Hindella cf. crassa (Sowerby, 1839)

Hints, Linda & Harper, David A. T., 2015, The Hirnantian (Late Ordovician) brachiopod fauna of the East Baltic: Taxonomy of the key species, Acta Palaeontologica Polonica 60 (2), pp. 395-420 : 415-416

Hindella cf. crassa incipens ( Williams, 1951)

Fig. 15A, E, F .

Material.— 102 specimens, mostly fragmentary, embedded in rock. Porkuni Regional Stage , Kuldiga Formation , Hirnantian ( Upper Ordovician ); western Latvia and southwestern Estonia. Drill core and depth (in meters) of sample intervals with brachiopods. Depths of fragmentary preserved specimens are marked with “?” Hindella cf. crassa incipiens ( Williams, 1951) in collection GIT 542 : Adze-6,?844.0–?844.5; Aispute-41, 990.95–998.55; Engure ,?882.8–?884.3; Ikla,?527.0; Krjukai,?968.0; Mežmaļi-16,?912.0–?913.8; Piltene-1,?1016.2; Piltene-30,?938.0; Priekule-20,?1357.3; Riekstini-15,?858.7; Ruhnu-500, 616.9; Stirnas-18,?899.5–?908.9; Vilcini-19,?906.3–?912.9; collections LDM G: Cicere,?897.8–?898.2; Dižrungi-17,?893.7–?894.5; Plikalne-14,?884.0–888.0; Adze-6,?837.0–?845.4; Mežvagari-13,?870.2–?875.0; Kandava-52,?930.3–?932.5; Remte-3,?958.0–?958.8; Kuili-9,?948.7; Ēdole-60,?837.5–?841.4; Dreimaņi,?952.2; Blīdene-5,?815.75–?818.0; Piltene-30,?937.6–?942.1; Talsi-55,?866.4–?866.7 .

Remarks.—Brachiopods characterized by a biconvex shell with weakly developed concentric growth lines occur in many of the studied samples, mostly as fragments and incomplete valves. A few more or less complete shells and valves reminiscent of H. crassa incipiens ( Sheehan 1977; pl. 2: 7, 9, 11) the common Hirnantian brachiopod in many parts of northern Europe and China ( Harper 1981, 1988; Rong and Li 1999; Chen et al. 2000, 2006; Brenchley et al. 2006, Rong et al. 2002). It is highly probable that the fragments of brachiopod valves with weak concentric ornaments belong to the same taxon group. These moderately biconvex specimens have a sub-circular outline with a length up to 17 mm and width up to about 20 mm. One dorsal valve has an anteriorly-thinning, long, dorsal septum ( Fig. 15E ) and one ventral valve has a pedicle chamber that widens slightly anteriorly ( Fig. 15F ). The East Baltic specimens differ from the other Upper Ordovician species, H. cassidea ( Sheehan 1977) , in having less convex valves, a less incurved ventral umbo which does not overhang the dorsal umbo, and by a more circular outline. H. cassidea is most similar to Hindella

1

2

from northern Estonia ( H. cf. cassidea in Modzalevskaya 1985) ( Fig. 15D ).

Figures

Fig. 15. Meristellid brachiopods of the genus Hindella from Porkuni Regional Stage, East Baltic, Kuldiga Formation, western Latvia (A–C, E, F) and Ärina Formation, northern Estonia (D). A, E, F. Hindella cf. crassa incipiens (Williams, 1951). A. Ventral valve, GIT 542-273, Aispute-41, depth 991.0 m, exterior (A 1), lateral (A 2), posterior (A 3), and anterior (A 4) views. E. Incomplete dorsal valve, GIT 542-278, Aispute-41, 991.0 m, interior view. F. Incomplete ventral valve, GIT 542-35, Stirnas-18, 907.5 m, interior view. B, C. Hindella sp. B. Ventral valve, GIT 542-34, Stirnas-18, 908.2 m, lateral (B 1) and exterior B 2) views. C. The bedding plane with brachiopods, including Hindella sp., GIT 542-4 (figured in Kaljo et al. 2008), Aispute-41, 998.25 m. D. Hindella cf. cassidea (Dalman, 1828), shell, GIT 542-267, erratics from the Kõnnu village, dorsal (D ) and posterior (D ) views. Scale bars 5 mm.