Orthidiella longwelli 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 : 102-103

Orthidiella longwelli Ulrich & Cooper, 1936

Pl. 26, Figs. 8–12; Table 35

1936 Orthidiella longwelli Ulrich & Cooper , n. sp. ―Ulrich & Cooper, p. 621.

1938 Orthidiella longwelli Ulrich & Cooper ―Ulrich & Cooper, p. 109, Pl. 17D, Figs. 15–33.

1938 Orthidiella striata Ulrich & Cooper , n. sp. ―Ulrich & Cooper, p. 110, Pl. 16B, Figs. 2–4 , 7–9.

1956 Orthidiella longwelli Ulrich & Cooper ―Cooper, pp. 339–340, Pl. 30D, Fig. 20.

Holotype. Complete specimen ( USNM 91299 ); Upper Pogonip (Middle Ordovician, Dapingian), Nevada.

Material. 22 conjoined valves, 334 dorsal and 326 ventral valves, and 30 undifferentiated fragments from the samples containing the trilobites A84235, A84258 , A84265 , A84267 , A84287 , A84288 , A84289 , A84290 , A84323 , A84324 , A84326 , A84330 , A84352 , A84353 , A84368 , A84379 , A84383 , X84356 and X84357 and from samples F3477, F4679, F4721, F4745, F4782, F4814, F4923, F4927, F4942, F4950, F4997, F5058, F5068, F5078, F5105B, F5114, F5116, F5268, F5273, JH-23, JH-25, JH-73–77, JH-79–92, JH-94–99, JH-101, JH-104–105, JH- 108, JH-111, JH-114–115, JH-117–124, JH-126, JH-158–164. The figured specimens are TSGF16891–16894 .

Diagnosis. Orthidiella with slightly convex dorsal valve and acute cardinal extremities; brachiophores merging with supporting plates and cardinal process to form a V; dental plates continuing as increasingly diverging ridges on valve floor.

Description of Spitsbergen Material. Shell slightly ventribiconvex, about 35% as high as long, semicircular to transversely subangular. L/W ratio 0.57–0.98. Largest specimen, a dorsal valve, 12.6 mm long and 16.8 mm wide. Cardinal extremities acute (70–85˚), defining widest part of shell. Anterior commissure unisulcate. Ornamentation equally or slightly unequally ramicostellate or multicostellate, with 6–9 angular costellae per mm at 1- mm growth stage. Ornamentation impressed on distal 15–40% of valve floor.

Dorsal valve slightly (rarely moderately) convex, with shallow, narrow and angular sulcus marked by interridge. Dorsal valve 10% shorter than ventral valve. Interarea concave or planar, anacline, its height equalling 9- 10% of valve length. Notothyrium triangular and partly closed by cardinal process and supporting plates. Brachiophores short (reaching 15% of valve length), rather high, rod-like, merging with the short cardinal process and supporting plates to form a V that diverges at 90–120˚. Fulcral plates absent. Notothyrial platform not developed. Median ridge slightly angular and broad, reaching about 60-65% of valve length. Cardinal process simple and high, pointing well behind interarea. Dorsal adductor field weakly impressed. Anterior adductor scars rather small, about half as large as posterior scars and located at 43–61% of valve length, bounding median ridge. Posterior adductor scars subcircular, located directly behind Anterior adductor scars at 33% of valve length, bounding median ridge. Mantle canal system obscure.

Ventral valve slightly to moderately convex, crested, deepest at 35% of valve length. Interarea moderately high and planar to concave, apsacline, its height equalling 15–23% of valve length. Delthyrium moderately wide, triangular, 19–22% as wide as valve. Pseudodeltidium present. Teeth moderately thick, triangular, supported by recessive dental plates. Dental plates slightly converging downward to valve floor but then diverging increasingly as low ridges on valve floor, reaching about 60% of valve length. Strong crural fossettes present. Muscle field located directly on valve floor or slightly raised, with slightly rounded anterior margin, reaching 28-35% of valve length. Diductor scars long, subcordate, separated by median area of similar width without adductor scar impressions. Pedicle callist absent. Valve floor thickened in the 30% of valve length anterior to the muscle field. Mantle canal system saccate, with moderately diverging vascula media reaching 65% of valve length.

Remarks. Orthidiella longwelli Ulrich & Cooper, 1936 is a morphologically variable species that was divided into two species, O. longwelli and O. striata , by Ulrich & Cooper (1938). Later, based on a study of many specimens, Cooper (1956) found O. striata to be a junior synonym of O. longwelli . The specimens from Nevada have generally more convex dorsal valves than the Spitsbergen specimens. However, this is the only consistent difference observed, other than the generally smaller size of the Spitsbergen specimens.

Occurrence. 17, 21, 30, 40–87, 90–94 and 98 m above base of Profilbekken Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen. Pogonip Formation, about 700 feet [215 m] below the Eureka quartzite at the first ridge east of Frenchman Flat, Las Vegas quadrangle, Nevada ( Ulrich & Cooper 1938).

Figures

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.