36 ILLINOIS NATURAL HISTORY SURVEY MANUAL 4 



mammals of Illinois. Keys are provided to aid in identifying the 

 animals, descriptions are given as a means of checking the re- 

 sults obtained by use of the keys, and brief statements on the 

 natural history and distribution are added to assist the user of 

 this book in learning about the mammals. 



To make identification of a specimen accurate and yet as eas\ 

 as possible, each key is divided into two parts. The first part 

 employs only external characters, including the teeth, which may 

 be examined as they are situated in the head, and should be used 

 for identifying the whole specimen or a study skin with a skull. 



The second part of each key is based entirely on skull and 

 tooth characters. This part can be used for identifying skulls 

 or incomplete specimens found in the field, in stomach contents 

 of animals, or in owl pellets. 



The scientific name of the species precedes the account of 

 each kind of Illinois mammal discussed in the Fieldbook. This 

 scientific name includes two words, first the name of the genus 

 to which the species belongs and second the name of the species; 

 these names are followed by the name of the man who first de- 

 scribed the animal. The name of the describer is in parentheses 

 if the animal is not now assigned to the genus in which it was 

 first placed. Below the scientific name is at least one common 

 name. When two or more common names are given, the name 

 on the left side of the page is the one preferred by the authors 

 of this Fieldbook. Each complete account is divided into the 

 following sections: description, life history, signs, and distribu- 

 tion. The description is a summary of the diagnostic characters 

 of the species, including such features as size, color, and dental 

 formula. The life history section includes information on the 

 life cycle, habits, and habitat. The section on signs outlines 

 characteristic identifying features such as nests, scats, food re- 

 mains, and runways. The section on distribution notes the abun- 

 dance of the species, its known range in Illinois, the subspecies 

 known to occur in the state, and a brief statement of the known 

 range of the species in North America. 



At the end of the accounts of the mammals known to occur 

 in Illinois during historic times, there is a section dealing with 

 species of prehistoric times. Following this are a glossary of 

 terms used in the keys and text and a list of books on mammals. 



How to Use the Keys. — In this Fieldbook, a key to the 

 orders of Illinois mammals is given, page 41, and, under each 



