17(5 



MONOOKAIMIK OF NORTH AMKIMOAN ItODFNTIA. 



Table XLV. 



-Measurements of thirteen alcoholic specimens of A. riparius from the United states west of the 



Mississippi. 



* Drexler's numerous Fort Bridget- specimens wo have not thought necessary to measure in detail, as they tliflVr but 

 little, and are precisely like the dry ones already presented. McCarthy's, from the same locality, show a good deal of difference 

 in length and stoutness of tail. It will be observed tliif these specimens, which we cannot distinguish even asa local strain, 

 from ordinary riparius, were collected in company with a lot of A. auaterus var. decurtatus, which seems common in that 

 locality, and is distinguishable at a glance. Even the collectors appear to have separated the two species, to judgo from tbo 

 labels. 



t By some misprint in Baird's work, Nos. 1QGU, 1270 are given as mounted, whereas they now lie before us in alcohol. 



Having exhausted our data of size and external shape, we will next inter- 

 rogate an extensive series of skulls of eastern and western Arvicolas of the 

 riparius section, to see if there be any cranial characters upon which more 

 than a single species may be predicable. 



