Abstract
Peridermal tissue, and thecal ''floors'' are shown to be present in some specimens of Pseudoretiolites, Retiolites and Stomatograptus. The development of a dense reticulum and thecal hoods is also recognized as being a progressive developmental feature in Gothograptus. It is suggested that all these structures, whether internal or external, are the product of mature or old-age development. It appears questionable whether the Rhabdopleural model of rhabdosomal developmental adequately explains late-stage membranes and other adventitious tissues such as discussed herein.

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