Low to moderately highly-diverse ostracode assemblages containing a total of 49 taxa occur in the Imo Formation (Mississippian, Chesterian) in north central Arkansas. The less diverse assemblages are dominated by the platycope Cavellina, while the more diverse are dominated by the palaeocopes Hollinella, Gortanella, Amphissites, Sargentina, and Deloia; the leiocopes Proparaparchites and Shivaella; and the metacopes Healdia and Healdioides. The change in assemblages up section in the central portion of the formation indicates a deepening of water with variations in the amount of influx of terrigenous clastics in a nearshore marine environment.

New taxa described include Aechminella prostata, Cornigella laterispinosa, Hollinella (H.) imoensis, H. (H.) denotata, Pseudokegelites dorsopeltatus new genus and species, Polytylites oblongus, Glyptopleuroides inregularis, Oliganisus amictus, Doricranos incohatus new genus and species, Knoxina sohni, Proparaparchites ignotus, Shivaella juxarecta, Orthobairdia redacta, Monoceratina arkansasana, Healdioides retusus, H. commensuratus, Seminolites orthapsis, Venula elegantula, Prodigious rostratus new genus and species, and Microcheilinella? lenticularis.

Several polyplacophoran plates are preserved as external molds in the Lower Permian Rio Genoa Formation, Chubut Province, Argentina. These are the first reported Permian polyplacophorans from South America. The new genus and species Asketochiton chubutensis is described based on this material.

Sphenothallus and fossils similar to Sphenothallus are found in Ordovician, Devonian, and Mississippian rock units in Ohio and adjacent states and provinces. Although the Ordovician of Québec, Ontario, and Indiana has yielded parts of tubes, Ordovician specimens from southwest Ohio and nearby areas consist almost entirely of holdfasts on hardgrounds and shelly fossils. Sphenothallus is abundant in the Chagrin Shale (Famennian) of northeast Ohio where it is found in about four percent of concretions that contain identifiable fossils. The Chagrin specimens, usually parts of tubes, are occasionally preserved three-dimensionally. The rate of distal expansion of Chagrin Sphenothallus tubes varies intraspecifically; thus, this rate cannot be used to distinguish species. Some Chagrin specimens are attached to larger, conspecific specimens and to articulate brachiopods. Brachiopods have also been found attached to Chagrin Sphenothallus. Bedford-Berea sequence (Famennian) specimens from northern Kentucky and Meadville Member (Kinderhookian or Osagian) specimens from the Cuyahoga Formation of northeast Ohio are usually preserved as flattened tubes. In both occurrences tubes are similar in width, indicating that individuals in each assemblage are probably the same age. Meadville tubes possess characteristics diagnostic of Sphenothallus, but Bedford-Berea specimens, which lack longitudinal thickenings and exhibit little tube tapering, cannot be assigned to Sphenothallus sensu strictu.

Sphenothallus was a gregarious, opportunistic species, tolerant of dysaerobic conditions and able to colonize environments ranging from hardgrounds to soft, muddy sea bottoms. No distinct branching was observed among the Chagrin, Bedford-Berea, or Meadville specimens, suggesting that larval dispersal was the primary mode of reproduction for the genus.

Fifteen species of Late Permian bryozoans occur in a biohermal bank in the Mission Argillite of northeastern Washington. These include two species conspecific with species described from Japan and 13 new species, one of which is the type species of a new genus. The presence of two species, Dyscritella iwaizakiensis Sakagami, 1961, and Hayasakapora cf. erectoradiata Sakagami, 1960, previously reported from Japan, and the similarity of new species with those previously described from Japan, China and Russia supports the idea that these rocks were originally deposited in the southeastern or central western Pacific Ocean and subsequently accreted to the North American Plate.

Bryozoans and previously reported fusulinids indicate that the biohermal bank is latest Wordian (Kazanian).

Newly described bryozoans include the new genus and type species Sakagamiina easternensis belonging to the Timanodictyidae. Other new species are Fistuliramus pacificus, Meekoporella inflecta, Neoeridotrypella missionensis, Coeloclemis urhausenii, Tabulipora colvillensis, Rhombotrypella kettlensis, Pamirella oculus, Pinegopora petita, Wjatkella nanea, Alternifenestella vagrantia, Polypora arbusca, and Mackinneyella stylettia.

