]40 Art. 6.— M. Yokoyamu, : 



Zone (Koshiba); Naganuma Zone (KikkGzan and Naganuma); 

 Upper Musashino of Musashi, Shimosa and Kazusa. 

 Living. — Northern Japan (Hakodate). 



Family Astartidae. 



Genus A starte, Soweeby. 



170. Astarte hakodatensis, YoKoyAMA. 



Pl. XI. Figs. 5, 6. 



Shell small, thick, compressed, ovately-trigonal, nearly equila- 

 teral, posteriorly broadly rounded, or even subtruncate, anteriorly 

 more sharply rounded, sometimes even bluntly angulate, ventrally 

 broadly arcuate; antero-dorsal margin slightly concave, postero-: 

 dorsal somewhat convex; surface coarsely and irregularly grooved; 

 beaks pointed, prominent; lunule short-lanceolate, distinctly 

 bounded by edges; area elongated; muscular impressions deep 

 and distinct: inner margin crenulate. 



( Generally rare, though less so at Koshiba. 



There are some variations in shape, especially in the form of 

 anterior margin. The largest specimen is that of a left valve from 

 Koshiba which is 12 millim. long, 11 millim. high, and 3,5 millim. 

 deep. Another one which is a left valve is 10 millim. long, 9,5 

 millim. high and 3 millim. deep. 



There are apparently two living species of Astarte in Northern 

 Japan which are still undescribed. The one is this Astarte liako- 

 datensix, while the other is a thinner, longer and posteriorly truncate 

 form with the posterior side longer than the anterior and the in- 

 ner margin smooth. 



Tokunaga also described a species of Astarte from the Upper 

 Musashino of Shinagawa under the name of Astarte japonica which, 

 however, differs from ours in having a more rounded shape and a 

 smooth inner margin. 



Among the fossil species hitherto described from Europe, 

 Aßtarte parvula Wood (Crag Moll,, Bivalves, p. 175, pl. XVII, fig. 

 1 1) and A. parva Wood (loo.' cit., p. 192, pl., XVII, fig. 12) from 

 the English Crag have some resemblance in shape to the Japanese, 

 but both possess the inner margin smooth. 



