DEFINITION OF THE PRAGIAN EMSIAN STAGE BOUNDARY/

The boundary for the Pragian-Emsian Stage Global Stratotype Section an d Point (GSSP) in the Lower Devonian has been ratified by the ICS and the IUGS and is placed in a section at the Zinzil'ban Gorge in the Kit ab State Geological Reserve, 170 km SSE of Samarkand, Uzbekistan, near the base of the Zinzil'ban Beds. The position of the boundary was sel ected by the Subcommission on Devonian Stratigraphy in 1989 to coincid e with the level at which the phylogenetic successor to the conodont P olygnathus pireneae appeared, that is the species then named Polygnath us dehiscens but in this report, because of uncertainties regarding th e holotype of Polygnathus dehiscens, the name Polygnathus kitabicus is used because the type material for the latter came from the GSSP, alt hough it is though by some to be a junior synonym of Po. dehiscens. Th e evolutionary series associated with these changes has already been p ublished. The GSSP is located very soon after a global sea level rise and the onset of changed conditions. Rich faunas of other fossil group s occur in the Zinzil'ban Formation. Several species of monograptids a nd several genera of brachiopods occur above the GSSP and new subspeci es of dacryoconarid genera and of brachiopods occur above the GSSP. Al so appearing above the GSSP level is the tabulate coral Favosites regu larissimus which is the name-giver for the Regularissimus Zone widely traced in Asia. This account documents the record. Since the acceptanc e of this GSSP has concluded decisions on all the Devonian system, ser ies and stages boundaries, comments are made on the problems that rema in, especially those resulting from the fact that most of the GSSP's h ave been defined in pelagic facies, leaving outstanding their correlat ion into neritic and terrestrial facies where auxillary stratotypes ar e required to provide a better international chronostratigraphic frame work for future international scientific work on the Devonian System.