Ripidiorhynchus chencinensis, Sokiran, 2002

Sokiran, Elena V., 2002, Frasnian-Famennian extinction and recovery of rhynchonellid brachiopods from the East European Platform, Acta Palaeontologica Polonica 47 (2), pp. 339-354 : 344-345

Genus Ripidiorhynchus Sartenaer, 1966 Ripidiorhynchus chencinensis sp. nov.

Figs. 6A–H , 7 .

Rhynchonella letiensis Gosselet ; Sobolev 1909: 508, pl. 6: 25a, b.

Rhynchonella aff. R. ferquensis Gosselet ; Sobolev 1909: 508–509, pl. 6: 24a, b.

Ripidiorhynchus aff. R. pskovensis Nalivkin ; Racki 1993b: 302, pl. 3: A–C, E, J, K.

Holotype: GIUS4−216 /R−10;complete,wellpreservedshell,illustrated in Fig. 6A–D .

Type locality: Abandoned western quarry, Góra Zamkowa, Chęciny, Holly Cross Mountains, Poland.

Typehorizon:JaźwicaMember(setA2; Racki1993b:96),lateGivetian. Derivationofthename:FromthevillageofChęciny,nearthetypelocality.

Diagnosis.—Close to R. livonicus but differs in having medianribinsulcusstrongerandthinnerdentalplatesinternally.

Material.—Six complete and ten damaged shells, and eight incomplete valves.

Description.—Shell medium sized, up to 19 mm long and 21 mm wide, usually wider than long, dorsibiconvex, transversally elliptical in outline; cardinal margin curved, lateral margins rounded; anterior commissure uniplicate.

Ventral valve moderately convex, beak small, slightly incurved, sulcus well marked begins at posterior one−third of thevalvelength,anteriorlyforminglongtrapezoidaltongue.

Dorsalvalvedeeperthanventralvalve,withwell−developed fold that begins at posterior one−third of the valve length.

Shell surface covered by simple ribs beginning from the beaks; 3 ribs on sulcus, with one median rib usually stronger, and 4 ribs on fold, with the medial rib usually stronger; up to 8–9 lateral ribs on each valve flank. Most with smooth fold and sulcus slopes; occasionally, rare parietal rib present.

Ventral interior as for the genus ( Fig. 7 ).

Remarks.— Racki (1993b: 302) described specimens from Góra Zamkowa and Stokówka as R. aff. R. pskovensis and noted that they are most similar to R. pskovensis from the early Frasnian of the Main Devonian Field. He suggested that the rhynchonellid from Poland might represent a new species that is described here. Although R.chencinensis sp. nov. proposed here is very close externally to R. livonicus (including R. pskovensis after revision) it differs from the latter in the usual absence of parietal ribs and development of a strong median rib in the sulcus opposed by two strong ribs on fold; R. livonicus has 2–5 equally developed median ribs and 2–3 parietal ribs.

Occurrence.—Latest Givetian ( Pa. falsiovalis Zone ) of the Holy Cross Mountains, Poland: Jaźwica Member at Góra Zamkowa and Stokówka.

Figures

Fig. 6. Ripidiorhynchus chencinensis sp. nov. from the late Givetian of Poland. A–D. Holotype, GIUS 4−216/R−10 in ventral, dorsal, lateral, and anterior views, × 1.5. E–H. Juvenile shell GIUS 4−216/R−10−1 in ventral, dorsal, lateral, and anterior views, × 1.5. Jaźwica Mbr., Góra Zamkowa.

Fig. 7. Transverse serial sections of Ripidiorhynchuschencinensis sp. nov. from the Givetian, Jaźwica Mbr., Góra Zamkowa, Poland. Numbers refer to distances in mm from the top of the ventral umbo. A. GIUS 4−216/R−10−2. B. Longitudinal section of GIUS 4−216/R−10−3.