Ophryacus, COPE, 1887

Jadin, Robert C., Smith, Eric N. & Campbell, Jonathan A., 2011, Unravelling a tangle of Mexican serpents: a systematic revision of highland pitvipers, Zoological Journal of the Linnean Society 163 (3), pp. 943-958 : 954

OPHRYACUS COPE, 1887

Type species: Trigonocephalus [ Atropos ] undulatus Jan, 1859 , by monotypy.

Etymology: The generic name is derived from the Greek ophrys, meaning brow, and the Latin acus, meaning pointed, obviously in reference to the distinctive supraocular spine-like scale.

Content: The genus Ophryacus contains only O. undulatus confined to the highlands of the Sierra Madre Oriental (Hidalgo, Veracruz, Puebla), the Mesa del Sur (Oaxaca), and the Sierra Madre del Sur (Oaxaca, Guerrero), where it occurs in pine-oak and cloud forest ( Campbell & Lamar, 2004: map 84).

Common name: Mexican horned pitviper.

Definition and diagnosis: Rostral broader than high, moderately to distinctly concave; three preoculars, upper largest and undivided, middle not fused with supralacunal, lower small, somewhat excluded from margin of orbit; three to four supraoculars along dorsal margin of eye including supraocular spine; ten to 13 supralabials; lip margin not scalloped; nine to 14 infralabials; single scale above eye forming long, relatively slender spine, slightly compressed to subcircular in cross section, not occupying most of dorsal margin of orbit, tip pointed; adjacent scales along dorsal ocular margin often also modified, projecting slightly; canthals and internasals often raised into short spines or with especially high keels; scales in the supraocular region small and keeled; ten to 20 (usually 12–18) intersupraoculars; top of head covered with small scales, most having tubercular keels; second supralabial usually separated from prelacunal by single small subfoveal; subocular and supralabial series separated by two to four rows of small, roundish scales; 21 mid-dorsal scale rows; middorsals at midbody not noticeably broad, obtusely rounded; keel generally extending to tip of scale or nearly so, apical pits not apparent; free portion of apex of dorsal scales moderate in extent, barely overlapping contiguous scale; interstitial epidermal fold at cranial end of scale well developed; 157–178 ventrals; 37–57 subcaudals, divided; tail spine straight, about as long as preceding two to three subcaudals, pointed or obtusely rounded.

Frontal bones with concave dorsal surface, strongly elevated margins, moderately longer than wide; postfrontals moderate in size, not contacting frontal, comprising about equal amount of dorsal perimeter of orbit as parietals; posterolateral edges of dorsal surface of parietals forming distinct flat shelf continuing onto parietal as a raised ridge; junction between parietal and pro-otic irregular, not particularly angular; anterior portion of ectopterygoid possessing a shallow depression on medial side accommodating attachment of ectopterygoid retractor muscle; ectopterygoid noticeably longer than expanded, flattened base of pterygoid (posterior to articulation with ectopterygoid) with flat shaft tapering posteriorly; apex of choanal process positioned at about midlength on palatine, process moderately reduced in height, apex broadly rounded; dorsal surface of parietal roughly triangular; zero to one (usually zero) palatine teeth, seven to ten pterygoid teeth, seven to nine dentary teeth; pterygoid teeth extending to level of articulation of pterygoid with ectopterygoid; maxillary fang relatively short, only slightly longer than height of maxilla; fang at rest extending to level of suture between supralabials 7 and 8; splenial and angular bones fused; haemapophyses in contact distally.

Dorsum with zig-zag pattern; ground colour olivebrown, green, or grey, sometimes orange or yellow pigment present; dorsal scales usually finely mottled or speckled with black.