MAMMALIA 2 29 



scientific names have been frequently changed; those given here are 

 the ones used in the Biological Survey of the United States Department 

 of Agriculture. 



The common rat of most parts of the country is the brown or Nor- 

 way rat, Rattus norvegicus, also known as the wharf rat, the sewer rat, 

 the grey rat, the house rat, etc., Fig. 146. Less common are the black 

 rat, Rattus rattus rattus, and the roof rat, Rattus rattus alexandrinus. 

 The latter two are somewhat smaller than the former, have longer ears 

 and tail and are not so vigorous and aggressive, so that they usually give 

 way before the brown species; they are similar in size and form but are 

 distinguished from each other by the difference in color, the roof rat re- 

 sembling more the brown rat in color while the black rat is much darker, 

 nearly black. The roof rat is common in some parts of the south. 



PIG. 146. Brown or Norway rat, Rattus norvegicus. X/4- (From Lantz, House 



Rats and Mice.) 



Key to Specie's of House Rats and Mice. (Lantz) 



Size, small. Total length of adult less than 200 millimeters .... M us musculus. 

 Size, large. Total length of adult over 300 millimeters. 



Ears moderate, when laid forward barely or not reaching eye; tail shorter 

 than (rarely equal to) the length of head and body, darker above than 

 below; color of body normally grey-brown above, whitish below: hind foot 



38-46 millimeters (Brown Rat) Rattus norvegicus. 



Ears larger, when laid forward reaching at least to middle of eye; tail longer 

 than head and body, dusky all around; hind foot 33-37 millimeters. Color 



blue black above, slaty below (Black Rat) Rattus rattus rattus. 



Color graying brown above, white or yellowing white below (Roof Rat). 



Rattus rattus alexandrinus. 



