Abstract.  Early Triassic ammonoids (eight species of Kashmiritidae, Melagathiceratidae, Prionitidae,
 Flemingitidae ? and Palaeophyllitidae ?) from Mt.  Saikhan Undur Ovoo area, Khentey Province, Mongolia
 are described in the first tirne.  One new subgenus and one new species of the family Kashmiritidae
 (subgenus Saikhanites and species Pseudoceltites (Saikhanites) khenteyensis) are proposed.  The fauna
 includes probable flemingitid ammonoids, common elements for Early Olenekian ammonold faunas in both
 the Tethys and Boreal realms.  The Early Olenekian age is also confirmed by the presence of Juvenites
 and prionitid ammonoids which closely resemble the Early Olenekian Gurleyites of the Tethys and
 Arctoprionites of the Boreal realm.
   The ammonoid fauna of Khentey Province, consisting mainly of Tethyan type, allows us to draw a
 supposed Tethys-Boreal realm boundary during Early Triassic time between the Uda River (Khabarovsk
 region) in the north and Khentey (Mongolia) and Bolshiye Churki Range (Amur area) in the south.  The
 presence of relatively rare typical Boreal elements in association with Tethyan ammonoids in the Olenekian
 ammonoid faunas of Khentey, Bolshiye Churki Range and South Primorye seems to be one of peculiarities
 of Olenekian sequences of peripheral parts of the Tethys.  During Anisian time the Tethyan and Boreal
 realms seemed to be more isolated than in the Olenekian.
   The existence of the ammonoid-bearing marine Triassic in Mongolia supports the idea that the
 Mongolia Okhotsk Ocean between the Siberia and Mongolia-North China continents still existed during the
 Triassic.