Recent biodiversity studies, reported here for the first time, have shown that the molluscan fauna of the Gulf of Mexico is far richer and more complex than previously thought. As a result of these new discoveries, the Gulf malacofauna is shown to contain large numbers of endemic species that reside within four separate biogeographical subdivisions of the larger Carolinian Molluscan Province: the Floridian, Suwannean, Texan, and Yucatanean Subprovinces. These four Gulf biotic components, with each supporting its own endemic fauna, are shown here to be separated by distinct ecological and oceanographic barriers. The resultant physical and genetic isolation has led to the evolution of spectacular sibling species radiations, many unknown and undescribed until now. Some of the most conspicuous and important of these are found in the gastropod families Fasciolariidae, Volutidae, Conidae, Muricidae, and Busyconidae, all of which are dominant predators in their respective benthonic ecosystems. The species within these ecologically-important families, along with hundreds of endemic taxa in 50 other gastropod and bivalve families, are illustrated here on 132 color plates and are discussed in detail in the individual chapters. Special attention is given to the mollusks of poorly studied and virtually unknown ecosystems such as those on the deep reefs off the Florida Keys and Dry Tortugas, the deep water coralline algal beds off western Florida, the Flower Garden Reefs off Texas, the petroleum seeps and brine pools of the Sigsbee Escarpment, the Campeche Bank Archipelago, and the deep water areas at the mouth of the Yucatan Channel. This new book is unlike previous taxonomic surveys of the Gulf of Mexico mollusks in that it highlights only the endemic species and genera and does not cover the large number of widespread Carolinian and Caribbean taxa that occur with them. In this aspect, the book is designed to be an augmentation to previous faunal surveys, adding hundreds more taxa that had been missed in these older surveys or were described after those earlier works had been published. The emphasis on endemic species and species complexes is meant to underscore the special nature of the Gulf of Mexico malacofauna, setting it aside from all others in the Tropical Western Atlantic Region.