plete rings
with a small number of variations in each specimen. In the two
largest paratypes nearly all the white rings are incomplete
ventrally, appearing to have been encroached upon by the darker
ground color. In the larger speicmens there is a tendency also for
the white rings to be one scale wide (rather than alternately one
and two scales wide) and to lack a zigzag appearance; this appears
to be due to the darkening of entire scales and to the darkening of
the edges of other scales.

_Relationships._--_Geophis aquilonaris_ is distinct from all other
Mexican representatives of the genus in having, on the body and tail,
numerous, alternating pale and dark bands. Both sets of bands are in the
form of complete rings or the dark bands are joined ventrally rendering
the belly dark.

Of the seven other Mexican _Geophis_ having 15 rows of scales, four
species (_cancellatus_, _dugesii_, _chalybeus_, and _semidoliatus_)
have alternating pale and dark transverse markings and therefore
superficially resemble _aquilonaris_. Of the latter two species, the
poorly known _G. chalybeus_ (Veracruz) has a much lower (137 to 142)
number of ventrals than _aquilonaris_, and _G. semidoliatus_
(southeastern Mexico--Veracruz, Hidalgo, and Oaxaca) has a narrower
head, fewer supralabials (four to five with only the third entering the
orbit), and fewer ventrals (136 to 169) than _aquilonaris_. _Geophis
aquilonaris_ seems to be most closely allied to _G. cancellatus_
(Chicharras, Chiapas) and _G. dugesii_ (known from two localities in
northern Michoacan); all three species resemble one another in the
number and arrangement of the scales of the head, in general coloration,
and in having relatively high numbers of ventral scales (171 in
_cancellatus_, 150 to 164 in _dugesii_). _G. cancellatus_ differs from
the other two species in lacking internasal scales. _Geophis
aquilonaris_ differs from both species in having a higher number of
ventral and subcaudal scales, a longer tail (tail contained in
snout-vent length three to four times in _aquilonaris_, four and one
half to six times in _dugesii_, 11 to 12 times in _cancellatus_), and in
having more bands on the body (28 to 32 in _cancel latus_, two to seven
in _dugesii_). The belly in _dugesii_ and _cancellatus_ is pale but in
_aquilonaris_ it is ringed or of a solid dark color.

As more specimens of _Geophis_ become available from intermediate
localities in Mexi