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Author: Gill, 1864

Field Marks:
A small, plain Mustelus with high-cusped teeth, a long, acutely pointed snout, very small eyes, broad interorbital, lanceolate lateral trunk denticles, and unfringed dorsal fins.

Diagnostic Features:
Body fairly slender. Head moderately long, prepectoral length 19 to 23% of total length; snout long and acutely angular in lateral view, preoral snout 6 to 8.8% of total length, preorbital snout 7.1 to 9.7% of total length; internarial space moderate, 2.1 to 3% of total length; eyes small, eye length 2.6 to 3.5 times in preorbital snout (over 3 times in adults) and 1.8 to 2.9% of total length; interorbital space very broad, 5.1 to 6.2% of total length; mouth long, greater than eye length, 3 to 4% of total length; upper labial furrows slightly longer than lowers or about as long, uppers 1.3 to 2.2% of total length; teeth cuspidate and asymmetric, with cusp prominent and cusplets occasionally present at all sizes; buccopharyngeal denticles present on anterior thirds of mouth floor and palate, and on gill arches. Interdorsal space 16 to 21% of total length; trailing edges of dorsal fins denticulate, without bare ceratotrichia; first dorsal broadly triangular, with posteroventrally sloping posterior margin, its midbase closer to pelvic bases than to pectorals; pectoral fins moderately large, length of anterior margins 12 to 16% of total length, width of posterior margins 8 to 14% of total length; pelvic fins moderately large, anterior margin length 6.7 to 9.1% of total length; anal height 2.7 to 3.4% of total length; anal-caudal space greater than second dorsal space and 4.8 to 6.8% of total length; ventral caudal lobe not falcate and weakly developed 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 38 to 44, diplospondylous precaudal centra 49 to 58, precaudal centra 92 to 99. Colour uniform grey or grey-brown above, light below, no white or dark spots or dark bars.

Development viviparous. Size small, adults 43 to 64 cm.

Geographical Distribution:
Eastern Pacific: Southern Mexico to Gulf of Guayaquil, Ecuador.

Habitat and Biology:
An uncommon, little-known inshore tropical bottom-dwelling shark of the Central and South American continental shelves. Viviparous, with a yolk-sac placenta; number of young 4 per litter. Eats manis shrimps and probably other crustaceans.

Size:
Maximum 64 cm, adult males maturing at about 43 cm, adultfemales at about 43 cm and reaching 64 cm; size at birth 21 to 23 cm.

Interest to Fisheries:
Probably caught along with other species of "tollo"
(Mustelus) and utilized by fisheries where it occurs, but details are lacking.

Remarks:
This small, distinctive smooth-hound has been confused with other eastern Pacific species. It somewhat resembles the western Atlantic M. higmani, but differs in its higher-cusped teeth, less falcate fins, lanceolate denticles, and more numerous vertebral centra.

Type material:
Syntypes: U.S. National Museum of Natural History, USNM 8068, 2 specimens 430 to 450 mm; another specimen included under the same catalogue number is M. Iunulatus (Heemstra, 1973). Type Locality: "Panama".

Sharptooth smooth-hound (Mustelus dorsalis)