Author: Cantor, 1849
Body rather slender. Head narrow, only moderately depressed, not trowel-shaped; snout narrowly parabolic in dorsoventral view, very long, with preoral length greater than internarial space and mouth width; eyes large, without posterior notches; spiracles absent; unique papillose gillrakers present on internal gill openings; nostrils small, internarial space about 2.5 to 3 times the nostril width; anterior nasal flaps very short and broadly triangular, not tubular; labial furrows very short with uppers shorter than lowers and with their ends falling far behind eyes; teeth well differentiated in upper and lower jaws; upper and anteroposteriors with broad, triangular, curved erect to oblique, serrated cusps but with no blades or cusplets (except in very young specimens); lowers with slender cusps, no blades or cusplets, and variable serrations; cusps of lower teeth not prominently protruding when mouth is closed; 24 to 31/25 to 34 rows of teeth. Interdorsal ridge absent; low dermal keels present on caudal peduncle; upper precaudal pit transverse and crescentic. First dorsal origin well behind pectoral rear tips, its midbase much closer to pelvic than to pectoral bases, and free rear tip slightly anterior to pelvic origins; second dorsal fin much smaller than first, its height 1/2 of first dorsal height or less; its origin slightly posterior to anal insertion; pectoral fins very narrow and somewhat falcate, pectoral length from origin to free rear tip 1/2 or less of pectoral anterior margin; pectoral origins varying from under interspace between third and fourth gill slits to under fourth gill slits; anal slightly larger than second dorsal, with slRort preanal ridges and a deeply notched posterior margin. Colour intense deep blueabove, white below, without a colour pattern. Large sharks, adults possibly reaching 4 m or more.
The complex nomenclatural and systematic history of this genus is discussed in detail in Bigelow and Schroeder (1948) and Compagno (1979). It is generally regarded as being monotypic, with a single, extremely wide-ranging species, the blue shark (Prionace glauca). The status of Thalassorhinus and its synonym Thalassinus is discussed in Compagno (1979).