JAPANESE MOLLUSKS, CYREXID.T'.. 159 



UNIONID^. 



Unio oxyrhynchus Martens. Osaka River (coll. by Gulich) ; Uji River below Lake 

 Biwa (Gaines). 



Unio schlegelii Martens. (Gaines). 



CYRENID.S:. 

 Corbicula orientalis Desh. 



Is^umerous specimens, collected by Stearns, which I cannot distin- 

 guish from the continental form. 



Corbicula japonica Prime, {-\-bifonms Reinh.). 



Yokohama, on tide-flats (Stearns). 

 Corbicula straminea Reinh. Mud flats, Kishiu coast (Stearns). 

 Corbicula martensii Clessin. {^yokohamensk Sowb.). 



Tokyo (Stearns, in the fish market). 

 Sphaerium heterodon n. sp. PI. Ill, figs. 15, 16, 17. 



Shell rhombic-oval, anterior end subtruncate-rounded, posterior 

 end truncated, nearly equilateral, moderately convex ; light gray, 

 with yellowish ill-defined concentric zones, and usually a darker 

 zone or two. Beaks calyculate ; interior bluish-white. Eight valve 

 with a single transverse, elongated cardinal in front of the beak ; a 

 double short anterior lateral lamella, a single posterior lamella. 

 Left valve with a single minute cardinal, a single short high ante- 

 rior lamella, posterior lamella double, short. Length 9^," alt. 7^ 

 diam. 5J mm. ' ' ' 



Kishiu, Hizen (Stearns). 



The cardinals are extremely minute, almost obsolete. Two speci- 

 mens have the beak caps conspicuous, a third having them ill-de- 

 fined. 



