云南武定节甲类的新材料

文中描述了采自云南武定中泥盆统一新的属种Yinostius maior gen.et sp.nov.属于短胸节甲类Heterosteidae科,这类化石在我国系初次发现。

NEW MATERIAL OF ARTHRODIRA FROM THE WUDING REGION, YUNNAN

A new form of Arthrodira, Yinostius major gen, et sp. nov., was collected from the Midale Devonian, Wuding region, Yunnan Province. Diagnosis: A very large arthrodira, the head and body are broad and dorso-ventrally compressed. The skull roof is wide posteriorly, but narrowing rapidly anteriorly. The plates covering the posterior part of skull roof are moderatelly long, while those on the anterior part are short. The nuchal plate is triangular, nearly half as long as the skull roof and embayed posteriorly; with a small medial process. The median dorsal plate is short and broad with a large keel and a projecting carinal process. The condyle on the anterior dorso-lateral plate is developed. The anterior lateral plate and the anterior dorso-lateral plate are fused and elongate, extends forward beneath the head. Orbits small and anteriorly placed, facing antero-lateraUy. The plates thickened and ornamented with tubercles of moderate size, irregulerly distributed, in some area fused to form wormlike ridges. Remarks: This new form is readily distringushed from the previously discribed Heterosteids by its nuchal plate. It resembles Heteroslus and Herasmius in the shape of the skull roof, the form of orbits and reduced trunk-shield. But there are many difference between these forms in the morphology of nuchal plate. In Herasmius the nuchal plate is extremely broad, its breadth reaching 70％ of that of the skull roof, in Heterosteus it is 54％ and in Wuding material is about 68％. The breadth/length index of skull roof is about 183 in Herasmius, in Hetrosteus about 140. There is also difference between them in the shape of the median dorsal plate. The anterior embayment and antero-lateral angle of the median plate in Wuding form is bigger than those in Heterosteus. So the form dealt with in this paper is named by the authors as a new genus and new species Yinostiua major gen. et sp. nov., "Yinostius" is presented to the Professor Yin Zanxun and "Major" refers to the big size of the fish.