摘要
志留纪扬子浅海繁衍了一个独特的慧星虫科(Encrinuridae)三叶虫,以江南古陆北侧滨、浅海区最为繁盛。本文根据3个剖面(插图1)的资料讨论下志留统秀山组上段三叶虫分带,并描述Encrinuridae科的一些新种,这些三叶虫标本是1981年李志明带领方德庆等6名学生实习时获得,赠予本人;化石图片由刘金华、陈斌拍摄,笔者在此表示衷心谢意。方德庆在利用上述资料编写毕业论文时对三叶虫进行了初步鉴定和描述,后由杨家騄重新研究完成。
This paper is to describe some species of Encrinuridae and to discuss some problems on their taxonomy, biostratigraphy and evolutionary trend. Here described are 9 new species in addition to 7 old species of trilobites. The present stud is only confined within the upper member of the Early Silurian Xiushan Formation in the northern Jiangnan Old Land (Text-fig. 1), which may be subdivided into three fossil assemblages (Text-figs. 2 and 3) as follows:Ⅰ. Pre-Coronocephalus Assemblage Ⅱ. Coronocephalus-Rongxiella-Kailia AssemblageⅢ. Coronocephalus-Senticucullus AssemblageEncrinuridae Angelin, 1854 Encrinuroides rhombiformis sp. nov. (Pl. Ⅰ, fig. 3)Frontal lobe of glabella strongly expanded, rhombic in outline, strongly contracted in posterior part. Three pairs of glabellar furrows: posterior two pairs transglabellar; third pair narrow (exsag.), shallow and discontinuous. Glabella covered with regular tubercles; no tubercles at the centre of the glabellar anterior lobe and along the axial line in posterior part. Preglabellar furrow very weak.Pygidium broadly triangular in outline; axial lobe broad, about one-third the width of the pygidium, with 19 axial rings; pleural regions carrying 11 pairs of pleural ribs.Encrinuroides hippocrepieus sp. nov. (Pl. Ⅰ, figs. 4—8)Glabella flatly convex. Posterior glabella with three pairs of glabellar furrows: posterior two pairs transglabellar; third pair discontinuous or continuous. Anterior lobe of glabella circular in outline, with distinct preglabellar furrow and broad (sag., exsag.) anterior border, showing Ushaped in outline, carrying 2—4 rows of granules. Median furrow present.Pygidium circular-triangular in outline; axial lobe composed of 17—21 rings; pleural regions with 9—10 pairs of pleural ribs. Test smooth.Kailia (K.) and K. (Parakailia) are considered as belonging to the Encrinurinae rather than to the Coronocephalinae based on the glabellar shape, short lateral glabellar furrows, and the presence of very narrow, weak median furrow and preglabellar furrow in a few species. In taxonomy and biostratigraphy the new materials enable us to work out the tentative phylogenetic scheme of Early Silurian genera under the Encurinuridae in the Yangtze Shallow Water (Text-fig. 4).Kailia (ParakaUia) granulosa sp. nov. (Pl. Ⅰ, figs. 9, 10)Glabella flatly convex, expanded gradually forward. Anterior glabellar margin strongly arched forward; median furrow very shallow; preglabellar furrow broad, deep for a short distance near dorsal furrow, and narrow, very shallow in the middle. Anterior lobe of glabella and anterior border carrying flat and weak tubercles. Three pairs of lateral glabellar furrows in posterior part short, broad and deep; 1p, 2p, and 3p lobes papillate laterally and hanging above broad, deep dorsal furrows.Pygidium circular-triangular in outline; axial lobe conical in outline, strongly convex and very broad, not less than half as wide as pygidium, with 20 axial rings; pleural regions with 6—7 pairs of pleural ribs; test smooth.Coronocephalinae Chang, 1983 Coronocephalus (Coronocephalus) hongyanxiensis sp. nov. (Pl. Ⅰ, figs. 16, 17)The new species is similar to Coronocephalus (C.) ovatus (Zhang Wen-tang, 1974, p. 185, pl. 83, fig. 2) in glabellar furrows, position of eye lobes, etc., but the latter differs from the former in the glabella circular in outline, the anterior margin well rounded, with dense tubercles on the fixed cheeks.Coronocephalus (Senticucullus) apodemes sp. nov. (Pl. Ⅱ, figs. 10—14; Pl. Ⅲ. fig. 1)Glabella expanded forward, subcylindrical in posterior part with three broad and shallow transglabellar furrows, and