Acteon? sachalinensis Nagao
1939 Actaeon sachalinensis Nagao [sic], p. 236, pl. 22, figs. 6, 7, 7a, b.
Type. —Syntypes (GMH no. 8328, two specimens) from the Upper Ammonite bed (Upper Yezo Group) at the Nishihogawa near Kawakami colliery, Toyohara-gun, south Saghalin.
Age and distribution. —Upper Cretaceous (Coniacian or Santonian). Known only from the type locality.

Pirsila sp.
1934. Actaeon (?) sp. [sic]: Nagao, p. 263, pl. 33, figs. 4, 4a.
Age and distribution. —Lower Cretaceous (Aptian). Hiraiga Formation of the Miyako Group in Tanohata area of Iwate Prefecture.

Colostracon (Ovactaeonina) yeharai (Nagao)
1934. Actoeonina (Ovactaeonina) yeharai Nagao [typographical error of Actaeonina], p. 263, pl. 33, figs. 3, 3a-c.-1970. Colostracon (Ovactaeonina) yeharai Nagao: Shikama, p. 116, pl. 35, fig. 1 [reproduction of an original figure].
Type. —Lectotype here designated (GMH? missing, Nagao, 1934, pl. 33, figs. 3, 3a-c) from the Hiraiga Formation of the Miyako Group at Matsushima islet near Moshi, Iwaizumi-cho, Shimohei-gun, Iwate Prefecture.
Age and distribution. —Lower Cretaceous (Aptian). Known only from the type locality.

Trochactaeon sp. aff. T. crisimensis Choffat
1966. Trochactaeon sp. aff. T. crisimensis Choffat: Nakazawa and Murata, p. 332, pl. 6, figs. 10, 11.
Age and distribution. —Lower Cretaceous (probably Neocomian). Kamihei Group at Omine mine area near Kamaishi, Iwate Prefecture.

Avellana minima Nagao [Pl. 6, Figs. 15a, b]
1934. Avellana minima Nagao, p. 265, pl. 36, figs. 12, 12a, b, 13-16, 17, 17a, b, 18, 18a, b.
Type. —Holotype (GMH no. 7071, Nagao, 1934, pl. 36, figs. 12, 12a, b, originally designated as "type") from the Hiraiga Formation of the Miyako Group at Haipe near Hiraiga, Tanohata-mura, Shimohei-gun, Iwate Prefecture.
Age and distribution. —Lower Cretaceous (Aptian). Hiraiga Formation of the Miyako Group in Tanohata and Iwaizumi areas of Iwate Prefecture.

Explanation of Plate 6 Fig. 1. Trajanella japonica Nagao. Holotype (GMH no. 7077). Apertural view, × 1. Loc. Haipe, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 2. Turrtella yaegashii Nagao. Lectotype (GMH no. 6802). Apertural view, × 2. Loc. Hiraiga, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 3. Turritella soratiensis Nagao. Holotype (GMH no. 8343). Adapertural view, × 2.5. Loc. Tomatsu-zawa, Hokkaido (Upper Cretaceous, Mikasa Formation of the Middle Yezo Group). Fig. 4. Itomelania basicordata Suzuki: type-species of genus Itomelania. Holotype (left). Adapertural view, × 2. Loc. Umatoge, Kyongsang-namdo (Lower Cretaceous, Shinshu Formation of the Naktong Group). Fig. 5. Brotiopsis wakinoensis (Kobayashi and Suzuki): type-species of genus Brotiopsis. Plaster cast of holotype (UMUT MM7940). Apertural view, × 1.2. Loc. Ryohori, Kyongsang-namdo (Lower Cretaceous, Naktong Group). Fig. 6. Siragimelania tateiwai tateiwai (Suzuki): nominate subspecies of the type-species of genus Siragimelania. Holotype (UMUT MM6315). Apertural view (la) and adapertural views (1b, c), × 2. Loc. Hyakuan-do, Kyongsang-bukdo (Cretaceous, Taikyu Formation of the Siragi Group). Fig. 7. Melanoides (Yoshimonia) yoshimoensis Ota: type-species of subgenus Yoshimonia. Apertural view, × 2. Reproduced from Ota, 1960, p. 8, fig. 3. Loc. Yoshimo, Yamaguchi Pref. (Lower Cretaceous, Yoshimo Formation of the Toyonishi Group). Fig. 8. Melanoides (Kumania) kawaguchiensis Ota: type-species of subgenus Kumania. Apertural view, × 1.5. Reproduced from Ota, 1960, p. 11, fig. 5. Loc. Shimomatsukuma, Kumamoto Pref. (Lower Cretaceous, Kawaguchi Formation). Fig. 9. Cirsocerithium reticulatuim (Nagao). Lectotype (GMH no. 6814). Adapertural view, × 3, Loc. Haipe, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 10. Bathraspira excavata Nagao. Holotype (GMH no. 7080). Apertural view, × 1.5. Loc. Raga, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 11. Cimolithium miyakoense (Nagao). Holotype (GMH no. 6803), Adapertural view, × 1. Loc. Hiraiga, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 12. Pyrazus? scalariformis Nagao. Holotype (GMH no. 7084). Apertural view (12a) and adapertural view (12b), ×1. Loc. Hiraiga, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group). Fig. 13. Aporrhais (Tessarolax) japonicus (Yabe and Nagao). Holotype (IGPS no. 22636). Apertural view (13a) and adapertural view (13b), × 1.5. Loc. Ikushumbetsu river, Hokkaido (Upper Cretaceous, Upper Yezo Group). Fig. 14. Aporrhais (Tessarolax) acutimarginatus (Nagao). Syntype (IGPS no. 51254). Apertural view (14a) and adapertural view (14b), × 1.5. Loc. Kawakami, south Saghalin (Upper Cretaceous, Upper Yezo Group). Fig. 15. Avellana minima Nagao. Holotype (GMH no. 7071). Apertural view, × 4. Loc. Haipe, Iwate Pref. (Lower Cretaceous, Hiraiga Formation of the Miyako Group).

Avellana? problematica Nagao
1932. Avellana problematica Nagao, p. 50, pl. 7, figs. 7, 7a, b.-1939. Avellana problematica Nagao: Nagao, p. 237.
Type. —Holotype (GMH no. 8212, Nagao, 1932, pl. 7, figs. 7, 7a, b) from the Upper Ammonite bed (Upper Yezo Group) at the left bank of the Abeshinai, south of Shibinnai, Nakagawa-cho, Teshio Province, Hokkaido.
Age and distribution. —Upper Cretaceous (Coniacian or Santonian). Upper Yezo Group in Nakagawa (Abeshinai) and Ikushumbestu areas of Hokkaido.

Cunulia (Oligoptycha) sp. cf. C. (O.) obliqua (Gabb)
1939. Oligoptycha cf, obliqua (Gabb): Nagao, p. 237, pl. 22, figs. 8, 8a.
Age and distribution. —Upper Cretaceous (Coniacian or Santonian). Upper Yezo Group in Notoro area of south Saghalin.