Author: Springer, 1940
Field Marks:
A small hammerhead with a moderately broad, anteriorly arched, mallet-shaped head with medial and lateral indentations on its anterior edge and transverse posterior margins, no prenarial grooves, snout rather long and about 2/5 of head width, small, strongly arched mouth, free rear tip of first dorsal fin over pelvic insertions, posterior margin of anal fin nearly straight.
Diagnostic Features:
Expanded prebranchial head malletshaped and moderately wide but longitudinally elongated, its width 24 to 29% of total length (mostly above 25%); distance from tip of snout to rear insertions of posterior margins of expanded blades over half of head width; anterior margin of head broadly arched with shallow lateral and medial indentations; posterior margins of head moderately wide, transverse, and broader than mouth width; prenarial grooves hardly developed anteromedial to nostrils; preoral snout about 2/5 of head width; rear ends of eyes well anterior to upper symphysis of mouth; mouth rather narrowly arched; anterior teeth with long slender cusps, not serrated, posterior teeth mostly cuspidate and not molariform. First dorsal moderately falcate, its origin just behind pectoral insertions, its free rear tip about opposite or behind pelvic origins; second dorsal fin moderately high, slightly lower than anal, with a weakly concave posterior margin; its inner margin moderately long, less than twice fin height, and ending well ahead of upper caudal origin; pelvic fins not falcate, with straight or slightly concave posterior margins; anal fin larger than second dorsal fin and rather long, base 8.2 to 9.2% of total length; its origin in front of second dorsal origin, its posterior margin shallowly concave to nearly straight. Total vertebral centra 135 to 140. A small hammerhead, maximum size less than 1 m. Colour grey above, white below, no prominent fin markings.
Geographical Distribution:
Eastern Pacific: ? Gulf of California, and southern Mexico to Peru.
Habitat and Biology:
Almost nothing is known of the biology of this small uncommon tropical hammerhead, which lives on the continental shelf, presumably inshore. Viviparous, with a yolk-sac placenta; number of young per litter 2 ?
Size:
Maximum about 92 cm; adolescent male 51 cm, adult male, 67 cm; size at birth at or above 23 cm. Probably the smallest species of hammerhead.
Interest to Fisheries:
Probably taken in local inshore fisheries where it occurs, but details are lacking.
Type material:
Holotype: SU-11882, 663 mm adult male. Type Locality: Panama, eastern Pacific.