144 Art, 6. -M. Yokoyama : 



Fossil occurrence. — Miyata Zone (Motowada); Koshiba Zone 

 (Koshiba). Upper Musasbino of Kazusa and Shi m osa. 

 Living. — Western Japan; Cbina. 



181. Myodora triangularis, A. Adams. 

 Pl. XI. Figs. 14, 15. 



My odor . triangularis, Dunker, Iudex Moll. Mar. Jap., p. 181, pl. VII, figs. 11, 12. 



The shell of this species is markedly triangular with the height 

 slightly less than the length. The valves are both nearly flat, the 

 left perhaps a little more so than the right. The surface is 

 ornamented with coarse, rather regular, concentric grooves. The 

 palliai sinus is small, but rounded and distinct. 



We possess four left and three right valves. The largest (left 

 valve) measures 11,5 millim. in length, 10,5 millim. in height 

 and only 1,2 millim. in depth. The largest right valve measures 

 10 millim. in length and height, and 2 millim. in depth. 



Fossil occurrence. — Naganuma Zone (Naganuma). 



Living. — Japan (according to Dtjnker). 



Family Mytilidae. 



Genus Mytilus. Linne. 



182. Mytilus hirsutus, Lamarck. 



Pl. XL Fig. 16. 



Mytilus hirsutus, Lamarck, Anim. sans vert., vol. VII, p. 38. Reeve, Conch. Icon. 

 Mytilus, pl. 3, fig. 8. Lischke, Jap. Meeresconch., I, p. 154. Dunkek, Index Moll., p. 222. 



The shell is ovately triangular, swollen, ornamented with a 

 varying number of close longitudinal or radiating ribs. In our 

 specimens which are all small, the lower or ventral margin is not 

 concave as is usually the case, but straight or even slightly convex. 

 The inner margin is finely crenulate as in the typical specimens. 

 A right valve from Yokosuka measures 15 millim. in length, 10 

 millim. in height and 4 millim. in depth. Kare. 



Fossil occurrence. — Miyata Zone (Kami-Miyata); Yokosuka 

 Zone (Yokosuka). 



Living. — Central and Western Japan. 



