HOFFMEISTER & MOHR: ILLINOIS MAMMALS 37 



order, a key to the Illinois species of that order. The key to the 

 orders is intended to help you decide which of the keys to the 

 species to use in identifying a specimen. 



The keys are made up of pairs of contrasting statements (in 

 abbreviated form) known as key couplets, each couplet pre- 

 ceded by a numeral. In using a key, start at the beginning, read 

 the two contrasting statements of the first couplet, and decide 

 which of the statements best fits the specimen you are trying to 

 identify. What you find at the end of the statement selected will 

 give you a clue as to your next step. If a number is at the end 

 of the statement, follow down the key to the couplet having 

 that number. Repeat the selection process until you have come 

 to a statement having a name at the end of it: the name of an 

 order in the key to the orders and the name of a species in the 

 key to the species. 



Some of the couplets contain references to illustrations that 

 will aid you in the identification of your specimen. 



If you do not understand terms used in the keys, turn to the 

 glossary for definitions. 



Occasionally a specimen will key out readily but be misiden- 

 tified because a statement in the key has been misinterpreted 

 or because the specimen is abnormal in one or more characters. 

 It is well, therefore, to check your identification by comparing 

 your specimen with the description of the species and the picture 

 of the mammal. It is frequently helpful to consult descriptions 

 of closely related or similar species to gain a knowledge of some 

 of the comparative characters used as a basis for diagnosis. 

 Sometimes the ranges of the species under consideration may 

 help you to decide. If, after following these steps, there is un- 

 certainty as to the identity of a specimen, it should be compared 

 with identified specimens in a reference collection, such as that 

 maintained by the Illinois Natural History Survey, the Uni- 

 versity of Illinois Natural History Museum, or the Chicago 

 Natural History Museum, or sent to a trained specialist for 

 identification. 



Professional mammalogists are usually glad to determine 

 diflicult-to-identify specimens sent to them by collectors if the 

 specimens are reasonably well preserved and well packed for 

 shipment, and if accurate locality data accompany them. 



Glass Mammalia. — Mammals belong to a large group of 

 animals called the Vertebrata, characterized by having in each 



