Latest Precambrian through Early Cambrian tectonic history and stratigraphy are comparable in southeastern Cape Breton Island and the western Placentia–Bonavista axis, southeastern Newfoundland. The lithostratigraphic nomenclature of southeastern Newfoundland is used for this interval in Cape Breton Island. Upper Precambrian volcanic rocks of the Forchu Group (=“Giant Lake Complex,’ designation abandoned) are unconformably overlain by uppermost Precambrian through lowest Cambrian strata termed the “Morrison River Formation’ (designation abandoned). This depositional sequence consists of three formations: 1) red beds through tidalites of the Rencontre Formation (to 279+ m; =“Kelvin Lake Formation,’ designation abandoned); 2) prodeltaic clastics of the Chapel Island Formation (to 260 m); and 3) macrotidal quartzites of the Random Formation (to 71 + m). Post-Random block faulting and 300 m of local erosion took place prior to onlap of the “MacCodrum Formation’ (abandoned). Siliciclastic mudstones of the lower “MacCodrum’ are re-assigned to the middle Lower Cambrian Bonavista Group. Sub-trilobitic faunas from the Bonavista Group include “Ladatheca’ cylindrica from the West Centre Cove Formation(?) and higher diversity faunas (23 species) in the Camenella baltica Zone of the Cuslett and Fosters Point Formations. Trilobite-bearing, upper Lower Cambrian (Branchian Series) strata (Brigus Formation, =upper “MacCodrum’ and overlying “Canoe Brook’ Formations) unconformably overlie the Placentian Series in Cape Breton Island, southeastern Newfoundland, Shropshire, and, probably, eastern Massachusetts. Correlations based on small shelly fossils indicate an earlier appearance of trilobites in Avalon than on the South China Platform. Twenty-six species are illustrated. Halkieria fordi n. sp., the conodont(?) “Rushtonites’ asiatica n. sp., and the zhijinitid(?) Samsanoffoclavus matthewi n. gen. and sp. are described. Ischyrinia? sp. may be the oldest ischyrinoid rostroconch.

This paper serves two roles. First, it acts as an introduction to Blender, an open-source computer graphics program, which can be of utility to paleontologists. To lessen the software's otherwise steep learning curve, a step-by-step guide to create an idealized reconstruction of a fossil in the form of a three-dimensional model in Blender, or to use the software to render results from ‘virtual paleontology' techniques, is provided as an online supplemental data file. Second, here we demonstrate the use of Blender with a case study on the extinct trigonotarbid arachnids. We report the limb articulations of members of the Devonian genus Palaeocharinus on the basis of exceptionally preserved fossils from the Rhynie Cherts of Scotland. We use these newly reported articulations to create a Blender model, and draw comparisons with the gait of extant arachnids to produce as accurate a representation of the trigonotarbid flexing its limbs and walking as possible, presented in additional online supplemental data files. Knowledge of the limb articulations of trigonotarbid arachnids also allows us to discuss their functional morphology: trigonotarbids' limbs and gait were likely comparable to extant cursorial spiders, but lacked some innovations seen in more derived arachnids.

Newly obtained foraminifer faunas from the Permian-Triassic (P-Tr) transition at the Dajiang and Bianyang sections in the Nanpanjiang Basin, South China, comprise 61 species in 40 genera. They belong to the Palaeofusulina sinensis Zone, the youngest Permian foraminifer zone in South China. Quantitative analysis reveals that the last occurrences of more than a half of species (28/54) fall into a 60-cm-interval at the uppermost Changhsingian skeletal packstone unit and thus calibrate the end-Permian extinction to the skeletal packstonecalcimicrobial framestone boundary. About 93% (54/58) of species of the latest Permian assemblage became extinct in the P-Tr crisis. Four major foraminiferal groups, the Miliolida, Fusulinida, Lagenida, and Textulariina, have extinction rates up to 100%, 96%, 92%, and 50%, respectively, and thus experienced selective extinctions. Both Hemigordius longus and ?Globivalvulina bulloides temporarily survived the end-Permian extinction event and extended into the earliest Triassic but became extinct soon after. The post-extinction foraminifer assemblage is characterized by the presence of both disaster taxa and Lazarus taxa. Foraminifer distribution near the P-Tr boundary also reveals that the irregular contact surface at the uppermost Permian may be created by a massive submarine dissolution event, which may be coeval with the end-Permian mass extinction. A new species, Rectostipulina hexamerata, is described here.

