Ordovician nautiloid fossils of Xainza region, Tibet

The Taerma bridge-Zhakang in the Xainza area is the second spot of Ordovician in northern Tibet based on the discovery of some reliable fossils. The strata contain a large amount of fossils of many taxa, which developed well enough to attain reliable support for era and distinctive boundary. It is the best spot for the fossil study of the Ordovician in the northern Tibet up to now and provides important clues to the classification and correlation of the Ordovician and to the paleogeography distribution as well as to the tectonic evolution of the northern Tibet. 29 species of Nautiloid fossils, which belong to 3 orders, 8 families and 15 genera, have been identified. Among them,3 genera and 9 species are new. Here only one new genus Eneoceras gen. nov. and six new species are described in detail as example. Other two new genera Taremaocera's and Variabioceras will be described in other papers.Genus Eneoceras gen.nov.Diagnosis:The new genus Eneoceras gen. nov. is characterized by the features as “Conch orthoconic, medium in size. The surface is decorated with annulus which array in a distance as the septa. Conch enlarging slowly. Compressed laterally. Circular in cross section. Siphuncle small, situated central from ventral in position. Spetal neck subcyrtochoanitic. Slightly expanded in connecting rings. Siphuncle appears as a string of beads with thin parietal deposits in it. Medium in spetal density. Thin epithecal and hypothecal deposits developed in cameras