Fossils from the Upper Musashino of Kazusa and Shimosa. ]^g3 



303. JPeeten laqueatits, Soweiby. 



Pecten laquentvs. Sowerby, Tbes. Concb., I, p. 46, pi. XY, fig. 101. Liscbke, Jap. 

 Meeresconcb., I, p. 1G7, II, p. 157, pL XII, figs. 1, 2. Scbrenck, Moll. Amurl. u. 

 d. nordjap. Meeres, p. 482. Brauus, Geol. Env. Tokio, p. 48. Tokunaga, Foes, 

 Env. Tokyo, p, 64. Yokoyama, Foss. Miura Peinn., p. 160, pi. XIY, figs. 9, 10. 



Very frequent. 



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

 Tega, Shito. Oji and Shinagawa. Lower Musashino of Miyata 

 and Yokosuka. 



Living. — Northern, Central and Western Japan. 



I504. Pecten eapenvatus, Anton. 

 PI. XV. Figs. 6, 7. 



Pecten excimitus. Anton, Verzeicbniss, p. 19, no. 710. Pbilippi, Abbild, u. Bescbr., 



I, Pecten, p. 201, pi. II, fig. 1. 

 Vüla excavaid. Dunker, Index Moll., p. 243. Pilsbry, Cat., p. 145. 

 Fecten sinensis. Sowerby, Tbes. Concb., I, p. 48, pi. XYI, figs. 120, 121, 134. 



This shell which resembles the preceding is smaller and 

 characterized by its valves being very unequal, more unequal than 

 in the latter, for its left valve is markedly concave instead of being 

 flat or only slightly concave, The right valve on the contrary 

 is strongly convex, more so than in Pecten laqucatus. The ears 

 are nearly equal, so that the shell appears to be almost equilateral. 

 The radiating ribs of the convex valve are broad and flattened 

 with lateral edges subangular and interspaces much narrower. 

 The number of ribs is over ten, but it is difiicult to give them 

 exactly, for, besides the main ribs, there are one or more much 

 weaker ones on both extremities of the shell, and also those in 

 the middle portion often show a tendency to split. Near the 

 beaks the ribs are almost obsolete, so that the surface becomes 

 more or less smooth, Licremental lines very distinct. On the 

 concave valve the ribs are narrower than the interspaces, with 

 concentric growth-lines often somewhat lamellated. When 

 lamellae are absent, the concave valve is often difiicult to 

 distinguish from that of Fecten laqueatus. 



