Article: Shell-growth in Recent terebratuloid Brachiopoda

The structure of the brachial valve of four Recent species of terebratuloids was investigated by techniques involving both electron microscopy and light microscopy. The combined approach reaffirmed the conclusions of some previous workers and provided new data on shell growth.The interpretation of patterns observed when sections are cut through the shells is complicated not only by the spatial orientation of the section itself, but by the habit of the truncated crystals as well. Changes in the nature of crystal growth, orientation, and distribution are shown to be related to retraction of the mantle evidenced at major growth-lines.