body heavy, spindle-shaped with conical snout and narrow tail stalk supported by stout lateral keels

long gill slits, extending about 2/3 the depth of the throat

mouth armed with teeth that are relatively few but large, triangular and serrated

second dorsal and anal fins small with pivoting bases

caudal fin lunate, with lower lobe nearly as large as the upper

eyes small but conspicuous, black with inconspicuous pupil

origin of first dorsal fin over rear base of pectoral fins

sharp demarcation between dark upper surfaces and white lower surfaces; trailing edge of pectoral fin white, underside of pectoral tips black; a black spot occurs at the pectoral axil ('armpit') in some individuals

Pups are 39-59 in (100-150 cm) long at birth

Most individuals encountered are 12-16 ft (3.7-4.9 m) long. 

Maximum known length is at least 20 ft (6.1 m) and maximum known weight is more than 2,730 lb (1,240 kg), but individuals up to 23 feet (7.1 m) in length and 5,070 lb (2,300 kg) are probable. 

On a per-length basis, individuals from California waters seem more massive than those from other regions - a 17.6 ft (5.4 m) female captured off Pt. Vincente in September 1986 weighed 4,140 lbs (1,878 kg).

Reproductive Mode: ovoviviparous, with oophagy

Age at Maturity: males 9-10 yrs, females 14-16 yrs

Gestation Period: 14 months

Number of Pups: 2-10, possibly to 17

Cosmopolitan in cold temperate to tropical seas

Perhaps the most widely distributed of living sharks, rivalled only by the Bluntnose Sixgill (Hexanchus griseus).