156 Art. 6.— M. Yokoyama : 



sometimes quite smooth and sometimes coarsely ribbed. Our 

 specimens seem to correspond to the variety gamma (fig. e and f) 

 of Wood, though not so orbicular in shape. 



Fossil occurrence in Japan. — Koshiba Zone (Koshiba). 



Fossil occurrence in Foreign countries. — English Crag from 

 the Coralline to the Chiliesford beds; Scaldisien of Belgium; 

 Pliocene of Italy. 



Living. — Brittany; North Sea; Norway, 



200. Pecten cosibensis, Yokoyama. 

 Pl. XIII. Figs. 7, 8. 



Pecten cosi'msis. Pectens from tlie Koshiba Xcogene, Jour. Geol. Soc. Tokyo, vol. XVIII, 

 No. 208, p. 4, pl. I, figs. 3, 4. 



Several specimens which, however, are more or less broken. 



The shell is rather thin though firm, ovately rounded, 

 inequiyalve, nearly equilateral, radiately ribbed and provided 

 with unequal ears. The right valve is very convex, while the left 

 is nearly flat, The ribs are rounded and very unequal, the larger 

 ones being generally in twos, rarely in threes and dividing them- 

 selves into two or sometimes even into three in the lower half of 

 the -hell. The valleys between the larger ribs are deep, broad or 

 narrow 7 and also ornamented with a few radial riblets. Concentric 

 constrictions are present in larger specimens which are not many 

 and at unequal distances from one another, The anterior ear is 

 the largest with interrupted radial ribs; the posterior is very 

 small. 



The largest specimen is that of a right valve, 56 millim. in 

 height and length, and 12 millim. in depth. 



Fossil occurrence. — Koshiba Zone (Koshiba). 



201. Pecten intuscostatus, Yokoyama. 

 Pl. XIII. Figs. 9. 10. 



Shell small, thin, compressed, nearly equivalve, equilateral, 

 nearly round, with antero-dorsal and postero-dorsal margins 

 sloping, straight or slightly concave and forming obtuse angles at 



