182 



Order RODENTIA 



Length measurements of one specimen from Illinois: head 

 and body 6^4 inches (171 mm.); tail 101/ inches (266 mm.): 

 over-all \7]4 inches (437 mm.) ; hind foot U/$ inches (37 mm.). 



The skull has the temporal ridges on the lateral margins of 

 the braincase bowed slightly outward, and the length of a parie- 

 tal measured along a temporal ridge is noticeably less than the 

 distance between these ridges; otherwise the skull is like that 

 of the Norway rat. Dental formula: I 1/1, C 0/0, Pm 0/0, 

 M 3/3. 



Life History. — In many places in the United States the ro<;f 

 rat has been driven out of favored habitats by its larger cousin. 



in 



Fig. 99.— Roof rat. 



the Norway rat. As a result it often makes its home in the 

 upper parts of buildings and in trees, for it is a better climber 

 than the Norway rat. It is slightly less prolific. 



Distribution. — In Illinois, the roof rat is known from one 

 specimen taken in Urbana, but it may occur from time to time 

 in other cities over the state through accidental introductions 

 from the South. The one known Illinois specimen, a black- 

 haired individual, belongs to the subspecies or variety Rat t us 

 rattus rait us (Linnaeus). The roof rat, introduced from the 

 Old World, commonly occurs along the Atlantic and Gulf 

 Coast states from New York to Texas and southwest through- 

 out central Mexico. It occurs also along the Pacific Coast 

 from southern British Columbia southward into Mexico and 

 occasionally in interior parts of the United States. A colony 



