. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. 38 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA (3) Clitambonites ty-pe (see pi. A, fig. 7^ pi. 8, fig. 6; t. fig. 10).—Here the brachiophores are simple blades or flattened rods, but are supported in a unique manner. Shell matter of the noto- thyrial platform is built up conspicuously under the cardinal process and is extended laterally for a considerable distance, forming, with the prominent median ridge and chilidium, an anchor-shaped structure. However, the original
. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. 38 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA (3) Clitambonites ty-pe (see pi. A, fig. 7^ pi. 8, fig. 6; t. fig. 10).—Here the brachiophores are simple blades or flattened rods, but are supported in a unique manner. Shell matter of the noto- thyrial platform is built up conspicuously under the cardinal process and is extended laterally for a considerable distance, forming, with the prominent median ridge and chilidium, an anchor-shaped structure. However, the original or youthful brachiophore is in some specimens clearly distinguish- able from the adventitious shell matter. This type of brachial apparatus occurs in Clitambonites, Vellamo, Gonambonites, Estlandia, Hemipronites, Deltatreta, and Pomatotrema; also in certain shells referred to the Plectambonitidse, as Plectambonites s. s., Plectella, and Ingria. Another modification of the clitambonitid type is visible in Productorthis, in which the brachio- phores are at first of the primitive flat blade type, but in later growth adventitious shell is laid down inside and outside of them and likewise around the distal end of the blade, forming cuplike structures. This type, in a somewhat modified form, also occurs in certain dalmanellids, totally obscuring the original brachial apparatus (see pi. 4, fig. 15). (4) Plectorthis-Hebertella type (see pi. 11, figs. 4, 26).—Here the brachiophores are sup- ported by concave plates which unite with the floor of the valve on each side of or beneath the. Fig. 10.—Estlandia marginata (Pahlen). Diagram showing brachiophores in place supported by a lateral swelling of adventitious substance. cardinal process. The socket is defined, not by the outer face of the brachiophore, but by a small concave plate called the fulcral plate^^ located between the outer face of the brachiophore and the wall of the valve. This type of brachial apparatus characterizes
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