Molluscan Assemblages — Okutani 
81 
Fig. 9. Bursa ranelloides (Reeve) var. from Uji 
Islet, 140 m, 48.6 mm X 30.3 mm. 
sula coast off Iro-Zaki ("Soyo” sta. 42, Apr. 2, 
1958, 34° 34.2' N, 138° 50.7' E, 80 m). No 
record from Boso Peninsula is available for the 
present study. A possible ecological equivalent, 
G. millegranosa Habe, is distributed on the 
Osumi Banks as well as in its adjacent waters, 
where G. guttata is not found. It is also inter- 
esting to note that one of the related species, 
Astraea caelata Gmelin, is indicated by Parker 
and Curray ( 1956) as a typical banks-associated 
mollusca from calcareous banks on the conti- 
nental shelf off Texas, U.S.A. 
1 4. Bursa ranelloides ( Reeve ) var. 
Fig. 9 
A rather small form of the species is widely 
distributed on the banks mentioned above. It 
has been collected from Hyotanse, 135 m; 
Zenisu; Kurose, 200 m; off Takeshima, 210 m, 
and the Uji Islets, 126 m. 
15. Small Arcid Pelecypods 
Figs. 10, 11 
On the submarine banks under study, some 
small species of Arcidae are abundant and are 
found together with other members of the 
group. The occurrence of species in the present 
material is as follows: 
IZU BANKS 
OSUMI BANKS (KYUSHU) 
Hyotanse 
Zenisu 
Kurose 
Goto 
Uji 
Sta. 114 
Acar congenitum (Smith) 
+ 
+ 
+ 
+ 
+ 
— 
Area mania takii Hatai, Niino, Kotaka.... 
— 
— 
+ 
— 
— 
+ 
Mimarcaria aizoi Sakurai (MS) 
+ 
— 
+ 
+ 
Hawaiarca uwaensis ( Y okoyama ) 
+ 
+ 
— 
+ 
+ 
— 
Samacar pacifica (Nomura, Zimbo) 
+ 
— ? 
+ 
+ 
+ 
— 
Striarca fansta Habe 
+ 
— 
— 
+ 
+ 
■ — 
16. Small Pectinid Pelecypods 
Figs. 12-14 
Chlamys vesiculosus (Dkr.) is known to be 
very abundant on the continental shelf border- 
ing southwestern Japan. Being a sandy bottom 
dweller, it is also distributed on the banks of 
the northern group at a depth of 32-118 m. A 
related species, C. tissotii ( Bernardi ) , often 
occurs in the same localities. They are not found 
Fig. 10. Area mania takii Hatai, Niino, and Ko- 
taka from Kurose ca. 200 m, 28.0 mm X 15.0 mm 
(Mr. Kurata coll.). 
