The Hydrozoan coral, Circoporella semiclathrata HAYASAKA is a rather rare, yet very characteristic fossil in the Torinosu limestone developed in the Outer zone of South-West Japan, and in the Kwanto and Abukuma Mountainlands of North-East Japan., Very recently it was unexpectedly discovered in a dark gray limestone intercalated in a complex chiefly of schistose schalstein exposed at the east bank of the Saru-gawa, about 1., 7 km east of Sinnito Mine in Horosari-mura, Saru-gun, Hokkaido., Although only a fragmental one, the present material exhibits features characteristic of the coenosteum of Circoporella semiclathrata as described by HAYASAKA ; it occurred at the locality cited in association with such fossils as Nerinea (ss., ), Thamnastrea and other hexacorals., As fully stated in the Japanese text, this species is an important key-fossil of the Upper Jurassic not only in Japan, but also in abroad., Circoporella is very similar to Sphaeractinia in having the coenosteum composed of concentric lamellae and vertical elements, the concentric lamellae being apparently two layered under high magnification, a thin film-like layer limiting the upper surface of a thick inner lying homogeneous substance, and having astorhizae though rarely., This genus was sometimes confounded with Burgundia MUNIER-CHALMAS, a stromatoporoid closely allied to Clathrodictyon and which possess coenosteum composed of trabeculae in vertical and horizontal sets, which are homogeneous in microstructure under high magnification ; further astorhizae are lacking to it and zooidal tubes are present., In the renewed examination, the writers are now confident in regarding Burgundia and Circoporella to be generically independent on account of the differences mentioned above, and the species of Burgundia of European writer (Burgundia cf., semiclathrata HAYASAKA from the Astartian of Villereversure, Ain, France) to be true Circoporella and not Burgundia., By way it may be pointed out that the Upper Jurassic marine deposits are divisible into three different types according to lithological and fossil contents, namely : 1) Torinosu type composed of shale and sandstone in alternation with lenses of limestone known under the name Torinosu limestone and often richly coralline, 2) Kitakami type of shale and sandstone and lacking limestone, and 3) Hokkaido type having considerable amount of schalstein with limestone lenses which contains at least Circoporella found in the Torinosu type.,
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