Revision and redefinition of the Permian ammonoid genus Yinoceras Chao, 1954, is based upon examination of the holotype of its type species, Y. lenticulare Chao, plus new material collected from the Kungurian Dangchong Formation of central Hunan, China. Yinoceras is a valid yinoceratin genus within the pseudohaloritid Superfamily Pseudohaloritoidea, Suborder Tornoceratina, Order Goniatitida.

Seven new monoplacophoran genera and species are described and figured from Cambrian and Lower Ordovician strata of the Ozark Uplift of Missouri; Biloboconus frizelli, Ulrichoconus bonneterrense, Potosiplina delorensis, Gayneoconus echolsi, Irondalia irondalensis, Titanoplina meramecensis, and Wildernessia inexpectans. A new species of Kirengella, K. oregonensis, is described, and Hypseloconus compressus (Ulrich and Bridge, 1930, and H. expansus Stinchcomb, 1986, are assigned to the genus Kirengella. The morphology of Kirengella is compared to highly arched forms of the plated mollusk genus Preacanthochiton and is found to converge with them. Association with stromatolite reefs of both Kirengella and plated mollusks is noted.

Four new molluscan species, a bivalve and three gastropods, are named from shallow-marine, lower Upper Cretaceous (Cenomanian Stage) strata in Oregon. The laternulid bivalve Cercomya (Cercomya) hesperia new species is from the Bernard Formation in east-central Oregon and from the Osburger Gulch Sandstone Member of the Hornbrook Formation in southwest Oregon. It is the first Cenomanian record of this genus.

The iteriid gastropods, Vernedia pacifica new species and Sogdianella oregonensis new species, are from unnamed Cenomanian strata in east-central Oregon and represent the first records of these genera in western North America. The actaeonellid gastropod Trochactaeon (Neocylindrites) allisoni new species from these same deposits represents the first record of this genus in Oregon.

The new species of Cercomya sensu stricto, Vernedia, and Neocylindrites are very similar to western European species, and the new species of Sogdianella is most similar to a Peruvian species.

Two new genera of the Chonostrophiidae are proposed herein to accommodate the resupinate shells from the Famennian sediments of the Late Devonian in the Santanghu Basin of the Balikun area, Xinjiang Province, northwestern China. Santanghuia santanghuensis new genus and species is distinguishable from other chonostrophiids by the possession of a pair of long dorsal anderidia and absence of a dorsal median septum. Balikunochonetes liaoi new genus and species is distinct because of the presence of a pair of anderidia with secondary anderidia, and a dorsal median septum. Santanghuia new genus is considered to be phylogenetically related to Chonostrophia of late Early to Middle Devonian age, while Balikunochonetes has possibly given rise to Chonostrophiella of Early Devonian age and is a likely ancestor of Tulcumbella of Early Carboniferous age.

The reticuloceratid ammonoid Arkanites relictus (Quinn, McCaleb, and Webb, 1962) is represented by hundreds to thousands of individuals from horizons isolated both stratigraphically and geographically in northern Arkansas. These assemblages appear to represent mass mortality events resulting from a semelparous reproductive strategy. Arkanites relictus occurs as a dimorphic pair (depressed, widely umbilicate, cadiconic conchs and compressed, narrowly umbilicate, pachyconic conchs) thought to reflect sexual dimorphism. Late stage ontogenetic modifications, such as septal crowding and change in aperture profile, are widely cited evidence of sexual maturity in ammonoids. Septal crowding begins at a predictable ontogenetic stage in the compressed forms of A. relictus, but specimens with cadiconic conchs do not have crowded septa even at the largest diameters available.

Depending on the trait examined and the proxy for age of individuals, the dimorphism in Arkanites relictus (using the depressed form as the reference morph) is the result of acceleration, neoteny, or hypermorphosis plus neoteny. If size (diameter) is considered a proxy for age, the dimorphs were the same age at death, and the septa in the compressed variants developed via acceleration relative to the depressed variants. Regarding conch shape (width vs. diameter), the compressed morphs developed via neoteny relative to the depressed morphs. If septal count is considered a proxy for age, the dimorphs were not the same age at death, and the compressed forms were produced by a combination of hypermorphosis plus neoteny, i.e., they grew longer yet slower than the depressed forms. In A. relictus, the heterochronic processes of hypermorphosis and neoteny may have been operating simultaneously, which is an interesting possibility because it is an example of a combination of both peramorphic and paedomorphic processes.

