178 Art - 6.— M. Tokoyama : 



Rare. 



This species resembles Leda confusa Hanley (Sowerby, 

 Thesar. Conch., vol. Ill, Nuculidae, p. 119, pi. 228, fig. 85) 

 living in our seas; but it is smaller, more solid, longer, more 

 inequilateral, with the lunula not so sharply bounded and the palli- 

 ai sinus more ascending and more uniform in breadth. 



Fossil occurrence. — Naganuma Zone (Naganuma). 



229. Leda naganumana, Yokoyama. 

 Pl. XIX. Fig. 6. 



Shell thin, transversely elongate-ovate, tolerably compressed, 

 slightly inequilateral, the anterior side being shorter than the 

 posterior. Anterior margin sharply rounded, the posterior obtuse- 

 ly pointed; antero-dorsal margin weakly convex, the postero- 

 dorsal weakly concave. Ventral margin broadly arcuate, going 

 over to the posterior without any distinct angle. On the surface 

 there is a single sharp keel running from the beak to the posterior 

 angle and forming the boundary of the lanceolate area with pout- 

 ing lips. The sculpture consists only of coarse unequal lines of 

 growth. Lunula lanceolate, distinct, with the lips pouting like 

 those of the area. The surface of the lunula as well as of the area 

 is furnished with sublongitudinal striations. Length about 19 

 millim. ; height 9,5 millim. ; thickness 5 millim. 



There is only a single example whose valves are closely 

 attached to each other, on which account it is not possible to 

 make out the characters of the inner surface. 



This species looks like Ledapernula Müller (Sowerby, Thes. 

 Conch., vol. Ill, Nuculidae, p. 113, no. 14, pl. 228, fig. 56-88) 

 n which, however, the shell is more inequilateral, the lunula 

 obsolete and the posterior end truncate. 



Fossil occurrence. — Naganuma Zone (Naganuma). 



