Genus Leptoplax (Carpenter MS) Dall, 1882

Type species. Chiton coarctatus Sowerby, 1841, by monotypy.

Genus distribution. Western Pacific: Japan, Vietnam, Philippines, Indonesia, Papua New Guinea, New Caledonia, South Australia and Spratly Islands now.

Remarks. For a long time the genus Leptoplax was considered synonymous with the genus Notoplax . Finally, Gowlett-Holmes [2001] restored its generic status, although she did not provide a diagnosis. Sirenko and Saito [2017] presented a diagnosis of the genus. Here I give a somewhat refined distinction of Leptoplax from Notoplax .

The main characters of Leptoplax distinguishing it from Notoplax are: 1) absence of diagonal line on tegmentum of intermediate valves, running from lateral incision to apex and decorated with large pustules; 2) presence of ribs on ventral flattened spicules and more often on dorsal spicules and needles; 3) absence of asymmetry of central and first lateral teeth of radula.

In the new species, the anterior margin of the apophyses of the tail valve is not concave, so I remove this feature noted in Sirenko and Saito [2017] from the diagnosis of Leptoplax .