FEB., 1912. MAMMALS OF ILLINOIS AND WISCONSIN CORY. 229 



est diameter was 6 feet. The inside chamber measured about 20 x 17 

 inches, the height above the water being about 14 inches at the highest 

 point, the ceiling being irregular. The floor of the chamber was about 

 7 inches above the water but slanted downward at one side to a large 

 hole or passageway leading out under water into the pond: The size 

 of the houses varies considerably, however, and many are larger. 



When a hole in a bank is made, it is usually a simple affair, a single 

 entrance under water and a passageway two or three feet long with an 

 enlarged chamber at the end. In some cases the holes are considerably 

 deeper, with two or more entrances and several connecting passageways, 

 but in such cases I believe they were used by several animals. In 

 winter when the ponds and streams are frozen over, these animals find 



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Muskrat burrow in a bank. 



more or less air in spaces under the ice, but there is generally a regular 

 air hole in the ice, which is kept open by frequent use. 



The food of the Muskrats consists mainly of vegetable matter, 

 aquatic plants and roots, but they are fond of fresh-water mussels and, 

 when a cultivated field or apple orchard is near by the pond in which 

 they live, they are not averse to an addition to their bill of fare in the 

 way of vegetables and fruit. They also occasionally eat fish and dead 

 birds when they can get them. In this connection, Dr. C. H. Merriam 

 quotes Mr. W. H. Dall as follows: 



" ' In 1863, 1 visited Kankakee, Illinois, on a collecting tour for river 

 mollusks, in July. You know how the Muskrats throw up mounds of 

 the shells they dig out. I examined many of these for Unios, etc. On 

 several I saw the skeletons of fish (chiefly suckers I believe) partly or 

 wholly denuded of their flesh, and showing the marks of Muskrat (or 

 at least rodent) teeth. I also saw the shell of a common mud turtle, 



