.Fossils from the Miura Peninsula and its Immediate North. ]53 



Miyata); Yokosuka Zone (Yokosuka); Naganuma Zone (Naganu- 

 ma); Upper Musashino of Musashi and Kazusa. 



Living: — Northern, Central and Western Japan. 



195. Pecten crassicostatus, Sowerby. 

 Pl. XII. Fig. 7. 



Pecten crassicoslalus. Sowerby, Tins. Conch., I, p. 75, pl. XV, fig. Ill, XVII. fig. 152. 

 Reeve, Conch. Icon., vol. VIII, Pecten, No. 61, pl. 48, fig. 64. Küster in Syst. Conch. Cab., 

 vol. VII, pt. II, p. 104, pl. 29, figs. 2-5. Denker, Ind. Moll., p. 239, pl. XIII, fig. 28. Yosm- 

 WAEi, Nihon San Kairui Zusetsu, Zool. Mag. Tokyo, vol. XIV, p. 142, pl. I, fig. 3. 



A single fragment of a right valve belonging to the portion 

 containing the anterior ear. It is readily distinguishable by 

 numerous equal radiating ribs which are closely scaly. 



Fossil occurrence: — Naganuma Zone (Naganuma). 



Living: — Central and Western Japan ; Shanghai, Hongkong. 



196. Pecten irregularis, Sowerby. 

 Pl. XIII. Figs. 1-3. 



' Pecten irregularis. Sowerby, Thes. Conch., vol. I, p. 69, pl. XIII, figs. 51, 52. Ltschke, 

 Jap. Meereseon eh., vol. I, p. 170. Ddneer, Index Meli., p. 210, pl. XI, fin's. 2, 15. Yoshiwaka, 

 Nihon San Kairui Zusetsu, Zool. Mag. Tokyo, vol. XIV, p. 210, pl. IV, fig. 12, Yokotama, 

 Pectens from the Koshiba Xeogene, Journ. Geol. Soc. Tokyo, vol. XVIII, no. 208, p. 2, pl. I. 

 figs. 5-7. 



This small-sized Pecten is ovate in form, subequivalve, rather 

 flattened, with the left valve flatter than the right, almost equi- 

 lateral and ornamented with about twenty-five subangular, scaly, 

 subequal, radiating ribs generally separated by intervals of a 

 greater breadth. The ribs are seen occasionally dividing into two 

 or three towards the ventral margin. The ears are very unequal, 

 the anterior being the largest; they are also furnished with scaly 

 radial riblets. 



Frequent at Koshiba, though rare at other places. 



The largest specimen of a right valve measures 21 millim. in 

 height, 10 millim. in length, and 4 millim. in depth. 



Fossil occurrence: — Miyata Zone (Harashita in Shimo-Miya- 