The Fossil Brook Member of the upper Chamberlain's Brook Formation is a thin (up to 14 m) but distinctive, unconformity-bound depositional sequence recognizable from Rhode Island to eastern Newfoundland in Avalonian North America. Its diverse trilobite fauna was first described more than century ago from the limestone-rich facies of the member in southern New Brunswick. However, the systematics, stratigraphic context, and biostratigraphic significance of these trilobites have remained poorly known. A revision of the conocoryphid and paradoxidid trilobites has been completed, and the taxa set into their stratigraphic context within the middle Middle Cambrian. The faunas of the Fossil Brook are assigned to the Eccaparadoxides eteminicus Zone of Avalon. Although biogeographic barriers between Avalon and Gondwana remained strong in the Middle Cambrian and few shared trilobite species are present, a generalized correlation of the E. eteminicus Zone into Gondwana is with the Badulesia tenera Zone of the Toushamian Stage in Morocco and the Badulesia Zone of the Caesaraugustian Stage in Spain.

Desmoinesian strata of the lower Bishop Cap Formation in Vinton Canyon, northern Franklin Mountains, west Texas, contain a rich gastropod fauna, in general resembling that of the upper Flechado Formation in north-central New Mexico. Distinctive elements of the Bishop Cap fauna include two new genera and five new species. Each species is represented by 30 or more specimens, sufficient to document ontogenetic change and intraspecific variability. The new taxa described here include the murchisonioid Altadema convexa new genus and species; the pseudozygopleurids Microptychis insolita new species, Trepsipleura chordanodosa new genus and species, and T. nodosa new species; and the orthonemid Hermosanema carinatum new species.

The Bathonian-Oxfordian ostreid fauna from the main ridge of the Tanggula Mountains of the Qinghai-Xizang Plateau, China, consists of six taxa: Actinostreon gregareum (J. Sowerby, 1815), Actinostreon sp. A, Liostrea birmanica Reed, 1936, Gryphaea (Bilobissa) bilobata (J. de C. Sowerby, 1835), Nanogyra nana (J. Sowerby, 1822) and Eligmus rollandi Douvillé 1907. Liostrea birmanica is only known from the eastern Tethys and south Xizang area, Eligmus rollandi is limited to the Tethys, G. (B.) bilobata occurs in northwest Europe and the northern Tethys, whereas A. gregareum and possibly N. nana have a complex global distribution between paleo-latitudes 60° north and south.

Actinosteon gregareum first occurs in the Sinemurian of northern Chile, and during the Toarcian it underwent trans-Pacific dispersal to arrive in east Africa. During the Bajocian it dispersed rapidly along the southern and northwestern margins of the Tethys, northwestern Europe, and western Canada (Stikine Terrane), but it disappeared from South America in the Aalenian. It occupied Kachchh, southern Xizang, and the northern and northeastern Tethys as early as the Bathonian but it did not reach the northwestern Pacific until the Late Jurassic. The species declined after the Kimmeridgian, being limited to northern Africa (southern Tunisia) and the northwestern Pacific (Japan) during the Tithonian. By the end of the Jurassic it was extinct.

Actinostreon gregareum apparently possessed very high fertility typical of opportunists that rapidly colonize new habitats. As a result of ocean current dispersal, presumably by both planktotrophic larvae and postlarval pseudoplankton, it rapidly spread along continental margins and island chains. Occasionally, either directly or by island hopping, it crossed the vast Tethys and Pacific oceans, colonizing all warm and temperate waters at low and intermediate paleolatitudes. It may also have used the Hispanic Corridor as a means of dispersal between the Tethys and Pacific oceans as early as the Toarcian.

Seven crinoid species and one very unusual column are recognized from the Ordovician, Dobrotivian (Llandeillian Stage) to Ashgill of Spain. Three previously described species, Heviacrinus melendezi Gil Cid, Domínguez, and Silván, 1996; Coralcrinus sarachagorum Gil Cid, Domínguez, and Silván, 1998; and Ortsaecrinus cocae Gil Cid, Domínguez, Torres, and Jiménez, 1999, are considered, and four new species assigned to three new genera are described herein, including Visocrinus castelli, Fresnedacrinus ibericus, Morenacrinus silvani, and Merocrinus millanae. Previous reports of Ramseyocrinus from Spain have been revised, and we agree that this disparid is not presently known from Spain. These crinoids represent the largest Ordovician crinoid fauna from Gondwana, including these localities and those from the Montagne Noire along peri-Gondwana during the Ordovician. The crinoids reported here, from the Montes de Toledo and Sierra Morena, and the Ordovician crinoids from Montagne Noire have very little in common with Ordovician crinoids from the Prague Basin. Thus, these new data support paleogeographic plate positioning that allows for either paleoclimatic, paleoenvironmental, or paleogeographic isolation between the Prague Basin and peri-Gondwana.

