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出典:Wikipedia
出典:『Wikipedia』 (2010/09/07 15:05 UTC 版)
Mackinnonia is a genus of small shelly fossil comprising straight or slightly-coiled shells of the helcionelloid type. The outer surface of their shell is smooth, whereas the inner surface has a net-like ridges. They are known from late Early Cambrian rocks across North America and Greenland.
Mackinnonia