228 BULLETIN OF THE 



chusetts specimens have the tail vertebra? equal to or longer than the 

 head and body together ; occasionally a specimen is found in which 

 the tail vertebrae alone exceed this length by one fourth to one half an 

 inch. At least four fifths, however, have the tail shorter than the head 

 and body, and occasionally one occurs with the tail only equal to the 

 body alone. In these latter the proportional length of the tail vertebra? to 

 the length of the head and body is as 68 to 100 ; in the other extreme, or 

 in those with long tails, as 118 to 100. The variation between these ex- 

 tremes is hence about fifty per cent of the mean, — a striking example of 

 the unreliability of this character as a specific distinction already claimed 

 in discussing the species of Mustelidce. The number of the vertebrae varies 

 from twenty-four or twenty-five to above thirty. In regard to absolute 

 size, the length of the head and body together, in Massachusetts specimens, 

 rarely exceeds four inches ; the average is between three and a quarter and 

 three and a half; perhaps nearer the latter. The variation in this respect 

 is well illustrated in Professor Baird's table of measurements of a large 

 number of Middleboro' and other specimens of this species, given in the 

 Mammals of North America (p. 462). 



Through the seasonal and other variations in color, as well as in size and 

 proportions, it becomes extremely difficult to distinguish the different North 

 American species of the restricted genus Hespernmys, if so many species are 

 to be recognized as have been described, similar variations apparently oc- 

 curring in all the species. That several exist in the eastern part of the 

 United States seems unquestionable, but the validity of many that have 

 been described from this region is at the same time highly doubtful. The 

 H. gossypinus, as defined by Professor Baird, would at first seem readily 

 distinguishable by its comparatively large size, coupled with a southern hab- 

 itat and its short tail; in color and proportions it closely resembles H. leu- 

 copus. But since in II. cofjnatm we have a form intermediate between 

 the two and intimately allied to both, the true standing and affinities of 

 each of the three become questionable. Some specimens of Ilesperomys 

 before me from Florida* differ in no essential particular from examples 

 of II. leucopm in summer pelage from Massachusetts and Maine. Well- 

 marked examples of either of the two first mentioned of these so-called spe- 

 cies seem sufficiently distinct, but a large series of specimens is constantly 

 presenting intermediate stages, and a large amount of variation in each of 

 the would-be distinctive characters. A single Florida specimen of //. 

 Nullallii (Mus aureolus Aud. and Bach.) differs much in color from the 

 other Florida specimens of Hesperomys, and from //. leucopm. 



* In addition to the specimens collected by myself in Florida the past winter, I am 

 indebted to Mr. C. J. Maynard for the opportunity of examining others obtained there 

 by himself the same season. 



