To characterize the biogeography of individual radiolarian taxa in relation to latitudinal climatic variation across the subtropical to subarctic zones, we investigated the spatial distribution of radiolarians in surface sediments along a 175°E traverse from 19°N to 48°N in the North Pacific Ocean. Census survey and statistical classification of taxa enabled us to recognize distinct radiolarian assemblages. Most characteristic taxa analyzed had restricted biogeographic ranges along the north–south traverse; the biogeographic ranges and abundance patterns related well to the modern oceanography of the upper layer. Water masses (subtropical, transitional, and subarctic zones) were characterized by abundance of certain taxa, and oceanic fronts (Kuroshio Extension, Kuroshio Bifurcation, and Subarctic Fronts) coincided with limits of species' biogeographic ranges and abrupt changes of frequency of some taxa. These results offer promise for pale-oceanographic interpretations of sedimentary records that will enhance the value of individual radiolarian species as keys to past water masses and hydrographic boundaries in the North Pacific.

The mid-Cretaceous Goshoura Group, non-marine to shallow marine fossiliferous clastic deposits, is typically exposed on Goshoura Island, Amakusa, western Kyushu, Japan. Based on precise sedimentological analyses, the group is subdivided into the following three formations, the Eboshi, Enokuchi and Karakizaki Formations in ascending order. These formations are herein redefined, and the Eboshi and Enokuchi Formations are newly subdivided into members, i.e., the Eboshi Formation is composed of the Tanoshiri, Hobashiraiwa and Arakuchizaki Members, and the Enokuchi Formation consists of Hokahira and Gannohana Members. Geological age of the group is determined by age-diagnostic ammonite species, e.g., the Late Albian Mortoniceras cf. rostratum from the Hokahira Member, and the Early Cenomanian Graysonites adkinsi from the overlying Gannohana Member.

Fifty-eight bivalve species belonging to 42 genera are identified from the group. These bivalve fossils are grouped into 7 fossil assemblages whose occurrences are closely linked with depositional facies. Several species occur as in life position in situ. Diversified Pterotrigonia are abundant in marine bivalve assemblages. Brackish-water bivalves such as Tetoria shishijimensis, Pulsidis higoensis and Crassostrea kawauchidensis repeatedly occur from tidal flat deposits at variable stratigraphic levels. The faunal diversity of the brackish-water assemblage increases from the estuarine deposits of the Eboshi Formation to the tidal-flat deposits on the shoreface of the Karakizaki Formation. These results in the Goshoura Group provide a new paleoecological scheme of the mid-Cretaceous bivalve fauna in the Far East Realm.

The shell microstructure of 44 species belonging to 19 genera and 5 families of Patellogastropoda was observed by scanning electron microscopy on the basis of material mainly from the Northwest Pacific. As a result, 17 microstructures of prismatic, crossed, and lamellar structures were recognized. The comparison among species revealed 20 shell structure groups which are defined by microstructures and shell layer arrangement. The relations between taxa and shell structural composition indicate that the Recent patellogastropods generally have distinctive and stable shell structures at the genus level. This high level of consistency provides a firm basis for the application of shell structural characters to identify fossil patellogastropods. However, the evolutionary process of microstructures and homology across different shell layers are mostly ambiguous in the absence of robust phylogeny and undoubted positional criteria for comparison. More studies from phylogenetic, ontogenetic and mineralogical viewpoints should be undertaken to discuss the process of shell structure diversification in patellogastropods.

A substantial lateral asymmetry of the shell is observed in the bivalve genera Claudiconcha (Petricolidae), Jouannetia (Pholadidae), Clavagella and Bryopa (Clavagellidae) that bore in rock or mineralised biogenic substrates. Two general adaptive patterns emerge from this study. (1) Lateral asymmetry is associated with cementation of one valve to the substrate, or is otherwise functional in preventing one valve from moving within the borehole, and (2) it is associated with determinate shell growth and appears only in the adult stage. The only important exception to the latter pattern is Bryopa, which secondarily lost the determinate growth pattern originally present in clavagellids. These features have evolved independently in each family, and differ in several constructional and functional respects among families.

Early shell development at the larval and early postlarval stages of a boring bivalve Zirfaea subconstricta is described using scanning electron microscopy, with discussion of its functional significance for achieving boring behavior. In Z. subconstricta, the boring function performed by the shell morphology drastically develops in a short time after the beginning of metamorphosis. This species shares common characteristics with other pholads regarding the early ontogenetic appearance of the boring morphology. These characteristics provide much information of primary shell morphology as basal condition of boring function, which is usually modified during the later growth.

Well preserved charophyte gyrogonites are discovered from the Kitadani Formation of the Tetori Group in the Takinamigawa area, Katsuyama City, Fukui Prefecture, central Japan. The Kitadani charoflora described in this paper is composed of five species of three genera, Clavator harrisii var. reyi (Grambast-Fessard), Mesochara harrisi (Mädler), Mesochara stipitata (Wang), Mesochara sp., and Stellatochara sp. C. harrisii var. reyi is a member of Clavatoraceae, which is a biostratigraphically well established charophyte group and is unique in Upper Jurassic to Cretaceous nonmarine deposits. The occurrences of C. harrisii var. reyi associated with other charophytes indicate that the charophyte-rich horizon of the Kitadani Formation is assigned to the Barremian, which well agrees with the age estimation established by the nonmarine molluscan assemblage.