Sinemurian and Pliensbachian Exogyrinae from northern Chile described herein as Nanogyra? cf. auricularis are considered the oldest members of the subfamily known to date. Comparisons with a large number of Jurassic Nanogyrini and aberrant Gryphaea species suggest that they are most closely related to Nanogyra? auricularis (Münster in Goldfuss) from the Toarcian of France, but probably not identical. Morphotypes of several Chilean specimens are transitional between gryphaeate and exogyrate forms, and their assignment to either Gryphaeinae or Exogyrinae appears arbitrary. In order to solve this taxonomic problem, the microstructures of Nanogyra? cf. auricularis and co-occurring typical Gryphaea species were examined and compared to a large database from previous studies. The results suggest that shell chambering is a feature common to all Exogyrinae but not to Gryphaea sensu stricto. Complex cross foliation and branching cross foliation are characteristic of both groups. However, they are more abundant in Gryphaea and apparently become phylogenetically reduced in the Exogyrinae. The transitory morphotypes and microstructures, especially of the Sinemurian specimens, are further evidence for the evolution of the Exogyrinae from the Gryphaeinae. Obviously, the Chilean specimens are very close in time and space to the origin of the subfamily. Thus, the lowermost Jurassic Andean back-arc basin of western South America is considered a plausible place of origin of the Exogyrinae.

The most important factor controlling the timing of Phanerozoic mineralogical evolution in the Bivalvia appears to be thermal potentiation of calcite deposition in colder marine and estuarine environments. Cold temperature has promoted mineralogical evolution in the Bivalvia by kinetically facilitating (potentiating) initially weak biological controls for calcite, thereby exposing their genetic basis to natural selection. Calcite has evolved in bivalve shells for a variety of selective advantages, including resistance to dissolution; resistance to chemical boring by algae and gastropods; reduced shell density in swimming and soft-bottom reclining species; enhanced flexibility in simple prismatic shell layers; and fracture localization and economy of secretion in association with certain foliated structures.

Endogenous calcite in bivalve shells varies from biologically induced to weakly and strongly biologically controlled. Biologically controlled calcite generally first appears in bivalve shells as an impersistent component of the outer shell layer, only later, in some groups, expanding to include the entire outer and then part or all of the middle and inner shell layers. The initial stages of mineralogical evolution are shown by certain modern Mytilidae, Veneridae and Petricolidae. In the latter two families, the calcite occurs as conellae in the outer part of the outer shell layer. Calcitic conellae in the inner shell layer of Pliocene Mercenaria are not barnacle plates, as previously indicated, but endogenous calcite comparable in origin to other venerid conellae. Their occurrence in Mercenaria may reflect thermal potentiation of weak biological controls for calcite, as well as local detachment of the secretory mantle epithelium near the pallial and adductor musculature.

The genera Lissopleura, Sphaerirhynchia, Pectorhyncha, Yanishewskiella, and Terebratuloidea have been investigated to elucidate their internal features and taxonomic relationships. Specimens of the type species of these genera were sectioned. Lissopleura remains slightly enigmatic in that the holotype of Lissopleura aequivalvis is thinner and has a less pronounced fold than most specimens in the collection, including the one sectioned by us. The holotype is probably immature and is within the range of variation of specimens from the type area. The internal features lead us to assign Lissopleura to the Trigonirhynchiidae. Sphaerirhynchia wilsoni has a short septalium without a cover plate and other features that place it in the Hebetoechiidae. Pectorhyncha obtusiplicata has a very thick shell and a septalium filled by a large, bilobed cardinal process. The genus has several features similar to Obturamentella, and is assigned to the Obturamentellidae. Yanishewskiella angulata, which is retained within the Tetracameridae, has a spondylium with lateral buttresses, and a septalium into which the medium septum projects. Terebratuloidea davidsoni has small dental plates, and is assigned to the Allorhynchidae.

Structures that mimic the general shape of cheilostome avicularia occur within the Paleozoic fenestrate bryozoan genus Fenestrapora. These structures, here termed aviculomorphs, are isolated within laminar extrazooidal skeleton and are characterized by an elongate triangular outline that surrounds a shallow, concave pit. The acute tip of the triangular structure was elevated above the general level of the surrounding skeleton, as is the case for many avicularia. The aviculomorphs could not have functioned precisely as do avicularia, but like avicularia they are inferred to have had a thickened cuticular mandible that matched the skeletal base and to have been able to articulate the mandible open and closed along a fulcrum on the short side of the triangular skeletal outline.

Scolecodonts, the jaws of polychaetes, are the fossil evidence of the rich and diverse fauna that prospered in shelf seas. Among eunicid polychaetes, the largest jaws in the jaw apparatus occur in pairs. Normally these pairs are not exact mirror images of each other. Rarely, left and right jaws are found to be reversed, the jaw in the left position having the morphology of a mirror image of the normal right jaw and vice-versa. This type of morphological reversal (reversed handedness) is recorded with a frequency that varies from one reversed jaw in 430 to one in 5,838 of normal jaws. Reversed jaws so far are documented in four species from the Upper Ordovician of Indiana, USA, and one species from the Silurian of Gotland, Sweden. The reversed morphology is thought to be a natural, genetically induced feature. The polychaetes with morphological reversal grew to normal size, but never became common.

