广西宜山法门期的珊瑚

SOME FAMENNIAN RUGOSE CORALS FROM YISHAN, GUANGXI

一、前言泥盆纪类型的珊瑚在晚泥盆世弗拉期(Frasnian)末已告绝灭.晚泥盆世法门期(Famennian)是珊瑚进化史上的一个'低潮'时期,因此过去在世界各地都很少有过珊瑚化石的报道.近年来,在波兰、比利时、西德以及苏联的奥莫弄和乌拉尔等地均相继发现了不少的法门阶的珊瑚化石。

The Famennian rugose corals decribed in the present paper were collected from the Yishan county of Guangxi, comprising 7 species in 6 genera, namely: Neaxon cheilos Weyer 1984, N. longiseptatum sp. nov., Kielcephyllum guangxiense sp. nov., Ufimia xiakouensis sp. nov., Prosmiliar yishanensis sp. nov., Yishanophyllum bellum gen. et sp. nov. and Zaphriphyllum sp. Although a majority of the above-mentioned corals are new species, however, they all bear obviously a much closer relationship with those of the Holy Cross Mountains of Poland and the Thuringian Mountains of GDR. Since the latest Devonian (Famennian) corals have rarely been reported in China, a brief description of these fossils seems desirable. Description of new genus and species Neaxon longiseptatum sp. nov. (Pl. II, figs. 1-16) Corallite solitary, small, cylindrical, with a maximum diameter of 5 mm in cross section. Septa of two orders, major septa long, numbering 14; minor septa rather long, about 4/5 as long as major ones. Aulos circular, about 1 mm in diameter. Tabulae horizontal in aulos and declined in periaxial area. Remarks: The new form differs from Neaxon cheilos Weyer and Neaxon bulloides Rozkowska in its longer minor septa, narrower aulos and inwardly inclining tabulae. Kielcephyllum guangxiense sp. nov. (Pl. II, figs. 19-23) Corallite solitary, about 11-18 mm in diameter. In adult stage, major septa long, extending to the centre, numbering 24-30; minor septa short or rudimental; dissepiments variable in cross section. In later stage, major septa with drawing from the centre, about half as long as the radius; cardinal septum shortened with cardinal fossula clear. Tabulae incomplete and cystose, dissepiments elongate or semiglobular. Remarks: Kielcephylltm cupulum Rozkowska differs from the present new species in its wider peripheral cystose and differential tabulae. Ufimia xiakouensis sp. nov. (Pl. IlI, figs. 1-8) Small solitary corallite about 2-3 mm in diameter. In adult stage major septa numbering 18, with four of them (including two alar ones and two counter-alar ones) longer, thicker and more rhopaloid than the others. Cardinal and counter septum slightly shorter. Acceleration of counter quadrant exceeding that of cardinal quadrant. Formula of septal arrangement expressed as Minor septa rudimental. Tabulae horizontal and complete; no dissepiments developed. Remarks: The new form differs from Ufimia makowskii Rozkowska in its smaller diameter and absence of stereoplasma. Prosmilia? yishanensis sp. nov. (Pl. I, figs. 1-21) Corallite small, solitary. In late brephic stage, cross section 3 mm in diameter; major septa numbering 10, with four septa (including 2 counter-alar ones and 2 alar ones) longer and rhopaloid; cardinal septum (?) also longer in some corallites; minor septa ridge-like; dissepiments only a few in number. In ephebic stage, cross section 5.0-6.5 mm in diameter; major septa numbering 18-20, with 11-13 in the counter quadrant and 7 in cardinal quadrant, arranged in the formula of cardinal septum shortened with cardinal fossula clear; four of the septa still appearing longer; minor septa very short. Some corallites with narrow peripheral dissepiments while others with a stereozone. Longitudinal section with 1-2 rows of dissepiments; tabulae complete, horizontal or slightly concave and convex, 1.0-1.5 mm apart. Remarks: Prosmilia fedorowski Rozkowska differs from our new form in its septa of two orders, with five longer ones; its counter septum is long but cardinal septum rather short. Genus Yishanophyllum gen. nov. Type species: Yishanophyllum bellum gen. et sp. nov. Diagnosis: Corallite small, solitary, with less septa. Cardinal, counter and the other two or three major septa meeting at the centre, forming a prominent columella reinforced by stereoplasma, but connecting with the counter septum only in the late ephebic stage. Minor septa very short or rudimental. Stereozone generally thick. Dissepimentarium narrow. Tabulae inclining outwardly or cystose. Remarks: This new genus closely resembles Lophophyllum, but differs from the latter in its smaller corallites, less septa, remarkable stereozone and character of tabulae. It also shows a close similarity to Rotiphyllum, Cyathaxonia and Metriophyllum, but differs from these three genera in the presence of dissepiments. The present new form is somewhat similar to Dematophyllum, but the latter is a compound coral. Geological age and distribution: Latest Devonian (Famennian): South China. Yishanophyllum bellum gen. et sp. nov. (Pl. III, figs. 9-21) Small solitary corallite, cylindrical. In neanic stage, cross section about 3 mm in diameter; major septa numbering 14; cardinal, counter and the other two or three major septa meeting axially, reinforced by stereoplasma and forming a Columella; minor septa inconspicuous. In adult stage, cross section about 5 mm in diameter, major septa 16 in number, attaining a length of about 2/3 the radius, being strongly dilated in some corallites; columella plate-like, connecting with the counter septum; minor septa conspicuous, about 1/3-1/2 as long as major ones. In longitudinal section, solid columella thick; dissepimentarium narrower and tabulae cydtose or alternate.