Ophryacus, COPE, 1887

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.