Problematic sclerites are common in Cambrian rocks around the world, but much less so in those of the Ordovician. Eurytholia prattensis new genus and species and E. elibata new species, described herein, are rare but widely distributed faunal elements in a narrow stratigraphical interval (Pygodus serra and P. anserinus conodont biozones) within Ordovician beds in an area bordering Iapetus (South Wales, UK; Alabama, USA; Dalarna, Sweden; and North Estonia). Specimens are minute plates (usually less than 1 mm wide), transversely ovoid, and hollow. They are not closely comparable with any previously described fossils. Eurytholia plates are interpreted as dorsal dermal sclerites from an animal of uncertain affinities. The scleritome is provisionally reconstructed as ovoid in form, with sclerites arranged in sub-longitudinal rows.

The lower Desmoinesian part of the Flechado Formation near Taos, New Mexico, contains a diverse marine fauna within predominantly dark gray shale and siltstone facies representing deposition in shallow marine environments adjacent to prograding lobes of a fan delta system. Gastropods are particularly abundant and diverse in a 60-m-thick section south of the town of Talpa; 157 species are described in this paper, including 19 new species and two new genera. New species are Euphemites hermosus, Luciellina ocultabanda, Spiroscala georgiannae, Glabrocingulum (Glabrocingulum) globosum, G. (Ananias) talpaensis, Worthenia legrandi, Cyclites diminutus, Platyzona hespera, Anomphalus? blancus, Stegocoelia (Donaldospira) taosensis, S. (Hypergonia) hoffmani, S. (H.) agraciada, Bicuerda procolumnare, new genus and species; Hermosanema varium, new genus and species, Pseudozygopleura (Stephanozyga) granda, P. (S.) lisaspira, Hemizyga (Hemizyga) larga, Strobeus immanis, and Meekospira delgada. Species of Pleurotomarioidea, Neritoidea, Trochoidea, and Murchisonioidea comprise 64 percent of the total gastropod specimens, with most specimens of each of the last three groups being contributed by large numbers of one or two very abundant species. The 20 most abundant species are represented by about 65 percent of all specimens, whereas 62 species (39 percent of total species richness, but only 1.1 percent of all specimens) are represented by six or fewer specimens, illustrating the significant contribution of rare species to total species richness. The Flechado gastropod fauna contains many species known from Desmoinesian strata in the Midcontinent and Appalachian Basin regions of the U.S.; many elements of Desmoinesian gastropod assemblages were distributed widely in shallow marine environments across North America. Potential paleogeographic barriers in the Colorado–New Mexico region, however, may have facilitated evolution of some endemic species in this area.

In many species of lower Paleozoic trepostomes (Bryozoa; class Stenolaemata) transverse partitions called skeletal diaphragms differentiated feeding from non-feeding regions of colonies. It has been thought that each diaphragm floored the living chamber of a feeding polypide. However, analysis of skeletal growth patterns has shown that many diaphragms were too close to colony surfaces or too closely spaced in ontogenetic sequences to have accommodated feeding polypides at any given life horizon. Apparently colonies were capable of maintenance and even robust growth with reduced numbers of active polypides, an interpretation supported by comparison with living stenolaemates.

A synthesis of the inferred functions of colonies of the extinct trepostomes with post-Triassic fossil and living stenolaemates suggests that walls of trepostome autozooids grew continuously outward so that living chambers starting from their basal diaphragms ranged from shallow to full-sized on colony surfaces. Under-sized polypides apparently grew with their under-sized living chambers and fed as they regenerated to full size, as in living stenolaemates. Actively feeding colony surfaces included autozooids either having polypides at similar or different stages of polypide regeneration, or fully regenerated. Nonfeeding colony surfaces included autozooids either having degenerated polypides, autozooids with diaphragms too closely spaced to skeletal apertures to have housed polypides, or possibly, autozooids that stopped skeletal growth in proximal regions of some large colonies.

