The cover of this kogo provides an interesting variation in that the chidori are flocking around one bird, apparently their leader, who is perched on an incense burner in the form of a tortoise; this version of nami-ni-chidori is rather rare. Kogo of this simple type are difficult to date because there is little to differentiate a 13th century example from a 16th century, thanks to the lacquer artist's gift for repitition. This example might be dated mid 15th century, or more loosely, Muromachi period (1395-1596)