Fossils from the Miura Peninsula and its Immédiate North. 37 



The specimens are rather numerous, especially at Naganuma. 

 From Koshiba we possess only young ones. 



Fossil occurrence. — Koshiba Zone (Koshiba) and Naganuma 

 Zone (Naganuma); Upper Musashino of Musashi and Shimosa. 



Living. — Northern, Central and Western Japan. 



18. Pleurotoma (Drillia) pseudo-principalis, Yokoyama. 

 Pl. I. Fig. 21. 



Shell turrete, pointed; whorls about thirteen, markedly 

 concave above, somewhat convex below, the boundary between 

 being very sharp and distinct; the concave surface is spirally 

 striated and bounded above by a prominent subsutural thread; the 

 convex surface which occupies the greater part of the whorl is 

 ornamented with oblique longitudinal ribs (about twelve on the 

 penultimate whorl) which are generally narrow and sharp in the 

 lower whorls, and broad and rounded in the upper; but in the 

 lower whorls also, there are occasionally such broad ones between. 

 These ribs begin abruptly below the concave surface and continue 

 to the lower suture either in the same strength or gradually 

 weakening. The interspaces between the narrower ribs are much 

 broader than the latter, while those between the broader ones in 

 the upper whorls are either equal to, or narrower than, the ribs; 

 they are everywhere spirally threaded, with threads equal and 

 generally indistinct or obsolete on the ribs. On the body-whorl, 

 the ribs are somewhat flexuons, weaker and closer together toward 

 its last part and vanishing on the base. Aperture elongated, with 

 a deep sinus below the infrasutural thread with the outer lip below 

 it broadly arched forward. Canal short, nearly straight. Height 

 28 millim. Diameter 8 millim. Length of aperture obliquely 

 measured 9 millim. Rather rare. 



This shell looks not unlike the preceding species, but the 

 body-whorl is comparatively longer, the shape more slender and 

 the sub-basal sinus is absent. 



Fossil occurrence. — Yokosuka Zone (Otsu); Naganuma Zone 

 (Naganuma). 



