The series with the largest number of individuals from one restricted
locality was selected for initial study. These individuals were
segregated by sex, and specimens of each sex were arranged from oldest
to youngest. Each series was divided into age-groups, and within a given
age-group of one sex from one locality of what was considered as one
species, estimation was made of the amount of individual variation.
Thus, it was possible when comparing different kinds of pocket gophers
to use only one age class of one season of one sex.
Age was estimated to some extent by size of animal and nature of its
pelage. The immature pelage is grayer and the hair is more crinkled than
in adults. A more certain guide to age, however, is furnished by the
skull. With increasing age some sutures disappear, the rostrum increases
in length and the ridges marking the limits of the temporal muscles come
to fuse and eventually, in males, form a high sagittal crest.
Cranial measurements were taken as follows:
Basilar length.--From the anteriormost inferior border of the
foramen magnum to a line connecting the posteriormost margins
of the alveoli of the first upper incisors.
Length of the nasals.--The greatest length of the nasals.
Zygomatic breadth.--The greatest distance across the zygomatic
arches.
Mastoid breadth.--The greatest distance across the mastoids.
Breadth of rostrum.--Width, perpendicular to long axis of the
skull.
Interorbital constriction.--The least distance between the
orbits.
Maxillary tooth row.--The greatest length of the upper
molariform tooth row at the alveolar border.
Extension of premaxillae posterior to nasals.--From the
posteriormost border of the nasals to the posterior end of the
extension of a premaxilla.
Depth of skull.--From the median suture of the frontals, on the
dorsal surface of the skull to the median suture of the
palatines at the level of the first molar (not premolar).
Length of rostrum.--From the anterior border of the nasal to
the maxilla at the lateral end of the hamulus of the lacrimal.
In the list of specimens examined, localities are arranged by
counties from west to east, beginning at the northwestern
corner of the state; specimens in each county are arranged from
north to south. If several localities are in the same latitude,
the westernmost is listed first. Capitalized color terms are
after Ridgway, Color Standards and Color Nomenclature,
Washington, D. C., 1912.
[Illustration: FIG. 1. Map showing the geographic distribution of the
five subspecies of the Mississippi Valley pocket gopher, _Geomys
bursarius_, in Kansas, with insert showing range of the species.]
In connection with this study each of the authors acknowledges
assistance from the John Simon Guggenheim Memorial Foundation
and one of us (Villa) is grateful for assistance also to Drs.
Isaac Ochoterena and Roberto Llamas of the Biological Institute
of Mexico. For the loan of specimens we are grateful to Dr.
William B. Davis, of the Agricultural and Mechanical College of
Texas; Dr. G. C. Rinker, of Hamilton, Kansas; and Mr. A. J.
Kirn, of Somerset, Texas. Unless otherwise indicated, specimens
are in the University of Kansas Museum of Natural History.