New collections of trilobites from the type section of the Parahio Formation in the Parahio Valley, Spiti, and from the Parahio, Karsha, and Kurgiakh formations in the Zanskar 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 75 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, andHimalisania, are established; new species includeHaydenaspis parvatya, Prozacanthoides lahiri, Probowmania bhatti, Xingrenaspis parthiva, X. shyamalae, Bhargavia prakritika, Kaotaia prachina, Gunnia smithi, Sudanamonocarina sinindica, Proasaphiscus simoni, Koldinia odelli, andTorifera 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 theHaydenaspis parvatyalevel, theOryctocephalus indicuslevel, theKaotaia prachinaZone, theParamecephalus defossusZone, theOryctocephalus salteriZone, theIranoleesia buteslevel, theSudanomocarina sinindicaZone, theLejopyge acanthaZone, and theProagnostus bulbusZone. The sections span from the upper part of the informal Stage 4, Series 2 of the Cambrian System, about 511 Ma old, to theProagnostus bulbuszone 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 bears strong affinity to the North China fauna. Juvenile trilobites are described for the first time from India. A new Chinese species,Monanocephalus liquani, is also described.
