A second specimen of Takahashia eureka Matsumoto, 1984, from the lowest Cenomanian in the Hobetsu area of Hokkaido (Northern Japan), is described, and the diagnosis of the taxon is revised following a careful reexamination of the holotype. The presence of partially developed, minutely crinkled ribs on the shell implies that Takahashia had a close phylogenetic relationship with the long-ranging taxon Lytoceras (upper Sinemurian-Cenomanian), and we therefore assign it to the subfamily Lytoceratidae of the family Lytoceratidae. Evolution of Takahashia from Lytoceras supports the existence of a unique fauna in the North Pacific at the Albian-Cenomanian transition.
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