Since the middle of the last century, with the publication of d'Orbigny's monumental synthesis (1849–52, 1850–52), it has been clear that the fossil record is divisible into a number of significant biostratigraphic units (his ”terrains” and ”etages”). It has also been clear that within each of these d'Orbigny-type units there are included a number of individual “biofacies,” the term used by the geologist, or “communities,” the term used by paleobiologists. I have referred (1983) to the major d'Orbigny biostratigraphic divisions as “ecologicevolutionary units,” because the term terrane is geologically preoccupied today, and the subdivision terms ”etage” and “stage” have different meanings.