Abstract.  The stratigraphical range and the boundaries of the Serpukhovian (or lower Namurian)
 ammonoid Eumorphoceras Zone are reviewed, and the ammonoids indicating this interval are docu-
 mented by their global distribution and biostratigraphy.  The number of related genera and species
 increased at the beginning of the Serpukhovian stage, but showed a gradual decline in diversity until
 the Mid-Carboniferous boundary.  The starting point of the Serpukhovian stage can not yet be cor-
 related worldwide with certainty, but the basic layers of the related sections seem to be stratigraphi-
 cally very close.  The next higher Bashkirian stage is marked by the first occurrence of the ammonoid
 genus Isohomoceras.  Aspects resulting from global comparisons of the Serpukhovian ammonoid
 faunas are discussed.