Morphologic variation of ve species of Parafusulina (P. yabei, P. tomeganensis, P. shimotsukensis, P. tochigiensis, and P. japonica) are described among samples from twelve stratigraphic levels in the Middle Permian Nabeyama Formation, Tochigi Prefecture, Japan. Variabilities of them were analyzed by showing many microphotographs and histograms of the frequency distribution of some measurable characters of the test, proloculus size, and length, width, form ratio, thickness of wall, and septal counts in the seventh whorl. Highly variable morphologic characters gradually changing from specimen to specimen distinguished in these ve species are thought to serve as a reference also for recognition and classi cation of other fusulinoidean species, and important for recognizing biodiversity of the past and for discussing related problems.
View full abstract