160 Art. 6.— M. Yokoyaiaa: 



206. Pecten laqueatus, Sowerby. 

 Pl. XIV. Figs. 9, 10. 



Peclcn laquea.us. Sowerby, Thes. Conch., vcl. I, p. 46, pl. XV, fig. 101. Lischkf, Jap. 

 Meeresconch., I, p, 167, IT, p. 157, pl. XII, fig. 1, 2. Scheenck, Moll. d. Amur], u, d. nordjap. 

 Meeres, p. 482. Küster in Syst. Conch. Cab., vol. VII, pt. 2, p. 79, pl. XX, fig. 5, p. 137, pl. 

 XXXVIII, fig. 1. Brauns, Geol. Env. Tokio, p. 48. Tokunaga, Foss.-Env. Tokyo, p. 64. 



l'ola laqucata. Dunkee, Index Moll., p. 243. Pjlsbrt, Cat. Mar. Moll. Jap., p. 143. 



Peclen antonii. Philippi, Abbild, u. Beschr., vol. I, p. 99, Pecten, pl. I, fig. 1. 



Specimens of this species are not numerous, but easily 

 recognized by their peculiar characters. The right valve is very 

 convex with broad, flat, radiating ribs, whose number is normally 

 eight, with one or two, rarely three, narrow secondary ribs on 

 both sides of the shell. The left valve is slightly concave with 

 narrower, flatly rounded radiating ribs whose normal number is 

 seven or eight, The ears are nearly equal, with a shallow notch 

 below the anterior one. 



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

 ll iyata); Yokosuka Zone (Otsu); Upper Musashino of Oji and 

 Shinagawa. 



Living: — Northern, Central and Western Japan. 



207. Pecten naganumana, Yokoyama. 

 Pl. XIII. Figs. 4-5. 



, Shell medium-sized, not very thick but firm, roundish, 

 broader than high, strongly inequivalve, nearly equilateral, the 

 lower margin describing a semicircle with the anterior and 

 posterior coiners obtusely angulate and the antero-dorsal and 

 postero-dorsal margins sloping and samewhat concave. Right 

 valve convex and swollen, with broad and flatly rounded, subequal, 

 radiating ribs separated by intervals of a less breadth; number of 

 ribs normally twelve, but sometimes thirteen or eleven with one 

 to three small subsidiary riblets at the anterior as well as at the 

 posterior ends. Left valve quite flat, or even a little concave, 

 also ornamented with flatly' rounded radiating ribs which, how- 

 ever, are much narrower than those of the right valve, so that the 

 interspaces become consequently wider than the ribs; their 