With this issue we mark publication of the 75th volume of the Journal of Paleontology, and celebrate the occasion with a series of review articles on the systematics of major groups of fossils. Instructions to authors were very broad: we suggested consideration of the history of study, current problems, and future directions, but otherwise left authors to focus their reviews as they saw fit. We hoped in this way, with a mix of traditions and approaches, to fashion a general overview of the systematics of fossil organisms as practiced today. With the enthusiastic efforts of the contributors, I think we've been successful. The papers in this issue comprise authoritative reviews of the state of the art in various branches of paleontology. But even if one is not concerned with the details of particular groups, the contributions provide a fascinating sense of where the discipline is, and where it might be going. Although concerned mainly with systematic history, they nevertheless provide a flavor of the kinds of concerns we have as a community for the future development of our science.

The Scotty Wash Formation on the Nevada Test Site (NTS), southern Nye County, Nevada has produced the first North American representatives of the globally significant index ammonoids Homoceras s.s. and Isohomoceras s.s. and contains the only ammonoid succession across an uninterrupted mid-Carboniferous boundary sequence known in North America.

Four ammonoid assemblages can be recognized at NTS that are homotaxial with the reference successions for the middle and upper Arnsbergian (E2) and Chokierian (H1) Stages, Namurian Series, in western Europe, and their equivalents worldwide. The upper Mississippian (Chesterian) portions of the NTS sections yield assemblages referable to a Eumorphoceras girtyi Ammonoid Biozone, representing the middle Arnsbergian Stage (E2b), followed by a Delepinoceras thalassoide Ammonoid Biozone, equivalent to the upper Arnsbergian Stage (E2c). The latter ammonoid biozone also occurs in the Imo and Rhoda Creek Formations of Arkansas and Oklahoma, requiring reassignment of those formations to the upper Arnsbergian Stage (E2c). The appearance of the Isohomoceras subglobosum Ammonoid Biozone marks the base of the Chokierian Stage (H1a) at NTS. The zonal name-bearer continues into lower Pennsylvanian (Morrowan) strata, where it joins the Homoceras coronatum coronatum Ammonoid Biozone assemblage in an interval equivalent to the upper Chokerian Series (H1b). A pronounced unconformity at NTS separates the Scotty Wash Formation from the overlying Tippipah Limestone, which contains a fifth ammonoid assemblage characterized by Cancelloceras cf. C. elegans that is equivalent to the Yeadonian Stage (G1), Namurian Series, of western Europe.

The conodont succession recovered from the ammonoid-bearing sections at NTS allows refined correlation of the Arnsbergian and Chokierian Stages with the Mid-Carboniferous Global Stratotype Section and Point (GSSP) at nearby Arrow Canyon, Nevada, and the North American midcontinent. The Lower Rhachistognathus muricatus Conodont Biozone of western North America is equivalent to the upper Arnsbergian Stage (E2c), and must include the upper portion of the Adetognathus unicornis Conodont Biozone as recognized in the midcontinent. The Upper R. muricatus Conodont Biozone is equivalent to that portion of the Chokierian Stage (H1a) below the appearance of Declinognathodus noduliferus, marking the mid-Carboniferous boundary horizon, including some of the R. primus Conodont Biozone as used in the North American midcontinent. The intercontinental mid-Carboniferous boundary, drawn at the appearance of D. noduliferus, does not correspond to the Arnsbergian-Chokierian Stage boundary (E2c-H1a) that is defined by the appearance of Isohomoceras subglobosum. A significant break occurs in the Arrow Canyon GSSP less than 4 m above the position of the mid-Carboniferous boundary, where Chokerian strata (H1) are probably succeeded by Kinderscoutian strata (R1). Higher at Arrow Canyon, the position of the Scotty Wash-Tippipah unconformity juxtaposes Kinderscoutian and Yeadonian (G1) strata and the entire upper Namurian Series is limited to no more than 54 m.

Comparison of Eurasian and North American ammonoid assemblage compositions suggests that at least intermittent faunal interchange persisted between the two regions until at least the close of the Chokierian.

Definition of the Mississippian-Pennsylvanian boundary, which has never been defined faunally in either type area, to correspond to the intercontinental mid-Carboniferous boundary would be compatible with relationships known in the Chesterian and Morrowan type areas.

