82 
PACIFIC SCIENCE, Vol XVII, January 1963 
on the southern half of Izu Banks but are dis- 
tributed on the Osumi Banks. C. lemniscata 
(Rve.) is similar in its distribution to the pre- 
ceding two species; it occurs rather oftener 
than C. mollita (Rve.) does on the banks un- 
der study. 
IZU BANKS 
OSUMI BANKS 
Hyotanse 
Zenisu 
Kurose 
Uji 
Sta. 114 
Chlamys vesiculosus (Dkr.) 
+ 
+ 
— 
+ 
+ 
C. tissotii ( Bernardi ) 
+ 
+ 
— 
+ 
+ 
C. lemniscata ( Rve. ) 
+ 
+ 
— 
+ 
— 
C. mollita ( Rve. ) 
+ 
— 
— - 
+ 
+ 
17. Tucetona hanzawai (Nomura and Zimbo); 
T. shinkurosensis Hatai, Niino, Kotaka 
Figs. 15, 16 
These small glycymerid species occur on the 
banks under study. As the former, T. hanzawai, 
originally described from a fossil bed of Ryukyu 
( Riu Kiu ) Limestone, was recorded from Hyo- 
tanse and Shinkurose (Niino, 1952, 1955). 
Hatai, Niino, and Kotaka (in Niino, 1952: 
106) stated that "the occurrence of this species 
Fig. 11. Samacar pacifica (Nomura and Zimbo) 
from off Miyake Island, 170 m, 12.5 mm X 6.5 mm. 
FIG. 12. Chlamys tissotii (Bernardi) from Hyo- 
tanse, 140 m, 12.6 mm X 13.4 mm. 
in the marine fauna of the environs of Hachijo I 
Island is interesting, because it may suggest j 
the occurrence of a submerged (geological) 
formation corresponding in age to the Ryukyu 
Limestone.” The latter species has been found 
from Shinkurose (the type locality), Hyotanse, J 
Zenisu, Watarinose, Niijima-Nishitai, Toshi- 
matai, as well as Ombase Islet (Fig. 20 b) . 
According to Hatai, Niino, and Kotaka (in 
Niino, 1952), T. shinkurosensis (loc. cit. p. 109, 
figs. 11, 12) is distinguished from T. hanzawai 
(Nomura and Zimbo, 1934, p. 152(44), pi. 
5(1), figs. 3a, b: as Glycymeris ) by the follow- 
ing points: The shell of T. shinkurosensis is 
longer than high, while that of T. hanzawai is 
higher than long; the radial ribs of the former 
are broad, flat, low, and are 27 in number, while 
