ONTOGENY OF HOMALOPHYLLUM SIMPSON,1900 AND A SEM STUDY OF ITS MICROSKELETAL STRUCTUfRES
Li Minglu He Xinyi (China University of Geosciences)
. In this paper two species, Homalophyllum ungulum and H. columnife-rum (sp. nov. ) are described and the ontogeny and minute skeletal structures of Homalophyllum are studied and illustrated as follows: (1) Ontogeny showing that, in early stage, the cardinal septum is thin and long; in late stage, the cardinal fossula became apparent, and the axial end of major septa expanded and reinforced and forming notable columella. (2) Fundamental skeleton unit is fibrous tissue (i. e. Laths expanded gradually upward). They are arranged into regular, complete trabecular forming a fan-^system in the septa. Lamellar skeleton is poorly developed and only compose the wall. The fundamental unit is calcite flakes. Description of New Species Homalophyllum columniferum sp. nov. Rather small solitary, at least in early stages calceoloid. Septa numerous, long, thickened to contiguity in wide marginarium. In late Stage, cardinal septum in deep fossula extending to axis into axial zone of septal thickening that forms notable columella or axial structure. No dissepiments, tabulae few, domed or declined, incomplete. Its monacanth trabeculae forms a fanystem in longitudinal section. Discussion: The present species differs from other known species of genus Homalophyllum in having well-defined columella. Horizon and Locality: Upper part of the Zhusileng Formation, Lower Devonian, Zhusilenghairhan area of western Nei Monggol.