Black Mesa in northeastern Arizona exposes sediments of late Cenomanian–Turonian age deposited during the transgressive–regressive Greenhorn cyclothem. These sediments contain a diverse selachian fauna that consists of 21 taxa: Hybodus sp., Ptychodus whipplei, P. decurrens, P. cf. P. mammillaris, Chiloscyllium greeni, Chiloscyllium sp., Scapanorhynchus raphiodon, Cretodus semiplicatus, Cretolamna appendiculata, C. woodwardi, Cretoxyrhina mantelli, cf. Leptostyrax sp., Squalicorax falcatus, Rhinobatos sp., Pseudohypolophus mcnultyi, Protoplatyrhina hopii n. sp., Ischyrhiza schneideri, I. avonicola, Onchopristis dunklei, Ptychotrygon triangularis, P. rubyae n. sp., and five types of dermal denticles. Two selachian assemblages, a nearshore and a deeper water assemblage, are present in this fauna. Though there is some provincialism in North Africa, Europe, and North America during the Greenhorn marine cycle, the wide dispersion of some shark taxa and the great similarities between widely separated selachian faunas are striking.

Eighteen gastropod and seven bivalve species are reported from Eocene to Oligocene cold-seep carbonates in Washington State, USA. Four species are new (Niso littlei, Turrinosyrinx hickmanae, Xanthodaphne? campbellae, and Lurifax goederti), and 16 are described in open nomenclature. Previously unknown features of protoconch or prodissoconch morphology and/or shell microstructure are provided for Retiskenea statura (Goedert and Benham), Provanna antiqua Squires, Nuculana? aff. N. grasslei Allen, and Bathymodiolus willapaensis (Squires and Goedert). Modiolus (M.) willapaensis is placed within Bathymodiolus based on the elliptical-triangular shape of its juvenile shell, indicating that the divergence between vent/seep and whale/wood-fall inhabiting bathymodiolines took place at least 40 Ma. The first fossil species of the vent/seep genera Pyropelta (Pyropeltidae), Lurifax (family uncertain), and Catillopecten? (Propeamussidae) are reported. Niso (Eulimidae), Xanthodaphne, Turrinosyrinx, Benthomangelia (Turridae), Ledella (Nuculanidae), Tindaria? (Tindariidae), and Delectopecten (Pectinidae) are reported for the first time from fossil cold-seep assemblages. Larval developmental strategies are inferred from protoconch and prodissoconch morphologies in 14 species, which largely reflect the species' phylogenetic groups, as in modern vent and seep molluscs. The data presented here indicate that the radiation of toxoglossate turrids (Gastropoda) into deep water took place already in the Oligocene, and not in the Miocene as previously thought. Healed shell injuries and presumed naticid drill holes represent the oldest known fossil evidence of predation at cold-seeps.

Carbonaceous bedded cherts of the late Neoproterozoic (Cryogenian) ∼800 to 750 Ma old Chichkan Formation of South Kazakhstan contain an abundant, diverse assemblage of exquisitely preserved microorganisms. Like many Proterozoic microbiotas, the Chichkan assemblage is dominated by prokaryotic cyanobacteria, both filamentous (oscillatorialeans and nostocaleans, represented primarily by cellular trichomes and empty sheaths) and coccoidal (chroococcaleans and pleurocapsaleans, including solitary, colonial, and stalk-forming specimens). However, unlike Proterozoic microbiotas reported from peritidal settings, the Chichkan fossils, permineralized in cherts deposited in the open shelf facies of the formation, include diverse microscopic eukaryotes: vase-shaped testate amoebae, spiny (acanthomorphic) phytoplanktonic unicells, large (up to ∼1 mm diameter) megasphaeromorphic acritarchs, and sausage-shaped vaucheriacean green alga-like filaments.

