162 Art 6.-M. Yokoyama : 



Family Ostreidae. 



Genus Ostrea, Linné. 



208. Ostrea gigas, Thunbebg. 



Pl. XV. Figs. 1, 2. 



Ostrea gigas, Thünberg, Kongl. Vetenkaps Akad. nya Hanrll., Tom. XIV, 1793, p. 140, pl. 

 VI, figs. 1-3. Lischke, Jap. Meeresconcb., vol. I, p. 174, III, p. 114. Dunker, Index Moll., p. 

 249. Brauns, Gool. Env. Tokio, p. 48, 51, 55. Tokdnaga, Foss. Env. Tokyo, p. 68, pl. I V.fig. 5. 



Ostrea laperousii. Schrenck, Moll. Amurl. u. d. nordjap. Meeres, p. 475, pl. XIX. 



Ostrea talienwJianensis. Crosse, Jour. Conchy]., vol. X (3d series, vol. II), p. 149, pl. VI-, 

 fig. 6. 



A few typical ovate as well as elongated forms which un- 

 doubtedly belong to a species of Ostrea most widely distributed in 

 Japan and everywhere used as food. 



Fossil occurrence. — Yokosuka Zone (Yokosuka and Otsu); 

 Koshiba Zone (Koshiba); Upper Musashino of Musashi, Kazusa 

 and Shimosa. 



Living. — Northern, Central and Western Japan; Strait of 

 Tartary; Coast of Manchuria and Shantung in China. 



209. Ostrea denselamellosa, Lischke. 

 Pl. XVI. Fig. 6. 



Ostrea dense! amdlosa. Lischke, Jap. Meeres conch., I, p. 79, pl. XIII, pl. IV, fig. 1. Brauns, 

 Geol. Env. Tokio, p. 58. Tokunaga, Foss. Env. Tokyo, p. 65, pl. IV, fig. 6. 



A single valve, somewhat broken at the posterior margin, 

 thick, longly ovate in form, about 95 millim. in height, slightly 

 convex and ornamented with numerous radial, lamellated folds 

 which, however, have been much obliterated by friction. Com- 

 paring it with the living specimens of Ostrea denselamellosa, it agrees 

 quite well in its general characters. 



Fossil occurrence. — Yokosuka Zone (Otsu); Upper Musashino 

 of Musashi and Shimosa. • 



Living: — Central and Western Japan; also Ryukyu Islands 

 (according to Pilsbry). 



