Austrohinnites polyaktinos (Ludbrook, 1955)
LUDBROOK, N. H. 1955. The molluscan fauna of the Pliocene strata underlying the Adelaide Plains. Part II - Pelecypoda. Transactions of the Royal Society of South Australia, 78: 18-87. [p. 30, pl. 4, fig. 16]
1955 Chlamys (Chlamys) polyaktinos Ludbrook, 1955
N. H. Ludbrook, 1955, plate 4.
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«Chlamys peroni Tate. N. H. Woods, 1931. Trans. Ray. Soc. S. Aust.. 65, (1), p. 150.
Diagnosis — Suborbicular, with from about 24 increasing by intercalation to 48 narrow riblets carrying imbricating scales with shagreen sculpture in the interspaces. Description of Holotype — (left valve). Shell small, rather thin, elongately suborbicular, slightly convex, sculplures with about 24 radial riblets, increasing by intercalation to 48 towards the ventral margin, of sub-equal strength, covered towards the ventral margin with imbricating scales. Interspaces finely shagreened. Auricles unequal, posterior auricle small, dorsal margin nearly horizontal, with about 10 fine rays with imbricating scales; anterior auricle larger, dorsal margin oblique, primary rays five with two secondary rays, crossed by fine, growth lamellae, not scaly; byssal sinus moderately wide and deep. Dimensions — Length 22, height 23·5, inflation (one valve), 3 mm. Type Locality — Abattoirs Bore., Adelaide; Pliocene. Location of Holotype — Tate Mus. Coll., Univ. of Adelaide. F15120. Observations — Although it resembles it fairly closely, this species is not the Balcombian C. peroni (Tate), from which it is distinguished easily by the shagreen sculpture between the riblets. It is close to the Recent C. aktinos Petterd, from which it differs in the more numerous riblets and in shape, being less elongate. The posterior auricle is larger than in aktinos. Material — Holotype and 16 paratypes, Abattoirs Bore (single valves). One valve Hindmarsh Rore, two fragments Tetinant's Bore. Stratigraphical Range — Dry Creek Sands. Geographical Distribution — Adelaide District.» NELLY HOOPER LUDBROOK, 1955
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«Description. Very similar to A. corioensis in most characters, differing in its smaller adult size, not exceeding c. 80 mm in height (compared with up to c. 120 mm in A. corioensis), its umbonal angle of c. 95º rather than c. 110º, its more strongly prosocline ‘Chlamys stage’, its much more closely and frequently subdivided and intercalated costae on the ‘Chlamys stage’ but markedly weaker sculpture on the ostreoid stage, reduced to c. 30-40 low, widely spaced, smooth costae; and the correspondingly much more obvious and dramatic, rapid change in sculpture between the ‘Chlamys’ and ostreoid stages.
Type material. Holotype of Chlamys polyaktinos Ludbrook, SAM F 15120, Abattoirs Bore, Adelaide, lower Dry Creek Sands, Bairnsdalian, Middle Miocene. Ludbrook (1955: 30) stated the type material as ‘Holotype and 16 paratypes, Abattoirs Bore (single valves). One valve Hindmarsh Bore, two fragments Tennant’s bore.’
Other material examined. Bairnsdalian: BOOKPURNONG FORMATION: PL3133, Wookool bend (179 specimens); DRY CREEK SANDS: PL3598, Bore 593, Waterloo Corner, South Australia (45 specimens); PL3299, Abattoirs Bore (45 specimens); PL3596, house bore, Angas home (179 specimens). Occurrence and time range. Abundant both in Dry Creek Sands in bores near Adelaide, St Vincent Basin, and Bookpurnong Formation near Loxton, Murray Basin; at both localities it is probably Bairnsdalian in age. Remarks. Ludbrook (1955, 1973) evidently was confused about the identity of specimens from Dry Creek Sands, as she identified juvenile, ‘Chlamys stage’ specimens and adults as different taxa in 1955, and in 1973 identified the same species, from Bookpurnong Formation, as H. tatei Cossmann, not recognising that the abundant juveniles in bores around Adelaide are conspecific with the abundant adults from Bookpurnong Formation. Dry Creek Sands samples not seen by Ludbrook include several showing the beginning of the irregularly growing stage, and at least one large, complete LV (Fig. 11D) closely comparable with Bookpurnong specimens (Fig. 8G, H). The abundant specimens from Bookpurnong Formation have very irregularly shaped adult stages, but the ‘Chlamys stage’ agrees in all details with specimens from Dry Creek Sands. Most diagnostic characters are stated above. Apart from the obvious differences from A. corioensis in size and closeness of sculpture, other significant differences are the radial interspaces being conspicuously narrower than in A. corioensis, the longer, more numerous, more prominent and more nearly semitubular costal scales than those of A. corioensis, and the obvious, rapid fading out of the scales and the more minor costae early on the irregularly growing stage. Coarse shagreen microsculpture is present in all radial interspaces on the ‘Chlamys stage’. The resulting ostreoid stage resembles those of the New Zealand Miocene species A. marwicki and A. trailli in its relatively subdued radial sculpture, but the more finely and closely costate and much more obviously scaly ‘Chlamys stage’ distinguishes A. polyaktinos readily from all other known species of Austrohinnites.» BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1–205. [p. 47, 49]
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Austrohinnites polyaktinos (Ludbrook, 1955); A. G. Beu & T. A. Darragh, 2001, Revision of southern Australian Cenozoic fossil Pectinidae, figures 8F-H (above); figures 11A-H (below).
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