Abstract- Carboniferous stratigraphy is dominated by the cyclic nature of the
 sediments with repeated, apparently eustatic, rises in sea level separated by
 regressive flowering or by virtual stillstands of sea level.  This results in the record
 of ammonoid evolution being discontinuous, a continuous record being pre-
 vented by repeated ecological restriction.  The appearance and extinction of
 Carboniferous ammonoids are closely correlated with the cycles - specific
 changes with the cyclothems and generic changes with the mesothems.  Abun-
 dant large-sized and diverse ammonoid faunas in the Urals and in Arkansas
 probably represent only the higher faunas of mesothems.  There is a phyletic
 increase in size of species during mesothems, which may be correlated with
 living space, and taxonomic diversity increases late in mesothems in response
 to environmental stress.  Extinctions at the Mississippian-Pennsylvanian bound-
 ary appear to be premature and to an extent catastrophic and regression-induced.