MURID^. — XIV. 31 



c. Molars rooted; coronoid process of lower jaw, not reaching 

 level of condyle ; ears overtopping the fur. Evotomys, 5. 



CO. Molars rootless ; coronoid process as high as condyle ; ears 

 more or less concealed. . . . Arvicola, 6. 



W Upper incisors grooved ; root of lower incisor ending 

 abruptly opposite the last molar ; ears large. 



Synaptomys, 7. 



Xtt Tail scant -haired, vertically flattened; hind feet partly 

 webbed; size large. Fiber, 8. 



/. MUS, Linajeus. Old World Rats and Mice. 



1. M. decumanus, Pallas. Brown or Norway Rat. 

 Tail nearly an inch shorter than head and body, grayish 

 brown above; paler below; feet dusty white; fur mixed 

 with stiff hairs; cosmopolitan; introduced into America 

 about 1775, and now the commonest species. 



2. M. raff us, L. Black Rat. Tail not shorter than 

 head and body; sooty black, plumbeous below; feet 

 brown; introduced about 1544, but now being supplanted 

 by the preceding. 



3. M. alexandrinus, Geoff. Roof Rat. White - 

 Bellied Rat. Introduced in the Southern States. 



4. M. musculus, L. Common House Mouse. Cosmo- 

 politan; every where too well known. 



2. NEOTOMA, Say. & Ord. Wood Rats. 



1. N. florid ana, S. & O. Wood Rat. Tail scantily 

 hairy, scarcely as long as body without head; feet 

 entirely white; L. 14; T. 6, or less. S. U. S., N. to 

 Mass. and Ills. 



3. HESPEROMYS, Waterhouse. White - footed Mice. 



* Fur soft and glossy; lower parts white; soles naked, or slightly 

 hairy ; tail closely hairy ; ears large. ( Vesperimus.) 



1. H. leucopus, (Raf.) LeC. Deer Mouse. White- 



