Mexico and
Central America, 1953) (American Geog. Soc., Culican Map, NG 13,
1935). Other maps show this bolson to include internally drained
portions of the Mexican highlands from northeastern Chihuahua to
the region near Lerdo and Torreon. Thayer (1916:73) pointed out
that the Bolson de Mapimi, in its larger sense, consists of a
series of basins separated by mountains of considerable elevation.

The range of _G. flavomarginatus_ appears to be limited ultimately
by the higher elevations of the Sierra Madre Occidental and the
Sierra Madre Oriental to the west and east, respectively, and to
the south by the Mexican plateau. The northern limits of the range
are less clear; possibly the range extends as far as the portions
of the United States adjacent to northeastern Chihuahua, but this
is doubtful. The range seems not to overlap that of any other
species of _Gopherus_, although the ranges of _G. flavomarginatus_
and _G. berlandieri_ closely approximate each other in central
Coahuila.

In September, 1958, when I was collecting turtles near Cuatro
Cienegas, Coahuila, I took the opportunity to query natives, as
well as an American rancher, about the possible occurrence of
tortoises in the area. Most persons had seen no tortoises in the
area or said they had seen them only rarely. Several older men who
had herded goats in the area all their lives said that tortoises
(referred to as "Tortuga del Monte") were common on the other side
of the Sierra de La Madera and Sierra de La Fragua ranges west of
Cuatro Cienegas. These men referred probably to _G.
flavomarginatus_. Americanos lies approximately 75 miles
west-northwest of Cuatro Cienegas.

It is indeed remarkable that a population of large tortoises in
northern Mexico has so long escaped the notice of naturalists. Also
remarkable is the fact that the late Dr. Leonhard Stejneger, in
view of his intense interest in North American chelonians and his
familiarity with the genus _Gopherus_, did not remark on the
specimens from Durango when he saw them; a thorough search of
Stejneger's notes revealed no clue that he had ever studied the
specimens. Perhaps his first reaction to the specimens, like mine
when I first examined the two disassociated skulls, was to consider
"Lerdo" a misspelling of "Laredo." However, a check of old
cor