Abstract.  Analysis of Late Mississippian ammonoid assemblages found in the Barnett Shale
 of Texas shows that a minimum of three distinct biozones are present.  These represent the
 upper-most portion of P2, the lower portion of the E1c, and the later E1c through E2b
 undifferentiated chronozones of the standard western European succession.  Previous studies
 indicated only two biozones were recognizable, one of  P2 age and another of E1 age.  No post-
 E2b assemblages are known. Preservation of  Barnett assemblages appears to have been
 strongly controlled by eustatic fluctuation, with abundant well-preserved material found only
 from intervals when sea-level was relatively low.  Ages of the youngest Barnett assemblages
 found near the Barnett-Marble Falls formational contact vary widely, ranging from E1c to E2b
 unpredictably.  Since the oldest ages indicated for the base of the overlying Marble Falls
 Limestone are middle Morrowan, it is almost certain that at least part of the Late Mississippian-
 Early Pennsylvanlan stratigraphic record is not represented.