Kitakamithyris sp.

Sun, Yuanlin & Baliński, Andrzej, 2011, Silicified Mississippian brachiopods from Muhua, southern China: Rhynchonellides, athyridides, spiriferides, spiriferinides, and terebratulides, Acta Palaeontologica Polonica 56 (4), pp. 793-842 : 833-834

Kitakamithyris sp.

Fig. 32 .

Material.—One almost complete and 13 fragments of ventral valves, and 7 fragmentary preserved dorsal valves, as well as 16 small fragments of valves showing characteristic micro−ornamentation, all from sample MH1. Two fragments of ventral valves and one incomplete dorsal valve from sample GT. Some small fragments of valves with well preserved micro−ornamentation come also from sample M2−8.

Remarks.—Of special interest are very sparse and fragmentary specimens, but with well preserved characteristic elythide micro−spinose ornamentation. These specimens (sample MH1 and M2−8) show concentric rows of elaborate double−barrelled, densely distributed spines (about 36 spines in 10 mm) similar to those illustrated by, e.g., Kozłowski (1914: fig. 18d) in Reticularia lineata var. perplexa (Mac Chesney, 1860) (= Martinothyris lineata ) and by Samtleben (1971: pl. 11: 11) in

http://dx.doi.org/10.4202/app.2010.0106

Phricodothyris guadalupensis (Schumard, 1859) . Unfortunately, our specimens with well preserved spines are so fragmentary that none of the internal shell features could be assessed. However, some co−occurring ventral valves are almost undoubtedly conspecific, because they also reveal a few preserved double−barrelled spines. These valves, the largest of which attains nearly 25 mm in length, show the presence of a medial sulcus, and internally well developed dental adminicula and median septum. Incomplete dorsal valves from sample MH1, representing probably the same species, has narrow inner socket ridges and ctenophoridium. Two fragments of ventral valves and one incomplete dorsal valve from sample GT also reveal elythid relations by having smooth shell with concentrically distributed scars marking the bases of broken off spines ( Fig. 32B ). The interior of these two ventral valves reveals the presence of well marked slightly divergent dental adminicula and strong and long median ridge. The growth lamellae preserved on a single dorsal valve indicate that this species was characterised by transverse shell and rounded cardinal extremities. However, the interior of the dorsal valve from sample GT shows shorter and wider inner socket ridges ridges than the specimens described above from sample MH1. It seems not unlikely that the elithid from sample GT may represent a different species.

This very fragmentary material from samples MH1, M2−8, and GT can be attributed quite convincingly to the genus Kitakamithyris mainly because of the ornamentation and general shell shape (indicated by growth lines) as well as the internal structure of both valves. Its very poor preservation, however, precludes a more detailed description and taxonomic assignment.

Stratigraphic and geographic range.—The species of Kitakamithyris are known from the Tournaisian of Japan, Russia, Australia, and North America.

Figures

Fig. 32. Reticularioid brachiopod Kitakamithyris sp. from the Tornaisian Muhua Formation, southern China. A. Incomplete ventral valve, PKUM02−0569, exterior (A1) and interior of the posterior region (A2). B. Ventral valve, PKUM02−0570, in exterior (B1), interior (B2), and lateral (B3) views, and enlargement of the interior showing well developed dental adminicula and median septum (B4). C. Posterior region of an incomplete dorsal valve, PKUM02−0571, in exterior (C1) and interior (C2) views. D, E. Two umbonal fragments of the ventral valve, PKUM02−0572 (D) and PKUM02−0573 (E), in exterior (D1, E1) and interior (D2, E2) views, showing concentric micro−ornamentation, dental adminicula, and median septum. F. Incomplete dorsal valve, PKUM02−0574, in exterior view. G. Fragment of ventral valve, PKUM02−0575, with well preserved external micro−ornamentation, in general view (G1) and enlargement (G2). H, I. Two specimens, PKUM02−0576 (H) and PKUM02−0577 (I), showing well preserved spinose micro−ornamentation, in general (H1, I1) and enlarged (H2, I2) views. G–I SEM micro−graphs. Samples MH1 (A−D, I), GT (E, F), and M2−8 (G, H).