Given the composition of this biota and the presence in it and similarly aged assemblages of numerous taxa typical of late Neoproterozoic deposits (e.g., Cerebrosphaera, Jacutianema, Melanocyrillium, Stictosphaeridium, Trachyhystrichosphaera, and Vandalosphaeridium), the Chichkan Lagerstätte appears representative of the Cryogenian biota as now known, thereby documenting the status of the marine biosphere at a time closely preceding the radiation of the Metazoa. As such, we interpret this and other coeval mixed assemblages of prokaryotic and eukaryotic microfossils as representing an evolutionary stage transitional between the predominantly prokaryote-dominated Precambrian and the eukaryote-dominated Phanerozoic biospheres.

As reported here, the Chichkan assemblage is composed of 39 taxa (of which two forms are described informally) that are assigned to 23 genera of microscopic prokaryotes and eukaryotes and that include two new species: Polybessurus crassus n. sp. and Vandalosphaeridium koksuicum n. sp.

Light microscope and scanning electron microscope observations on new material of unicellular microfossils Dictyosphaera macroreticulata and Shuiyousphaeridium macroreticulatum, from the Mesoproterozoic Ruyang Group in China, provide insights into the microorganisms’ biological affinity, life cycle and cellular complexity. Gigantosphaeridium fibratum n. gen. et sp., is described and is one of the largest Mesoproterozoic microfossils recorded. Phenotypic characters of vesicle ornamentation and excystment structures, properties of resistance and cell wall structure in Dictyosphaera and Shuiyousphaeridium are all diagnostic of microalgal cysts. The wide size ranges of the various morphotypes indicate growth phases compatible with the development of reproductive cysts. Conspecific biologically, each morphotype represents an asexual (resting cyst) or sexual (zygotic cyst) stage in the life cycle, respectively. We reconstruct this hypothetical life cycle and infer that the organism demonstrates a reproductive strategy of alternation of heteromorphic generations. Similarly in Gigantosphaeridium, a metabolically expensive vesicle with processes suggests its protective role as a zygotic cyst. In combination with all these characters and from the resemblance to extant green algae, we propose the placement of these ancient microorganisms in the stem group of Chloroplastida (Viridiplantae). A cell wall composed of primary and secondary layers in Dictyosphaera and Shuiyouisphaeridium required a high cellular complexity for their synthesis and the presence of an endomembrane system and the Golgi apparatus. The plastid was also present, accepting the organism was photosynthetic. The biota reveals a high degree of morphological and cell structural complexity, and provides an insight into ongoing eukaryotic evolution and the development of complex life cycles with sexual reproduction by 1200 Ma.

Restudy of upper Pliocene (ca. 2.4-1.8 Ma) and possible lower Pleistocene dinoflagellates from the Royal Society borehole at Ludham, eastern England has revealed the presence of more than 29 dinoflagellate species, substantially revising earlier records of this important locality. Assemblages reflect climates that fluctuated within a warm- or mild-temperate to cool range, as shown by the discovery that specimens earlier assigned to the warm-water Tectatodinium pellitum all belong to a cool-water element comprising Bitectatodinium tepikiense, Filisphaera filifera, F. microornata, and Habibacysta tectata. This element appears to have been widely mistaken for Tectatodinium pellitum in coeval deposits of the North Sea basin and beyond. The following are among several species reported for the first time from coeval deposits of the North Sea basin: Filisphaera filifera, F. microornata, Operculodinium? eirikianum, O. giganteum, Spiniferites ludhamensis n. sp., S. rubinus, and Trinovantedinium glorianum. The dinoflagellate Spiniferites ludhamensis n. sp. and acritarch Nannobarbophora walldalei n. sp. are formally described.

