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Author: Springer, 1940

Field Marks:
An unspotted Mustelus with a short, narrow head, narrow internarial space, relatively large eye, long mouth, upper labial furrows shorter than lowers, strongly falcate fins and 87 to 100 precaudal vertebral centra.

Diagnostic Features:
Body fairly slender. Head short, prepectoral length 16 to 20% of total length; snout moderately long and bluntly angular in lateral view, preoral snout 4.2 to 6.5% of total length, preorbital snout 5.9 to 7.2% of total length; internarial space narrow, 2.3 to 2.9% of total length; eyes fairly large, eye length 2.1 to 2.7 times in preorbital snout and 2.3 to 3.4% of total length; interorbital space narrow, 3.3 to 4.2% of total length; mouth length greater than eye length, and 2.5 to 3.7% of total length; upper labial furrows as long as lowers and 1 to 1.7% of total length; teeth molariform and asymmetric, with cusp reduced to a low point; buccopharyngeal denticles covering anterior half of palate and floor of mouth. Interdorsal space 18 to 26% of total length; trailing edges of dorsal fins denticulate, without bare ceratotrichia; first dorsal falcate, with posterior margin nearly vertical from apex, its midbase about equidistant between pectoral and pelvic bases; pectoral fins fairly small, length of anterior margins 12 to 15% of total length, width of posterior margin 7.9 to 12% of total length; pelvic fins fairly small, length of anterior margins 6.7 to 8.5% of total length; anal height 2,6 to 3.7% of total length; anal-caudal space greater than second dorsal height, and 7.3 to 9.7% of total length; ventral caudal lobe strongly falcate in adults. Crowns of lateral trunk denticles lanceolate, with longitudinal ridges extending their entire length. Skeleton not hypercalcified in adults; palatoquadrates not subdivided; monospondylous precaudal centra 33 to 38, diplospondylous precaudal centra 54 to 65, precaudal centra 87 to 100. Colour uniform grey above, light below, no white or dark spots or dark bars, but tips of dorsal and caudal fins dusky in newborn young. Development viviparous. Size moderately large, adults 50 to 100 cm.

Geographical Disbribution:
Western Atlantic: Florida and northern Gulf of Mexico to Venezuela; southern Brazil.

Habibat and Biology:
A common tropical-subtropical bottom-dwelling shark of the continental shelves, found on sand and mud bottoms from close inshore to at least 80 m depth. The species is thought to be migratory in the Gulf of Mexico, moving inshore into water shallower than 55 m in the winter months and apparently retreating into deeper water in other seasons (Heemstra, 1973).

Viviparous, with a yolk-sac placenta; number of young 7 to 14 per litter.

Eats mostly crabs and shrimp, but also small bony fishes.

Size:
Maximum about 100 cm, males maturing at about 58 cm, females at about 65 cm; size at birth 30 cm.

Interest to Fisheries:
Probably regularly taken within its range, but details of commercial fisheries are lacking.

Remarks:
Close to the larger, stockier Mustelus canis, and compared with it under that species. See Heemstra (1973) for a discussion of the characters separating the two species.

Type material:
Holotype: US National Museum of Natural History, USNM 107739, 723 mm adult male. Type Locality: Off Englewood, Florida

Narrowfin smooth-hound (Mustelus norrisi)