MUSEUM OF COMPARATIVE ZOOLOGY. 231 



leitcopus than many of the rodents possess, particularly the smaller species, 

 but no greater than seems to be admitted for Jaculus hudsonius, its some- 

 what near ally. The habitat of Jaculus hudsonius, as now commonly de- 

 fined, extends from ocean to ocean, and from the Arctic regions southward 

 through at least the Middle States and to Missouri. This, also, is a species 

 remarkable for its variability in color, size, proportional length of the tail 

 to the body, etc. ; but in the General Report on the Mammals of North 

 America these differences were allowed only their proper value, and sev- 

 eral species of authors were reduced to synonymes in consequence. Had 

 the same course been taken in respect to the genus Hesperomys, undoubt- 

 edly a large proportion of the nominal species now admitted would have 

 been referred to their proper rank. There seems to be no reason why 

 Hesperomys leucopus may not range as widely as Jaculus hudsonius, and 

 but little to show that such is not the case. 



62. Arvicola Gapperi Vigors. Red-backed Mouse. Ap- 

 parently not very rare in some localities in the eastern part of the 

 State. Professor Baird mentions seven specimens sent him by Mr. J. 

 "W. P. Jenks from Middleboro'.* There are also several specimens in 

 the Museum of Comparative Zoology from localities near Cambridge. 

 It has not yet been met with, however, in the vicinity of Springfield. 

 It is apparently less southern in its distribution than the next following 

 species. 



63. Arvicola riparius Ord. Common Meadow Mouse. Abun- 

 dant ; periodically excessively so. At such times they often do great 

 harm by destroying fruit and other trees. Apple-trees a foot in diam- 

 eter are sometimes killed by being girdled by these destructive animals. 

 They also occasionally destroy large numbers of those of smaller size, 

 as well as of young pitch-pines (Pinus rigida Linn.) and other native 

 trees. Their excessive increase is generally coincident with a series 

 of winters during which the ground is covered with a heavy deposit 

 of snow, which protects them from cold, and beneath which they 

 burrow and commit their ravages. Their decrease generally occurs 

 during a series of "open" winters, when in searching for their food 

 they are wholly unprotected from severe cold, and the deep freezing 

 of the ground obstructs their shallow burrows, within which they 

 are doubtless often frozen. They frequent every variety of situa- 



* N. Am. Mam., p. 521. 



