Short Notes ©Malacological Society of Japan53

A New of (Marmarostoma) (: ) from the Miocene Yugashima Group of Izu Peninsula, Central Japan

Susumu Tomida1* and Masahito Kadota2 1Chukyo Gakuin University, Nakatsugawa City, Gifu 509-9195, Japan; *[email protected] 2Kanagawa Prefectural Museum, Odawara City, Kanagawa 250-0031, Japan

Many turbinid fossils were obtained from Systematic description limestones intercalated in the light green tuffaceous sandstone of the middle Miocene Sakurada Family Turbinidae Rafinesque, 1815 Formation, the Yugashima Group, at Shikura, Genus Turbo Linnaeus, 1758 Matsuzaki-cho and Shirakawa, Nishi-izu-cho, in Subgenus Marmarostoma Swainson, 1829 Shizuoka Prefecture. Examination of the specimens revealed that they represent a single new species, Type species: Turbo chrysostomus Linnaeus, and it is described in the following lines, with a 1758 (by original designation). discussion of the paleo-environment of its habitat. Turbo (Marmarostoma) matsuzakiensis n. sp. Localities and Geologic Notes (Figs. 3–7)

According to Sawamura et al. (1970), the late Type material: Holotype, KPM-NN0006593 (in Neogene series that outcrops in the present study Kanagawa Prefectural Museum of Natural History) area can be divided into the Yugashima Group and The surface of the last whorl is damaged by a cutter, the Shirahama Group, in ascending order (Fig. 2). In and the anterior part of the is damaged by and around the present fossil localities in Shikura polishing. Paratypes, four mature shells, MFM and Shirakawa, the Shirahama Group is 40008 (in Mizunami Fossil Museum), KPM- unconformably underlain by the middle Miocene NN0006594, KPM-NN0006595 and an operculum, Yugashima Group. Fossils of the present new KPM-NN0006596. species were obtained from the Sakurada Formation Type locality: The Sakurada Formation, the in the middle part of the Yugashima Group. They middle part of the middle Miocene Yugashima were accompanied by some shallow water mollusks Group, at Shikura (34°44´27˝N; 138°47´18˝E), such as Chlamys sp. and Spondylus sp. (from Matsuzaki-cho, Kamo-gun, Shizuoka Prefecture Shirakawa), Virgiconus sp. and Clypeomorus sp. (type locality: Fig. 1), in limestones intercalated in (from Shikura), and also by some other tropical the light green tuffaceous sandstone. Additional elements such as reef-building corals, calcareous material was obtained in the same formation at algae and the large calcareous foraminifer Shirakawa (34°47´59˝N; 138°49´43˝E), Nishi-izu- Nephrolepidina japonica. Concerning the geological cho, Kamo-gun, Shizuoka Prefecture. age of the Yugashima Group in this area, Koyama Etymology: This species is named after its type (1986), Okada et al. (1986) and Okada (1987) locality, Matsuzaki. reported that the Sakurada Formation can be Description: Shell rather large in size, solid, assigned to the CN4 calcareous nannofossil zone tumid and turbiniform. Spire rather high, with 4.5–5 (15.5–13.5 Ma). The Izu Peninsula is known to have whorls. Protoconch consisting of about 1.5 whorls, drifted northward on the Philippine Sea Plate, and it worn in all specimens. Teleoconch whorls was located in the tropical West Pacific Ocean ornamented with thick, raised and rounded spiral around 15°N during the middle Miocene (Hirooka et cords with sometimes sparsely arranged weak al., 1985). Judging from these facts, the paleo- nodules in adult stage, and fine spiral threads, environment of the Sakurada Formation was a crossed by fine growth lines. Last whorl large (ratio tropical shallow rocky bottom during this era. 0.53–0.55 of total shell height), and well inflated, strongly angulated at shoulder, weakly angulated at periphery and at base, and ornamented with three rows of thick and rounded primary spiral cords on 54 VENUS 70 (1–4), 2012

