entral views of four subspecies of _Pseudemys scripta_:
_Upper left_--_P. s. ornata_ (KU 40131 [Female]), Rio
Playa Vicente, San Andres Tuxtla, Veracruz, x 1/3; _Upper
right_--_P. s. gaigeae_ (IU 43583 [Female]), 1 mi. E La Cruz,
Chihuahua, x 3/8; _Lower left_--_P. s. elegans_ (CNHM 55627
[Male]), Muzquiz, Coahuila, x 2/3; _Lower right_--_P. s.
taylori_ new subspecies (KU 46970 juvenile), paratype, 6 mi.
W Cuatro Cienegas, Coahuila, x 11/16.]

_Natural history._--Specimens of _P. s. taylori_ were caught in hoop
nets in clear deep pools and in the Rio Chiquito. No specimens were
collected or observed in marshy situations where the water was shallow
or stagnant. Individuals were seen only near dusk and in early morning
when a number floated just below the surface with only their heads
showing. They were never seen on land during our short stay in the
basin. The few stomachs that were opened contained vegetable material.
In terms of number of specimens trapped, _P. s. taylori_ was the most
abundant turtle in pools at and near the type locality (Webb and
Legler, 1960).

_Relationships and phylogeny._--The basin of Cuatro Cienegas now
drains, via the Rio Salado, into the lower Rio Grande. Brief
descriptions of habitats and topography in the basin are given by
Gilmore (1947:148-150, fig. 2) and Webb and Legler (1960). In the more
northern parts of the Salado drainage (for example, in the Rio Sabinas
near Muzquiz) slider turtles are typical _P. s. elegans_. Assuming
that conditions which permit genetic exchange between populations of
turtles in the Salado drainage system differ in no major respect from
conditions in other parts of the range of _Pseudemys scripta_, it is
logical to suppose that the differentiation of _P. s. taylori_ at
Cuatro Cienegas was preceded by the isolation of a population in that
basin.

The Rio Chiquito drains through a narrow gap in the northeastern end
of the basin of Cuatro Cienegas. Interruption of this stream would
effectively isolate aquatic habitats in the basin.

It is here proposed that _P. s. taylori_ is a relict of an earlier,
lower Rio Grande stock, part of which became isolated in the basin of
Cuatro Cienegas in postpluvial times. The morphological similarity of
_P. s. taylori_ and _P. s. elegans_ indicates that both were derived
from this parent stock; similarity of both subspecies to populations
of _P. s. ornata_ in Tamaulipas suggests that the latter sub