Taxonomic treatment of the Chokierian ammonoid assemblage from Syncline Ridge, NTS provided herein includes Proshumardites karpinskii Rauser-Tschernoussova, 1928; Eosyngastrioceras inexpectans Titus, 2000; Somoholites cf. S. merriami (Miller and Furnish, 1940b); Euroceras ellipsoidale Ruzhencev and Bogoslovskaya, 1971a; Isohomoceras subglobosum (Bisat, 1924); Homoceras diadema (Beyrich, 1837); H. coronatum coronatum (Haug, 1898); and H. leedomi new species.

Phylogenetic reconstructions of two tropical American venerid genera, Chione and Chionopsis (subfamily Chioninae) were attempted at the species-level. The purposes of the analyses were to provide historical reconstructions of origination and extinction events in the two clades, as well as patterns of invasion and diversification. The analyses were based entirely on conchological characters to facilitate the inclusion of a substantial number of fossil taxa, but difficulties were encountered due to the quality of preservation and availability of material. Nevertheless the two genera were established as monophyletic clades, and the reconstructions yielded considerable insight into their histories in tropical America. The analyses suggest that both genera originated in the tropical western Atlantic, Chionopsis by at least the early Oligocene, and Chione in the early Miocene. Various branches of both genera subsequently invaded the tropical eastern Pacific several times prior to Seaway closure, with only one possible reciprocal invasion of the western Atlantic. Pliocene extinction affected both genera more significantly in the western Atlantic relative to the eastern Pacific, and diversity is higher today in the latter region. These conclusions are not entirely consistent with the fossil records of the genera, but this incongruency highlights the need for much more extensive sampling of the eastern Pacific Cenozoic record.

Exceptionally large quantities of outstandingly well-preserved, free specimens of larger foraminifera from late Miocene sediments of the Dominican Republic invite an analysis of their structure in detail. The structures of the porcelaneous larger foraminifera reveal that most of them are not candidates for a direct ancestry of the species living today in the Caribbean. Although the late Miocene period has produced Caribbean endemists, in particular within the agglutinated group of the textulariellids and the lamellar-perforate group of the amphisteginids, the porcelaneous archaiasines and soritines are more closely related to the early Miocene forms of the Neotethys than to the Recent Caribbean endemists. These relationships are derived from their relative structural similarity and call for the proposition of appropriate additional taxa on the generic and specific levels. Miocene Miarchaias new genus develops several centimeters large, cyclical agamonts with meandropsinid structures covering the lateral surface of the disc (M. meander new species) whereas species of smaller shell size do not have cyclical generations (M. modestus new species). On the other hand, populations of cyclical schizonts and/or gamonts exhibit structures similar to the Recent, spiral Androsina: Androsinopsis radians new genus and species. The other new taxa erected here, Annulosorites spiralis new genus and species and Cyclorbiculina miocaenica new species, reflect differences in the apertural face and the respective arrangement of radial partitions as used to differentiate Recent Sorites from Amphisorus. Specimens to be attributed to the genera Cycloputeolina and Parasorites are present in the late Miocene of the Dominican Republic. They exhibit an exoskeleton in contrast to true soritids, and will need an eventual worldwide revision on the species level.

Through an examination of the contents of the Journal of Paleontology (JP), this paper traces the growing interest in biological problems in mid twentieth-century invertebrate paleontology. While noting the continued dominance of descriptive morphology and systematics, the paper tracks the increasing attention paid to paleoecology, evolution and geographic distribution, and quantitative methods. An analysis of the debate over the relative importance of biology and geology for paleontology, and J. Marvin Weller's evolving views on the subject, further illustrate the main point. Neither Welter nor JP initiated the interest in biological questions, but both played an important role in bringing new developments to the attention of the paleontology community.

Linguliform brachiopods were recovered from the Upper Cambrian Downes Point Member (lower Sunwaptan) and from the Middle Ordovician Factory Cove Member (Arenig) of the Shallow Bay Formation, Cow Head Group, of western Newfoundland. These rocks are a series of Middle Cambrian to Middle Ordovician conglomerates, lime mudstones, and shales that formed a sediment apron at the base of the lower Paleozoic continental slope of Laurentia. The linguliform brachiopod fauna consists of sixteen species assigned to twelve genera. Three new species are described: Picnotreta lophocracenta, Neotreta humberensis, and Siphonotretella parvaducta.

