38 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



The animal varies from 1 to 6 inches in length of head and body; but 

 neither of these extremes is ordinarily reached. The average length settles 

 at very nearly 5 inches. The variation is 50 per cent, of the minimum, and 



.">3 per cent, of the maximum. 



The length of tail ranges from 2.25 to 3.5)0 inches. These appear to be 

 exceptional figures, however; and to be within safe limits, we will take 2.50 

 and 3.75 as ordinary extremes; the variation 1.25, exactly the same percent- 

 age as that of the body. The average tail stands hard upon 3 inches. 



The ear (measured from the notch in front) runs from 0.55 to 0.75, set- 

 tling at about 0.66, or two-thirds of an inch, in height. This dimension is sub- 

 stantially the same as the distance from nose to eye. The limits of variation 

 accord in their percentage with those already found for trunk and tail. The 

 fore paws (measured from the wrist) are a little below this dimension (about 

 0.60); their variability is about the same. ' 



The hind feet run from 1.00 to 1.30 inches as extremes; more fre- 

 quently from 1.10 to 1.25, settling near 1.15 as an average. This dimension 

 averages a little less than the distance from nose to ear. 



The head is about 1.50 inches long, but runs from 1.25 to 1.66. 



The ratio of tail to head and body is this: No. 979, 3.20 to 6.00, or tail 

 little over half the length of the head and body; No. 1237, 3.10 to 4.10, tail 

 only an inch shorter than head and body, about three-fourths the head and body. 

 The average tail (3.00 +) is to the average body (5.00 — ) about as 0.66 is to 

 1.00 ; that is, it is about two-thirds as long. 



The coloration of this series is remarkably constant ; in fact, we see 

 nothing that calls for special comment. Some of the specimens are a little 

 darker or a little paler, from presence of more or fewer black hairs above ; and 

 some are quite pure white underneath; others grayer; others again of a pale 

 muddy-brownish; but these variations are not at all striking. 



We next insert a table of specimens of Sigmodon from Carolina to 

 Southern Mexico. They embrace the type of S. " berlandieri'' and all Baird's 

 oilier specimens of that supposed species; typical examples of "Hesperomys 

 (Deilemys) toltecus", De Saussure ; rusty individuals agreeing with " Arvicola 

 ferruginous", Harlan; LeConte's, Audubon's, and Bachman's samples, &c. 