Many trilobite species of the order Agnostida have short stratigraphic ranges and global distribution in open-marine deposits. They are most abundant and most diverse from about the middle Middle Cambrian to the middle Upper Cambrian where they are proving to be excellent biostratigraphic indices. We describe unusually rich agnostoid faunas of that age from two thick, well-exposed sections, one near Paibi and one near Wangcun, in northwestern Hunan Province, China. All collections are from the Huaqiao Formation, the definition of which is revised and its stratigraphic content is expanded. Most of the fossils are well preserved in dark, laminated, argillaceous carbonates that were deposited in lower slope environments. These are assigned to 76 species and 33 genera. New species described are Agnostus? babcocki, Ammagnostus? cryptus, Ammagnostus histus, Ammagnostus hunanensis, Ammagnostus wangcunensis, Baltagnostus? ambonus, Linguagnostus stenus, Lisogoragnostus hybus, Lisogoragnostus mictus, and Utagnostus songae. Species reassigned in a new generic combination are Ammagnostus laiwuensis (Lorenz, 1906), Glaberagnostus? cicer (Tullberg, 1880), Kormagnostus minutus (Schrank, 1975), and Pseudophalacroma scanense (Westergård, 1946). The subfamily Ammagnostinae öpik, 1967, is elevated to family rank.

The bases of eight agnostoid biozones are defined by the lowest occurrence of a common species having a relatively short stratigraphic range and wide geographic distribution. In ascending order, these zones are named for Ptychagnostus atavus, Ptychagnostus punctuosus, Goniagnostus nathorsti, Lejopyge laevigata, Proagnostus bulbus, Linguagnostus reconditus, Glyptagnostus stolidotus, and Glyptagnostus reticulatus. Each zone is further characterized by an assemblage of agnostoid species that may vary from place to place. By extrapolating from recently published uranium-lead geochronology, we estimate that the average duration of these agnostoid zones was approximately one million years.

Formal division of the Cambrian System into global series and stages is a current project of the International Subcommission on Cambrian Stratigraphy. If the base of an upper Cambrian series of whatever name is selected to correlate closely with the traditional Middle-Upper Cambrian boundary in Europe, we propose the base of the Linguagnostus reconditus Zone in the Wangcun section as a potential Global Standard Stratotype-section and Point (GSSP). Alternatively, if the base of an upper Cambrian series is selected to coincide with the base of the Glyptagnostus reticulatus Zone, we propose the base of that zone in the Paibi section as a potential GSSP.

Access to the dimension of time makes paleontology unique as a discipline, and it is stratigraphical data that allows paleontologists to tackle a wide range of evolutionary questions unanswerable by neontologists. Some of these need only a vague and imprecise hypothesis of evolutionary relationships. For example, considerable headway has been made in documenting the evolution of morphological disparity with only the crudest of phylogenetic information (Foote, 1997). However, it is undoubtedly true that more precise and probing questions can be formulated if accurate phylogenies were available. But how do we construct such phylogenies?

Gnamptorhynchos, a rhynchonellid-like orthid brachiopod, evolved from Platystrophia in Maysvillian (early Ashgill) time, and survived both the end-Richmondian and end-Hirnantian episodes of the latest Ordovician mass extinction. The name of the type species of Gnamptorhynchos, G. inversum Jin, 1989, is rejected and replaced by Gnamptorhynchos globatum (Twenhofel, 1928), which is a senior synonym. Gnamptorhynchos manitobensis new species is described here from the Selkirk Member (Maysvillian) of the Red River Formation, southern Manitoba. The new species is characterized by a transversely extended, strongly biconvex to globular shell with prominent umbones, relatively numerous costae and a notothyrial cavity supported dorsally by a short median ridge. It constituted part of a Late Ordovician epicontinental fauna that once spread widely in shallow, equatorial seas of North America. The new species is a morphological intermediate between Platystrophia and Gnamptorhynchos, with Platystrophia-like interareas, hingeline, and cardinal process, but Gnamptorhynchos-like shell posterior and notothyrial platform. Previously, Gnamptorhynchos was known from Hirnantian to mid-Aeronian rocks. The new species extends the lower range of the genus to Maysvillian.

The distinctive cheilostome bryozoan Stictostega durhami Shaw, 1967, from the Upper Campanian Ozan Formation of Arkansas, is redescribed and its relationships are reconsidered. Originally interpreted as a hippothoid ascophoran, the presence of a cryptocystal frontal shield and other characters suggest that it is a coilostegan anascan. Pores in the frontal shield are inferred to have served for the passage of parietal muscles (or their ligaments), which operated on the frontal membrane to raise hydrostatic pressure and protrude the lophophore in the same way as recently demonstrated in living Macropora. Stictostega is provisionally interpreted as a stem-group macroporid.

