174 Art - 6- -M. Yokoyaina; 



sloping, ventral arcuate with the postero-ventral corner, also more 

 or less rounded. Surface with numerous, course, unequal, 

 elevated, couceritric lines of growth crossed by fine, close, impress- 

 ed, radiating lines which make them finely crenulate. There are 

 also a few hroad concentric grooves on the surface. Beaks small 

 and acute. Hinge-line arcuate with ten to fifteen teeth. Liga- 

 mental pit triangular, the height of the triangle being somewhat 

 greater than the breadth of the hase. Inner margin finely crenu- 

 late. 



The form of the shell is somewhat variable, but may generally 

 be said to be roughly oblong or elliptical, the longer axis being 

 only a little longer than the shorter, with their proportion about 

 10 to 8,4. The thickness of a perfect shell is about two-thirds 

 of the longer axis. The largest specimen does not exceed 13 

 millim. by 11 mill im. 



This species is readily distinguished from the preceding by 

 its smaller size, a more tumid and less oblique shell and the 

 crenulate inner margin. 



Frequent in the Miyata Zone. 



Fossil occurrence. — Miyata Zone (Yamagayado, Iwaiguchi, 

 Jinyaato, Shishiana and Matsubara in Kami-Miyata; Harashita 

 and Motoyashiki in Shimo-Miyata); Kamakura Zone (Kewaizaka 

 in Kamakura); Kanazawa Zone (Nojima); Koshiba Zone (Koshi- 

 ba). Upper Musashino of Kazusa. 



Living. — Northern and Central Japan. 



225. Limopsis azumana, Yokoyama. 

 Fl. XVIII. Figs. 19, 20, 21. 



Limopsi* a umana. Yokoyama, Species of Limopsis found in the Xeogene of Koshiba, 

 Jour. Geol. Soc. Tokyo, vol. XVII, no. 205, Oct. 1910, p. 3, pi. IX, figs. 16-18. 

 LimopsU truncata. Yokoyama, Ibid. p. 4, pi. IX, figs. 13, 14. 



Shell small, generally moderate in thickness, tolerably infla- 

 ted, oblique, ovate to oval, 'the height nearly equal to, or some- 

 what greater than, the length, very inequilateral, the posterior 

 margin broadly rounded and passing gradually into the more 

 sharply rounded ventral margin, the anterior margin generally 



