Lenatoechia octjabrensis, Modzalevskaya, 2003

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 87-88

Lenatoechia octjabrensis n. sp. ( Figs 14 J-P, R, S; 16)

HOLOTYPE. — N 40/12991, CNIGR Museum , St. Petersburg ( Fig. 14 N-P), conjoined valves; L = 8.8 mm, W = 8.3 mm, T = 7.2 mm.

ETYMOLOGY. — After the October Revolution Island . TYPE LOCALITY. — Loc. 11, Matusevich River, October Revolution Island ; Samojlovich Formation.

AGE. —?Llandovery-Wenlock.

MATERIAL EXAMINED. — Mainly conjoined valves of good preservation, one specimen from loc. 11, bed 6B, 10 specimens from loc. 2, bed 66, Matusevich River ; 65 specimens from loc. 117v, Ushakov River , October Revolution Island ( Männik et al. 2002: figs 1, 2, 5) ; Samojlovich Formation.

MEASUREMENTS (IN MM). — L = 4.7-8, W = 5.7-8.3, T = 4.6-7.2.

DIAGNOSIS. — Shells subtriangular in outline, strongly biconvex in lateral profile; costae rounded, low and numerous; anterior margin uniplicate.

DESCRIPTION

Shells small, equally (strongly) biconvex, with subtriangular outline and numerous ribs. Ventral umbo and pointed beak incurved, narrow, with delthyrium closed by deltidial plates. Ventral sinus and dorsal fold weakly developed, anterior margin uniplicate. Surface covered by rounded, equal and high ribs (in total 35) with the width of the ribs exceeding their interspaces. Ventral valve with long dental plates and massive teeth. The dorsal interior contains a discrete cardinal plate and septalium, supported by broad, massive, short septum, that extends approximately half the valve length ( Fig. 16 ).

COMPARISON

The pattern of the ribs, weakly developed sinus, fold, and uniplicated anterior margin are similar to those of Lenatoechia ramosa ( Nikiforova, 1961) from the Talikit and Omnutakh formations of East Siberia ( Nikiforova & Andreeva 1961: 207, pl. XLIV, figs 8, 9). The new species differs from L. ramosa by having smaller size and possessing a subtriangular outline.

Figures

FIG. 14. — A-E, Stegerhynchus? decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968; A, ventral view; B, dorsal view; C, lateral view; D, anterior view; E, enlarged external surface of a complete shell (N 38/12991), loc. 13, bed 89, Vodopad Formation; F-I, V, Anabaria? latens n. sp.; F, dorsal view; G, ventral view; H, lateral view; I, anterior view of a complete shell (holotype N 50/12991), loc. 11, bed 6B, Samojlovich Formation; V, enlarged external surface of a poorly silicified shell (N 51/12991), loc. 29a,?Vodopad Formation; J-P, R, S, Lenatoechia octjabrensis n. sp.; J, ventral view; K, dorsal view; L, lateral view; M, anterior views of a complete shell (N 41/12991), loc. 11, bed 6B, Samojlovich Formation; N, ventral view; O, dorsal view; P, lateral view of a complete shell (holotype N 40/12991), loc. 2, bed 66, Samojlovich Formation; R, ventral view; S, dorsal view of complete shell (N 42/12991), loc. 117v,?Samojlovich Formation; Q, T, U, Anabaria? latens n. sp.; Q, pedicle valve of a complete shell (N 52/12991), loc. 13, bed 27, Srednij Formation; T, ventral view; U, dorsal view of a complete shell (N 53/12991), loc. 13, bed 64, Golomyannyj Formation. Scale bars: A-D, F-M, 5 mm; E, V, 2 mm; N-U, 3 mm.

FIG. 16. — Selected transverse serial sections, illustrating the development of internal structures in Stegerhynchus? decemplicatus duplex Nikiforova & T. Modzalevskaya,1968 (N 39/12991). Measurements: length 7.7 mm, width 10.3 mm, thickness 4.9 mm; loc. 13, bed 89, Vodopad Formation. Numerical designations are the same as on Fig. 11. Scale bar: 2 mm.