Nuculana yokoyamai (Kuroda, 1920) Shell small, 8.1 mm in length, 4.2 mm in height, rather thick, inequilateral, umbo situated anterior from the middle; anterior margin acutely rounded and truncated, posterior end slightly gapped; two ridges running from the umbo to the postero-dorsal and posteroventral corners; surface covered with yellowish-green periostracum, and sculptured with concentric ribs; escutcheon lanceolate, smooth, without concentric ribs; hinge teeth about 15 on the anterior series and 20 on the posterior. Distribution: Huanghai Sea (Yellow Sea); Honshu, Kyushu and Shikoku in Japan. Ecology: Muddy bottom of 30-450 m depth.