162 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



tat for the last several years of numbers of the small yellow 

 catfish, (no specimens were secured but they possess strong simi- 

 larity to the stone cat Notiirus flavus Rafinesque, in habits and 

 appearance except that they seldom attain more than eight 

 inches in length) and Neuropterous larvae {CorydaUs cornuta 

 Linneus). Neciurus maculosus Rafinesque has also been taken 

 here occasional!}'. Needham and Llo3'd (Needham, J. G., and 

 Lloyd, J. T., 1916) record similar data from their observations 

 on Fall creek, Ithaca, New York. 



Hand in hand with the above mentioned changes in the bottom 

 of the stream occur changes in the nature of its banks whicli 

 may be abrupt and cut in clay (see figure 19) or rock, or gradual 

 and con.sist of sand (see figure 19), gravel or mud, crowded with 

 vegetation or swept bare, depending upon the action of the 

 stream at flood time. Each of these conditions brings about cor- 

 responding variations In the character of the animal life that is 

 in predominance. In portions of the Ohio river valley the pres- 

 ence of luuskrats {Fiber zihethicKS Linneus) and the location of 

 their burrows along the banks bears evidence to this fact. Fig- 

 ures 29 and 30 show the above-water entrance to one of these 

 burrows in a soil bank. 



In general the topography of the flood-plain is altered in two 

 ways— by the removal of material and by the deposition of 

 material. The removal of material most commonly results in 

 what are known as "wash-outs." These may be of varying 

 size and depth from mere cuplike excavations where the wat^r 

 has swept about some obstruction to great holes many feet deep 

 and in some cases of acres in extent. The smaller of these are 

 permanently dry, containing water for only a few hours or diys 

 after the recession of the flood, while many of the larger ones 

 are of sufficient depth that they mark the location of permanent 

 pools and contain associations of animals adapted to quiet aqua- 

 tic life. Such washouts are shown in figures 18, 23, 24, 25 

 and 26. The pool shown in figure 18 is at the bottom of a 

 washout of more than an acre and the water persists with a 

 depth of four to five feet throughout the year alth.ough it is 

 several hundred yards from the stream. From sucli pools the 

 winter has taken crayfish, water beetles, turtles (Chehjdra and 

 Chrysemys) and several species of fish, including Ci/prinus car- 

 pio Linneus of two and three pounds in weight, common sucker 

 Catostomus commersonii Lacepede, hogsucker Catostomns nigri- 