The sponge Neoguadalupia oregonensis new species is described from the Upper Triassic Martin Bridge Formation in the southern Wallowa Mountains, Oregon. It is the first authenticated Triassic occurrence of the genus Neoguadalupia, previously known from the Permian of South China and suspected to occur in Upper Triassic of Nevada. This discovery provides evidence at the generic level of survival of a Lazarus taxon in an island-arc terrane of western North America.

Juvenile specimens of the short-looped terebratulid brachiopod genus Pseudorhaetina Sandy have been investigated by the use of transverse serial sections. Internal structures indicate a simple brachidium (loop) is present with long flanges in adult specimens; the brachidium is approximately half the length of the dorsal valve; there is no complex loop metamorphosis in the central cavity of the brachiopod (i.e., no median septum). This combination of characters presents a taxonomic problem—Pseudorhaetina can neither be referred with confidence to superfamily Terebratuloidea, nor superfamily Loboidothyridoidea. Consequently Pseudorhaetina is, for the time being, assigned to a new and as yet unnamed superfamily representing a previously unrecognized part of the post-Paleozoic recovery and reradiation of Mesozoic articulate brachiopods (Rhynchonellata of Williams et al., 1996).

Ribbing became an increasingly common feature of pentamerid shells, especially the family Stricklandiidae, during the later Llandovery (Early Silurian). The thin shells of stricklandiids from the Llandovery (Aeronian-Telychian) equatorial carbonate rampshelf of Anticosti Island reveal at least three ribbing designs in various genera; 1) radially arranged ribs, e.g., Costistricklandia; 2) divergent, chevron-like ribs, e.g., Ehlersella; and 3) diagonally criss-cross, mutually intersecting divaricate ribs, as in Kulumbella and Microcardinalia (Chiastodoca) new subgenus. Weakly divaricate species previously assigned to Kulumbella, Stricklandia or Microcardinalia from Anticosti Island, South China and the Baltic region, are assigned to the new subgenus Chiastodoca (type Stricklandinia salterii Billings, 1868), and they are suggested to have evolved their divaricate ribbing from smooth forms, independently from the earlier genus Kulumbella, in the same sense that radial or divergent ribbing was developed separately in a number of pentamerid and stricklandiid lineages in the late Llandovery and Wenlock. In Anticosti, the divaricate genus Kulumbella, originally described from Siberia, appeared, without a known ancestral form, in the Anticosti Basin (as K. xacta n.sp.), and became extinct equally suddenly in the upper part of the Gun River Formation (mid-Aeronian). This sudden arrival of immigrant taxa, originally appearing earlier in other areas, is matched in other brachiopod groups and corals in the Anticosti section. Weakly divaricate ribbing in Chiastodoca is characteristic of the early Telychian (Ferrum Member, Jupiter Formation), and radial ribbing is typical of the late Telychian genus Costistricklandia (Pavillon Member, Jupiter Formation).

Phylogenetic relationships among higher taxa of articulate brachiopods that developed a spiralium as mineralized support for the lophophore, and the resulting classifications, are not universally agreed upon due to the complex pattern of character evolution within the phylum. Our results, using phylogenetic methodology in conjunction with traditional methods, showed a more complete and easily testable picture of this evolution than either method used alone. A detailed working hypothesis of athyridide phylogeny and the supporting evidence on character distribution is given, and a new classification of the impunctate and punctate athyrids sensu lato is presented with diagnoses to subfamily. Agreement between the stratigraphical first appearance of athyridid subfamilies and their cladistic rank was quite good (except for the koninckinoids), suggesting that both outgroup and traditional paleontological methods indicate a similar direction of character polarity in the evolution of the group. The classification is proposed based on a mix of external and internal characters which persisted during unbroken lineages. New taxa are the families Parazygidae and Triathyrididae; the subfamilies Whitfieldellinae, Triathyridinae, Septathyridinae, Cleiothyridininae, Ochotathyridinae and Plectospirinae, and the genera Brimethyris, Carteridina, Tetraloba and Cooperispira. We studied the great morphological diversity among the athyridids. Their complete stratigraphical ranges help in building phyletic lineages.

Twenty species of bivalves are described from the Ixtaltepec Formation, in Nochixtlán, México. Representatives of the genera Parallelodon, Myalinella, Septimyalina, Leptodesma, Pterinopectinella, Aviculopecten, Limipecten, Streblopteria, Euchondria, Schizodus, Permophorus, Astartella, Edmondia, and Ectogrammysia are present. These species, and those of nuculoid bivalves previously described from the same formation, include infaunal and epifaunal forms that lived in shallow marine environments from Morrowan to Desmoinesian ages. Pennsylvanian bivalves from Nochixtlán are related to the Midcontinent and Appalachian faunas, which indicate that there was an oceanic connection between these areas in a latitudinal belt near the equator that partially covered southeastern Mexico.