The presence of the bivalve mollusks Astarte (Tridonta) borealis Schumacher and A. (T.) hopkinsi new species, in uppermost Miocene or lower Pliocene strata of the Milky River Formation on the Alaska Peninsula, southwestern Alaska, signals the earliest opening of Bering Strait. These species migrated from the Arctic Ocean into the North Pacific when the Bering Strait first flooded and, along with co-occurring marine diatoms, are primary evidence for the earliest opening of the strait, in the latest Miocene or early Pliocene. These paleogeographically important Alaskan Astarte have been cited in this context, but have not been previously illustrated or discussed.

From the early Cambrian of Yunnan, China, new chancellorid scleritomes assigned to Allonnia junyuani new species are described and compared with scleritomes of Chancelloria eros Walcott, 1920 from the Middle Cambrian of Utah, USA and isolated phosphatized chancellorid sclerites from the Georgina Basin of North Australia. Characters of the entirely preserved chancellorids offer new insight into the paleobiology of Chancelloridae. An irregular thickening at the inferred base of the narrow body end of Chancelloria eros from Utah is interpreted as a root bulb that anchored the sessile animal in the soft bottom sediment. Sclerites show gradual increase in size from the narrower towards the broader upper end of the chancellorid body. A central “gastral” lumen was not directly observed in any of the investigated specimens, but the orientation of sclerites towards the outer body surface indicates that the fossils are secondarily flattened due to compaction and were originally hollow. Taphonomy of isolated chancellorid sclerites from the Georgina Basin, Australia, indicates a biomineralization very different from that of sponge spicules, including the spongin spiculoids of demospongid Keratosa. Allonnia junyuani from Chengjiang (Yunnan) exhibits a prominent epidermis, probably with stable epithelian cell-to-cell connections. This feature excludes a sponge affiliation of the Chancelloridae and points towards a systematic position of this group within the epithelian-bearing animals and thus well above the Porifera.

Quintuplexacrinus new genus with Dendrocrinus oswegoensis Meek and Worthen (1868) as the type and only known species is described and assigned to the Merocrinidae. The new genus is characterized by a unique stem with a highly pentalobate axial canal; the distal column is highly differentiated with large and very high nodals and thin intemodals. A cladistic analysis indicates that Quintuplexacrinus n. gen. is closely related to Praecupulocrinus. The numbers of the various orders of brachs are independent of the size and age of the animals. Within the arms only the numbers of primibrachs and secundibrachs are positively correlated. Some variation is related to position of the rays. The C ray bears the smallest number of primibrachs. The outer half-rays possess more numerous tertibrachs than the inner ones. Aboral cup growth produces a wide-based and distally expanding outline at all sizes. In general, the widths of the cup and the cup's component plates are positively allometric relative to their heights. Likewise, the width: height ratios of the proximal brachs, primibrachs through tertibrachs, increase in older and larger individuals because the widths grow faster than the heights. The number of columnals in both the proximal and distal stem regions is typically stabilized throughout ontogeny. However, the entire stem becomes longer and wider in larger specimens due to calcite deposition on the columnals. Development of the columnals is isometric so their shapes do not change with size and age.

A new glyptocystitidoid rhombiferan, Cheirocystis fultonensis, is described from the contact zone between the Point Pleasant Formation and lower Kope Formation exposed 50 km south east of Cincinnati, Ohio. This species, the second known glyptocystitidoid rhombiferan from the Cincinnatian Series and the youngest known species of Cheirocystis, shows significant suture modification where pectinirhombs are placed. Growth of large pectinirhombs along vertical sutures results in an unusual bowing-out of thecal plate sutures that is also seen in the related species Cheirocystis anatiformis. A juvenile specimen shows that ontogenetically the lateral shared ambulacra become less pronounced, pectinirhombs are added until the eight standard positions are expressed, and the periproct becomes proportionately smaller with age.

