Abstract.-Morphologic analysis of 281 species of ammonoids from Great Britain, the North American
mid-continent, and the South Urals, at eight successive levels within the Namurian Series (ca. 18 Myr
duration), using bivariate plots and principal-cornponents analysis, perrnits definition of morphologic
diversity and identification of morphotypic patterns in tirne and space.  Narnurian ammonoids exhibit the
same general range of shell geometry that characterizes ammonoids as a whole; there were few post-
Namurian innovations in the basic geometry of planispiral ammonoids.  Within this overall  range of
geometry, there are eight preferred rnorphotypes: two were phylogenetically monopolized by long-ranging
forms; three were generalized and reoccur in successive horizons; two others were homeornorphically
utilized at different times by different lineages; and one represents morphologic innovation followed by
radiation.  Such patterns seem to represent combined effects of function, phylogeny, and ecology.  Synchro-
nous variations in isolated successions suggest global controls such as eustatic sea-level fluctuations, whereas
provincial differences in diversity may be attributable to paleogeographic and ecologic factors.  We predict
that the Namurian record of amrnonoid morphologic diversity and change will be found to be distinctive
and differentiable from earlier and later intervals.