. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. Rhipidium (costate) Brooksina Cymbidium / Conchidium. Harpidium (smooth) .Virgiana Clorinda (GvPiDULiNiE) smooth or with faint undulations at the front. Shell substance fibrous, impunctate. Ventral interior.—The dental plates are convergent and with their septal plates unite to form a spondylium duplex. Dorsal interior.—A tripartite division of the crural plates is recognizable. Thin inner plates unite with the walls of the valve to form lateral chambers. The sockets are notch
. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. Rhipidium (costate) Brooksina Cymbidium / Conchidium. Harpidium (smooth) .Virgiana Clorinda (GvPiDULiNiE) smooth or with faint undulations at the front. Shell substance fibrous, impunctate. Ventral interior.—The dental plates are convergent and with their septal plates unite to form a spondylium duplex. Dorsal interior.—A tripartite division of the crural plates is recognizable. Thin inner plates unite with the walls of the valve to form lateral chambers. The sockets are notches in the partitions of these chambers next to the wall of the valve. The brachial processes are long. The septal plates are discrete, divergent or parallel, continued to the internal surface of the valve. Between the septal plates a low median septum divides the septal chamber into two parts. The cardinal process is a callosity under the beak. Geologic range. — Throughout the Silurian of Europe and North America and probably widely elsewhere. American Species Pentamerus bisinuatus McChesney 1861 P. comfressui Kindle and Breger 190+ P. corrugatus Waller and Davidson 1896 European Species Pentamerus borealis Eichwald 1842 P. esthonus Eichwald 1860? P. gothlandicus Lebedeif 1 892 P. Iwvis Sowerby 1812 P. oblongus Sowerby 1812 P. samojedicus Keyserling 1846 P. schmidti Lebedeff 1892 Distinguishing characters.—The genus Pen- tamerus is characterized by its comparatively smooth exterior, long spondylium duplex, discrete septal plates, and tripartite cardinalia. Discussion.—Hall and Clarke state that Pentam- erus "is an exceedingly plastic type," and limit the name to smooth shells typified by P. Icevis Sowerby. The latter is considered by European paleontologists as the young of P. oblongus. The specific name P. oblongus has in America been applied to a wide variety of forms, among them P. oblongus subrectus Hall and Clarke. In this form the septal plates of the
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