Analysis of previously unstudied shell characters reveals the existence of three new genera of Cenozoic muricid neogastropods. These are the new genera Muregina (type species: Murex lugubris Broderip, 1833; ?early Miocene, Pliocene to Recent, eastern tropical Pacific); Kestocenebra (type species: Murex curvicosta Grateloup, 1840; early to late Miocene, Europe); and Edithais (type species: Concholepas drezi Vokes, 1972; early to late Miocene, circumtropical).

A review of muricids with a labral tooth (a ventrally directed projection on the outer lip) shows that this structure forms in several distinct ways. It may form at the end of an external groove (as in Muregina) or cord (as in Kestocenebra), grow continuously or discontinuously, and lie at positions ranging from the upper end of the siphonal canal to just below the middle of the outer lip. The labral tooth evidently evolved independently several times, often quite recently in genera such as Muregina, in which older representatives lack a labral tooth.

A new genus, Geniculigypa, and a new subfamily, the Geniculigypinae, are established. Both taxa are monotypic and have as their type species, Sieberella newtonensis Imbrie, 1959, from the Newton Creek Limestone (early Givetian) of Michigan. This species dramatically differs from all other known gypiduloid species in its possession of a prominent geniculation in both valves and by its radially grooved micro-ornament.

Three new species of the shallow-marine, warm-water bivalve Plicatula are reported from the upper Paleocene Santa Susana Formation of southern California. Plicatula simiensis new species is from the middle part of the formation on the south side of Simi Valley and occurs as a displaced specimen in deep-marine turbidites. Plicatula lapidicina new species and P. trailerensis new species are both from coralline-algal-rich muddy siltstone just beneath a nearshore, coralline-algal limestone interval in the upper part of the formation in the Santa Ynez Canyon area, east-central Santa Monica Mountains. These three new species represent the first late Paleocene records of genus Plicatula on the west coast of North America and the first Paleocene records of this genus in southern California.

A new actinocerid genus, Kobayashiceras, is defined on the basis of Kobayashiceras gifuense new species from the Lochkovian (Early Devonian) of the Fukuji Formation, central Japan. This genus shares with known actinocerids in the apical shell morphology, but is diagnosed by its orthocerid like stenosiphonate form in the adoral shell. Its taxonomic and paleobiogeographic implications are discussed.

During the Cambrian and Ordovician trilobites belonging to a variety of clades developed distinctive inflated bulbs on the preglabellar field. We make the case that these bulbs were brood pouches, which were employed for retaining and protecting larval trilobites in order to ensure a higher rate of survivorship. Living arthropods of several classes develop comparable spherical structures—for example the domicilium of certain ostracodes. Living limuloids, likely the trilobites' closest living relatives, carry large and yolky eggs in an homologous, prelabral site. There are some trilobite examples where “species pairs” found in the same fossil sites appear to differ only in the presence or absence of the preglabellar bulb. These may represent the female and male of a single species, respectively. If so, this is the first well-supported case of sexual dimorphism in trilobites. Some more problematic examples are discussed, where alleged dimorphism would have to be more extreme.

Anactolasma yukonanum new genus and species is described from the Pragian of Yukon Territory and is assigned to the Anactolasmatinae, a new subfamily of the Mucophyllidae Hill. Adult stages of Anactolasma resemble gerontic stages of Kobeha Merriam, although the genera have distinct ontogenies. Kobeha is revised on the basis of new material of its type species K. walcotti Merriam. The Papiliophyllinae Stumm are promoted to family status. Kobeha ketophylloides Merriam, from the Pragian of Nevada, and Endophyllum banksi Jell and Hill, from the Pragian of Tasmania, are restudied using new topotypic and other material. A new endophyllid genus named Murphyphyllum is erected for them, with E. banksi as type species. Asarcophyllum ramosum new genus and species, from the Emsian of Nevada, is made type species of a new cyathophyllid genus. Spongophyllum nevadense Stumm and S. expansum Stumm, both also from the Emsian of Nevada, are placed in the new genus, as is Asarcophyllum corona new genus and species, from the Emsian of Yukon Territory. Biostratigraphic settings, with emphasis on associated corals, brachiopods and conodonts, are given for the new and revised genera and species.

We describe three scleractinian corals and one species of hydrozoan from the New Pass Range, central Nevada, which together constitute the oldest Triassic cnidarian assemblage from North America. They occur in carbonate rocks tentatively correlated with the Augusta Mountain Formation, Star Peak Group. At generic and higher levels, these cnidarians seem representative of early Mesozoic Tethyan faunas and carbonate lithofacies, but they indicate some endemism. Although the original aragonitic skeletons and microstructure are destroyed by recrystallization, the corals still yield important details allowing their correct taxonomic assignment. They contain the minitrabecular cerioid coral, Ceriostella variabilis new genus and species, the thick-trabecular, thamnasteroid coral Mesomorpha newpassensis new species, and an undeterminable cuifastreid coral tentatively assigned to Cuifastraea. The discovery of Mesomorpha marks the first occurrence of this genus outside the Jurassic and Cretaceous seas. Also discovered is a remarkably corallike hydrozoan, Cassianastraea reussi (Laube), already known from the Carnian stage of the western Tethys. This is the first occurrence of this species outside the western Tethys.