Pseudoporambonites Zeng 1977

Pseudoporambonites ? sp.

Pl. 28, Figs. 5–8

Material. Ten exfoliated specimens, including at least two dorsal and six ventral valves, from samples F4295, F4323, F4351, F4356, F4359, F4376, F4407 and F4426. The figured specimens are F4356, F4359 and F4426.

Description. Shell large, inflated, biconvex with maximum thickness at mid-length. Valves moderately thickwalled. Outline transversely subangular to subcircular with maximum width at 35–50% of valve length. Hinge-line straight, 85% as long as maximum valve width. L/W ratio 0.72–0.88. Largest specimen (a ventral valve) 19.9 mm long and 22.6 mm wide. Cardinal extremities obtuse. Commissure rectimarginate or slightly uniplicate. Shell impunctate. Multicostellate ornamentation of weak and rather dense equicostellae. Costellae 4–6 per mm, impressed on distal 12–20% of valve floor.

Dorsal interarea short.

Ventral sulcus narrow and weak, not always developed, but otherwise beginning well anterior of umbo, sometimes disappearing distally. Ventral interarea slightly concave and apsacline, 85% as wide as total valve width. Median ridge or septum extending from muscle field to about 45% of valve length. Muscle scars bounded by ridge, reaching 36% of valve length. Two lateral ridges or septa forming a lyre-shaped configuration on proximal part of valve floor. Mantle canal system saccate, moderately impressed, with gonadal sacs reaching anterior of mid-valve length.

Remarks. The Spitsbergen specimens resemble the type species, Pseudoporambonites yichangensis Zeng, 1977, but differ in having denser costellae (normally 5 per mm compared to the 3 per mm of the type species); a more angular outline with a broader posterior margin; a markedly less plicate anterior margin; and smaller shells. The Chinese Dapingian P. hupeihensis (Wang, 1955) is elongate and strongly dorsibiconvex. Two additional species from SW China are here assigned to this genus: the Floian “ Punctolira ” resupinata Xu et al., 1974 and the Dapingian “ Punctolira ” magna Xu et al., 1974. “ Punctolira ” resupinata has about 2–3 costellae per mm, nearly straight lateral ventral ridges, and a rather poorly impressed mantle canal system. “ Punctolira ” magna has an L/W ratio of about 1.0–1.1, about 2–3 costellae per mm, and a median ventral septum reaching about mid-valve length.

Currently, the Spitsbergen specimens are the oldest specimens referred to the genus from outside China. Poulsen (1927) described some specimens under open nomenclature from the Floian Nunatami Formation of northwestern Greenland that appear to belong to the same genus. Compared to the Spitsbergen specimens, they have much more strongly impressed ventral gonadal sacs and central and lateral ridges that extend into the anterior half of the ventral valve floor.

Occurrence. Middle and upper parts of Nordporten Member, Kirtonryggen Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Plate 28

Palaeostrophia ? sp.

Kirtonryggen Formation, Spora Member. Coll. G. Vallance & R. Fortey, 1967.

1. F5745, dorsal valve exterior. Sample F5745.

2. F5709, ventral valve exterior. Sample F5709.

3. F5708, ventral valve exterior. Sample F5708.

4. F5738, ventral valve exterior. Sample F5738.

Pseudoporambonites ? sp.

Kirtonryggen Formation, Nordporten Member. Coll. G. Vallance & R. Fortey, 1967.

5. F4426, dorsal valve exterior. Middle part of member. Sample F4426.

6. F4359, exfoliated ventral valve exterior with visible mantle canal system. Upper part of member. Sample F4359.

7–8. F4356, exfoliated ventral valve exterior and detail of partly exfoliated ornamentation. Upper part of member. Sample F4356.

Porambonitoid? indet.

Valhallfonna Formation, Profilbekken Member.

9–10. TSGF16770, detail of ornamentation and whole fragment of ventral valve exterior. 83 m above base. Coll. J. Hansen, 01.08.2008, sample JH-161.

Camerella sp.

Valhallfonna Formation, Profilbekken Member.

11. TSGF16772, ventral valve exterior. 63 m above base. Coll. J. Hansen, 24.07.2008, sample JH-90.

Idiostrophia valdari Ross, 1972

Valhallfonna Formation, Olenidsletta Member.

12. TSGF16773, valve exterior. Coll. J. Hansen, 17.07.2008, sample JH-188.