MtJIlID^E. XIV. 31 



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



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



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



more or less concealed. . . . ARVICOLA, 6. 



tt Upper incisors grooved ; root of lower incisor ending 



abruptly opposite the last molar ; ears large. 



SYNAPTOMYS, 7. 



|H Tail scant -haired, vertically flattened; hind feet partly 

 webbed ; size large FIBER, 8. 



/. MUS, Linnaeus. OLD WOULD 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. H. rattus, 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. floridana, 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. HESPEffOMrS,Wsiterhouse. 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- 



