, P. trivolvis, Lymnaea humilis, Physa heterostropha, and 

 Succinea retusa, and a single specimen of Ancylus fuscus were obtained. 

 There were also collected, but in lesser numbers, Planorhis campanu- 

 latus and a form of that species in which the aperture was deflected, 

 Lymnaea reflexa, Physa heterostropha, Goniobasis livescens, and Anini- 

 cola limosa, from Potaniogeton, etc., near the middle of the bayou; and 

 Planorbis campanulatus, P. parvus, ■ Physa heterostropha, Amnicola 

 limosa, and Ancylus parallelus, from the under-side of lily-pads near 

 the shore. 



Vegetation is fast fihing in this bayou. There is a filled-in marsh 

 along the inner shore which has in places become a rod wide, and the 

 upper end has already been converted into a flat, about fifteen rods 

 long, which is only under water during flood seasons. This rapid de- 

 position is not to be wondered at, as the bottom growth of higher 

 aquatic plants is remarkably luxuriant even for an ox-bow pond. 



23. Creek portion. Above the lower portion of the river, described 

 under habitat twenty-one, the stream becomes swifter and smaller and 

 runs thru a clay country. It has a gravelly bed, and presents the gen- 

 erak appearance of a typical small creek of the glacial region. People 

 living in Caseville say that the rapids and the most shallow spots be- 

 come dry in the late summer so that the rapid creek is converted into 

 a series of stagnant pools. In the spring, on the other hand, the stream 

 becomes a torrent so both extremes of conditions are present during 

 the year. This is extremely detrimental to moUuscan life as in the 

 spring the forms living in the algae probably tend to be washed out, 

 while in the summer the shells which prefer swifter water die. The 

 older inhabitants state that these conditions have not always prevailed, 

 but that formerly the stream used to flow thruout the year. The 

 change is probably due to the fact that the woods, which fed a more 



