Fossils from the Miura Peninsula and its Immediate North. 39 



subequal spiral threads. In the body-whorl the. ribs disappear 

 below the rounded periphery, with only spiral threads on the base. 

 Aperture sub-rhombic, angular behind, passing in front into a 

 short wide canal slightly bent backward. Columella smooth. 

 Outer lip thickened but sharp-margined. Sinus moderately deep, 

 somewhat below suture, with the margin below it broadly arched 

 forward. Sub-basal notch wide and shallow. Height 17 millim. 

 Diameter 5,5 millim. Length of aperture and canal together 6, 5 

 millim. Rather frequent. 



This species is also allied to Pleur otoma principalis above 

 mentioned, but is smaller and the ribs much more numerous. 



Fossil occurrence. — Koshiba Zone (Koshiba). 



21. Pleurotoma (Drillia) nivalioides, Yokotama. 

 Pl. I. Fig. 27. 



Shell small, turrete, with body-whorl nearly one-half the 

 shell-height; whorls eleven, shouldered with the exception of two 

 embryonal ones which are convex; shoulders furnished with 

 obliquely elongated tubercles separated by somewhat wider inter- 

 spaces; surface above shoulders flatly concave, transversely 

 striated, with a subsutural thread in the upper part; surface below 

 shoulders nearly perpendicular with two vertical threads preceding 

 from each tubercle and crossed by a few unequal transverse threads 

 with cross-points more or less tubercular. On the body-whorl, the 

 infra-;ubercular vertical threads are crossed by many unequal, 

 rather distant, transverse ones, so that the whole surface appears 

 cancellated, with cross-points more or less tubercular as in the 

 upper whorls. Inner lip smooth, with a thin callus, somewhat 

 flexuous. Canal short, recurved. Sinus rather shallow. 



There are two specimens, one from Koshiba and one from 

 Naganuma. Both lack the outer lip; but that it was broadly 

 arched forward below the sinus is quite certain. The Koshiba 

 specimen measures 16 millim. in height. 4,5 millim. in diameter, 

 and millim. in length of aperture, and shows twenty tubercles 

 on the penultimate whorl, while that of Naganuma is 14 millim. 



