Abstract: Five new Barremian to Upper Albian rudist zones are defined in depositional cycles of the Trinity, Fredericksburg, and Washitagroups of the U.S. Gulf Coast. The stratigraphically lowermost Barremian-Lower Aptian Huetamia buitronae Assemblage Zone isrecognized in Texas, Mexico, and Trinidad. This assemblage in the Sligo Formation consists of Huetamia buitronae Alencaster and Pantoja-Alor, 1998 , Pantojaloria sphaerica Alencaster and Pantoja-Alor, 1995 , Caprina douvillei Paquier ( Skelton, 1982 ), and Douvillelia skeltoni Alencaster and Pantoja-Alor, 1998 . In coeval formations in southern Mexico this assemblage zone also includes Amphitriscoelus waringi Harris and Hodson, 1922 , Amphitriscoelus pluriloculata Alencaster and Pantoja-Alor, 1996 , and Caprina massei Alencaster and Pantoja-Alor(1995 , 1998 ), three species endemic to the Western Hemisphere. The Sligo is correlated with the Barremian to Lower Aptian stage /substageby benthic foraminifers and nannofossils and by its stratigraphic position below Lower Aptian deposits of the OAE1a chemostratigraphicevent. Rudists are quite abundant in the interior-shelf and shelf-margin facies of the Sligo. The Upper Aptian James Limestone in theFairway field of East Texas ( Achauer, 1985 ) also has rudists, as in south Texas, where requienids overlie coral-stromatolite boundstone( Loucks and Bebout, 1984 ). But, these species have not yet been identified. The uppermost Aptian to Lower Albian Coalcomana ramosa Interval Zone spans the total range of this species. This zone contains fourrudist species in the Glen Rose Formation of Texas and the Mural Limestone of Arizona: Coalcomana ramosa Boehm, 1898 , Planocaprinatrapezoides Palmer, 1928 , Caprinuloidea perfecta Palmer, 1928 , and Caprinuloidea multitubifera Palmer, 1928 ( Scott, 2002 ). The first two of thesefour species appear to be restricted to the Glen Rose and equivalent strata, but the latter two species range up into the Middle to lowermostUpper Albian Fredericksburg Group. The uppermost Lower to lowermost Upper Albian Caprinuloidea Interval Zone is the interval from the last appearance of Coalcomanaramosa to the last appearance of Caprinuloidea. Four rudist species occur in this assemblage: Caprinuloidea perfecta, Caprinuloidea multitubifera , Texicaprina orbiculata ( Palmer, 1928 ), and Texicaprina vivari ( Palmer, 1928 ). This interval generally spans much of the Middle to basal UpperAlbian Fredericksburg Group ( Scott, 2002 ). The Upper Albian Kimbleia Interval Zone is defined as the interval from the first appearance of Kimbleia to the first appearance of Mexicaprina , and it includes the rudist species Kimbleia albrittoni Perkins, 1961 , and Kimbleia capacis Coogan, 1973 . This zone spans the lowerpart of the Upper Devils River Limestone, which correlates with the Adkinsites bravoensis Zone, the Eopachydiscus marcianus Zone ( Scott, 2002 ), and the Drakeoceras wintoni Zone ( Scott, 2002 ). The Upper Albian Mexicaprina Interval Zone is the total range of Mexicaprina including M. cornuta Coogan, 1973 (1977) , M. quadrata Alencaster and Oviedo-Garcia, 1998 , and M. alata Filkorn (2002) . This interval correlates withthe uppermost Albian Plesioturrilites brazoensis Zone and directly underlies the Lower Cenomanian Del Rio Shale.