Five Species of Microporina (Bryozoa, Cheilostomata) from the Pleistocene Setana Formation at Kuromatsunai, Hokkaido, Japan

Abstract. Fossils of Microporina species were collected and examined from the Soebetsu Sandstone Member of the Pleistocene Setana Formation in southwestern Hokkaido. A description is provided for M. japonica Canu and Bassler, and four species (M. sakakurai, M. minuta, M. quadristoma and M. soebetsuensis) are newly described. Some of them were previously reported as M. articulata (Fabricius). Among the five species, three (M. japonica, M. sakakurai, M. minuta) have a semielliptical or elliptical orifice, relatively large and deep frontal pseudopores, opesiules occluded with a thin plate showing vein-like surface sculpturing, and avicularia that are longer than wide. The other two (M. quadristoma, M. soebetsuensis) have a rounded-quadrate orifice (sometimes with a convex proximal margin), smaller frontal pseudopores, opesiules occluded but lacking vein-like surface sculpturing, and avicularia that are circular or wider than long. Marked orificial dimorphism is observed in two species, M. sakakurai and M. soebetsuensis.