The "Ryukyu Limestone" is divided into the Ryukyu Limestone Group and terrace-forming limetones on the basis of the investigations of the Okinawa-, Miyako-, Kume-, Aguni- and Izena-jima in the Ryukyu Islands. The Ryukyu Limestone Group representing the principal series of the "Ryukyu Limestone" is also classified to the Itokazu Limestone Formation and "Alternated" Limestone Formation in southern Okinawa-jima. The Itokazu Formation is mainly composed of hard and compact calcareous elastics containing a "marked bed" which includes exclusively abundant Cycloclypeus fossils. The Formation can be correlated to the Yajagama Limestone Formation of Kume-jima and the Itokinabaru Limestone Formation of Aguni-jima. The "Alternated" Limestone Formation is characterized by the alternation of compact and loose limestone beds, though the Formation also reveals to be the calcareous elastics. The thickness of each bed ranges 30 to 50 cm. Miyako-jima Limestone Formation encrusting Miyako-jima, can be correlated to this Formation. The "Alternated" Limestone Formation is considered to be younger than the Itokazu Formation from various reason, though the direct relationship has not been found yet. However, the possibility of the contemporaneous heterotopic fades to the Itokazu limestome Formation in some places is still open to question. These Formations resulting from the sediments originally of extensively large basins in the early Quaternary age were tilted and displaced by faulting and afterwards were eroded. Therefore, it is clear now that the geomorphological correlation is not suitable for the Ryukyu Limestone Group. The terrace-forming limestones are represented by the Yomitan Limestone and "Awaishi" Limestone of Okinawa-jima, and the Yanoshita-jima Limestone of Izena-jima. The "Awaishi" Limestone show a typical forminiferal biosparudite which signifies calcareous shallow sea sediment, while the other terrace-forming limestones are biolithites including bioherms and patch reefs in some places. The limestones distributed sporadically throughout the islands, are generally thin formations with less than 10 meters approximately. It is significant that the terrace-forming limestones fringed as the coral reefs the islands which had been formed owing to the tectonic movement occuring after the Ryukyu Limestone Group had constructed. Therefore, the limestones can be correlated to the gravel beds of the non-calcareous terrace deposits. The terrace composed of non-calcareous deposits are typically developed in the northern part of Okinawa-jima, and can be divided into the Higher Terrace (100-180 m a. s. 1.), the Middle Terrace (30-70 m a. s. l.) and the Lower Terrace (15-20 m a. s. l.). Besides them, the post-glacial benchs of less than 10 m above sea level are seen in some islands. The Yomitan Limestone and the "Awaishi" Limestone are correlated to the Middle Terrace deposits and the Yanoshita-jima Limestone is to the Lower Terrace deposits. The Iribishi Limestone formed at the post-glacial optimum stage is typically represented by the limestone bench of the north-western shore of Kumejima.

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Tomes' process of the ameloblast plays an important role in the formation of the final shape of enamel prism. The chief pattern of the elephant enamel as observed by the horizontal section was similer to the maiden-hair frond (KOZAWA, 1974), and the section shows a round head facing the enamel surface and two winged processes directing to the dentino-enamel junction. For the purpose of discussing the ameloblast morphology of the fossil elephant, e.g. fossil mammoth (Elephas primigenius) and nauman-elephant (Paleoloxodon naumanni), etc, developing enamel surface from the tooth germ of indian elephant was offered to the present investigation, assuming the surface morphology of the developing enamel was the replica of the tip of Tomes' process. Most of the pits, which contained Tomes' process, were rectangle when obderved from the surface, while round or oval pits were also found. Pits were surrounded by wall-like ridges, which were supposed to be the interprismatic substance in the mature enamel. On the either edge of the short diameter of rectangular pits, a small depressions of bif treated tip of the ameloblast, which were comon to that forming maiden-hair prism. Round or oval pits were surmised to form the ameloblast, cross section of which revealed key-holes or arched appearance. As Tomes' process of Indian elephant teeth is bifurcated at the tip, the two dents are supposed to be impressions of the tip.

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[in Japanese]

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Diastereomers of isoleucine have been investigated on the insoluble fractions of 41 molluscan fossils yielded from the Pleistocene deposits in the Kanto district. The results are as follows. 1) The rations of D-alloisoleucine to L-isoleucine (D/L) show different values even in the fossils belonging to the same stratigraphic horizon, probably owing to the recent amino acid addition to the fossil ones in the shells. 2) The maximum D/L ratio in each formation which represents the value with the least contamination of recent L-isoleucine, becomes greater with an increasing in geological ages of the Pleistocene formations treated in this paper. Racemization of isoleucine could be a useful tool for the stratigraphic correlation among the Pleistocene formations. 3) The reaction rate constant of L-isoleucine to D-alloisoleucine in the fossils of the Narita Formation is 5.0×10^-7 yr.^-1 from the calculation based on the following values in eq. (2) ; D/L=0.07 and absolute age by the fission track method=1.4x 10⁵yr. B. P. 4) The absolute age of the Yabu Formation is calculated at 2.6×10⁵yr. B. P. by using this rate constant to eq. (2), which is in good agreement with the age 2.75×10⁵yr. B. P. determined by the fission track method.

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