Hermit crabs have left a rich fossil legacy of epi- and endobionts that bored or encrusted hermit crab-inhabited shells in specific ways. Much of this rich taphonomic record, dating from the middle Jurassic, has been overlooked. Biological criteria to recognize hermitted shells in the fossil record fall within two major categories: 1) massive encrustations, such as encrusting bryozoans; and 2) subtle, thin encrustations, borings, or etchings that surround or penetrate the aperture of the shell. Massive encrustations are localized in occurrence, whereas subtle trace fossils and body fossils are common, cosmopolitan, and stratigraphically long-ranging. Important trace fossils and body fossils associated with hermit crabs are summarized here, with additional new fossil examples from the eastern Gulf Coast. Helicotaphrichnus, a unique hermit crab-associated trace fossil, is reported from the Eocene of Mississippi, extending its stratigraphic range from the Pleistocene of North America and the Miocene of Europe.

The taxonomy of the European stenonoid horses is revised using multivariate statistical techniques in this paper. The objectives are: to identify the taxonomic status of this group; to revise the specific and subspecific diagnoses, and the valid taxa; and to analyze their paleoecology and evolution. We conclude that: 1) there are six species among the Plio-Pleistocene European stenonoids: Equus major Depéret, in Delafond and Depéret 1893, ex Boule; Equus livenzovensis Bajgusheva, 1978; Equus stenonis Cocchi, 1867; Equus senezensis Prat, 1964; Equus altidens von Reichenau, 1915; and Equus sussenbornensis Wüts, 1901; 2) There are seven subspecies, three of E. stenonis, two of E. senezensis, and two of E. altidens; 3) There are two monophyletic groups according to the “neighbor-joining method,” one composed of the middle-to-small-size species, and the other of the biggest ones; 4) There is a trend toward decreasing body size through time in stenonoid horses. This trend, that follows the inverse direction of Cope's rule, can be related to the climatic-environmental changes that occurred from the middle Villafranchian to the early Galerian; 5) Large stenonoids were recorded in the middle Villafranchian and were associated with open and dry habitats (steppes), whereas the small ones lived in more closed and wet habitats (savanna-mosaic, woodlands) from late Villafranchian to earliest Galerian.

Based on biostratigraphic investigations in the eastern Siljan district, central Sweden, and combined with earlier studies at Hunneberg, south-central Sweden, it is shown that the early post-Tremadoc-age Paroistodus proteus conodont Zone can be divided into four successive subzones. These are, in ascending order: the Drepanoistodus aff. D. amoenus Subzone; the Tripodus Subzone; the Paracordylodus gracilis Subzone; and the Oelandodus elongatus-Acodus deltatus deltatus Subzone. The lowermost of the subzones is a concurrent range zone, with its reference section at Storeklev, Hunneberg, and the other three interval zones with the reference section at Sjurberg in the eastern Siljan district. Correlations between these two areas, as well as with the Flåsjö area, Jämtland, the Finngrundet core, and some other areas, are discussed, and it is concluded that the Drepanoistodus aff. D. amoenus Subzone and the Tripodus Subzone together correspond to the Megistaspis (Ekeraspis) armata trilobite Zone, and occur below the Hunnegraptus copiosus graptolite Zone. The Paracordylodus gracilis Subzone is equivalent with the lower part of the Megistaspis (Varvaspis) planilimbata trilobite Zone, and may correspond to the Hunnegraptus copiosus Zone. The uppermost subzone, the Oelandodus elongatus-Acodus deltatus deltatus Subzone, equals the upper part of the M. (V.) planilimbata Zone, and the local base of the Tetragraptus phyllograptoides graptolite Zone is close to the base of this conodont subzone. The last occurrences of T. phyllograptoides are close to the top of this conodont subzone. Also included in the investigation are the uppermost part of the uppermost Tremadoc Paltodus deltifer Zone and the conodont zones overlying the P. proteus Zone in the eastern Siljan district, the Prioniodus elegans Zone and the Oepikodus evae Zone; the latter zone corresponds to the trilobite zones of Megalaspides (M.) dalecarlicus and Megistaspis (Varvaspis) estonica. A few samples from the superimposed Baltoniodus triangularis, B. navis, and Paroistodus originalis Zones have been investigated and are described as well. The correlation of these conodont zones and subzones with those of areas outside Baltoscandia, particularly North America, is also discussed.

