は　じ　め　に
　秩父盆地の新第三系より，生痕化石群を発見したので報告する．産出地点は，秩父盆地南西部，埼玉県秩父郡荒川村大字贄川(にえがわ)で，秩父鉄道「白久(しろく)」駅の北東約400mの国道140号線の北側に面した採石場跡地である．ここには，層理面が広く露出し，ほぼ一面にリップルマ−クが認められる．このリップルマークについて，1987年より調査をすすめてきたところ，数多くの生痕化石を発見した．これらの生痕化石について記載し，古環境についても若干検討したい．

桜井層産の生痕化石群について
　調査地点の桜井層産の生痕化石群のうち,筆者らの識別したものは次のとおりである.
�T　水平な桿状生痕(Domichnia SEILACHER, 1953)
　1)湾曲した弓型のもの
　2)短い桿状生痕A型
　3)短い桿状生痕B型
　4)水平なパイプ状生管
　5)不規則な分岐生管
�U　環節状彫刻をもつ足痕(Movichnia SEILACHER, 1953)
　6)放射状足痕
　7)帯状足痕A型
　8)帯状足痕B型
　9)帯状足痕C型
　10)帯状足痕D型
�V　密集する小生管群(Fodichnia SEILACHER, 1953)
　11)分岐する小生管群A型
　12)分岐する小生管群B型
�W　特殊な形態をした生痕
　13)強く湾曲した結節をもつ生痕
　14)弱く湾曲した正弦曲線型生痕
　15)多数の並走線条がつくる生痕
　16)扇形の多数の小数珠状管群(食事痕)
　17)火焔型をした生管
（以下省略）

1: Radial trails (Asteronerleites n. ichnogen.) 2: Fan-shaped cluster of beaded tubes like Fodichnia SElLACHER, 1953

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Fossil Ichnofauna from the Miocene Sakurai Formation in the Chichibu Basin, Saitama Prefecture, Central Japan

Masae OMORI
Shakujii-dai 3-32-5, Nerima-ku, Tokyo 177
Yoshiaki ISHIDA
Hitotsubashi High School, Chiyoda-ku, Tokyo 101
Kiichi OBATA
Toyooka HighSchool, Iruma-shi, Saitama 358
and
the Research Group of Ripple Mark in the Chichibu Basins

Resume Writers found abundant trace fossils from one locality exposing thin alternation of sandstone and mudstone of the Miocene Sakurai Formation in the Chichibu basin, Saitama Prefecture. It situates at the upperpart of the Oganomachi group overlain by the Chichibumachi and Yokozemachi groups in ascending order, and overlies on the Hikokubo group.
　　　Fossils were distributed on the bedding plane of the fine sandstone with fine ripple marks. The lithofacies intercalating conglomerates often, and associated fossils such as molluscs, bernacles and plant remains suggest that the paleo-bathymetry of the Sakurai Formation was deemed not so deep.
　　　The ichnofauna from this locality consits of the following forms :

Horizontal rod-type (Movichnia SEILACHER, 1953)
　　Gently arched specimen.
　　Type-A of short rod specimen
Type-B of ditto
Small pipe-like specimen
　　Irregular branching one
　Trails with annular structures (Domichnia SEILACHER, 1953)
　　Radial trails (Asteronerleites n. ichnogen.)
　　Type-A of linear trails (Arthropodichnus sp. A)
　　Type-B of ditto (Arthropodichnus sp. B)
　　Type-C of ditto (Neonereites ? sp.)
　　Type-D of ditto
　Cluster of small tubes (Fodichnia SEILACHER, 1953)
　　Type-A of branchig one Chondrites cf. maekawaensis (HATAI & NODA)
　　Type-B of ditto (Tosaorbis ? sp.)
　Peculiar form
　　Deep sinuated one with nodes (Paleodactyon sp.)
　　Gently sinuated one without node (Protodactyon ? sp.)
　　Cluster of parallel short striae (Monomorphichnus sp.)
　　Fan-shaped cluster of beaded tubes like Fodichnia SElLACHER, 1953
　　Flame-like hyporelief
　　　Considering from the above composition this ichnofauna belong to Nereites ichnofacies, however whose bathymetric status might be shallower than that proposed by FREY and PEMBERTON (1984), because of the above-cited litho-and macrobio-facial characters of the Sakurai Formation.