Palaeostrophia, Ulrich & Cooper, 1936

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 108-109

Palaeostrophia ? sp.

Pl. 28, Figs. 1–4

Material. Four dorsal and five ventral valves from F5703, F5709, F5718, F5724, F5736, F5738 and F5745. The figured specimens are F5708, F5709, F5738 and F5745.

Description. Non-strophic shell thin-walled, slightly to moderately biconvex and subtriangular to transversely suboval. Anterior margin lacking tongue-like extension. Anterior commissure gently rounded, uniplicate. Largest measured specimen 6.6 mm long and 8.0 mm wide. Ornamentation consisting of weak growth lines.

Dorsal umbo broad and rounded. Maximum valve depth located slightly anterior of mid-valve length; maximum width located at mid-valve length. Dorsal fold originating at 1.0– 2.5 mm of valve length and widening strongly to constitute half of valve width in larger specimens. L/W ratio 0.69–0.79.

Ventral umbo small and pointed. Maximum valve depth located at 35% of valve length; maximum width located at 65% of valve length. Ventral sulcus originating at 1.0– 2.5 mm of valve length and widening strongly to constitute half of valve width in larger specimens. L/W ratio 0.72–0.83.

Remarks. At present, we lack information about the valve interiors. Until this information can be obtained through specimen peels or collection of new material, the identification remains uncertain. Several genera within the family Clarkellidae , such as Clarkella , Diaphelasma and Syntrophina , may show many of the same external features as Palaeostrophia .

Occurrence. Spora Member, Kirtonryggen Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Figures

FIGURE 1 Locality maps of the Svalbard Archipelago. a) Locations of sites yielding Lower Palaeozoic fossils mentioned in this paper. b) Geological map of the Basissletta plain, northeastern Ny Friesland; redrawn from Fortey & Bruton (1973). The base map is based on aerial photos made available by the Norwegian Polar Institute and on field observations made by the authors in 2008.

FIGURE 2 Stratigraphical ranges and diversity of brachiopod species at Basissletta, Spitsbergen, and relative sea levels and percentages of linguliform brachiopods in the total brachiopod fauna. White shading in the last graph indicates stratigraphical intervals without brachiopods. Thicknesses of units are according to Fortey & Bruton (1973). Lithological log and sea level curve are from Hansen & Holmer (2010).

FIGURE 3 Rose histograms for the umbonal orientation of the large brachiopod Ectenoglossa? oviforma sp. nov. found in the Olenidsletta Member, Valhallfonna Formation. a) Histogram of 58 specimens from 88 m above the base of the member. b) Histogram of 13 specimens from 94 m above the base of the member.