Through a review of older type collections and identifications of undescribed collections, using a broad species definition, the Devonian succession is divided into 10 assemblages. The names of many species are revised. With the exception of the Pragian, all stages of the system are represented by one or more assemblages. The ranges of important taxa are plotted and shown to be relatively short and diagnostic of the 10 intervals. In the absence of conodonts in the reef facies, stromatoporoids offer a supplementary method of correlation. Many species occurring in Canada can be recognized in the stromatoporoid faunas of the former Soviet Union, China, Europe, and Australia.

The Middle Permian Chihsia and Maokou formations in Laibin, central Guangxi, South China contain 19 rugose coral species; of these taxa, Lophocarinophyllum sandoi, Asserculinia solida, and Innixiphyllum wuae are new. Innixiphyllum represents a new genus characterized by contratingent minor septa. Ten species are reviewed and described in detail, and the diagnoses of three of these species, Allotropiophyllum heteroseptatum (Grabau, 1928), Lophocarinophyllum taihuense (Yan and Chen, 1982), and Ipciphyllum regulare (Wu, 1963), are newly emended. The morphological variation and ontogenetic changes of the solitary, nondissepimented species are particularly emphasized. Six additional taxa are described and illustrated but are left in open nomenclature.

The corals from Laibin are typically Tethyan. Four biostratigraphic assemblages are recognized: an assemblage of massive corals in the upper Chihsia Formation represented by Polythecalis longliensis; an assemblage of small solitary and nondissepimented corals in the lower Maokou Formation, dominated by species of Allotropiophyllum, Innixiphyllum and Lophocarinophyllum; an assemblage of mixed massive colonial and small solitary corals in the middle Maokou Formation, characterized by Ipciphyllum regulare; and an assemblage of solitary nondissepimented corals in the uppermost Maokou Formation, characterized by Ufimia elongata. These assemblages correspond well to those from other areas of South China. In Laibin, only two rugose taxa, Amplexocarinia sp. and Paracaninia minor, occur in the basal part of the Wuchiaping Formation of Lopingian age.

Archaeocyaths are calcareous, conical, Cambrian fossils with a long history of phylogenetic uncertainty and changing interpretations. The history of phylogenetic interpretation of archaeocyaths reveals five distinct schools of thought: the coelenterate school, the sponge school, the algae school, the Phylum Archaeocyatha school, and the Kingdom Archaeata school. Late nineteenth century and early twentieth century paleontologists worked within a paradigm of inexorably increasing diversity through time, and they did not believe in the concept of extinct phyla. Consequently, prior to about 1950, archaeocyaths were bounced around from coelenterates to sponges, to algae. By the 1930s, after considerable study, all workers agreed that archaeocyaths were sponges of one type or another. In the mid-twentieth century a significant paradigm shift occurred in paleontology, allowing the viability of the concept of a phylum with no extant species. Correspondingly, two new schools of thought emerged regarding archaeocyathan taxonomy. The Phylum Archaeocyatha school placed them in their own phylum, which was inferred to be closely related to Phylum Porifera within Subkingdom Parazoa. A second new school removed archaeocyaths and some other Paleozoic problematica from the animal kingdom and placed them in Kingdom Archaeata (later Kingdom Inferibionta). The Phylum Archaeocyatha school was the mainstream interpretation from the 1950s through the 1980s. However, the widespread use of SCUBA beginning in the 1960s ultimately led to the rejection of the interpretation that archaeocyaths belong in a separate phylum. SCUBA allowed biologists to study deep fore-reef and submarine cave environments, leading to the discovery of living calcareous sponges, including one aspiculate species that is morphologically similar to archaeocyaths. These discoveries in the 1960s and 1970s stimulated a re-examination of sponge phylogeny generally, and comparisons between archaeocyaths and sponges in particular. The result was the abandonment of the Phylum Archaeocyatha school in the 1990s. Present consensus is that archaeocyaths represent both a clade and a grade—Class Archaeocyatha and the archaeocyathan morphological grade—within Phylum Porifera.