Rattus

The rats, a genus of rodents, family Muridae. R. r., the black r., is the species most commonly responsible for transmitting plague to humans by means of the flea, Xenopsylla cheopis; it is smaller and darker than the Norwegian, sewer, or brown rat (R. norvegicus) and has longer ears and tail. See rat.

* * *

Rat·tus 'rat-əs n a genus of rodents of the family Muridae that comprise the common rats and are distinguished from members of the closely related genus Mus by bevel-edged upper incisors and comparatively large second and third molars

* * *

Rat·tus (ratґəs) a genus of small rodents, including several common species of rats (q.v.). R. norveґgicus is the brown rat and R. ratґtus is the black rat.