GO MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



lit" maximum at 3.75. Even with ! his liberal cutting-off of extremes, we 

 God Hcsperomys leucopus to range from 2.75 to 3.75 in the same locality, and 

 establish a variability of a full inch — that is, over twenty-five per cent, of 

 the mean length. 



In length of tail- vertebrae, one specimen stands 2.10; but this may be 

 excluded, and 2.40, of which there arc several instances, be accepted as a 

 normal adult minimum. The figure 3.40 is probably the normal adult maxi- 

 mum. When we take in the pencil of hairs at the tip, we should widen the 

 limits a trifle, since this last is a very variable feature. The whole tail, there- 

 fore, varies in length at least one inch, and probably a little more, just as we 

 should have anticipated from the nature of the case. We have already seen 

 that the tail averages 0.25 of an inch shorter than the head and body — that 

 is, it just reaches to half-way between the eyes and the snout, the latter dis- 

 tance being 0.50. Now, for its variation of relative length, we have : — In 

 several specimens, the tail is a full inch (even after striking off a margin for 

 possible error) shorter than the head and body; in others, the tail is equal to 

 or longer than the head and body — sometimes over a fourth of an inch longer. 

 So that, as the head of this species averages a little over an inch in length, it 

 follows that the tail of leucopus may barely exceed the body alone, or it may 

 considerably exceed the head and body together. 



It gives us pleasure to find that our results agree very closely with those 

 Mr. Allen reached in his valuable paper* on the Mammals of Massachusetts. 

 The slight difference comes from the fact that to keep largely within bounds, 

 and- so to be unquestionably on the safe side, we lopped off a certain 

 margin from our extremes, while Mr. Allen presented his. His paragraph is 

 well worth quoting in this connection : — 



"The most variable character consists in the relative length and number 

 of the caudal vertebra?. About one-fifth of the Massachusetts specimens have 

 the tail-vertebrae equal to or longer than the head and body together; occa- 

 sionally, a specimen is found in which the tail-vertebra? 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 



" Bull. Mum. Comp. Zool. i, 2->7. 



