Homotreta aff. gorjanskii ( Pelman, 1973 )

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 363-364

Homotreta aff. gorjanskii ( Pelman, 1973)

Fig. 12 .

Material.—Several hundred calcium phosphatic dorsal and ventral valves, including figured SMNH Br151223–151232, from sample 19/92, Yunkyulyabit-Yuryakh Formation, Khorbusuonka River, Siberia, Russia. Anopolenus henrici – Corynexochus perforatus Zone, Mayan stage (correlated with the Drumian Stage).

Description.—Shell rounded in outline, covered with fine concentric growth lines with occasional sets of drapes. Ventral valve high conical with umbo situated anteriorly to the posterior margin. Ventral pseudointerarea steeply procline. Apical foramen in a short tube, external pedicle opening enclosed within brephic shell at its margin. Dorsal valve gently convex, rounded with a marginal umbo. Dorsal pseudointerarea orthocline, with a broad triangular median groove and short propareas. Dorsal interior a broad indistinct median ridge. Brephic shell broadly oval in outline, 150–170 μm long and 150–170 μm wide, covered with pits, ca. 1 μm in diameter.

Remarks.—This form is different from Homotreta gorjanskii in having anteriorly placed umbo and a higher ventral valve. Similar specimens are attributed to H. gorjanskii by Pelman (1977: pl. 8: 2а, 2в, 2г).

Figures

Fig.12. Lingulid brachiopod Homotreta aff.gorjanskii (Pelman, 1973) from the middle Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; sample 19/92. A. Specimen with both valves preserved, SMNH Br151223.A1, posterior view;A2, lateral view.B, D, E, I. Ventral valves, SMNH Br151224– 151227, respectively. I1, oblique posterior view, I2, inner surface. C, F–H, J. Dorsal valves, SMNH Br151228–151232, respectively. H1, inner surface; H2, oblique inner view; J2, close-up showing brephic shell. Scale bar: 500 µm (A–E, G, H, I1, J1), 250 µm (F, I2), and 60 µm (J2).