|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Rhynchonellata - Orthida - Draboviidae
|Year||Name and author|
|1851||Orthis sagittifera McCoy|
|1935||Hirnantia sagittifera Lamont p. 313|
|1982||Hirnantia sagittifera Cocks pp. 763 - 764 figs. Plate 78, figs. 6-10; Plate 79, figs. 1-3; Plate 80, fig. 8|
|2006||Hirnantia sagittifera Brenchley et al. p. 16 figs. 12A, C, F|
|2008||Hirnantia sagittifera Jin and Zhan pp. 52-53 figs. Pl. 36, figs. 1-16|
|2012||Hirnantia sagittifera Hints et al. pp. 67 - 70 fig. 2|
|2015||Hirnantia sagittifera Hints and Harper|
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|L. R. M. Cocks 1982||Exterior. Biconvex, with convexity of brachial valve considerably greater than pedicle valve. Faint trace of very weak pedicle valve fold and corresponding brachial valve sulcus seen in a few valves only. Small anacline brachial valve interarea · and fairly small apsacline pedicle interarea. Open delthyrium with small pedicle collar and open notothyrium. Relatively fine radial ornament (84 ribs counted at 10 mm growth line on BB 93984, PI. 79, fig. 2), with new costellae arising both by bifurcation and intercalation, the costellae curving round laterally to merge with the hinge line. Growth lines obscure, except anteriorly in old specimens.
Pedicle valve interior. Teeth supported by dental plates extending to the valve floor and diverging at right angles, merging antero-Iaterally with the variably developed muscle-bounding ridges. Thin lanceolate adductor muscle scars between well-impressed anteriorly rounded diductor muscle scars, the whole muscle field bilobed, and extending anteriorly for about one-third of the valve length. Vascular markings obscure.
Brachial valve interior. Cardinal process small, simple (PI. 79, figs. 1,3), becoming stronger and more bulbous in the most gerontic specimens (PI. 78, fig. 9). Pair of stout but relatively short socket plates (the 'supporting plates' of Temple 1965, p. 400) diverging at right angles and attached to the valve floor. Variably developed, poorly defined, thin and low median septum extends for up to one-third of the valve length. Adductor muscle field weakly impressed, but each muscle scar is subcircular and extends anteriorly from between one-quarter and one-third of the valve length.