_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 × 6).] [Illustration: FIG. 2. _Geophis aquilonaris_ new species, KU 44265, Holotype; scalation and coloration at mid-body showing 19th and 20th white rings (approximately × 7).] Head slate-black above, having dim pale mark on anterior part of each prefrontal and another on interparietal seam; an indistinct pale gray crescent on posterior border of nostril; narrow cream band covering posterior edges of parietal and half of first dorsal scale row, widening laterally to include temporal and posterior two or three supralabials; throat cream (except for dark markings on mental, on first three infralabials, and on anterior chin shields), its pale area continuous with pale band on head; body and tail marked with alternating white and black rings; white rings (excluding band on head) 38 on body, 17 on tail; each white ring alternately one and two scales wide dorsally (producing wavy or zigzag effect), widened laterally, and three to four scales wide on belly; black rings three to four and one half scales wide on middorsal line, and two to three scales wide on belly; black and white rings (excepting first black ring behind head) continuous around body and tail. Colors described above nearly same as in living specimens.