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Author: Springer, 1940

Field Marks:
A white-spotted Mustelus with a very narrow internarial space and dorsal fins with naked ceratotrichia on margins.

Diagnostic Features:
Body fairly slender. Head short, prepectoral length 17 to 21% of total length; snout moderately long and bluntly angular in lateral view, preoral snout 5.7 to 7.4% of total length, preorbital snout 5.8 to 7.8% of total length; internarial space very narrow, 1.8 to 2.4% of total length; eyes fairly large, eye length 2 to 3.1 times in preorbital snout and 2.1 to 3.5% of total length; interorbital space fairly narrow, 4.3 to 5.3% of total length; mouth short, subequal to eye length and 2.3 to 3.2% of total length; upper labial furrows considerably longer than lowers and 1.8 to 2.6% of total length; teeth molariform and asymmetric, with cusps low and rounded; buccopharyngeal denticles not known. Interdorsal space 17 to 23% of total length; trailing edges of dorsal fins naked, with a band of bare ceratotrichia; first dorsal broadly triangular, with posteroventrally sloping posterior margin, its midbase closer to pelvic bases than to pectorals; pectoral fins fairly small, length of anterior margins 12 to 16% of total length, width of posterior margin 8.6 to 13% of total length; pelvic fins small, anterior margin length 6.7 to 8.7% of total length; anal height 2.5 to 3.5% of total length; anal caudal space slightly greater or subequal to second dorsal height, and 5.8 to 7.8% of total length; ventral caudal lobc not expanded and falcate in adults. Crowns of lateral trunk denticles lanceolate, with longitudinal ridges extending at least half their length. Cranium, hyomandibulae, scapulocoracoids not hypercalcified in adults; palatoquadrates not subdivided; monospondylous precaudal centra 36 to 39, diplospondylous precaudal centra 45 to 54, precaudal centra 82 to 88. Colour grey above. light below, often with numerous white spots but no dark spots or dark bars.

Development ovoviviparous. Size moderate, aduits 48 to 74 cm.

Geographical Distribution:
Western South Atlantic: Southern Brazil to northern Argentina.

Habitat and Biology:
A common bottom-dwelling shark of the continental shelf of Atlantic South America, at depths of 60 to 195 m. Ovoviviparous, without a placenta, 2 to 7 pups per litter. Eats crabs and probably other crustacea, and presumably small fishes.

Size:
Maximum at least 74 cm; males maturing at about 48 cm and females at about 55 to 60 cm; size at birth 26 cm.

Interest to Fisheries:
An important fishery for this species exists off Argentina, 9000 metric tons catch being reported for 1975 and 5981 metric tons for 1978 (FAO Yearbook of Fishery Statistics, 1978). The species is also regularly caught off Uruguay, and utilized there for meat (marketed fresh and dried salted for human consumption) and oil.

Remarks:
A distinctive species, not close to any of the other white-spotted ovoviviparous smooth-hounds.

Type material:
Holotype: U.S. National Museum of Natural History, USNM 1077409 742 mm adult male. Type Locality: Off coast of Uruguay.

Narrownose smooth-hound (Mustelus schmitti)