Harpidium sp.

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 85

Harpidium sp. ( Fig. 13 )

MATERIAL EXAMINED. — Five poorly preserved specimens from loc. 13, beds 87 and 102 (coquina), Matusevich River, October Revolution Island, and five external moulds from loc. 20533, Komsomolets Island ( Männik et al. 2002: figs 1, 2, 5); Vodopad (lower Snezhinka) Formation.

REMARKS

Shells are large (up to 60 mm in length), with a massive incurved ventral umbo and a rectimarginate anterior margin. Inside the pedicle valve there are double septum extending to the anterior third of the shell, and supporting long spondylium with a moderately wide floor. The dorsal interior consists of a discrete brachial plate which extends for the length of the valve and is gently divergent anteriorly. The ventral muscle field is divided deeply by septum. The dorsal muscle field is longitudinal in outline, limited by brachial plates laterally and divided by a narrow low crest. The specimens cannot be assigned to Pentamerus J. de C. Sowerby, 1813 because of the strongly convex valves and lack of a trilobate external structure. The specimens from Severnaya Zemlya resemble those studied by Poulsen (1943: 35, pl. 3, fig. 21) and by Boucot & Johnson (1979) from the Offley Island Formation ( Greenland). V. P. Sapel’nikov (1985) proposed that these specimens, but also some other species of Harpidium , may be assigned to one of the forms of H. angustum Poulsen, 1943 . Harpidium occurs in the upper Llandovery to Ludlow in the Urals, Central Asia, Kazakhstan, Altaj Mountains, North East Russia, North America (Alaska, Iowa, Wisconsin, Ohio, Illinois), and Greenland.

Order RHYNCHONELLIDA Kuhn, 1949

Figures

FIG. 13. — Harpidium sp., complete shell (N 37/12991), loc. 13, bed 27, Vodopad Formation; A, dorsal view; B, lateral view; C, posterior view. Scale bar: 10 mm.