98 Field Museum or Natural History — Zoology, Vol. XI. 



less herbivorous and many of them are practically omnivorous. Of 

 the large number of families belonging to this great order, lo are rep- 

 resented in North America, of which 7 occur within our limits. 



KEY TO THE SUBORDERS AND FAMILIES. 



GROUP 1. Upper incisors 2 (Suborder SIMPLICIDENTATA), p. 98. 



SECTION 1. Body largely covered with sharp, stiff spines or quills partly 

 concealed by fur. Family ERETHIZONTID^. 



American Porcupines, p. 253 . 



SECTION 2. Body not largely covered with sharp quills. 



Part 1. Tail broad, flattened (paddle shaped), naked, and scaly; size large. 



Family CASTORIDiE. Beavers, p. 158. 

 Part 2. Tail not broad, flattened and paddle shaped. 



A. Hind legs and feet noticeable elongated (kangaroo-hke). 

 Tail very long; size small (about that of a Mouse). 



Family ZAPODID.^. Jumping Mice, p. 246. 



B. Hind legs and feet ordinary, not greatly elongated, 

 bi. Tail closely or scantily haired or naked. 



Claws of fore feet not greatly elongated; no external cheek pouches. 



lilamily MURIDiE. Rats, Mice, etc., p. 171. 



Claws of fore feet greatly elongated; external cheek pouches 



present. Family GEOMYID^. Pocket Gophers, p. 239. 



b2. Tail thickly haired and more or less bushy. 



Family SCIURID^. Squirrels, Woodchucks, etc., p. 98. 



GROUP 2. Upper incisors 4, the second pair much smaller and placed behind the 

 front pair. (Suborder DUPLICIDENTATA), p. 258. 

 Ears long; hind legs long. Family LEPORIDiS). Hares and Rabbits, p. 259. 



Suborder SIMPLICIDENTATA. 



Family SCIURID^. Squirrels, Woodchucks, 



etc. 



The Sciuridce are a highly specialized and widely distributed family, 

 being cosmopolitan with the exception of the Australian region. Some 

 exotic species are highly colored, showing much red, orange and yellow. 

 They vary in size from the diminutive S. soricinus of Borneo, which 

 is about the size of a Mouse, to the Malayan species, 5. bicolor, which 

 is as large as a Cat. A caecum is always present, which in most of our 

 species will average from one-seventh to one-ninth the length of the 

 large intestine. 



Those which occur within our limits differ greatly in form and 



