Molluscan Assemblages — Okutani 
87 
Fig. 19. Lima fujitai Oyama from Hyotanse, 118 
m, 15.5 mm X 12.0 mm. 
Ryukyu Archipelago, which is situated 
farther south than Kikaijima Island. 
3) S triarc a fausta is another example de- 
scribed from a fossil bed (at Moeshima 
in Kagoshima Bay, Kyushu) containing 
warmer water species. 
4) Some elements of tropical origin are 
found in the banks fauna, e.g., Chicoreus 
superbus, which has been known from the 
Bonin (or Ogasawara) Islands, and Area 
mauia takii, which is presumably an en- 
demic form of a Hawaiian species. These 
two species are found at Kurose, which is 
the most southern bank in the area. 
An assumption that the molluscan assem- 
blage of the Izu Banks is an isolated shelf fauna 
representing species derived from warmer wa- 
ter corresponds to that of Parker and Curray 
(1956: 2438) for the Gulf of Mexico. They 
concluded from their studies that the banks- 
associated molluscan assemblages in waters off 
Texas represented a population now isolated 
from the main centers of abundance ranging 
from southeast Florida to the West Indies and 
different from the surrounding level-bottom 
communities. 
According to Teramachi (personal communi- 
cation), there are some distributional gaps of 
upper-shelf mollusca even within the warm 
Kuroshio area, though they are far less con- 
spicuous than those existing at about 36° N on 
the Pacific coast of Honshu. One such type of 
gap presumably is found around Ashizuri-Saki, 
for instance. The distributional difference of 
certain species of Fusinus, Siphonalia, Ancilla, 
and Fulgoraria off the east and west coast of 
the cape (about 34° 42' N, 133° E) may be 
found there. Regardless of this fact, the typical 
Fig. 20. Distribution of bank-associated mollusca. a, Galeoastraea guttata; b, Tucetona shinkurosensis; c, 
Chama argentata; d, Spondylus anacant bus -Lima fujitai-Plicatula muricata (or any two of these). 
