Scaphelasma lamellosum Krause & Rowell, 1975

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 66-68

Scaphelasma lamellosum Krause & Rowell, 1975

Pl. 17, Figs. 8–16; Pl. 18, Figs. 1–4 ; Table 20

1975 Scaphelasma lamellosum new species ―Krause & Rowell, p. 49–51, Fig. 42; Pl. 6, Figs. 13–29.

Holotype. UKMIP 79705 , conjoined valves; Orthidiella zone (Dapingian) , Antelope Valley Formation; Meiklejohn Peak , Nevada ( Krause & Rowell 1975).

Plate 17

Semitreta spitsbergensis sp. nov.

Valhallfonna Formation, Olenidsletta Member, 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136.

1–4. TSGF16928 , paratype, ventral valve exterior, oblique anterolateral view, larval shell, and detail of larval microornamentation .

5–6. TSGF16930 , holotype, posterior view of ventral valve, apical process and internal pedicle tube .

7. TSGF16929 , paratype, ventral valve interior .

Scaphelasma lamellosum Krause & Rowell, 1975

8–9. TSGF 16976, dorsal valve exterior, larval shell. Valhallfonna Formation, Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23.

10–11. TSGF 16974, dorsal valve exterior, oblique lateral view. Valhallfonna Formation, Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184.

12–13. TSGF 17007, dorsal valve exterior and larval shell. Kirtonryggen Formation, Nordporten Member, upper beds. Coll. J. Hansen, 29.07.2008, sample JH-153.

14. TSGF 17006, dorsal valve interior. Kirtonryggen Formation, Nordporten Member, upper beds. Coll. J. Hansen, 29.07.2008, sample JH-153.

15. TSGF 16975, dorsal valve interior. Valhallfonna Formation, Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23.

16. TSGF 16977, median septum of dorsal valve. Valhallfonna Formation, Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23.

Material. 178 dorsal, 88 ventral, 82 undistinguished, and 15 conjoined valves from samples F3475, F3477, F3478, F3673, F3675 ½, F3797, F4997, F5032, F5273, F5316, F5642, F5690, F5765, TS92.3, JH-23, JH-54, JH- 139, JH-153, JH-161 and JH-184. The figured specimens are TSGF 16973–16977, TSGF 17006 and TSGF 17007.

Description of Spitsbergen material. Shell small, with planar to ventribiconvex profile, transversely oval or subangular outline, and nearly straight or concave posterior margin. L/W ratio 0.71–0.85. Largest measured specimen deformed, 1.5 mm long and 1.2 mm wide. Larval shell subcircular, about 0.14–0.16 mm long. Larval microornamentation consisting of rather large, shallow, flat-bottomed, circular pits among dense, fine pitting of various sizes. Large pits up to 5 µm in diameter. Postlarval ornamentation of coarse, laminate rugae, usually separated by three to four closely spaced, tread-like, even, concentric ridges; about 35–90 concentric ridges per mm. Rugae coarsest on dorsal valve and impressed on valve floor.

Dorsal valve slightly convex to planar, with broad sulcus and marginal, pointed umbo. Propareas low to moderately anacline, concave. Median groove shallow and short but wide (21% of valve width), with convex anterior margin. Median buttress absent. Median septum high, triangular, with posterior edge located at 0.3–0.4 mm of valve length, apex located at 66–73% of valve length, and anterior edge located just over 0.1 mm from anterior valve margin. Median septum absent in juvenile specimens. Cardinal muscle scars poorly impressed. Anterocentral muscle scars absent. Mantle canal system not impressed.

Ventral valve low subconical, with rounded apex located at 34–46% of valve length. Pseudointerarea procline, 33–57% as wide as valve, poorly defined. Intertrough moderately deep. Foramen rather large (10% of valve length), elongate-oval, not enclosed by larval shell. Larval shell bilobed, constituting valve apex. Apical process absent. Vascula lateralia occasionally moderately impressed, diverging at about 70˚.

Remarks. According to the original description of Scaphelasma lamellosum Krause & Rowell, 1975 , the density of the tread-like ridges is about 10 per 0.1 mm. This measurement is highly variable in Spitsbergen specimens, although in general there the ridge density decreases toward the valve edge.

Occurrence. Uppermost beds of Nordporten Member, Kirtonryggen Formation; 80–87, 92.3–93 and 140 m above base of Olenidsletta Member, Valhallfonna Formation; and 21, 26, 50–54 and 83 m above base of Profilbekken Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen. Orthidiella zone (Dapingian) of basal Antelope Valley Formation, Nevada ( Krause & Rowell 1975).

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.