36 Art. 6.— M. Yokoyama: 



nrillim. in diameter. It lacks, however, both apex and lower end 

 of the canal, and also the outer lip. 



Fossil occurrence. — Koshiba Zone (Koshiba); Kanazawa Zone 

 (Nojima, Kanazawa, Teramae). 



Living. — Central Japan. 



16. Pleurotoma mediocarinata, Yokoyama. 

 Pl. I. Fig. 18. 



Shell short-fusiform ; spire moderately high, but shorter than 

 body-whorl; whorls seven, the two uppermost ones being 

 embryonal, smooth and convex, the others with an elevated 

 rounded spiral keel in the middle representing the sinus-band; the 

 surface above this keel is concave, below it flatly convex and 

 vertical, both being ornamented with fine spiral threads. Lines 

 of growth very coarse, especially on the keel, making it appear 

 finely toothed. The body-whorl below the keel is broadly convex, 

 forming a rounded periphery, and ornamented with numerous 

 unequal spiral threads. Aperture longly rhombic, nearly half as 

 long as the shell, pointed behind, narrowed in front passing into a 

 short, somewhat curved canal. Inner lip smooth, with a thin 

 callus spread over it. Outer lip thin, sharp, with a deep sinus at 

 some distance from the impressed suture; the lip below the sinns 

 is arched forward. Height 25 millim. Diameter 11 millim. 

 Length of aperture together with canal 12 millim. 



A single specimen, but well preserved. The high elevated 

 rib-like sinus-band is very characteristic. 



Fossil occurrence. — Kanazawa Zone (Nojima). 



17. Pleurotoma (Drillia) principalis (Pilsbky). 

 Pl. I. Fig. 20. 



Pleurotoma (Drillia) principalis. Tokunaga, Foss. Env. Tokyo, p. 14, pl. I, fig. 23. 

 Drillia principalis. Pilsbjry, Cat. Mar. Moll. Japan, p. 17, pl. II, figs. 9, 10. 



Pilsbey in the above cited work describes this species in full. 

 Therefore I add here only that the oblique longitudinal folds in 

 the body-whorl decrease in size near the last part of it, often be- 

 coming obsolete. 



