Genus Stenoplax Dall, 1879

Stenoplax: Dall 1879: 296 .

Type species: Chiton limaciformis Sowerby, 1832, by original designation.

For synonymy, see Kaas & Van Belle (1987).

Diagnosis: Of small to large size, elongate, the length 2 to 3 times the width, tail valve relatively large, depressed, mucro subcentral and inconspicuous, slit formula many /1 or more /many, girdle decorated with minute to large, more or less elongate scales, or with stout, bent, striated spines (Kaas & Van Belle 1987).

Distribution: East Pacific Ocean (from Canada to Peru), Indo-Pacific Ocean (from Japan to India), Indian Ocean (Madagascar), West Atlantic Ocean (from Florida to Brazil). Eocene – Recent.

Remarks: The genus Stenoplax is divided in two subgenera, Stenoplax s.s. (having the insertion plates of intermediate valves single-slitted), and Stenoradsia Dall, 1879 (having the insertion plates of intermediate valves multi-slitted). This character does not reflect phylogenetic affinity amongst the scattered, non-eastern Pacific species (Eernisse pers. comm.), so we do not consider an attribution at subgeneric level.