2 g4 -^^t- 1« — M. Tokoyama : 



The specimens are all young, the largest being only 22 millim. 

 both in height and length. 



Fossil occurrence. — Otake (not rare), Tega, Shito. ( )ji and 

 Shinagawa. 



Living. — Northern and Central Japan. China Sea. . 



:{05. Peetett fettuicostiilafus, Yokoyama. 

 PI. XVII. Fi--. 15. 



Three left valves. 



Shell small, thin, flatly convex, nearl}' circular, almost 

 equilateral. Surface with weak, rounded, scaly, radiating rihlets 

 which are rather distant, more or less unequal and at unequal 

 distances from one another; interspaces much broader with one or 

 more interstitial riblets. The number of main ril)S is not constant, 

 but usualty about twenty or a little more. Ears somewhat 

 unequal with anterior larger than posterior. 



The largest specimen measures 8.9 millim. both in length and 

 height and 1.5 millim. in depth. 



Fossil occurrence. — Shito. 



Family Ostreidae. 



Genus OSTREA, Liune. 

 306, Ostrea f/if/ns, Thuiiberf,^ 



Ostrea giyas. Tlmuberg, Kougl. Veteusk. Akad. nya Haucll., XIV, 1793, p. 140, pi. 

 VI. figs. 1-3. Pilsbiy, Cat., p. 145. Toknnaga, Foss. Euv. Tokyo, p. 68, pi. IV, 

 fig. 5. Brauns, Geol. Euv. Tokio; pp. 48, 51, 55. Yokoyama, Foss. Miiira 

 Penin, p. 162, pi, XV, figs. 1, 2. 



Ostrea laperousii. Schrenck, Moll. Amurl. n. d. nordjap. Meeres, p. 475, pi. XIX. 



The elongated as well as the ovate form in numerous exam- 

 ples. Some are rather thin-shelled and even provided with some 

 longitudinal folds. 



Fossil occurrence. — Otake, Shisui, Kamenari, Kioroshi, 

 Tega, Shito. Oji and Shinagawa. Lower :\[usashino of Yokosuka 

 and Koshiba. 



Living. — Northern, Central and Western Japan. Coast of 

 Manchuria and Shantung in China. 



