330 REPORT OF NATIONAL MUSEUM, 1884. 



Upon the discovery of a new form having a terete tail, simple feet, 

 and four cusps in the posterior lower molar, the re-entrant angles being 

 alternate, the question at once arises as to the validity of these char- 

 acters as generic distinctions. In introducing Neofiber into the sys- 

 tem several plans are open for adoption. The new form might be made 

 a subgenus under Arvicola by degrading the characters drawn from 

 the last lower molar to subgeneric rank. On the other hand, it could 

 be introduced as a subgenus, or even species, under Fiber by degrad- 

 ing the characters derived from the tail and feet in the same manner 

 to subgeneric or specific rank. Again, the genus Arvicola might be 

 enlarged to include Arvicola, Neofiber, and Fiber as subgenera. Finally, 

 the round-tailed muskrat might be made the type of a new genus in- 

 termediate between Arvicola and Fiber. 



The last-mentioned course is, to my mind, the most satisfactory, and I 

 have therefore adopted it. With the present absolute incommensura- 

 bility of genera, I see no especial advantages, except in certain extra* 

 ordinary cases, in introducing a grade between genus and species. On 

 the other hand, no one probably would seriously consider the proposi- 

 tion of placing Neofiber as a species under Fiber. One can conceive, 

 however, of the existence of species of the latter genus which should 

 differ from F. zibethicus in proportions, quality and color of fur, web- 

 bing of the toes, and other similar details of structure. 



It is somewhat remarkable that a rodent so large as Neofiber should 

 have remained unknown to American naturalists until the present. It 

 is true that exploration has not been so active in Florida as in some 

 other parts of the country, yet the State has been traversed many times 

 by observant naturalists and collectors. One feels convinced that the 

 species must be very rare or is confined strictly to a limited area. The 

 former opinion would appear to be the correct one, since the locality 

 from which the type specimen came is a favorite resort for sportsmen, 

 some one of whom must have recorded the species were it very abun- 

 dant. 



What the habits of the Florida muskrat are can be learned only 

 from future observations. The structure of the animal would lead one 

 to believe that it is not so thoroughly aquatic as F. zibethicus. 



