that I have examined, there is but one enlarged spur, although
several pointed osteodermal scales may be present on the back of
the thigh.

_Gopherus berlandieri_, the closest relative of _G. flavomarginatus_
in a geographic sense, has a highly arched shell and pronglike gular
projections, between which there is nearly always a deep notch.
_Gopherus agassizii_, morphologically the closest Mexican relative
of _flavomarginatus_, differs from it in having a narrower head and
in lacking the contrasting pale and dark coloration of the plastron
and lateral marginal area. _Gopherus polyphemus_ seems to be the
closest relative of _flavomarginatus_ and differs from it in having
an unflared shell (anterior and posterior widths of carapace
subequal or carapace narrower behind) and in the characteristics of
color mentioned above. Certain proportional differences between the
living species of _Gopherus_ are summarized in table 2.

_Distribution._--The discovery of a new _Gopherus_ from
north-central Mexico increases to four the recognized forms of the
genus and extends the known range of the genus onto the Mexican
highlands, approximately 410 miles eastward from Alamos, Sonora
(_G. agassizii_), approximately 100 miles westward from a point 2
mi. W of Monclova, Coahuila (_G. berlandieri_), and approximately
200 miles westward from Monterrey, Nuevo Leon (_G. berlandieri_).

TABLE 2. Bodily Proportions in the Known Species of Gopherus. Two
Specimens of G. polyphemus from Harmon, Mississippi (USNM 53166-7),
Are Considered Separately Because of Their Notably Narrower Heads.
The Size of Each Sample Is Given in Parentheses Above the Average;
Extremes Are in Parentheses Following the Averages.

---------------------+-----------+-------------+-------------+--------
Species |Greatest |Height | Height |Diameter
and |width of |of | of |of
General Locality |skull as a |shell as a | shell as a |hind foot
|percentage |percentage | percentage |as a
|of |of width | of length |percentage
|condy- |of | of |of width
|lobasilar |carapace | carapace |of head
|length | | |
---------------------+-----------+---------