Fossils from the Miura Peninsula and its Immediate North. 1 Ai 



number is normally eleven, but may lessen to ten or increase to 

 twelve and may also be accompanied by a few subsidiary riblets at 

 both ends of the valve. Fine dense concentric elevated lines 

 cross the ribs as well as the interspaces, most distinct on the flat 

 valve, often obsolete on the ribs of the convex valve, on which we 

 often observe several longitudinal striae. Ears are nearly equal 

 especially on the flat valve, the anterior ear of the right valve 

 being marked by a shallow byssal notch. 



The largest specimen in our possession measures 82 millim. 

 in height, 95 millim. in length and 25 millim. in depth. 



This species is very close to the preceding one in the form of 

 the shell, but is at once recognized by the number of ribs. In 

 Pecten laqueatus the normal number of the ribs of the convex 

 valve is eight, which may rarely increase to nine, with or without 

 some subsidiary riblets at both extremities of the shell. Some- 

 times one or two ribs may be split into two by a- median groove, 

 but this groove never attains such a breadth as to make them 

 appear as two separate ones. The left valve has also only eight 

 or nine ribs. Still it may not be impossible that the intermediate 

 forms occur, but so far as my present investigation goes, both on. 

 the numerous fossil as well as on recent shells, I have not been 

 able to discover any. 



Pecten fumatus Reeve (= Pecten blfidus Menke, Philippi, 

 Abbild., > t o1. I, Pecten, pi. II, fig. 6 and Syst. Conch. Cab., vol. 

 7, Pecten, p. 160, pi. 45, figs. 1, 2) from Australia (near Sydney) 

 is also closely related to our fossil, though the beak of the right 

 valve is a little more swollen and the ribs are somewhat wider in 

 the Australian shell. 



Very frequent. Some of the specimens show traces of an 

 orange-red colour. 



Fossil occurrence: — Naganuma Zone (Naganuma). 