Neritic dinoflagellates from periplatform (slope) carbonates of the Clino borehole, located on the western, leeward margin of the Great Bahama Bank, record environmental fluctuations on the platform top. A lower Pliocene interval (3.6–4.2 Ma) contains platform-top sediments shed onto the lower slope when the platform was open and ramplike. Despite this open topography, abundant Polysphaeridium zoharyi indicate the presence of restricted marine environments on the platform top. Terrestrial palynomorphs are rare throughout this interval and imply a mostly or fully submergent platform top.

By late Pliocene times (about 2.1–2.3 Ma) the platform had become flat-topped and steep-sided, with the Clino site located on its upper slope. Samples characteristic of sea-level highstands and lowstands were selected for analysis. Polysphaeridium zoharyi is abundant only in lowstand samples and may have thrived in proximity to terrestrial vegetation. In highstand samples Lingulodinium machaerophorum replaces P. zoharyi, perhaps in response to less restricted marine environments on the platform top. This change in assemblages, along with apparent variations in cyst influx, reflects a fluctuating history of currents and salinities over the platform top in the late Pliocene. Upper Pliocene lowstand samples contain anomalously high proportions of terrestrial palynomorphs, allowing the identification of two phases of emergence and vegetation of the platform top. Palynology therefore appears to be a sensitive indicator of short-term (4th-order) sea-level change on carbonate platforms.

Dinoflagellate concentrations correlate positively with carbonate compaction, and infer that compacted layers have undergone dissolution of their metastable constituents. Dinoflagellate concentrations therefore can be useful in the often difficult task of assessing compaction and dissolution in fine-grained limestones where other indicators are absent.

The following dinoflagellate species are formally proposed: Operculodinium bahamense Head new species, Operculodinium? megagranum Head new species, and Spiniferites rhizophorus Head new species.

The uppermost Precambrian(?)–Lower Cambrian of the Avalon Zone in the northern Antigonish Highlands is composed of two dissimilar sequences in thrust contact. These include the sandstones and slates of the Doctor's Brook allochthon and the volcanoclastic-rich Malignant Cove authochthon.

Lithostratigraphy of the “Black John Formation” (designation abandoned) in the Doctor's Brook allochthon is comparable to the uppermost Precambrian–Lower Cambrian in eastern Placentia Bay, southeastern Newfoundland, and Cape Breton Island. A unified stratigraphic nomenclature is appropriate in these Avalonian areas. The lower part of the “Black John” is an unconformity-bounded depositional sequence with subaerial rift facies (Rencontre Formation, 178+ m), overlying marine siliciclastic mudstones and fine sandstones (Chapel Island Formation, 59 m), and a quartzite cap (Random Formation, 2.05 m). The Chapel Island Formation has the oldest faunas from mainland Nova Scotia (Watsonella crosbyi Zone, lower Placentian Series). A post-Random unconformity known in Newfoundland and Cape Breton Island lies at the Random-Bonavista Group (Cuslett Formation) contact in the upper “Black John Formation.”

Fossiliferous Lower Cambrian limestones and siliciclastic mudstones previously reported from the Malignant Cove autochthon are actually clasts in basalt pebble-dominated slope deposits of the Arbuckle Brook Formation. These clasts were eroded from shallow-marine facies comparable to those in the Doctor's Brook allochthon during local uplift associated with Middle Cambrian(?) extension and mafic volcanism.

Eight species are illustrated from the Placentian and Branchian Series. Anabaritellus Missarzhevsky, 1974, emend. (=Selindeochrea Valkov, 1982) is a Lower Cambrian calcareous tube-dwelling metazoan(?) known from tri- through multisulcate conchs that are morphologically intermediate between Anabarites and Coleoloides.

The extinction of the Olenellina on Laurentia can be located within centimeters in the C-shale or uppermost Combined Metals Limestone members of the Pioche Formation in eastern Nevada. Olenellid species diversity beneath the extinction boundary is not diminished. One of the richest Laurentian intervals for articulated olenellids is in the 50 centimeters of shale immediately below the extinction boundary at Ruin Wash. Additional morphological information about some of the species comes from a silicified fauna 1.8 m below the extinction boundary at Hidden Valley. The olenellid fauna from the 2-meter interval below the extinction boundary is described. Questions about current generic and subgeneric relationships are discussed. Among general observations, intraspecific variability unrelated to size or taphonomic effects is minimal for most species; at least two species may have been capable of enrollment; and visual surfaces of one species show no evidence of facets. New species include: Olenellus (Olenellus?) fowleri, Olenellus (Paedeumias) chiefensis, Olenellus (Paedeumias) terminatus, Bolbolenellus brevispinus, and Nephrolenellus geniculatus. Olenellus (Olenellus) gilberti Meek and Olenellus (Olenellus) howelli Meek are revised.

