619
_E. dorsalis_ 620
_E. merriami_ 621
_E. quadrivittatus_ 621
_E. ruficaudus_ 622
_E. cinereicollis_ 624
_E. quadrimaculatus_ 624
_E. speciosus_ 625
_E. panamintinus_ 625
_E. umbrinus_ 626
_E. palmeri_ 627
_E. bulleri_ 627

Figures 1-19. Lateral views of bacula 629

Discussion 630

Literature Cited 631

INTRODUCTION

The baculum is the bony part of the penis. In the species of the
subgenus _Neotamias_ the proximal part of the baculum is termed the
shaft, and the distal upturned part is termed the tip. On the dorsal
side of the tip there is a longitudinal ridge termed the keel. The
proximal end of the shaft is termed the base (see fig. 19). Depending on
the species, the shaft varies from 2.11 to 5.28 mm. in length, and the
base may or may not be widened or deepened.

The purpose of this report is to: (1) Show the usefulness of the
structure of the baculum as a taxonomic character in chipmunks; and (2)
compare a classification based on the structure of the baculum with a
classification based on the structure and appearance of the skull and
skin.

METHODS, MATERIALS, AND ACKNOWLEDGMENTS

The bacula which were borrowed from the University of Michigan,
Museum of Zoology, were processed according to the method
described by Friley (1947:395-397), whereas all others were
processed according to the method described by White (1951:125).
Thus the bacula that were borrowed from the University of
Michigan, are maintained there in a separate collection, whereas
the bacula borrowed from other museums and those that are at the
University of Kansas, Museum of Natural History, are housed with
the skulls of the corresponding speci