38 Art. 6.— M. Yokoyama: 



19. Pleurotoma (Drillia) quantoana, Yokoyama. 



Pl. I. Fig. 22. 



Shell turrete; spire moderately high, consisting of in any 

 whorls; whorls somewhat angulated a little below the middle, the 

 angle being formed by a spiral riblet; the surface above the angle 

 is flat, sloping, ornamented with five to six spiral threads, the 

 second one of which from above is stronger than the others and 

 almost equal to the riblet of the angle; the surface below the angle 

 is perpendicular with two riblets of about the same size as the one 

 above them, except on the body-whorl in which there are subequal 

 riblets which generally gradually decrease in size toward below. 

 Periphery rounded. Canal short, straight. Sinus moderately 

 deep, a little distant from suture, with the lip below arched 

 forward. 



Unfortunately a single specimen obtained lacks both apex and 

 outer lip. The preserved whorls are only five, but they seem to 

 have been about ten in number which would make the height 

 about 25 millim. Diameter 7 millim. 



In general form this species reminds us of Pleurotoma 

 vertebrata Smith (Proc. Zool. Soc, 1879, p. 180, pl. XIX, fig. (1) 

 from Central Japan which is, however, tricarinate. 



Fossil occurrence. — Naganuma Zone (Nagarmma); Upper 

 Musashino of Musashi. 



20. Pleurotoma (Drillia) cosibensis, Yokoyama. 



Pl. I. Fig. 26. 



Shell small, fusiform; whorls eight, the two first smooth and 

 rounded, the others shouldered, with the surface above shoulders 

 concave and below them convex; the concave surface has an 

 impressed spiral line in its bottom; the convex surface is 

 ornamented with many oblique, obtuse, longitudinal riblets, 

 nineteen in the penultimate whorl, gradually diminishing in size 

 toward the lower suture and separated by interspaces of a less 

 breadth ; the interspaces as well as the ribs are provided with fine 



