キーワード：Munida nishioi，秩父盆地，中新統，子ノ神層，古環境．

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The Occurrence of Munida nishioi　(Crustacea: Decapoda: Galatheidae) from
the Miocene Nenokami Formation of the Chichibu Basin in Central Japan,
and some Discussions on Palaeoenvironment and Geological Age

Kiichi OBATA
Toyooka High School, 1-15-1 Toyooka, Iruma-City, Saitama 358

Abstract
　　　Munida nishioi Karasawa, 1993 (Crustacea: Decapoda: Galatheidae) has been described from the Nenokami Formation of the Chichibu basin in central Japan for the first time. Though the specimens are decomposed into carapace and many segments of chelipeds and pereopods, most of them are well preserved.
　　　 An emended diagnosis of M. nishioi is presented from observing the holotype of it.
　　　 Considering from the co-occurred molluscan fossils, the palaeoenvironment of their deposition are deemed to be the depth of 100m〜150m in the warm sea, which is within that of living M. japonica.
　　　 M. nishioi has ever been reported from the Middle Miocene in the districts of Setouchi and Hokuriku (Karasawa, 1993), so the discovery of the species extend its known geographic range to the Chichibu basin in central Japan. The occurrence of M. nishioi supports the view that the geological age of the Nenokami Formation is the early Middle Miocene.