_Paratypes._--(Total of five alcoholic specimens, all from
Chihuahua) Male (probably subadult), KU 44266, same data as
holotype; male, UMMZ 117770, Mojarachic, 23 July 1957, Irving W.
Knobloch; females, UMMZ 111501-2, Maguarachic, August 1954, and UMMZ
117771, Maguarachic, August 1957, Irving W. Knobloch.

_Diagnosis._--Size small; 15 rows of smooth scales; a high number of
ventral (173 to 183) and subcaudal (55 to 64) scales; alternating
dark and pale rings on body and tail; dark rings, and often pale
rings, complete.

_Description of Holotype._--Snout-vent length 327 mm.; length
of tail 93 mm.; anal scale entire; ventral scales 181 + anal;
subcaudal scales 63 + tip; dorsal scales in 15 rows on all parts of
body; six supralabials (fifth and sixth fused on left side), third
and fourth entering orbit; fifth supralabial largest and in broad
contact with parietal, posterior temporal, and postocular; six
infralabials on each side, first pair in contact behind mental;
enlarged chin shields in two pairs, anterior pair longer than
posterior pair; anterior chin shields in contact for half their
length with fourth infralabials; rostral nearly as high as broad;
internasal and prefrontal scales paired and distinct; anterior and
posterior segments of nasals distinct and nearly equal in size;
loreal twice as long as high, in contact with eye; preocular lacking
(represented by minute scale on left side); vertical diameter of eye
equal to distance from lower rim of orbit to free edge of upper lip;
temporal formula 0 + 1, the single temporal scale separating sixth
supralabial and parietal; one postocular and one supraocular on each
side; all scales perfectly smooth; no scale-pits evident; dentary
bone bearing eight teeth; maxillary bone bearing seven teeth;
posterior tooth longest, thinnest, and separated from other teeth by
slight diastema (maxillary teeth in UMMZ 111502, 6/7, dentary teeth
8/8, no diastema in maxillary series).

[Illustration: FIG. 1. _Geophis aquilonaris_ new species, KU 44265,
Holotype; lateral, dorsal, and ventral views of head and neck
(approximately x 6).]

[Illustration: FIG. 2. _Geophis aquilonaris_ new species, KU 44265,
Holotype; scalation and coloration at mid-body showing 19th and 20th
white rings (approximately x 7).]

Head slate-black above, having dim pale