78 



MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



4709, are not marked for locality, but probably came from Ohio, Wisconsin, 

 or Michigan, and are really his types. They are exactly the size of ordinary 

 leucopus; the tail a little shorter, relatively, than the average of leucopus, but 

 not shorter than is often found in leucopus; and they are colored exactly as 

 in gossypinus, the upper parts being very dark, the under impure white, and 

 the tail indistinctly bicolor. 



Here, then, is an exactly intermediate form between leucopus and gossy- 

 pinus, proving that the latter cannot properly be regarded as specifically 

 different from the former. 



It is obviously a matter of indifference where we make our break in the 

 chain between the two ; i. e., whether we assign the links "cognatus" to one or 

 the other. Practically, however, it will be found most convenient to assign 

 "cognatus LeC." to leucopus, so that we only recognize the extreme of differ- 

 entiation in gossypinus. This course is the more commendable, since "cog- 

 natus Baird", based as above explained, is assuredly leucopus. 



Table XVIII. — List of specimens of Hespeuomys leucopus var. gossypinus. 



" We hesitate in the determination of this specimen, since part of its size is due to overstuffing ; 

 the under parts are white, and the tail sharply bicolor; the locality, too, is against the supposition that 

 it is gossypinus ; and it is accompanied by other Kansas specimens that we cannot determine, and some 

 that are certainly pure leucopus. In the length of the feet, however, and in general coloration, it seems 

 to agree better with gossypinus than with true leucopus. Dr. Gesner's specimens, likewise, we refer here 

 on account of locality and their large size, though the mouth, feet, and tail underneath, are very pure 

 white, and the under parts nearly so. (These specimens are both males, and exhibit the maximum 

 development of tho testes we have ever seen in the species. The glands form an immense bulging mass 

 on the nates, about f long by J wide, of flattened, oblong shape, quite sharp-pointed behind, and mostly 

 divided by a deep median raphe\) 



