94 Merrimn — Rediscovery of the Mexican Kangaroo Rat 



Rcmarl-H on tJie Accompanying Table. 



The table on the })receding page is believed to possess certain 

 advantages over the ordinary method of tabulating measure- 

 ments of mammals. It presents to the eye in the brief space 

 of four lines a sunniiary of the average measurements, ratios, 

 maxima and minima, and percentages of variation, by localities, 

 of Gl specimens, instead of covering a numl)er of pages witli the 

 detailed measurements of each individual. 



The usual object of measuring zoological s])ecimens is to as- 

 certain one or more of the following facts : (1) the normal* size 

 of the animal ; (2) the proportions (or ratios) of some of its 

 parts, and (3) the limits or extremes of variation in a large 

 series of individuals (which may be expressed both in actual 

 maximum and minimum measurements and in percentages of 

 the normal). The accompanying tal)le not only summarizes 

 this information for each locality in a single line, but also, by 

 bringing into sharp contrast corresponding data from different 

 localities, shows the amount of geographic variation in the 

 species. Tables of the ordinary sort may contain the material 

 from which these important facts can ])e ascertained, but the 

 labor of digging them out from the l)ewildering mass of figures 

 in which they are buried is so great that it is rarely undertaken. 



Note on Macrocolus Jialticus Wagner. 



A word is necessary, jjcrhaps. concerning the Macrocolus haltlcm 

 of Wagner,t wdiich has been a stuml)ling block to naturalists 

 for many years, though its true position was correctly indicated 

 by Baircl thirty-five years ago. Baircl's remarks were as follows : 

 ''Although Wagner expressly states that there were no external 

 cheek pouches in his specimen, and that in consequence it 

 could not Ijelong to Gra3''s genus, Dijyodomys, yet the coincidence 

 in every other respect — skull, teeth, skeleton, and external 

 form — is so very intimate as to render it almost certain that the 



*The normal of any measurement is the average or mean of that mea- 

 surement in a large series of adult individuals from the same locality. 

 In i)reparing such tables care should be taken to exclude all immature 

 and impetfect specimens. 



t i^facrocolns lialticuK A.Wagner, Wieginann's Archiv. fiir Naturgesch- 

 ichte, 1846, 172-177. 



