localities, and found the prairie completely covered with them for acres. The majority were along the sides of a sluggish brook that held water scarcely an inch deep, and from here they extended away up the slope, so that the most distant heaps were perhaps two hundred feet away from the stream; and, in some cases observed in other localities, no stream or brook could be found, a low, damp spot being the center from which the mounds seemed to radiate or branch. So vast were the numbers of heaps that I could walk for a long distance by merely stepping from one to another, and not unfrequently they were in such close proximity that walking was difficult: a horse in passing over the field presented a curious appearance, evidently finding it hard work; and a carriage would have been wrenched to pieces or badly strained in a short time. The makers of these mounds or heaps were discovered by digging, and proved to be a genus of the common fresh-water cray-fish; and, though I was familiar with their mound-building habits, their location so far from streams was entirely new, and shows that the little creatures are better adapted to a semi-amphibious life than many of their allies that are considered true water-livers.
In making inquiries and investigations into their habits, I found that they differed from our species of the East in certainly, at times, not requiring water. In other words, they passed a certain portion of the time out of the water, and occasionally they would retreat from it; and when floods came they would leave what would be naturally considered their native element entirely and take to dry land.
In a small river that flows through the prairie north of Freeport, Illinois, I found great numbers of cray-fish close in shore, nearly every stone concealing one or more that were well protected by their almost exact resemblance to the bottom in color. Four or five feet above the level of the water were numerous heaps formed in the black clay mud, and almost every one of these contained a cray-fish that was living in water that must have come from above, as the holes had no connection with the river below. Generally I found the little animal out of water, just within the hole, and upon being alarmed it would drop down. Investigation with a stick would show that there were several inches of muddy water in the bottom. The inmates, having no loop-hole for escape, were quite savage, biting at the intruding stick with their powerful claws, and allowing themselves to be almost lifted from the mound.
It would seem strange to find these animals living in this condition if there were not some rational explanation, and it is evident that too much water is equally as disagreeable to the cray-fish here as, if not more so than, not enough, and the mounds and heaps—above and away from the streams—are in this locality the results of the animals' attempts to obtain a location where they can remain in the water or out in safety. To crawl out upon the open bank of a brook would expose them to