less than five granules on ech lobe. Anterior lobe of glabella flatly convex and subcircular in outline, with dense tubercles on its poterior part but with fewer tubercles forward Preglabellar furrow very short, only showing one pair of indentations on the anterior-lateral margin of the glabella. One pair of apodemal pits in occipital furrow and three pairs of apodemal pits in glabellar furrows distally situated. Fixed check narrow, sloping downward toward the axial furrow, with tubercles. Postero-lateral limb broad (exsag.) and long (tr.) with tubercles in proximal part and pits in distal part. Fixigenal spines thin and projected rearward on 7th segment of the thorax.Pygidium subtriangular in outline, straight on the anterior margin. Axial lobe narrow, with more than 25 rings; pleural regions composed of 13 pairs of pleural ribs with thinner and longer distal spines; test smooth.Coronocephalus (Senticucullus) serratus sp. nov. (Pl. Ⅲ, figs. 2—6)The new species is similar to Coronocephalus (Senticucullus) simplex Zhou, but differs from the latter in the presence of only two transglabellar furrows, the absence of occipital spine, the longer fixigenal spines, with two rows of shorter and stouter tuberculate denticles arranged on outer side and inner side of them (each side with more than 10 tuberculate denticles in number).Coronocephalus (Senticucullus) keloidus sp. nov. (Pl. Ⅲ, figs. 10—12)Cranidium transversely broad, about three times as wide as long. Glabella flatly convex moderately expanded forward and contracted in posterior part, narrowest (tr.) at the second glabellar furrow. Three pairs of glabellar furrows: posterior two pairs transglabellar; all posterior glabellar furrows and lobes bent and W-shaped. Anterior lobe of glabella quadrately-circular in outline, carrying weak keloids; median furrow shallow and short. Distal margin of postero-lateral limb carrying three additional spines.Pygidium triangular in outline; axial lobe composed of about 38 rings; pleural region composed of 12—13 pairs of pleural ribs with relatively longer and thin distal spines.Coronocephalus (Senticucullus) flammus sp. nov. (Pl. Ⅲ, fig. 13)This new species is distinctively characterized by the flaming form of nine spines on the free cheek.Rongxiella? longshanensis sp. nov. (Pl. Ⅳ, fig. 1)Glabella clavate in outline, moderately contraced in posterior part, expanded forward: anterior lobe of glabella flatly convex, subcircular in outline, carrying fewer tubercles. Three pairs of transglabellar furrows shallow; fixed cheek narrow; postero-lateral limb broad band-like outline, projected curvedly to latero-posterior part. Fixigenal spines unknown. Due to the greater breadth (Tr. at posterior glabella, and the possession of distinct transglabellar furrows, this species should be questionably referred to the genus 'Rongxiella'.Rongxiella generalis sp. nov. (Pl. Ⅳ, figs. 11—14)Cranidium triangular in outline; glabella flatly convex, strongly contracted in posterior part and narrowest at first and second glabellar furrows. Three pairs of transglabellar furrows in posterior part; anterior lobe of glabella strongly expanded, circular in outline, carrying large tubercles in posterior part, and becoming smooth forward. Occipital ring very broad band-like (sag. tr.), with a length (tr.) equivalent to 4/5 the width of anterior glabellar lobe; fixed cheek very broad, 1.3 times as wide (tr.) as the narrowest part of glabella; postero-lateral limbs (exsag.) broad. Free cheek triangular in outline; surface of gena flatly convex and smooth; border narrow; margin carrying more than six nodes. Pygidium circular-triangular in out|ine; axial lobe narrow, with 28—30 or even up to 36 rings; pleural flatly convex, composed of 16—18 pairs of pleural ribs.
出处
《古生物学报》
CAS
CSCD
北大核心
1991年第2期246-264,共19页
Acta Palaeontologica Sinica
