Coeloterorhynchus aff. kayserii ( Rigaux, 1908 )

Baliński, Andrzej, 2006, Brachiopods and their response to the Early-Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf, Acta Palaeontologica Polonica 51 (4), pp. 647-678 : 667

Coeloterorhynchus aff. kayserii ( Rigaux, 1908)

Fig. 16A, B .

aff. 1908 Coeloterorhynchus kayserii n. sp.; Rigaux 1908: 24, pl. 1: 12. aff. 1981 Coeloterorhynchus kayserii ( Rigaux, 1908) ; Brice 1981: 150–

151; pl. 6: 27–30.

Material.—Nine complete to nearly complete and two fragmentarily preserved shells. Majority of the material comes from bed 4 and 14 of Wietrznia Id−W section; two specimens were recovered from bed 48 and 60 of Wietrznia Ie section.

Description.—Shell small averaging about 12 mm in width, wider than long, dorsibiconvex, subpentagonal in outline; cardinal margin obtuse attaining 105–120°, lateral margins rounded, anterior margin truncated, anterior commissure strongly uniplicate and serrate.

Ventral valve gently convex in lateral profile with erect to slightly incurved beak; sulcus wide but rather shallow, originating about valve midlength; tongue long, strongly bent dorsally, often with anteriorly directed top, with slightly concave to convex bottom.

Dorsal valve moderately convex in lateral profile, sometimes with flattened anterior, regularly and highly domed in anterior view, slightly concave near cardinal margin; fold very poorly defined, best marked anteriorly.

Shell smooth in posterior two−third, anteriorly costate; number of median costae very variable, on fold from 3 to 5, occasionally up to 7 costae; flanks with 3–5 costae. Microornamentation rarely preserved in form of delicate radial capillae and concentric growth lines.

Interior of the ventral valve with short, delicate, slightly convergent dental plates. Dorsal interior with thin horizontal hinge plates and very short median myophragm. Other details of the internal shell structure are strongly obliterated due to recrystalization of the shell interior.

Remarks.—The studied specimens are characterised by small shell dimensions, subpentagonal outline, strongly bent dorsally tongue, and variable number of median costae. They are externally most closely related to Coeloterorhynchus kayserii ( Rigaux, 1908) described by Rigaux (1908) and Brice (1981) from the Formation de Beaulieu (Early Frasnian) of France. The essential difference is, however, in the number of costae on fold and in sulcus which in C. kayseri oscillate from two to four whereas in specimens from Wietrznia there are up to seven costae. Also the number of costae on flanks is greater in the latter form attaining 3–5 costae in comparison to 1–3 costae in the former.

Occurrence.—The species is rather uncommon in the studied fauna. It was recovered in several layers of Wietrznia Id−W and Ie sections representing Palmatolepis transitans conodont Zone (Figs. 2, 3). In France C. kayseri was described from the Formation de Beaulieu of Ferques (Boulonnais); the occurrence is restricted to the Polygnathus asymmetricus conodont zone ( Brice 1981).

Figures

Fig. 16. Rhynchonellid brachiopod Coelotero− rhynchus aff. kayserii (Rigaux, 1908) from the middle Wietrznia Beds of Wietrznia Id−W. A, B. Two shells GIUS 4−273 Wt/EB−4 (A) and GIUS 4−273 Wt/EB−3 (B) in dorsal (A1, B1), ventral (A2, B2), lateral (A3, B3), posterior (A4, B4), and anterior (A5, B5) views.