Phosphorites of the uppermost Neoproterozoic Doushantuo Formation (ca. 570 ± 20 Ma) exposed at Weng'an, South China, contain globular microfossils characterized by distinctively sculpted outer coverings and precise patterns of cell division. Forms assigned to the genera Megasphaera and Parapandorina were originally interpreted as problematica and volvocacean green algae, respectively, but newly discovered populations support their reinterpretation as the eggs and embryos of early animals. The fossils' large size (about half a millimeter in diameter), persistent enveloping membrane, precise cleavage pattern, and inferred physiology are fundamentally different from those of volvocaceans or other algae, but are expected features of animal embryos preserved in early stages of cleavage. In this light, Megasphaera is interpreted as an egg enveloped within its egg case, and Parapandorina represents equally and totally cleaving stereoblastulas. Despite their exquisite preservation, the phylogenetic placement of Megasphaera and Parapandorina cannot be resolved with confidence, due largely to the absence of recognizable adult morphologies to which they might be linked. Individual characters of Megasphaera and Parapandorina can be found in eggs and embryos of extant sponges, cnidarians, and bilaterians.

Three other distinctive globular forms, Megaclonophycus onustus, Caveasphaera costata n. gen. and sp., and Spiralicellula? bulbifera? occur in the same deposit. Interpretations of these fossils are more problematic, although they may also be animal embryos.

Extraordinarily large, thick shelled polyplacophorans occur in the Permian limestone in the province of Perak, Malaysia. Three new genera and species are proposed: Hadrochiton pileus, Pyknochiton lunatus, and Kraterochiton magnificus. The occurrence of K. magnificus extends the range of the family Acutichitonidae into the Middle Permian.

A new genus and species of tentaculitid, Hidagaienites arcuatus, is described from calcareous beds near the Carboniferous–Permian boundary in the Hida-Gaien Terrane, Central Japan. Its mode of occurrence excludes the possibility that the specimens are derived from older strata. Thus, this tentaculitid represents the youngest record of the class Tentaculitoidea, which was previously thought to have become extinct in the Late Devonian.

A silicified fauna from the early Permian Coyote Butte Limestone within the Grindstone terrane of central Oregon contains a diverse fauna including five polyplacophorans, one rostroconch, and one problematic taxa. New taxa include Gryphochiton planoplata new species, Arcochiton soccus new species, Homeochiton triangularis new genus and species, Arceodomus sphairikos new species, and Diadeloplax apiculatus new species.

Forty species of gastropods (six of them new: Calliomphalus (Planolateralus) mexcalensis, Nododelphinula diminuta, Potamides temalacensis, Ptychopotamides ancestralus, Amaurellina guerrera, and Drilluta gloriae), and 13 species of bivalves are described from the lower Maastrichtian marls of the basal Mexcala Formation from Guerrero State, southern Mexico. Age interpretation was based on planktic foraminiferans. Associated fauna includes planktic and benthic foraminiferans, ostracods, solitary corals, crustaceans, echinoids, and vertebrates. The distribution of bivalve and gastropod species suggests that this area has affinities with the Gulf Coast Plain Province of the United States, although some species also are reported from the Middle East, Europe, and South America.

Tubes suspected to be those of vestimentiferan worms are abundant in carbonate boulders at one locality in the lower Oligocene part of the Lincoln Creek Formation along the Canyon River, Grays Harbor County, Washington. The largest tubes exhibit the same general orientation and are arranged in clusters. The tube walls are preserved as aragonite that is, in some cases, replaced by silica. The original tube walls either had a high carbonate content or were indurated very early by aragonite mineralization of the organic wall. The carbonate cements around, on, and inside of the tubes were precipitated due to the microbial oxidation of hydrocarbons at a cold-seep. After lithification, the carbonate fragmented as it slid or slumped, along with other sedimentary debris, downslope into deeper waters. This is one of the few reports of an ancient cold-seep chemosynthetic community dominated by tube worms, and the third report of an allochthonous cold-seep carbonate within a deep-water depositional setting.

Moderately well-preserved Late Permian to Middle Triassic radiolarians are identified in chert beds that occur in the Shan-Thai Block of northern Thailand. These radiolarians are identical to the faunas of the Late Permian Neoalbaillella ornithoformis and N. optima Assemblage Zones and the Triassic Parentactinia nakatsugawaensis and Triassocampe coronata Assemblage Zones reported in chert sequences of Japan. We discovered the radiolarian faunas, apparently indicating Late Permian and Early Triassic ages, in almost continuous sequences of chert and shale exposed in the north of Chiang Mai. The occurrence of these radiolarian faunas provides important data to solve the P/T (Permian/Triassic) boundary in pelagic sequences. Our present discovery also furnishes significant data to reconstruct the paleobiogeography of Mainland Thailand during Late Permian to Middle Triassic times. Fifty species belonging to 35 genera, including three unidentified genera, are investigated taxonomically. Four new species Pseudospongoprunum? chiangdaoensis, Cenosphaera igoi, Cenosphaera? rugosa, and Tlecerina? apsornae are described.