Two new distinctive families, Crassimarginatidae and Scoliostomatidae, each characterized by unusual gerontic apertural morphotypes, are established on the basis of study of the richly diverse Lower Devonian gastropod fauna of the Road River Formation in the Royal Creek area, Yukon Territory. The Early Devonian genus Crassimarginata Jhaveri, 1969, is transferred from the family Palaeotrochidae and placed, together with the new genus Yukonoconcha, into the new family Crassimarginatidae, which is characterized by a pupiform shell with an explanate outer apertural lip in the gerontic growth stage. The new family Scoliostomatidae unites Devonian gastropod genera (Scoliostoma Braun, 1838; Brilonella Kayser, 1873; Anarconcha Horný, 1964; Eoscoliostoma new genus; Mitchellia Koninck, 1877; and Pseudomitchellia new genus), which are characterized by a distinctive, free, twisted (both outwards and backwards) gerontic final half whorl. More detailed morphological comparison of members of this family has allowed their division into two new subfamilies: the Scoliostomatinae and Mitchelliinae. New genera include Yukonoconcha, Eoscoliostoma, and Pseudomitchellia. The former two genera are represented each by a single new species from Yukon Territory, Yukonoconcha pedderi and Eoscoliostoma norrisi. The latter genus is represented by two species, the type Pseudomitchellia bohemica (Perner) from the Koněprusy Limestone (Pragian) of the Czech Republic and Pseudomitchellia macqueeni new species from Yukon Territory.

The fluted margins of ammonite septa were thought to resist the hydrostatic pressure upon the phragmocone while the ammonoid dived. However, ammonoids probably did not dive deeper than the extant nautilids, whose conchs, with the simple septa, sustain pressure correlative to depth of about 800 m. The backward and forward stretching lobes and saddles actually provide resistance to pressure perpendicular to the septum. Ammonoids lived for about three to five years, and septa were precipitated in intervals of nearly two weeks to two days, which explain the small dimensions of the scars of the adductor muscles, which were periodically detached and reattached. The weak hold between these small muscles and the buoyant conch was compensated for by the backward branching and expanding folds (forming the sutural lobes), into which the soft tissue penetrated and stiffened for a required period to firmly anchor the body to the conch throughout its whole circumference. The greater the complexity of the septa marginal fluting, the better the ammonoid could withstand the dragging force between the body and the buoyant conch, and hence the more aggressively the ammonoid predated and competed with other creatures.

A middle Cenomanian faunule from the Moonkinu Formation of Bathurst Island in Northern Australia contains the best-preserved suite of benthic Mollusca known from the Cretaceous of the Australian region. Twenty-four species of bivalves, gastropods, and scaphopods, many exquisitely preserved with original aragonitic nacre, are recognized. Thirteen are new: Nucula s.l. meadinga n. sp. (Nuculidae), Nuculana bathurstensis n. sp. (Nuculanidae), Jupiteria? n. sp. A (Nuculanidae), Varicorbula cretaustrina n. sp. (Corbulidae), Vanikoropsis demipleurus n. sp. (Vanikoridae), Euspira n. sp. A (Naticidae), Amuletum praeturriformis n. sp. (Turridae), Granosolarium cretasteum n. sp. (Architectonicidae), Echinimathilda moonkinua n. sp. (Mathildidae), Acteon bathurstensis n. sp. (Acteonidae), Biplica antichthona n. sp. (Ringiculidae), Goniocylichna australocylindricata n. sp. (Cylichnidae), and Dentalium (Dentalium) n. sp. A (Dentaliidae). Nominal species of Nuculana, Grammatodon, Cylichna, and Laevidentalium also are present. The occurrence of ammonites, including taxa that occur in the type Cenomanian, securely establishes the fauna as middle Cenomanian (Acanthoceras rhotomagense Zone). The Moonkinu Formation and its faunule were deposited in a high-energy, shallow-shelfal setting, as part of a large-scale regressive cycle recognized as the Money Shoals Platform of northern Australia. The assemblage represents a parauthochthonous suite which experienced little or no post mortem transport. Epifaunal and infaunal suspension feeders (some 60 percent) dominate the bivalve fauna with a subordinate representation of deposit-feeding infaunal burrowers (some 40 percent). Nearly all of the gastopods were carnivores with the aporrhaid Latiala mountnorrisi (Skwarko), probably a deposit feeder, the only exception. The scaphopods were probably micro-carnivores. Concentrations of the ammonite Sciponoceras glaessneri are likely the result of mass kills in surface waters. The cosmopolitan nature of the Bathurst Island fauna at the genus-level reflects unrestricted oceanic circulation patterns and an equitable climate on a global scale during the Cenomanian. The retreat and disappearance of the Australian epicontinental sea at the close of the Albian coincided with reduced endemism in the molluscan faunas, after which time the continental shelves hosted a rich suite of cosmopolitan affinity. The high number of endemic species in the Moonkinu Formation probably represents an early stage of broad-scale genetic separation among Southern Hemisphere molluscan stocks, a trend that became increasingly pronounced through the Late Cretaceous. The new records of Varicorbula, Amuletum, Granosolarium, Echinimathilda, and Goniocylichna represent the oldest occurrences recorded for these genera and are suggestive of Southern Hemisphere origins.