The morphology of Tuzoia is reinterpreted in the light of abundant new specimens from the Middle Cambrian Burgess Shale (British Columbia, Canada) and Kaili (Guizhou, China) Lagerstätten. Tuzoia was a very large (up to 180 mm long) bivalved arthropod with a nonmineralized domelike carapace strengthened by prominent pointed features and often flanked by a lateral ridge bearing a spiny frill. The reticulate pattern of Tuzoia is comparable with that of present-day crustaceans (e.g., myodocope ostracods) and is interpreted as a structural compromise between exoskeletal lightness and high resistance to mechanical stress. Tuzoia had a pair of large, stalked, spherical, possibly compound eyes facing forward. Flagella-like antennae protruded through the anterior notch. No other appendages are known except possible filamentous setae underlying the carapace. Tuzoia typically occurs as laterally (lc) or dorsoventrally (dvc) compacted carapaces or single valves. Each type (lc or dvc) emphasizes particular aspects of the morphology (e.g., spiny lateral ridge, ventral margin) that were often interpreted as specific differences by previous authors. A revision of Tuzoia validates only 7 of the 23 named species. Tuzoia is placed tentatively within a group of large bivalved arthropods along with Isoxys and the possible ancestors of Thylacocephala (Lower Cambrian–Upper Cretaceous). In the Middle Cambrian, Tuzoia occurs across Laurentia, South and North China, and the Perigondwanan area (Bohemia) within a relatively narrow subtropical belt, indicating a high dispersal capability and possible latitudinal control on its distribution. Functional morphology, taphonomy, and the distributional pattern indicate that Tuzoia was a free-swimming arthropod.

Late Cretaceous dinosaur eggshell assemblages from six localities of the Tremp basin (Southern Pyrenees, Lleida, Spain) are studied and compared with those of Southern France, to correlate their temporal succession. Fontllonga 6 reveals the most diverse eggshell assemblage known so far, with seven oospecies, among which one new structural type (Pseudogeckoolithus nodosus new genus and species), a new Ratite-type eggshell (Ageroolithus fontllongensis new genus and species) and a new Prismatoolithidae are described; four other taxa are shared with Southern France. The correlation of both Spanish and French eggshell successions allows us to recognize three main periods characterised by different eggshell assemblages: a lower assemblage with Megaloolithus petralta, M. aureliensis, Prismatoolithus tenuis and P. matellensis from the French Lower Rognacian and the Spanish sites Fontllonga 6 and Moro; a middle one with M. siruguei from the Middle Rognacian and Biscarri; and a late one from the Late Rognacian with M. mammilare (from Abella and Bastus) and M. pseudomamillare (from Suterranya). Some contradictions appear when comparing results with paleomagnetism and charophyte correlations but the eggshell correlations are consistent with other stratigraphic studies.

