Four morphospecies of foraminifera, Glabratella opercularis, G. subopercularis, G. nakamurai, and G. patelliformis, all of which have similar test morphologies, were reclassified by the use of both morphological characters and interbreeding experiments. Because specimens of Glabratella have been shown to reproduce sexually, it should be possible to determine breeding populational boundaries within Glabratella and to compare these with morphologically based taxonomic boundaries. Using stable characters, three morphogroups were reclassified from the four morphospecies. Laboratory interbreeding experiments revealed that individuals belonging to the same morphogroup formed gamontogamous pairs and then reproduced. However, individuals belonging to different morphogroups did not produce any gamontogamous pairs. This indicates that each of the reclassified morphogroups represents a distinct breeding population. Within the same morphogroup, individuals collected from two different localities closer than 100km apart could interbreed with each other. However, individuals from more than 500km apart could not breed with each other, even though the morphological characters of the individuals were very similar. This suggests that the population structure of the P. opercularis morphogroup is very similar to those of ring species.

抄録全体を表示

Rotaliid foraminifera have a complicated foraminal structure that has been recognized as the so-called toothplate. As to the interpretation of this toothplate, however, there has been confusion among foraminiferologists as to whether it is the same as the buliminid toothplate or not. In order to elucidate the apertural and foraminal structure, we examined some Japanese species of the genera Ammonia and Pararotalia. The apertures of Ammonia and Pararotalia show fundamentally the same style of construction, but the resultant structures are different among species. We recognized two main components instead of the indefinite toothplate in the aperture : foraminal plate and umbilical coverplate. The foraminal plate constructed out of a foramen is a free structure of the bilamellar wall. This plate is originally formed in the final chamber where it delimits the posterior side of the final aperture. The umbilical coverplate closes the umbilical side of the preceding foramen. This coverplate is originally bilamellar and is continuous from the foraminal plate. Both the foraminal plate and umbilical coverplate are formed when the final chamber is constructed. The umbilical coverplate interconnects the new and preceding foraminal plate, which may lead to the original concept of toothplate. However, the umbilical coverplate is not associated with the final chamber wall, but assists in closing the umbilical side of the preceding chamber wall. Such a chamber construction is restricted to rotaliids, thus we reject the term toothplate as only indicating modified structures that pass through the aperture. Descriptions of the rotaliid aperture are of value when we note the foraminal plate and umbilical coverplate. Thus two types of foramen, Ammonia-type and Pararotalia-type, were developed in the rotaliids.

抄録全体を表示

Mariella (Mariella) lewesiensis (Spath, 1926) from the Cretaceous of the Hobetsu district, south-central Hokkaido, is described. It is represented by a large specimen, from which a question may arise about the previous view of dimorphism. This species is not directly related to M. (M.) dorsetensis (Spath, 1926). It has some affinities with M. (M.) cenomanensis (Schluter, 1876).

抄録全体を表示

Ten types of dicotyledonous angiosperm cuticle are described from bore core samples from the Early Cretaceous (latest Albian-earliest Cenomanian) of the Eromanga Basin, central Queensland. To date, these are the oldest organically preserved angiosperm macrofossils in Australia. Most of this material is found as small dispersed fragments, but two more intact lobed leaves were found. The affinities of some specimens are suggested to lie with the Chloranthaceae and Illiciales, and possibly the Platanaceae, but the rest are unknown. None of the cuticles show the paracytic stomatal arrangement which is common in extant plant families often regarded as 'primitive'. However, one of the cuticle forms exhibits a 'plastic, ' variable form of subsidiary cell arrangment, which has previously been suggested as the most primitive condition. These angiosperms were a small component of an overwhelmingly gymnosperm (mostly conifer) dominated flora. They grew in clastic swamps, but may also have occured in coal swamps or sandy levees. The notably thin cuticle of some forms is consistent with an understory or deciduous habit.

抄録全体を表示

A new cephalopod species, Dolorthoceras nakazawai (Orthocerida : Pseudorthoceratidae), is described from the Permian Mizuyagadani Formation, Central Japan. Its Kazanian age, based on a fusulinid species, makes this the youngest record of Dolorthoceras. This is the first undoubted occurrence of the genus in Japan.

抄録全体を表示

The first authenticated Early Carboniferous miospores in Japan are described from the upper part of the lower Hikoroichi Formation (HK2 Member) in the Hikoroichi area, southern Kitakami Mountains, northeast Japan. The stratigraphically significant miospores are Auroraspora sp. cf. A. macra, Crassispora trychera, Schopfites sp., Spelaeotriletes crustatus, and S. sp. cf. S. pretiosus, which suggest a late Tournaisian to early Visean age and the "Vallatisporites Microflora" provincialism.

抄録全体を表示

Pisulinella is proposed as a new monotypic genus in the neritopsine family Neritiliidae, with the single species Pisulinella miocenica sp. nov. This new taxon occurs in subsurface Miocene sediments from Eniwetok Atoll, Marshall Islands, western Pacific. Nine specimens of P. miocenica were previously regarded as close to Nerita (Amphinerita) polita Linnaeus of the Neritidae. Reallocation of this species from Neritidae to Neritiliidae is based mainly on the shape of the protoconch, which is conspicuously tilted relative to the teleoconch whorls and has several spiral ridges. The discovery of this neritiliid species, previously allocated to the Neritidae, suggests that detailed examination of protoconchs is necessary for defining the systematic position of fossil neritopsines. Pisulinella miocenica sp. nov. may have lived in a cryptic habitat.

抄録全体を表示

A new species of a fossil bonito, Gymnosarda prisca (Scombridae, Perciformes) from the Early Tertiary shows an interesting combination of characters not seen in other, Recent, bonitos. The new species is based on hypural bones from the caudal region. Although a bonito, the fossil hypural plates possess a caudal notch, a character not known in Recent bonitos. The discovery of this new taxon causes a redefinition of the synapomorphies of the caudal region that define bonitos and their relatives, the tunas and Spanish mackerels. The fossil species has previously been described as part of Scomberomorus saevus.

抄録全体を表示