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Journal of Paleontology 91(6):1123–1147 Alvarez and Rong (2002, p. H1556) elevated the Hyattidi-
ninae to family status, but did not mention the subfamily Hindellinae, and assigned Hindella to the family Meristellidae within the superfamilyMeristelloidea, and transferred the smooth- shelled Hyattidina Schuchert, 1913 to the superfamily Athyridoi- dea (hereinwe assignHindella and Hyattidina to the same family, Hindellidae). They did not discuss the lack of skeletal connection between the crura and brachidium, nor the simple jugum, in such early athyrides. Davidson’s (1882) reconstruction of the Hindella
brachidium (shown in Alvarez and Rong, 2002, p. H1564, fig. 1063v) incorrectly shows fused crura. In the revised Treatise, Alvarez and Rong (2002) assigned
various early athyride genera (e.g., Hindella, Hyattidina, and Koigia) with a simple jugum into different families, abandoning the name Hindellinae. Herein, we propose to treat the Hindellinae as a natural group of early athyrides, and raise it to family status, the Hindellidae Schuchert 1894, characterized by a simple jugum and crura that may or may not directly connected to the spiralia. These early forms may have a smooth or capillate shell surface. These hindellides may have evolved from the older athyrides, such as Nikolaispira Nikitin and Popov in Nikitin et al., 1996 and Kellerella Nikitin and Popov in Nikitin et al., 1996, from the Anderken Formation (Dulankara Stage, mid–late Katian) of Chu Ili, Kazakhstan (see also Popov et al., 1999, 2002; Nikitin et al., 2006). These Kazakh forms show more primitive characters, such as short, spine-like jugul processes that are not medially connected. The subfamily Hyattidinae, therefore, is subsumed in the family Hindellidae on account of their jugum and brachidium that resemble those of Hindella, Koigia, Cryptothyrella, and Elkanathyris n. gen. (see descriptions of these genera below).
Genus Hindella Davidson, 1882
Type species.—Athyris umbonata Billings 1862; Juncliff Member, Ellis Bay Formation, Hirnantian, Anticosti Island.
Species assigned.—The following species are assigned to Hindella:
Athyris umbonata Billings, 1862.—Type species (see below). Athyris prinstana Billings, 1862.—PrinstaMember and its
stratigraphic equivalent to the west, Fraise Member, Ellis Bay Formation (see Copper et al., 2013). Athyris turgida Shaler, 1865.—Probable junior synonym
of H. prinstana (see below). Anomites terebratulinus Wahlenberg, 1818.—Upper Boda
reef-capping limestone, Hirnantian. Atrypa cassidea Dalman, 1828.—Borenshult, Ostergöt-
land, Sweden, Dalmanitina Beds, Hirnantian. Whitfieldella ovoides, Savage, 1913.—Bryant Knob
Formation, Hirnantian herein (the age of the Bryant Knob is debated because some have dated it as early Rhuddanian). Whitfieldella speciosa Savage, 1913.—Edgewood Group
(Amsden, 1974 synonymized it with W. ovoides). Meristina crassa incipiens Williams, 1951.—Cyrn-y-
brain Formation, Hirnantian, Denbighshire, U.K. Hindella kiaeri Sheehan, 1977.—Nesoya, Asker Region,
Oslo, “calcareous sandstones”, likely Hirnantian. Hindella bulbusa n. sp.—Parastro Member, Ellis Bay
Formation (this study).
Species questionably assigned.—Hindella shianensis Reed, 1912; Horizon 5, Shian, Pin Valley, Himalayas, precise age unknown (Hirnantian?); interior unknown, but the elongate shell resembles H. umbonata.
Diagnosis.—Relatively small to medium sized, smooth or capillate, globose, biconvex shell with incurved beak, apical to transapical foramen, small distinctive interarea, and minute deltidial plates; gently folded anterior commissure, rare median
ventral groove. Internally, ventral muscle scars deeply incised, flanked by prominent dental plates and dental cavities, and vas- cular markings and ovarian pits; apical ventral cavity partially infilled by prismatic callus, leaving shallow groove; dental plates relatively straight, subparallel to plane of symmetry. Crura short and delicate, diverging slightly laterally; umbonal blades equally short and hooked; simple jugum postero-medial, gently arched posteriorly; spiralia with 6–8 whorls, laterally directed.
Occurrence.—A Hirnantian age for the genus is confirmed in Laurentia, Baltica, and South China (Rong, 1984). The Ashgill–Llandovery age was given by Alvarez and Rong (2002) because they synonymized Aeronian Cryptothyrella Cooper, 1942, with Hindella. There has been confusion about the age of the Ellis Bay Formation, but recent studies have confirmed its Hirnantian age based on microfossils, megafossils, geochemistry, and sequence stratigraphy (Achab et al., 2013; Copper et al., 2013; Mauviel and Desrochers, 2016). On Anticosti Island, Hindella is the only athyride genus in the Hirnantian, co-occurring with Hirnantia, but it is absent lower in the Katian, or higher in the Silurian. In Estonia, Hindella occurs in the Hirnantian Porkuni
Stage. This distribution matches that of the type Hirnantian in the UK, where the species Hindella incipiens occurs (Harper and Owen, 1996). The Estonian “Hindella crassa (Sowerby)” is given a Juuru (early Rhuddanian) age by Modzalevskaya (1985, p. 46), but its affinity should be re-examined because it may be Koigia. “Cryptothyrella” terebratulina (Wahlenberg, 1818) from
the Boda Limestone of Sweden was given a Late Ordovician age by Sheehan (1977); we consider it as true Hindella. Brenchley et al. (1997) suggested that the Boda Limestone was Katian, but Webby (2002) indicated that the top of the Boda mounds stopped growth in the mid-Hirnantian. The species comes from the upper part or tops of the Boda mounds and should be of Hirnantian age. Sheehan (1977) identified Hindella crassa (Sowerby, 1839) from the Hirnantian Dalmanitina Beds of Sweden. This suggests that all species of Hindella from Baltica and the UK are of Hirnantian age, as are those of Laurentia. Amsden (1974) identified “Cryptothyrella” ovoides
(Savage, 1913) from the Bryant Knob Formation and assigned it to the Edgewood Group. Amsden (1974) tentatively assigned the Bryant Knob (=Leemon Formation) to the early Llandov- ery, which should be reconsidered as Hirnantian because it shares nearly all the shelly fauna of the underlying Noix Formation, which has the genus Hirnantia as a component. Sheehan (1977, p. 25) referred the Edgewood “Cryptothyrella” ovoides to the Silurian (its external morphology is that of Hirnantian Hindella). More recently, Bergström et al. (2006)
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