This paper summarizes and highlights the history of descriptive genus-level taxonomy on Paleozoic radiolarians grouped in five major phases: 1) initial discoveries in the 1890s; 2) ignored during the first half of the 1900s; 3) renewed interest during the 1950s to 1970s; 4) the “fast” years of the late 1970s to 1990s; and 5) the early 21^st century quest for the oldest and significant progress in the late Permian. In the 1890s, radiolarians were identified with certainty by Hinde in Ordovician radiolarian cherts. Following Hinde's great discovery, and after a 50-year dormant period, Deflandre revived the study of Paleozoic radiolarians through his groundbreaking study of Albaillella from Carboniferous phosphatic nodules, combined with his genius for understanding evolutionary implications. Additional important work was conducted in this third phase by Foreman, particularly with respect to the description of the radiolarian internal structures based on material extracted from Devonian carbonate nodules. The late 1970s saw an expansion in studies that made extensive use of the SEM for the description of Paleozoic radiolarians, many of which had been extracted from chert using HF methods. The potential of radiolarians to unveil the structure and geodynamic evolution of Paleozoic orogenic belts stimulated taxonomic interest during the 1980s and 1990s, a prerequisite for the elaboration of radiolarian biostratigraphic schemes, which was successfully achieved for the upper Paleozoic. The fifth phase follows the discovery of well-preserved Middle Cambrian radiolarians from Australia at the end of the 20^th century and subsequent description by Won of beautifully preserved Cambrian and Ordovician fauna from western Newfoundland. Research on early Paleozoic radiolarians was the main driver for the increase of the number of new genera for the last two decades.

The purpose of this paper is to present a revised classification of Paleozoic radiolarians at the genus level in the form of a series of plates displaying the images of the type species of each genus. These photos are supplemented by an indication of the status of the genus decided by an international team of specialists in this fossil group (Chapter “The catalogue”). The catalogue itself is presented by orders and families. It is also possible to find a genus using the alphabetical list or the list according to the classification (Appendices 1 and 2). After some remarks that illustrate the complex task undertaken to reach a consensus, a “guide for users” is proposed.

This chapter is to be used as companion text with the companion chapter, an illustrated catalogue of Paleozoic radiolarian genera found in this volume, and serves the purpose of giving the reader explanation for any taxonomic operations undertaken during the course of constructing the catalogue. These operations refer to the status of the genera as valid, junior synonym, homonym, nomen nudum, nomen dubium, or not Radiolaria. We also include diagnoses and/or descriptions in the original language published, English translations where needed, and locality and age information for the type material.

The current knowledge of Paleozoic radiolarian ranges, proposed zonations, and faunal assemblages that have been used in biostratigraphy over the past few decades is compiled herein. More than 90 assemblages can currently be readily recognized and many of these, although regional in their construction, have elements that can be correlated throughout a widespread paleogeographic area. A number of the existing zonations utilize robust, relatively common, and easily recognized morphotypes that may be easily identified when they are moderately or even poorly preserved. These schemes are readily applied to deciphering stratigraphic complexities in complex orogenic belts. Other assemblages and zones summarized herein have been developed from well preserved materials, such as that from concretions, and their applicability to dating chert sequences remains relatively untested. Uneven geographic coverage is apparent, where some time periods are largely represented by only a few well known regional radiolarian rich units. There is also uneven temporal coverage, where certain time periods have few data. Undoubtedly, the Permian schemes are the most robust, relying heavily on data acquired from Asia, and to a lesser extent North America. The present work provides an opportunity to address critical gaps and opportunities for future work in radiolarian biostratigraphy, and to provide information on the ranges of biostratigraphically useful genera and species employed in the Paleozoic which can be used for both correlation and understanding the evolution of this important group.

This paper presents, for the first time, a complete list of Paleozoic radiolarian species (mainly Polycystina) described between 1880 and early 2016. It records 2323 names of taxa described originally as new species or subspecies that have been assigned to radiolarians. This list attempts to only provide an objective record without revision of taxonomic status, and thus includes invalid taxa, junior objective or subjective synonyms, nomina dubia and nomina nuda.