152 Art. 6.— M. Yokoyama: 



little convex, the right valves being nearly flat. The 

 left valve is 27 millim. long and possesses twenty-one radiating 

 ribs, of which about six larger ones are scaly. The interspaces 

 between the ribs are finely reticulate, a character also seen in our 

 living specimens. The right valves are strongly water-worn 

 The larger is 31 millim. long and 34 millim. high, while the 

 smaller is 24 millim. long and 25 millim. high. The ribs in the 

 former number twenty-four, while in the latter twenty. They 

 are unequal and at unequal distances from one another, and also 

 devoid of scales by rubbing. The posterior ear is small, triangular 

 and radially sculptured either by riblets or striae. 



Fossil occurrence. — Naganuma Zone (Naganuma), 



Living. — Central Japan; Philippines. 



194. Pecten laetus, Gould. 

 Pl. XIV. Figs. 1, 2. 



Pecten laetus. Gould, Otia Conch., p. 177. Ltschke, Jap. Meeresconch., T, p. 169, pl. XII, 

 figs. 6, 7, II, p. 157. Dünker, Index Moll., p. 241. Schrekck, Nordjap. Moll., p. 603. 

 Brauns, Geol. Env. Tokio, p. 57. Tokunaga, Foss. Envir. Tokyo, p. 65, pl. V, fig. 2, Yoshi- 

 waea, Xihon San Kairni Zusetsu, Zool. Mag. Tokyo, vol. XIV, p. 143, pl. II, fig. 1. Küster in 

 Syst. Conch. Cab., VII, pt. LI, p. 134, pl. XXXVII, figs. 4, 5. 



Several specimens of Gould species were obtained, though 

 none with both valves complete. This species resembles the 

 preceding in many respects, but is generally distinguished by 

 somewhat more convex valves and a greater number of ribs. 

 Pecten islandicus Müller, living in Northern Japan is also not 

 unlike Pecten laetus, but it has more ribs than the latter which are 

 also less scaly. 



The un equality of ribs in Pecten laetus, is especially conspicu- 

 ous on the left valve, the larger ones among them showing rough 

 and high erect scales which may be many or few and are generally 

 at unequal distances from one another. The largest of our 

 specimens is a left valve measuring 56 millim. in length, 54 

 millim. in height and 10 millim. in depth. 



Fossil occurrence: — Miyata Zone (Kami-Miyata and Shimo- 



