中文摘要：

报道西藏西部仲巴县休古嘎布晚三叠世的一个新种Tragorhacoceras xiugugabuense sp.nov.,该种属于Discophyllitidae Spath,1927,代表休古嘎布首次的晚三叠世菊石记录,并且确定化石所属地层的时代为诺利期（Norian）。

英文摘要：

This paper reports the discovery of a new ammonoid species, Tragorhacoceras xiugugabuense sp. nov. , from the Late Triassic （Norian） period in western Tibet, which belongs to the family Discophyllitidae Spath, 1927. The discovery represents the first record of Late Triassic ammonoid fauna from the Xiugugabu, Zhongba County and confirms a Norian age for the newly discovered strata in western Tibet.SYSTEMATIC DESCRIPTION The specimen described in this paper is housed in the Xizang Institute of Geology Survey. The classification of ammonoids adopted herein follows Moore （1957） and Tozer （1981）.Class Ammonoidea Zittel, 1884 Order Phylloceratina Arkeil, 1950 Superfamily Phyllocerataceae Zittel, 1884 Family Discophyllitidae Spath, 1927 Genus Tragorhacoceras Spath, 1927 Type species Phylloceras occultum （Mojsiso- vies, 1873） Diagnosis Shell discoidal, more or less evolute, smooth and round venter, with principal saddles having plump diphyllic terminations, with numerous auxiliaries, and ornamentation on the larger whorls. Remark This genus is generally close to the Carnian genus Rhacophyllites in view of its suture line, but differs in its very simple diphyllic saddles with large terminal leaflets..Tragorhacoceras xiugugabuense Mu and Liu sp. nov. Etymology Xiugugabu, where the specimen was found.Holotype XZDDY2011XH2-1. Description The single specimen （Fig. 3） is compressed laterally and not very well preserved. Nevertheless, the following features are observed. The preserved part is a phragmocone, almost without body chamber. The conch diameter is 39.8 ram, height of last whorl is 18.5 mm, width of whorl is 11. 5 mm and umbilical diameter is 6.4 mm. The approximate proportion of height to diameter is 46%, the proportion of the width to diameter is 29% and the proportion of the umbilical diameter to diameter is 16%. The conch form is discoidal and involute, with rounded venter and elliptic whorl section. Mature modifications comprise formation of constriction with accentua- ted ocular and hypono