Molluscan Assemblages — -Okutani 
79 
FIG. 5. Perotrochus beyrichii (Hilgendorf) from 
Kurose, ca. 200 m, 72.7 mm X 70.0 mm (Mr. Kurata 
coll.) . 
known localities of the species are as follows 
(numbers for records refer to those of localities 
shown in Fig. 4) : 
1) Off Iioka, Pacific side of Boso Peninsula; 
dead shells collected by commercial trawl- 
ers ( Sakurai, 1954). 
2) Off Hachiman-Saki ("Soyo” sta. 40a; July 
4, 1956; 35° 04.7' N, 140° 21.5' E), 250 
m in depth; a fragment only. 
3) West coast of Boso Peninsula, off Katsu- 
yama and Tomiura, about 200-300 m 
in depth (Wada, 1954). 
4) Sagami Bay, west coast of Miura Penin- 
sula. Type locality is off Misaki. Also col- 
lected by the H. M. "The Emperor” near 
Hayama. 
5 ) Okinoyama, a small bank located near the 
southwestern tip of Boso Peninsula. 
6) Senzu, northwestern coast of Oshima Is- 
land; dead shell with hermit crab, col- 
lected by Mr. Kurata. 
7) Around Omurodashi Bank (Shirai, 1958). 
8) Hyotanse, 128, 134, 160 m (Niino, 1955). 
9) Niijima-Nishitai, 104, 120 m; and Toshi- 
matai, 88 m (Niino, 1955, and Shirai, 
1958). 
10) Kurose, collected by Mr. Kurata. 
As is shown above, this pleurotomariid gas- 
tropod is characteristically distributed on the 
lower shelf and submarine banks around the 
area. Other species of Perotrochus, as ecological 
equivalents, are also found in similar habitats in 
other districts; Perotrochus hirasei Pilsbry is 
known to be distributed around the Pacific coast 
of Kii Peninsula and Tosa Bay, and as an in- 
habitant of the continental shelf around the 
main Japanese islands. According to Mr. Tera- 
machi ( personal communication ) , P. hirasei has 
been collected by him from depths of 60 fath- 
oms (ranging 20-180 fathoms) in such locali- 
ties. 
1 ) Okezoko Deep located south of Okino- 
shima Islet in Bungo Straits. This is col- 
lected from thanatocoenose, mainly of 
Glycymeris rotunda, with Siphonalia fil- 
osa, etc. 
2) Off Urado in Tosa Bay, 70-80 fathoms, 
sometimes with Erronea hirasei, Chicoreus 
dilectus, and some other common shelf 
dwellers. 
3) Off Tanabe, southwestern coast of Kii 
Peninsula. 
4) Somewhere in Hyuga-Nada, eastern 
waters off Kyushu. 
Recently, Kuroda and Habe (1953) have 
shown that this species is also distributed in the 
Fig. 6. Perotrochus salmiana (Rolle) from Uji 
Islet, 126 m, 65.0 mm X 62.7 mm. 
