CAMBRIAN TRILOBITES FROM THE PARAHIO AND ZANSKAR VALLEYS, INDIAN HIMALAYA

New collections of trilobites from the type section of the Parahio Formation lit the Parahio Valley, Spiti, and from the Parahio, Karsha and Kurgiakh Formations in the Zariskar Valley permit biozonation based on material precisely located within measured stratigraphic sections. Specimens preserved in limestone with mild tectonic deformation clarify, the features of several Himalayan taxa known previously only from severely deformed specimens preserved in shale. A total of 5 trilobite taxa from the Cambrian of Spiti and Zanskar can be referred, questionably at least. at the generic level or below, and 61 of these are present in our new collections. This new material is assigned with confidence to 29 existing species, and to 12 new species. Three new genera, Haydenaspis. Bhargavia, and Himalisania, are established: new, species include Haydenaspis parvatya. Prozocamboides lahiri, Probowmania bhatti. Xingrenaspis parthiva. X. shyamalae, Bhargavia prakritika Kaotaia prachina, Gunnia smithi Sudanamonocarina sinidica, Proasaphiscus simoni, Koldinia odelli, and Torifera jelli. Ten additional Himalayan forms are assigned at the generic level only and another 11 are questionably assigned to genera or species. The zonation proposed includes 6 zones and 3 levels, including the Haydenaspis parvatya level, the Oryctocephalus indicus level, the Kaotaia prachina Zone, the Paramecephalus defossus Zone, the Oryctocephalus salteri Zone. the tranoleesia butes level, the Sudanomacarina sinindica Zone, the Lejopyge acantha Zone, and the Proagnostus bulbus Zone. The sections span from the upper part of the informal Stage 4, Series 2 of the Cambrian System, about 511 Ma old, to the Proagnostus bulbus zone of the Guzhangian Stage near the top of Series 3, dated at about 501 Ma. This time interval is represented by about 2000 m of section, which is thick compared to similar intervals elsewhere and is consistent with high rates of sedimentation along the Himalayan margin at the time. The fauna resembles others from equatorial peri-Gondwanaland, with closest similarity to that of South China. It also brings strong affinity to the North China fauna. Juvenile trilobites arc described for the first time from India. A new Chinese species. Monanocephalus liquani, is also described.