Part 2

Artificial Key to the Species of the Genus Zapus 384

Systematic Accounts of Species and Subspecies 385

Zapus trinotatus 385

Zapus princeps 394

Zapus hudsonius 420

Tables of Measurements 455

Literature Cited 466

INTRODUCTION

The jumping mice (Genus Zapus) are widely distributed over northern North America, occurring as far north as the Arctic Circle and as far south as Georgia, Missouri, Oklahoma, New Mexico, Arizona, and central California. In some years these small rodents are locally common in moist places that are either grassy or weedy; the jumping mice are notable for the much enlarged hind legs and the exceptionally long tail.

Members of the Genus as a whole have received no serious comprehensive taxonomic attention in the 54 years since Preble's (1899) revisionary work. In this time 15 new names have been proposed, mostly for subspecies, and only a few attempts have been made at grouping related named kinds.

In the present account it is aimed to record what is known concerning geographic distribution, taxonomically significant characters, and interrelationships of the known kinds as well as to provide means for recognizing the species and subspecies in the genus. In addition, attention is given to the probable center of origin of the subfamily Zapodinae and to the relationships and taxonomic positions of the genera Zapus, Napaeozapus, and Eozapus.

MATERIALS, METHODS, AND ACKNOWLEDGMENTS

The present report is based on a study of approximately 3,600 specimens that were assembled at the Museum of Natural History of the University of Kansas or that were examined at other institutions. Most of these specimens are stuffed skins with skulls separate. Skulls without skins, skins without skulls, entire skeletons, and separately preserved bacula are included as a part of the total. Almost every specimen is accompanied by an attached label, which bears place and date of capture, name of collector, external measurements, and sex.

Specimens used in the study of geographic variation were arranged by season of capture and according to geographic location; then they were segregated as to sex, and, under each sex, by age. Next, individual variation was measured in comparable samples of like age, sex, season, and geographic origin. Finally, comparable materials were arranged geographically in order to determine variations of systematic significance.

The only external measurements used were total length, length of tail, and length of hind foot; these measurements were recorded by the collectors on the labels attached to the skins. Height of the ear was not used since it was not recorded by many of the collectors.

In order to determine which cranial structures showed the least individual variation but at the same time showed substantial geographic variation, a statistical analysis was made of the 30 measurements, of cranial structures, heretofore used in taxonomic work on Zapus. The following measurements of the skull showed the least individual variation but showed some geographic variation and therefore, were used in this study. See figs. 1-3 which show points between which measurements were taken:

Occipitonasal length.--From anteriormost projection of nasal bones to posteriormost projection of supraoccipital bone. a to a´

Condylobasal length.--Least distance from a line connecting posteriormost parts of exoccipital condyles to a line connecting anteriormost projections of premaxillary bones. b to n

Palatal length.--From anterior border of upper incisors to anteriormost point of postpalatal notch. b to b´

Incisive foramina, length.--From anteriormost point to posteriormost point of incisive foramina. c to c´

Incisive foramina, breadth.--Greatest distance across incisive foramina perpendicular to long axis of skull. f to f´

Zygomatic length.--From anteriormost point of zygomatic process of maxillary to posteriormost point of zygomatic process of squamosal. d to d´

Zygomatic breadth.--Greatest distance across zygomatic arches of cranium at right angles to long axis of skull. j to j´

Breadth of inferior ramus of zygomatic process of maxillary.--Greatest distance across inferior ramus of zygomatic process of maxillary taken parallel to long axis of skull. d to e

Palatal breadth at M3.--Greatest distance from inside margin of alveolus of right M3 to its opposite. g to g´

Palatal breadth at P4.--Same as above except taken at P4. g to g´

Mastoid breadth.--Greatest distance across mastoid bones perpendicular to long axis of skull. h to h´

Breadth of braincase.--Greatest distance across braincase taken perpendicular to long axis of skull. i to i´