Globulirhynchia minima, 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 : 349

Genus Globulirhynchia Brice, 1981 Globulirhynchia minima sp. nov.

Figs. 14A–E , 15 .

Pugnax lummatoniensis ( Davidson, 1864) ; Sarycheva and Sokolskaya 1952: 167, pl. 47: 256.

Pugnax lummatoniensis ; Ljashenko 1959: 197, pl. 70: 8, 9. Holotype:CompleteshellCNIGR13/13076,illustratedinFig.14A–D. Type locality: Zadonsk area , Don River basin, central Russia.

Type horizon: Evlanovo Horizon, Late Pa. rhenana Zone.

Derivation of the name: From small size of shell.

Diagnosis.—This small, smooth pugnacid is closely related to Globulirhynchia lemesli Brice, 1981 , but differs from the latter by a smaller sizes and less convex shell. Internally G. minima has shorter dental plates whilst G. lemesli exhibits longer dental plates.

Material.—50 complete shells.

Description.—Shell small size, up to 8 mm long and 9 mm wide, usually wider than long; biconvex to dorsibiconvex; subpentagonal in outline; cardinal margin short and slightly curved; lateral and anterior margins rounded; anterior commissure uniplicate.

Ventral valve with well−defined and convex umbo; beak small, slightly incurved; mesothyrid foramen with open delthyrium; wide sulcus starting in anterior half of the valve; tongue high and trapezoidal.

Dorsal valve sometimes slightly more convex than ventralvalve;lowfoldstartinginanteriorpartofvalve.Umbonal part smooth; low, rounded and infrequent ribs begin near to the anterior margin of shell; two low ribs are on flanks; 2–3 on fold and 1–2 on sulcus. Shell surface smooth, with concentric growth lines rarely preserved.

Ventral interior with short dental plates that are divergent in apical part, and parallel anteriorly. Crural bases directed dorso−laterally.

Remarks.—The G. minima was previously ( Sarycheva and Sokolskaya 1952; Ljashenko 1959) described as Pugnax lummatoniensis ( Davidson 1864) . The investigation of recently collected material showed that this form is indeed related to Globulirhynchia lemesli from the early Frasnian of Ferques (Biozone 2 in Brice et al. 1976, Po. asymmetricus Zone : see Brice 1981). It is possible, that “ Pugnax ” limula Ljashenko, 1959 and “ Pugnax ” elevatus Ljashenko, 1959, from the Rechitsa Horizon (Late Pa.hassi – Pa.jamiae conodont zones) of the central Russia could be referred to Globulirhynchia after their restudy.

Occurrence.—Late Frasnian, Evlanovo Horizon, Late Pa. rhenana Zone , central Russia.

Figures

Fig. 14. A–E. Globulirhynchia minima sp. nov. from late Frasnian, Evlanovo Horizon, Chlevnoe village, Don River Basin. A–D. Holotype, CNIGR 13/13076, ventral, dorsal, lateral, and anterior views, × 5. E. CNIGR 14/13076, × 2. F–M. Paromoeopygma koscharica (Nalivkin, 1934) from early Famennian, Zadonsk Horizon, Koschary village, Zadonsk region. F–I. Neotype, CNIGR 1085/4572 ventral, dorsal, anterior, and lateral views, × 1.5. J–M. CNIGR 1083/4572, × 1.5.

Fig. 15. Transverse serial sections of Globulirhynchiaminima sp. nov. from the early Famennian, Evlanovo Horizon, Don River basin, Zadonsk region, central Russia.Numbers refer to distances in mm from the top of the ventral umbo. A. CNIGR 15/13076. B. CNIGR 16/13076. C. CNIGR 17/13076.