A NOTE ON THE SHELL STRUCTURE OF THE TRIPLESIACEAN BRACHIOPODS

The triplesiacean shell has long been accepted as being impunctate, and has recently (Williams 1968) been shown to be of the laminar type which characterises the non-plectambonitacean strophomenids. Examination of a specimen of the triplesiid Oxoplecia , however, shows a clear development of pseudopuncta; and what appears to be a differentiated primary layer external to the laminar shell in this specimen is confirmed from the shell of another Oxoplecia species.
The presence of rarely developed pseudopuncta within the superfamily supports the association of the Triplesiacea with the Davidsoniacea by Williams (1970), while the establishment of a primary layer in the Triplesiacea confirms his expectation based on its presence in the presumed billingsellacean ancestors.