60 



MONOCIHAPIIH OF NOUTH AMEKICAN KODENTIA. 



\U'.: iiiJixiiriiim id .'5.75. Even with lliis liberal cutting-ofT of exlromcs, we 

 liiui 1 Icsprromys Iciicopus lo niii^'n Croiii 2.75 to 3.75 in the snnie locality, and 

 cstiihlisli a variability of a full inch— that i.^ over twenty-five per cent, of 

 tilt! tncan lrii<(th. 



Ill length of tail-vertehra', one specimen stands 2.10; but this may be 

 exclii(!;:!l, and 2.40, of which tlnire are several in.stances, be accepted as a 

 normal ailiilt niiniinum. TIk; figure .'{.40 is probably the normal adult maxi- 

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

 limits a trille, since this la.st is a very variable feature. The whole tail, there- 

 fore, varies in length at least one inch, and probai)ly a little more, just ns wc 

 should have anticipated from the; natun; 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 n^iches to half-way between the eyes and the snout, the latter dis- 

 tance l)eing 0.50. Now, for its variation of relative Icu^.h, we have: — In 

 several specimens, the tail is a full inch (even af\er striking off a margin for 

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

 or longer than the liead 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 

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

 consideraljly exceed the head and 'jody 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 sligiit diirercnce comes from the fact that to keep largely within bounds, 

 and .so to be unquestionably on the safe side, we lopped off u certain 

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

 well worth fpioting in this connection ; — 



"The most variai)le character consists in the relative length and number 

 of the caudal vertebrae. Ai)out one-fiflh of the Massachusetts specimens have 

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

 sionally, a specimen is found in which the tail-vertebrae alone exceed this 

 lenutli by one-i()iii1h to one-half an inch. At least four-liflhs, however, have 

 the tail shorter than the head and body, and occasionally one occurs with tlie 

 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 



• Itiill. MiiH. Cdiiip. Z(«)l. i, !W7. 