Fig. 1. Maps showing the fossil locality in central Japan. The fossil localities are plotted on a 1:50,000-scale topographic map of Japan. Quadrangle “Shimoda”, Geographical Survey Institute of Japan. Scale bar represents 1 km. each angle, weak secondary spiral cords and fine inflated and ornamented with some rounded spiral spiral threads, crossed by fine growth lines. Suture cords and fine spiral threads, crossed by fine growth rather deep with suture-ramp bending obliquely lines. Columella anteriorly projected with narrow downwards and ornamented with spiral cords and and smooth space facing toward aperture. Aperture interstitial threads. Shoulder strongly angulate with rather large and nearly round. Umbilicus thick, raised and rounded spiral cord on teleoconch, imperforate. Operculum slightly ovate, strongly and ornamented with rows of short but large hollow convex on outside and flat inside; outside with weak spines sparsely arranged and open at their tops on granules; inside smooth, flat, and with 3–4 whorls. body whorl; first row of spines occurs strongly at Measurements: see Table 1. shoulder, second row weak at periphery in rare Remarks: Although the operculum (paratype) cases, and third row rather strongly at basal was not found in situ within the shell, it was periphery; spines on shoulder ordinarily being considered to belong to this new species, because strongest but prominently short. Base slightly this is the only species in the genus that was found Short Notes 55

Fig. 2. Upper Neogene sequence and stratigraphical level of the occurrence of the fossil specimens of Turbo (Marmarostoma) matsuzakiensis n. sp. from the Shikura and Shirakawa Limestones in the Nishi-izu area. (★: fossil horizon). Calibration of calcareous foraminiferal zones and nannofossil zones modified after Saito (1999).

Figs. 3–7. Turbo (Marmarostoma) matsuzakiensis n. sp., shells (3–6), and an operculum (7). 3. Holotype, KPM-NN0006593, Shikura; apertural (A) and dorsal (B) views. 4. Paratype, MFM40008, Shikura; apertural (A) and dorsal (B) views and enlarged surface (C). 5. Paratype, KPM-NN0006594, Shikura; dorsal view. 6. Paratype, KPM-NN0006595, Shirakawa; dorsal view. 7. Paratype, KPM-NN0006596, Shikura; inner (A) and outer (B) views. Scale bar represents 10 mm; all specimens at the same scale, except for 4C. 56 VENUS 70 (1–4), 2012

