Author: Gill, 1862
Diagnostic Features:
Head wing- or arrow-shaped in dorsoventral view and very broad, width across head about 40 to 50% of total length; lateral blades of head very narrow and winglike; nostrils greatly enlarged, their widths 0.8 to 0.9 times in internarial width and nearly twice mouth width; bumps present along anterior margin of head opposite nostrils. Upper precaudal pit longitudinal and not crescentic.
Remarks:
For the taxonomic history of this genus, and the rationalle for recognizing it, see Compagno (1979). Bigelow and Schroeder (1948) revived this genus, but it has met with mixed acceptance. Bigelow and Schroeder noted that it differed from Sphyrna by having its nostrils closer to the midline of the snout than the eyes rather than vice-versa, while Fraser-Brunner (1950) and Gilbert (1967, 1967a) distinguished it (as a subgenus) by the presence of "outer narial grooves" extending laterally nearly to the eyes. Compagno (1979) found that these grooves are not simple, dermal depressions like the prenarial grooves but are enormous lateral extensions of the nostrils.