In Volume IV descriptions of of the following are continued and/or completed (Ancyrognathus Drepanodus, Paltodus, Paroistodus, Polygnathus, Protognatbodus, Protopanderodus). Newly introduced genera are Aphelognathus, Belodina, Doliognathus, Eotaphrus, Gnathodus, Kockelella, Oulodus, Paracordylodus, Periodon, Phragmodus, Plectodina, Pseudohelodina, Pseudopolygnathus, Scaliognathus. Each catalogue entry contains concise but comprehensive data about a taxon: The original reference is followed by details on the holotype, the locus typicus and the stratum typicum. The original diagnosis section is followed by a separate section on relations and current understanding of phylogenetic relationships. When necessary, the original diagnosis has been amended, revised or completed. A more or less complete list of synonyms expresses the subjective opinion of the respective catalogue author. The section on age and range covers the vertical distribution of a taxon within the conodont zonation as well as general stratigraphic data and evidence on other associated index fossils. Each entry concludes with a section on the regional occurrence of the taxon. These occurences are listed according to continents, countries, and the geographic-geologic units from which they were reported by the original authors. In this section as well as in the synonymy lists, only references have been included that contain identifiable illustrations of the taxon under discussion. In addition, the section on regional occurrence includes data on the rocks yielding the described taxon. The completeness of these data, of course, dependson the information provided by the original author. In many cases, this section informs about the occurrence of the taxon in various types of lithologies. In this section as in others, the mode of spelling the names of the conodont zones is strictly in accord with the spelling given by the original author [asymmetricus-Zone and Neogondolella timorensis-Zone]. For illustration of species, photographs mounted on plates were given preference over line drawings; as a rule the holotype or, in rare cases, one of the syntypes is illustrated. In some cases only reproductions of the published illustration of the types were available. In a few cases where even these photographs were found to be unreproduceable, illustrations of hypotypes and topotypes of subsequent authors had to be used.