Table 1. Measurements (mm) of Turbo (Marmarostoma) matsuzakiensis n. sp. (Shell) Maximum width Minimum width Height Body whorl height KPM- 51.5 45.3 68.7 38.1 NN0006593 MFM40008 — 41.4 63.6 34.0 KPM- 51.8 45.6 64.6 34.1 NN0006594 KPM- 54.1 — 66.9+ 37.0 NN0006595 (Operculum) Maximum diameter Minimum diameter Thickness KPM- 35.9 30.0 11.3 NN0006596 in this Formation, and also opercula with the same of Azumino City, for kind aids and the preparation morphological features were abundantly found in of the figures and photographs. the Formation. Comparisons: Two middle Miocene turbinids, References Turbo (Marmarostoma) ozawai Otuka, 1938, and Turbo (Marmarostoma) minoensis Itoigawa, 1960, Hirooka, K., Takahashi, T., Sakai, H. & Nakajima, have been recorded from southwestern Japan. The T. 1985. Paleomagnetic evidence of the present new species is distinguished from those by northward drift of the Izu Peninsula, central having a larger sized shell with stronger raised and Japan. In: Nasu, N., Kobayashi, K., Uyeda, S., Kushiro, L. & Kagami, H. (eds.), Formation of rounded primary spiral cords and larger hollow Active Ocean Margins, pp. 775–787. Terra spines. Scientific Publishing Company, Tokyo. The present new species can also be compared Koyama, M. 1986. The geological history of the Izu with some Recent turbinid species in the Indo-West Peninsula, and the Pleistocene of Ashigara and Pacific. It resembles Turbo (Marmarostoma) Oiso regions. Gekkan-Chikyu 8: 743–752. (in cernicus G. B. Sowerby III, 1886, endemic to the Japanese) western Indian Ocean, in having well inflated Okada, H., Niitsuma, N., Kano, K. & Arai, S. 1986. whorls with strongly raised and rounded primary Guidebook of Field Excursion to Subduction and Collision Areas, Shizuoka, Izu and spiral cords, a strongly angled shoulder and a Tanzawa. 36 pp. International Kaiko weakly angled periphery, and a superficial Conference, Tokyo. ornamention of fine axial growth threads, but it is Okada, H. 1987. Calcareous nannofossil distinguished from the latter by having a larger shell biostratigraphy and paleoenvironmental with short but large hollow spines on the shoulder analysis of marine formations exposed in the and basal periphery. This new species also South Fossa-Magna region. Fossils (43): 5–8. resembles Turbo (Marmarostoma) chrysostomus (in Japanese with English abstract) Saito, T. 1999. Revision of Cenozoic Linnaeus, 1758, which is widely distributed in the magnetostratigraphy and the calibration of Indo-West Pacific, in having well inflated whorls planktonic microfossil biostratigraphy of Japan with a strongly angled shoulder, weakly angled against this new time scale. Journal of the periphery and basal periphery, and regular axial Japanese Association for Petroleum growth threads, but it differs by having a larger shell Technology 64: 2–15. ornamented with stronger raised and rounded Sawamura, K., Sumi, K., Ono, K. & Moritani, T. primary spiral cords and larger hollow spines, and 1970. Geology of the Shimoda district. by lacking a thick spiral cord around the columella. Quadrangle series scale 1:50000, Geological Survey, Tokyo 8 (105), 41 pp. +4 pp. (in Japanese with English abstract) Acknowledgements: The authors wish to express our thanks to Mr. Yoshitsugu Okumura, formerly of (Accepted September 21, 2011) the Mizunami Fossil Museum, for cleaning the fossil specimens, and also to Mr. Takashi Ishibashi Short Notes 57

静岡県伊豆半島の中新統湯ヶ島層群 から産出したサザエ類化石の一新種

冨田 進・門田真人

要 約

静岡県西伊豆の松崎町伏倉と西伊豆町白川に分 布する新第三系中部中新統湯ヶ島層群桜田層の淡 緑色凝灰質細粒砂岩中に挾まれる石灰岩体から産 出したサザエ類の化石を新種 Turbo（Marmarostoma） matsuzakiensis n. sp.として記載した。 本種はやや大型で，螺層の肩，中央，殻底周縁 に 3本の丸く太い第一次螺肋と弱い第二次螺肋お よびその間に細い螺脈をもつ。肩を形成する螺肋は 最も強く高まり太く，体層の肩には短いが太い棘を 並べる。表面には螺肋と交差する放射成長細脈があ る。臍孔は閉じる。近似種との比較では，西南日 本の中新統から産出する Turbo（Marmarostoma） ozawai Otukaや T.（M.）minoensis Itoigawaとは， より大型の殻と，大きな刺のある太い螺肋をもつ ことから区別できる。また，同亜属の現生種のい ずれにも相当するものはなく容易に区別できる。 産地の石灰岩は造礁サンゴ，石灰藻，大型有孔 虫，岩礁性貝類などの浅海性の化石を含み，礁性 の異地性岩体として湯ヶ島層群桜田層中に狭在す るものである。層準は湯ヶ島層群の中部であり， ナンノ化石の CN4帯（15.5～13.5 Ma）に相当する。 伊豆のフィリピン海プレート上の移動を考えると， 中期中新世の約 15 Ma前は北緯 15度前後の現在の フィリピン東方の熱帯西太平洋に分布していたと 考えられる。