Study on the Carboniferous strata started in 1886, and that of Pusulinids in 1906. Stratigraphic study of the Korean Carboniferous strata in 1919 resulted in the four fold division of the Pyeongan System which embraces the Permo -Carboniferous, though a new scheme of subdivision of the Carboniferous has been proposed by the study of fusulinids in 1969. More than 60 species of Carboniferous fusulinids belonging to 20 genera have been described from South Korea. Of these fusulinids the Pseudostaffella-Neostaffella -Xenostaffella line shows an interesting development. Small Pseudostaffella gave rise to Pseudostaffella kimi which may have developed into the larger forms with the ooncave peripherise and concave umbilici. These are Neoataffella, N. hanensis, N. papilioformia, and N. magna. For these four-sided concave larger form8 a new subgenus name Hanostaffella is proposed. Genus Xenoataffella is the extremely squeezed form with the evolute outermost volution, though the other biocharacters are almost the same as in Hanostaffella.

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