陕西南郑、湖南桃源早奥陶世的两种海林檎化石

TWO FOSSIL CYSTOIDS FROM LOWER ORDOVICIAN OF NAN ZHENG, SHAANXI AND TAOYUAN, HUNAN

前言海林檎纲(Cystoidea)属棘皮动物门,硬体由腕、萼、茎三部分组成。萼部常保存为化石,其形态呈梨形、椭球形或球形,外表由数目不等和形状不定的萼板缝合而成,其腹面具口、肛门、水孔、生殖孔等构造,成为鉴定特征的主要标志。这类动物化石发现于北美、欧洲、亚洲奥陶纪至泥盆纪地层中,尤以奥陶系最多。我国以前仅在云南、贵州奥陶系中发现,有过正式报道(Reed, 1917; Sun Y.C.,1937)。

The paper deals with two species of cystoids from Liangshan of Nanzheng, Shaanxi and Jiuxi of Taoyuan, Hunan. One is a new species of Sinocystis, namely, S. shaanxiensis discovered from the Early Ordovician middle Siliangsuu Formation ('Yangtzeella bed'), while the other, Homocystites sp., was found from the Early Ordovician lower Panjiazui Formation. Their discovery offers two new occurrences of cystoids in China. Description of New species Genus Sinocystis Reed, 1917 Sinocystis shaanxiensis sp. nov. (P1. Ⅰ, figs, 1—7, 10, 11, 13) Diagnosis: Theca spheroidal, pyriform, or ellipsoidal, attached by tip of short stem, less than 40mm in height and maximum diameter, composed of very numerous thick polygonal (mostly pentagonal and hexagonal) plates arranged in fairly definite circlets near the base. Arrangement of other plates unclear due to the worn-away boundaries of plates. Diplopores numerous, irregularly arranged, covered by 'worm-like' epistereoms or exposed where the episteroms have been removed. Mouth straight, slit-like, situated in middle of adoral area, bifurcating at each end into a pair of short divergent branches terminating in single brachiole-facets. Hydropore conical, near mouth, with a small circular opening at its tip. Gonopore small, also conical, situated close to anus. Anus larger, hexagonal, sometimes pentagonal or heptagonal, covered by six (sometimes five or seven) triangular plates forming a periproct. Dimensions of specimens as shown in Table Ⅰ. Discussion: The new species is distinguished from other described species by its smaller size, conical hydropore, 'worm-like' epistereoms, and smooth surface of theca. Type specimens: Holotypes: P1.Ⅰ, figs. 2—5; Paratypes: P1. Ⅰ, figs. 1, 6, 7, 10, 11, 13. Occurrence: Middle Siliangssu Formation, Early Ordovician; Liangshan, Nanzheng, Shaanxi.