Author: Whitley, 1940
Requiem sharks with second dorsal fin about as large as first, very short, broadly rounded or angular snouts, usually no spiracles, labial furrows confined to mouth corners, narrow-cusped, largely smoothedged upper teeth (serrations when present confined to upper tooth blades), no cusplets on any teeth, no keels on caudal peduncle, longitudinal precaudal pits, first dorsal midbase closer to pelvic bases than pectorals, anal fin with preanal ridges virtually absent and with a deeply notched posterior margin.
Body stout. Head very broad and flattened but not trowel-shaped; snout broadly rounded or almost wedge-shaped in dorsoventral view and short, with preoral length subequal to internarial space and much less than mouth width; eyes small, without posterior notches; spiracles absent; no papillose gillrakers on internal gill openings; nostrils small, internarial space about 3 to 5 times the nostril width; anterior nasal flaps short, broadly triangular, but not tubular; labial furrows very short, essentially confined to mouth corners, with uppers shorter than lowers and with their ends falling far behind eyes; teeth strongly differentiated in upper and lower jaws; upper anteroposteriors with more or less erect, slender, narrow cusps, no cusplets, and serrations either absent or confined to crown feet; lowers without cusplets but with mostly erect, fairly long slightly hooked cusps and no serrations; cusps of lower teeth not protruding when mouth is closed; 27 to 33/27 to 33 rows of teeth. Interdorsal ridge absent; no lateral keels on caudal peduncle; upper precaudal pit longitudinal and not crescentic. First dorsal origin over or behind pectoral free rear tips, its midbase considerably closer to pelvic bases than pectorals and its free rear tip slightly anterior, over, or slightly posterior to pelvic fin origins; second dorsal fin nearly or quite as large as first, its height 4/5 or more of first dorsal height, its origin about opposite or slightly anterior to anal origin; pectoral fins broad and triangular or falcate, their lengths from origin to free rear tip over 2/3 of pectoral anterior margins; pectoral origins under interspace between third and fourth gill slits; anal fin somewhat smaller than second dorsal, with preanal ridges hardly developed and a deeply notched posterior margin. Colour grey, yellow or brownish above, without a colour pattern. Large sharks, adults reaching over 3 m.
The arrangement of this genus follows Bass, D'Aubrey and Kistnasamy (1975a) and Compagno (1979) in recognizing only two living species. Some 11 nominal species fall in this genus, but most of them can be synonymized with Carcharias acutidens Rüppell, 1837. An exception is the Atlantic Hypoprion brevirostris Poey, 1868, from which the eastern Pacific Carcharias fronto Jordan and Gilbert, 1882 may not be separable and is tentatively included as a synonym (however, S.P. Applegate, pers. comm. notes that the two are apparently separable by dentitional differences). The classification and species of Negaprion are discussed in detail in Compagno (1979).
The genus Mystidens was based by Whitley (1944) on strips of teeth from a shark from western Australia. The writer has examined the holotype of Mystidens innominatus Whitley, 1944 in the Australian Museum (Sydney), AMS IB 278, and was able to confirm his earlier hypothesis (Compagno, 1979) that these are very similar to teeth from large N. acutidens and that M. innominatus is a probable synonym of N. acutidens.
The genus Hemigaleops was based by Schultz (in Schultz et al 1953) on a new species of shark (H. forsteri) with spiracles thought to be close to Hemigaleus, but this proved to be a Negaprion, probably N. acutidens (Garrick and Schultz, 1963; Compagno, 1979).