A phylogenetic analysis was used to determine evolutionary relationships within the Early Cambrian superfamily Olenelloidea Walcott, 1890. Phylogenetic patterns within the suborder Olenellina Walcott, 1890, which contains the Olenelloidea and the Fallotaspidoidea Hupé, 1953, are also discussed. The Olenelloidea are monophyletic, and synapomorphies uniting them include the condition of the ocular lobes where they intersect the frontal lobe of the glabella, and the condition of the lateral margins of the glabellar lobes. In contrast, taxa formerly assigned to the Fallotaspidoidea are shown to represent a paraphyletic grade of several genera, some more closely related to the Olenelloidea, and some more closely related to the Redlichiina Richter, 1933. Seventy-nine exoskeletal characters were coded for 26 taxa within the Olenellina. These included 22 ingroup Olenelloidea and four outgroup taxa that have traditionally been assigned to the Fallotaspidoidea. When subjected to parsimony analysis these character data yielded a single most parsimonious cladogram that provides an hypothesis of relationship for the generic clades within the superfamily. Two new genera are recognized herein, Fritzolenellus and Lochmanolenellus. It has been argued that genetic flexibility was so great and trilobite morphology was so plastic in the Early Cambrian that suprageneric classification of Early Cambrian trilobites is precluded. Although levels of intraspecific variability may have been slightly higher in the Early Cambrian relative to the mid Paleozoic, based on the extent of polymorphic character codings, it was not so high as to obviate attempts at recovering phylogenetic structure in a major clade of Early Cambrian taxa. In addition, the consistency index recovered by this analysis is not unduly low for a phylogenetic database of this size. The phylogenetic analysis also has bearing on patterns of allometric heterochrony, which have often been held to be significant in Early Cambrian trilobites. The paedomorphic retention of advanced genal spines into the adult probably evolved at least four times. Three of the episodes can be best described as neoteny, the fourth, as progenesis. Finally, based on the phylogeny, it is likely that rates of speciation in trilobites may have been two to three times higher in the Early Cambrian than in the mid Paleozoic.

The marine offshore shelf mudstones of the Early Cambrian Buen Formation at Sirius Passet, North Greenland, contain a rich Konservat-Lagerstätte which includes abundant well-preserved material of the bivalved arthropod Isoxys volucris new species. The new material confirms Isoxys Walcott, 1890 as a component of the earliest arthropod faunas worldwide. Isoxys species are known from the Early Cambrian of Spain, Siberia, South Australia and Southwest China and also from the Early to Middle Cambrian of Laurentian North America. Isoxys occurs in the Redlichiid, Bigotinid and Olenellid trilobite faunal realms but is restricted to within tropical/subtropical regions, attesting to possible paleolatitudinal controls on its distribution. Isoxys resembles some phyllocarid and bradoriid arthropods but without knowledge of its soft-parts the affinity of the genus remains uncertain.

This paper describes a unique deepwater brachiopod fauna from the upper part of the Talung Formation at the Dongpan Section, southern Guangxi, South China. This brachiopod fauna includes 10 species belonging to 10 genera. New taxa are Anidanthus mucronata n. sp., Dongpanoproductus elegans n. gen. and sp., Costatumulus dongpanensis n. sp., and Spinomarginifera semicircridge n. sp. This fauna is characterized by small, thin-shelled species with high abundance and low diversity, and therefore is different in generic and species composition from the coeval faunas of the Late Permian limestone facies in South China. The brachiopod fauna can be safely assigned to the latest Changhsingian as indicated by the presence of abundant Paracrurithyris pigmaea, the immediately underlying radiolarian Neoalbaillella optima Zone of late Changhsingian age, and the overlying ammonoid Ophiceras sp. cf. O. tingi Tien of the lowest Triassic. This fauna is most likely to have lived in a deepwater environment as indicated by coexistence with the radiolarian Latentifistularia, small thin-shelled brachiopods, and the dominance of silica-bearing mudstone.

Deutler's classic work (1926) provides the basis for an analysis of plate growth in echinoids. Deutler showed that the concentric growth rings found within each plate may be used to reconstruct the ontogeny of the entire plate pattern.

New observations of growth-line configurations, particularly in Strongylocentrotus pallidus (Sars), have been used to derive a general model for echinoid growth. The plate mosaic is assumed to be the result of close packing of the growing plates. The shape of a given plate thus depends on its size and position relative to surrounding plates.

The rate of meridional growth of a plate can be shown to change regularly with increasing distance from the echinoid's apical system. Migration of plates away from the apical system thus causes change in the rate of plate growth. The rate of plate migration is strongly influenced, in turn, by the rate of supply of new plates at the apical system.

A mathematical model has been developed from these considerations which, when treated by digital computer (with x-y plotter output), produces ideal plate patterns (including growth rings). The constants in the model may be varied to produce a broad spectrum of echinoid plate patterns.