Introduction

Carcharhinus velox Gilbert, 1898, is a small (up to 1.5 m total length) carcharhinid from the Eastern Pacific that differs from all other members of its genus by several characters of cranial anatomy and external head morphology. Beginning with its describer (Gilbert, in Jordan and Evermann, 1898), all workers on Eastern Pacific sharks, including Beebe and Tee-Van (1941), Rosenblatt and Baldwin (1958), and Kato et al. (1967) have placed velox in Carcharhinus or one of its synonyms. However, we feel that the peculiarities of C. velox are sufficient to warrant its separation from Carcharhinus in a new genus, Nasolamia.

Nasolamia belongs to the generic group of "advanced carcharhinids" delimited by Compagno (1970): Carcharhinus (including Hypoprion and Aprionodon), Negaprion, Prionace, Isogomphodon, Lamiopsis, Triaenodon, Scoliodon, Loxodon, Rhizoprionodon, and Galeocerdo. Compagno (1970) discussed the familial systematics of carcharhinoids and merged the families Triakidae and Carcharhinidae because the characters (dentition and nictitating lower eyelid) traditionally used to separate these two families failed to do so. However, he noted that the conglomeration of genera in the expanded Carcharhinidae was heterogeneous and might be redivided when further data on their comparative morphology were obtained. Subsequent studies of higher carcharhinoids (Compagno 1973a, 1973b, 1979) have restricted the family Carcharhinidae to the "advanced carcharhinid" genera. A comprehensive definition of the family Carcharhinidae is presented in Compagno (1979), but because that account is not generally available, major characters defining the family are given in the next section below.