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Author: Jordan and Gilbert, 1883

Field Marks:
An unspotted Mustelus with a short head, broad internarial space, relatively small eyes, narrow head, long mouth, upper labial furrows shorter than lowers, strongly falcate fins and 74 to 82 precaudal vertebral centra.

Diagnostic Features:
Body fairly slender. Head short, prepectoral length 19 to 21% of total length; snout moderately long and bluntly angular in lateral view, preoral snout 5.6 to 6.7% of total length, preorbital snout 6.3 to 8.1% of total length; internarial space broad, 2.3 to 3.3% of total length; eyes fairly large, eye length 2.9 to 3.7 times in preorbital snout and 2.2 to 3% of total length; interorbital space fairly broad, 4.3 to 4.9% of total length; mouth very long, greater than eye length and 3.4 to 3.9% of total length; upper labial furrows shorter than lowers, upper furrows 0.8 to 1.2% of total length; teeth molariform and asymmetric, with cusp reduced to a low point, cusplets absent except in very young sharks; condition of buccopharyngeal denticles unknown. Interdorsal space 18 to 22% of total length; trailing edges of dorsal fins denticulate, withoutbare ceratotrichia; first dorsal falcate with posterior margin vertical from apex, midbase closer to pectoral bases than to pelvics; pectoral fins fairly small, length of anterior margins 13 to 16% of total length, width of posterior margin 10 to 13% of total length; pelvic fins moderate-sized, anterior margin length 7.4 to 9.1% of total length; anal height 3.1 to 3.9% of total length; anal-caudal space greater than second dorsal height, 5.9 to 7.4% of total length; ventral caudal lobe strongly falcate in adults. Crowns of lateral trunk denticles lanceolate, with longitudinal ridges extending about 2/3 of crown length. Skeleton not hypercalcified in adults; palatoquadrates not subdivided; monospondylous precaudal centra 28 to 34, diplospondylous precaudal centra 43 to 51, precaudal centra 74 to 82. Colour uniform grey or grey-brown, above, light below, without white or dark spots or dark bars. Development uncertain. Size large, adults 70 to 110+cm.

Geographical Distribution:
Eastern North Pacific: Southern California to Panama.

Habitat and Biology:
An abundant but little-known warm-temperate to tropical bottom-dwelling shark of the eastern Pacific continental shelves, close inshore to well offshore. Mode of reproduction uncertain; presumably viviparous.

Size:
Maximum possibly 170 cm, males mature between 70 and 83 cm, and reaching 110+cm; adult female 97 cm; size at birth between 32 and 35 cm.

Interest to Fisheries:
An abundant inshore species in warm-temperate to tropical waters in the eastern Pacific, commonly taken by longline in the Gulf of California, and utilized for human consumption.

Remarks:
Kato, Springer and Wagner (1967) called attention to the existence of "at least two unidentified smooth-hounds with fins similar to those of the sicklefin smooth-hound" in the eastern Pacific. Heemstra (1973) studied the matter further and indicated that these are undescribed tropical species ranging from the Gulf of California south to Ecuador and the Galapagos Islands, and plans to describe them in a revision of his 1973 Ph.D. thesis (P.C. Heemstra, pers. comm.).

Type material:
Syntype: U.S. National Museum ofNatural History, USNM 29211, 620 mm. Type Locality: Mazatlan, Mexico.

Sicklefin smooth-hound (Mustelus lunulatus)