Numerous specimens (having the general aspect of Estheria) lie on the bed-planes of a bluish, slightly micaceous, noncalcareous shale from the “Shale and Sandstone Series” of the Federated Malay States. The valves lie flatwise in the strata, either singly or in still connected pairs; and are not so much compressed but that they show the concavity of the insides, and the convexity and special features of the outsides. There are many examples of valves in different stages of growth, but a striking similarity of character indicates that all belong to one species. The shell itself is absent, but hollow moulds of one valve and solid casts of the other supply material for defining its character. No other organisms have been recognized in the shale.