154 Art. 6. — M. Yokoyama: 



ta); Yokosuka Zone (Yokosuka); Koshiba Zone (Koshiba); 

 Upper Musashino of Kazusa. 



Living: — Central and Western Japan; East Indies. 



1 ( J7. Pecten vesiculosus, Dunkee. 

 Pl. XIII. Figs. 11-13. 



Pecten vesiculosus. Ddnkeb, Index Moll., p. 241, pl. XI, fig. 1. Küster in Syst. Conch. 

 Cab., vol. VII, pt. 2, p. 138, pl. XXXVIIl, fig. 4. Yoshiwara, Xihon Ban Kairui Zusetsu, Zool. 

 Mag. Tokyo, vol. XIV, p. 212, pl. IV, fig. 16. Yokoyama, Pectens from the Koshiba Xeogene, 

 Jour. (JeoT. SoC. Tokyo, vol. XVIII, no. 208, 1911, p. 1. pl. I, figs. 8 10. 



'Hie shell is rather small, firm, roundly ovate, slightly 

 Lnequivalve, the left valve being a little oblique, and moderately 

 convex, the convexity of the two valves being nearly equal. The 

 surface is furnished with about sixteen equal, rounded, smooth or 

 transversely striated, radiating ribs which are accompanied on 

 both sides and close to their base by a small riblet. The inter- 

 spaces between the ribs are about, as wide as the latter, and 

 ornamented with fine longitudinal lines crossed by fine transverse 

 ridges which also continue to the flanks of the ribs. Ears un- 

 equal, ribbed, with ribs rongb and snbscaly. Byssal notch dis- 

 tinct. 



Many specimens, the largest valve (right) in our collection 

 measuring 26,5 millim, in height, 26 millim. in length and 6 

 millim. in depth. 



Fossil occurrence: — Koshiba Zone (Koshiba). Upper Musa- 

 shino of Kazusa. 



Living: — ('entrai Japan. 



198. Pecten swiftii, Beenaedi. 

 Pl. XIV. Fig. 11. 



Pecten swiftii. Bernard] in Journ. de Conchy],, VII, 1858, p. 90,- pl. I, pl. n, fig. 1. 

 Sohrenck, Nordjap. Moll., p. 487, pl. XXI, figs. 1-3. Donkee, Index Moll. Mar. Jap., p. 242. 

 KusTiK m Syst. Conch. Cab., vol. VII, pt. II, p. 142, pl. 40, fig. 3. Yoshiwara, Xihon San 

 Kaisui Zusetsu, Zool. Mag. Tokyo, vol. XIV, p. 144, pl. II, fig. 3. 



A single right valve of a young shell, 21, o millim. in height 

 and IS.;") millim. in length. It is only little convex, ovate in 



