Abstract
The writers studied on the internal structure, mineral component, inorganic elemental composition and others of some tests of fossil Echinarachnius having various macroscopic characteristics from the Neogene and Quaternary sediments, mainly the Narita Formation, Pleistocene. They used for these investigations the optical microscopic observation, X-ray analysis, chemical analysis and EPMA method. Summary of the results obtained is described in the following. 1. Three types of the internal structure of optical microscopic level have been recognized in fossil echinoidean tests examined. The first one is that retain the network structure which is observed in the recent sample, the second is that partially preserved the network structure and the third is that completely lost the original structure. It does not always follow that these types of the structural pattern correspond to the external view of preservation of the fossil tests. 2. The tests which have clear network structure are mainly composed of high magnesian calcite, and the tests in which the network does not recongnized are composed of low magnesian calcite. Namely, the change of the morphological pattern of the internal structure well corresponds to that of the mineral component. 3. The internal structure and the mineral component of the brownish tests resemble to those of recent samples. It may be considered that the brownish color due to some iron compound, and the positive relation can be recognized between iron contents and magnesium contents.
