Nothorthis, Ulrich & Cooper, 1938

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 97-99

Nothorthis ? sp. 1

Pl. 25, Figs. 15–16

Material. One articulated specimen and four dorsal and two ventral valves from sample JH-153. The figured specimens are TSGF 17088 and TSGF 17089.

Description. Shell slightly ventribiconvex, moderately unisulcate and subangular, with obtuse to rectangular cardinal extremities. L/W ratio apparently at least 0.6–0.7. Largest specimen 2.3 mm long. Ornamentation unequally ramicostellate, with 6–8 low, angular costellae per mm at 1-mm valve length. Ornamentation well impressed on distal 25% of valve floor.

Dorsal sulcus moderately deep, V-shaped.

Ventral valve slightly to moderately convex with weak median crest.

Remarks. The specimens are poorly preserved and no interiors are exposed, making the identification tentative. Externally, the specimens from Svalbard appear closely comparable with the type species, Nothorthis delicatula Ulrich & Cooper, 1938 , but the latter species has well-impressed costellae on the distal 10–20% of the valve floor and 5–6 costellae per mm at 1-mm valve length. N. algainensis ( Severgina, 1967) from the Tremadocian of the Altai Mountains has a very slightly convex ventral valve, weaker costellae and a weaker sulcus. N. asiatica Severgina, 1984 from the Altai Mountains has 4–5 costellae per mm at 1-mm valve length, is very slightly biconvex and has an L/W ratio of about 0.8. N. fascicostata Xu & Liu, 1984 has more strongly impressed costellae on the valve floor and a weaker dorsal sulcus. N. neichiaensis ( Chang, 1934) from the Floian to Dapingian of southwestern China has distinctly obtuse cardinal extremities and subequal costellae. N. penetrabilis Rubel, 1961 from the Dapingian of Estonia is widest near mid-valve length. N. pennsylvanica Ulrich & Cooper, 1938 is equicostellate and gently unisulcate. N. perplexa Xu & Liu, 1984 from the Floian of southwestern China appears to have a gentler sulcus and less convex dorsal valve. N. rude Xu & Liu, 1984 from the Floian of southwestern China is strongly unequicostellate and has an L/W ratio of about 0.8. N. sella Severgina, 1984 from the Tremadocian of the Altai

Plate 25

Archaeorthis groenlandica Poulsen, 1937

1. TSGF16755, ventral valve exterior. Kirtonryggen Formation, Basissletta Member, upper 0.5 m. Coll. J. Hansen, 03.08.2008, sample JH-170.

2. TSGF16756, ventral valve exterior. Kirtonryggen Formation, basal portion of Nordporten Member. Coll. J. Hansen, 22.07.2008, sample JH-63.

3–4. TSGF17075, dorsal valve interior, oblique anterolateral view. Kirtonryggen Formation, basal portion of Nordporten Member. Coll. J. Hansen, 22.07.2008, sample JH-64.

5. MGUH 29704 , dorsal valve interior. Cape Weber Formation, upper end of Devon Canyon in East Greenland. Coll. C. Teichert, 30.09.1931, sample 125 .

6. TSGF16881, ventral valve interior. Kirtonryggen Formation, basal portion of Nordporten Member. Coll. J. Hansen, 22.07.2008, sample JH-64.

Nothorthis subpyramidalis sp. nov.

Valhallfonna Formation, Profilbekken Member, 67 m above base. Coll. J. Hansen, 24.07.2008, sample JH-95.

7–8. TSGF16887 , paratype, dorsal valve exterior, oblique anterolateral view .

9. TSGF16888 , holotype, ventral valve exterior .

10–11. TSGF16886 , paratype, dorsal valve interior, oblique anterolateral view .

12–13. TSGF16890 , paratype, ventral valve interior, oblique anterolateral view .

14. TSGF16889 , paratype, ventral valve interior .

Nothorthis ? sp. 1

Kirtonryggen Formation, Nordporten Member, uppermost beds.

15. TSGF17088 , ventral valve exterior. Coll. J. Hansen, 29.07.2008, sample JH-153 .

16. TSGF17089 , dorsal valve exterior. Coll. J. Hansen, 29.07.2008, sample JH-153 .

Mountains is 16–20 mm long and has a shallow sulcus. N. tangshanensis Wang & Xu in Liu et al., 1983 from the Lower Ordovician of eastern China has nearly rectangular cardinal extremities, a moderate dorsal sulcus, and strongly impressed costellae on the valve floor. N. tarda Cooper, 1956 from the Darriwilian of Alabama has 6–7 costellae per mm at the 1-mm growth stage, distinct growth stop, and is gently unisulcate. N. termalis ( Herrera & Benedetto, 1989) from the Floian of Argentina has a higher L/W ratio but is otherwise difficult to distinguish based on its external features. N. tianjingshanensis Fu, 1982 from the Lower Ordovician of China has a weak dorsal sulcus and an L/W ratio greater than 0.8. N. transversa Cooper, 1956 from the Darriwilian of Alabama has generally more obtuse and rounded cardinal extremities, but otherwise its exterior is closely comparable.

Occurrence. Uppermost beds of Nordporten Member, Kirtonryggen Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.