Animals of the Mississippi Bottoms near Qiiincy. 149 



season was exceptionally unpropitious with respect to this. 

 Those small creatures which did occur in the pools were thus 

 deprived of the protection which a rank growth of vegetation 

 affords, and could not be expected to maintain themselves 

 where every square yard of bottom must have been searched 

 each day by hungry fishes. Notwithstanding this condition of 

 things, certain species occurred in considerable numbers. Such 

 as have the curious habit of remaining motionless in the pres- 

 ence of enemies and such as burrow readily in mud, were very 

 common in some of the pools. Consequently, when it is said 

 that invertebrate animals were not common in these waters, it 

 is meant that, as compared with permanent lakes elsewhere, 

 there was not here a great diversity of forms represented each 

 by an abundance of individuals. 



MOLLUSC A. ( Shell Fish. ) 



The Mollusca were represented in the locality by both 

 Gasteropoda and Lamellibranchiata. 



The snails were nearly all of small size, none of those seen 

 having shells over 1.25 inches in length. These creatures are 

 well suited to a residence in these ponds. Some of them, at 

 least, can breathe either in water or in air, and hence can travel 

 to other pools if the water dries up. A part of them never 

 need to do this, for when the pools dry up, either in winter or 

 summer, they resort to the mud and rubbish of the exposed 

 bottom, close up their shells, and remain inactive till the water 

 comes again. They are ordinarily seen creeping about over 

 the bottom, where they feed upon microscopic plants and 

 animals or upon decaying organic matter in the form of a 

 slimy coat on sticks and mud. If pressed with hunger, they 

 have been known to resort to animal food, and in some instan- 

 ces devour their own kind. Some of them burrow into the 

 mud at the bottom and become torpid in winter, but more active 

 species may be seen moving over the bottom under the ice. 

 The eggs are laid in spring, attached in masses to sticks and 

 dead leaves. The young hatch in two or three weeks, accord- 

 ing to temperature. 



