MURIDAE— SIGMODONTES— HESPEROMYS LEDOOPUS. 



61 



between these extremes is hence about fifty per cent, of the mean — a striking 



example of the unreliability of this character as a specific distinction 



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." 



In continuation of this matter, we next bring in our entire series of 

 Hesperomys leucopus from Eastern North America, embracing specimens from 

 Labrador to the Carolinas, and westward to Kansas, inclusive (our Arctic 

 and western examples are elsewhere tabulated and discussed). We admit to 

 this series only what we claim as unquestionable leucopus proper, excluding 

 even the recognizable geographical races. And even after this exclusion, 

 there are six nominal species from the region just indicated requiring our 

 attention. 



Table XI. — Measurements of about one hundred (and list of many more) specimens of Hesperomys leucopus 



from Eastern North America. 



