Three new species and one new genus Masaophaedusa of fossil terrestrial Mollusca are described from fissure deposits within the Ryukyu Limestone in Okinawa and Yoron islands of the central Ryukyu Islands. They are Masaophaedusa takae, which occurred in Nishiku Fissure in Yoron Island and Katsuren Fissure in Okinawa Island, Chalepotaxis kenjii from Nishiku Fissure, and Coniglobus sashikiensis from Chinen Fissure in Okinawa Island. Masaophaedusa takae has characteristic, strong and long plicae, and its specialized clausilium has no relations with other genera of the Family Clausiliidae in Japan and adjacent areas. Chalepotaxis kenjii possesses a light brown, narrow band on the body whorl, and is closely related to Chalepotaxis spadix distributed in southern Taiwan. Coniglobus sashikiensis has a large shell and may be the ancestor of C. mercatorius, a living species of Okinawa Island.

The upper part of the Cretaceous Upper Yezo Group, which is distributed throughout the Kotanbetsu-Haboro area, Hokkaido, north Japan, contains a regressive sequence from outer shelf to shore-face sediments and is sedimentologically divided, from top to bottom, into four facies: Facies 1 (hummocky cross-stratified sandstone), Facies 2 (bioturbated fine-grained sandstone), Facies 3 (intensely bioturbated sandy mudstone), and Facies 4 (massive mudstone). The strata commonly yield bivalve fossils. With the exception of inoceramids, the bivalves are classified into three fossil assemblages: the Parvamussium-Nucula, Thetis-Nucula, and Nucula-Heterotrigonia assemblage, respectively. These assemblages are mostly autochthonous and include remarkable benthic fauna such as Propeamussiidae, Lucinacea, Nuculacea, and Tellinidae that were adapted to live under oxygen-poor conditions. In particular, the bivalves of Facies 3 inhabited favorable surroundings in terms of a rich supply of organic material and a suitable depositional environment.

The valve opening system of the Permian concavo-convex productid brachiopod Waagenoconcha imperfecta is discussed in reference to the mode of the valve articulatory system and the reconstructed musculatory system. The analysis of the articulatory system suggests that it could open to a maximum angle of 6 degrees. The characters that seem to have played the most important roles in that process are: (1) narrow ginglymus, (2) overhanging beak above the dorsal valve, and (3) relatively narrow interior space in the posterior ventral valve, which provides little space for rotating the cardinal process and in result prevents excessive shell opening. For reconstruction of the musculatory system in productide, the relationship between the contracting direction of the adductor muscles and its mode of attachment to the dorsal valve was examined in well preserved specimens of W. imperfecta. The furrows of the attachment scars are cup-shaped, and their axes are concordant to the direction of adductor contraction. This structural relationship indicates that the paired anterior and posterior muscle scars in the median sulcus represent the attachment sites of the adductor and the diductor, respectively. The reconstructed musculatory system is fairly similar to that of the extant terebratulides. The “scars” that were thought in previous studies to be the places for attachment of the massive and powerful diductor muscle in productides seem to be the imprints of the mantle canal on the interior ventral valve. All this suggests that the previous interpretation claiming that productides could open and close valves actively, should be abandoned.

Two batillariid and four potamidid species from the middle to upper Middle Miocene Kukinaga Group, Tanegashima Island, southwest Japan are described systematically. Of these, the two batillariid species are new to science. Batillariids and potamidids from the Kukinaga Group are composed of three elements: (1) survivors from the late Early to early Middle Miocene, (2) species confined to the middle to late Middle Miocene, and (3) earliest records of living species. The occurrence of Vicarya japonica Yabe and Hatai from the Kukinaga Group marks the last appearance of the species in the Neogene of Japan, and the presence of Telescopium telescopium (Linné) and Cerithidea (Cerithideopsilla) cingulata (Gmelin) marks their first appearance in the Neogene in the Indo-Pacific region. The Kukinaga molluscan fauna, characterized by the occurrence of these gastropods, flourished during the Middle Miocene along the Pacific coast of southwestern Japan under the strong influence of a paleo-Kuroshio warm current. This period corresponds to a remarkable marine climatic warming event correlated with Neogene Climatic Optimum 2.

Four species of trigonoceratid nautilids from the late Chesterian (Early Carboniferous) strata in the Imo Formation of Arkansas, Midcontinent North America are described. A specimen of Aphelaeceras arkansanum Gordon, 1964 reveals the external juvenile whorl morphology. Based on the discontinuous points of its surface lirae, we suggest the possibility that the hatching shell of A. arkansanum is cyrtoconic with two septa and a length of approximately 4.9 mm. Species previously described or assigned to Aphelaeceras are reexamined. Epistroboceras lesliense sp. nov. differs from E. caneyense Niko and Mapes, 2004 and E. pitkinense Niko and Mapes, 2005 in its lower ratios of umbilical zone height per whorl height and lower siphuncular position ratios. Epistroboceras? sp. indet. is also identified in this fauna. A new genus, Imonautilus, is erected on the basis of I. meeki sp. nov. The most characteristic features of this genus are the Stroboceras-like juvenile whorl, the obsolescence of the adoral ventrolateral grooves at or near maturity, and the roundly inflated adoral venter. Based on early ontogenetic similarities, a close evolutionary relationship between Aphelaeceras and Imonautilus is suggested.