Austrohinnites corioensis (McCoy, 1879)
MCCOY, F. 1879. Geological Survey of Victoria: Prodromus of the palaeontology of Victoria; or, figures and descriptions of Victorian organic remains. Government Printer, Melbourne. Decade 6, 42 pp., pls. 51-60. [p. 31, pl. 58]
1879 Hinnites corioensis McCoy, 1879
1887 Pecten deformis Tate, 1887
1907 Hinnites tatei Cossmann, 1907 [nomen novum pro Pecten deformis Tate, 1887]
1922 Hinnites mulderi Chapman, 1922
1887 Pecten deformis Tate, 1887
1907 Hinnites tatei Cossmann, 1907 [nomen novum pro Pecten deformis Tate, 1887]
1922 Hinnites mulderi Chapman, 1922
F. McCoy, 1879, plate 58.
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«DESCRIPTION.--Young stage from ½
to 1½ inch in length, regular, ovate, very slightly oblique, with nearly equal subquadrate ears, valves nearly equally and moderately convex; surface closely radiated with narrow subangular ridges, nearly equal near the beaks, but each pair receiving between them irregularly from one to five smaller ridges towards the margin (in some specimens the original ridges remain so much more prominent than the intercalated ones that angular bundles are formed); each ridge is roughened by hollow semiconical spines formed of projecting angularly arched scales a little furtlier apart than the thickness of the ridge, interspaces varying from the width of the ridge to four or five times the width of the ridges, and closely covered with a perfectly regular pattern of oblique intersecting lines of equal rounded granules, less than their diameter apart, about twelve in two lines; usually about eight ridges in two lines at an inch from beak, but varying from three to ten. Adult growth beyond the young regular stage — valves suddenly becoming irregular in growth, often obliquely extended posteriorly, the upper or left valve irregularly undulated and flatter than the right valve, but varying from concave to convex; the ridges nearly equal, very irregularly undulating, the spinose scales less regular, and becoming obsolete at margin of old specimens; flat intervening spaces about twice the width of the ridges, crossed by concentric lines of growth; right valve with a scar of attachment, and with large irregular projecting concentric scaly fringes. The muscular impression large. Length of large specimen, 3½ inches; depth from beak to opposite margin about the same; width varying from 1 to 2 inches.
This extremely common fossil in our Miocene Tertiary strata is a representative of the European Hinnites Cortesii (de Franc.) of the Coralline Crag of England and corresponding Tertiary strata on the European continent. The characters of the extinct genus Hinnites are well seen in this species, appearing to connect the genera Pecten and Ostrea. The young regular Pecten-like stage of growth being seen for about an inch from the beaks corresponding with the time it was attached by a byssus; the older stage of growth, when it became fixed by the shelly substance of the lower or right valve, being marked by sudden irregularity of general growth and change of the character of the ridging, and by the development on the lower or right valve of the large concentric irregular shelly fringes like those of Spondylus. Extremely common in Miocene Tertiary of Corio Bay; and in similar beds near Bairnsdale, on the Nicholson River.» FREDERICK MCCOY, 1879
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«Occurrence and time range. Janjukian to Mitchellian; unlikely to range as young as Cheltenhamian; a few specimens seen from Jan Juc Formation and Waurn Ponds Limestone, Otway Basin, a few from Mannum Formation, Murray Basin, and a few from Freestone Cove Sandstone near Wynyard, Tasmania; more than 90% of material is Bairnsdalian in age, from the Otway and Gippsland basins.
Remarks. The most obvious diagnostic character of Austrohinnites corioensis is the relatively few (12-14 on most specimens, max. c. 16) narrow, widely spaced, primary radial costae. Although secondary and tertiary costellae are formed on the 'Chlamys stage’ of most specimens by subdivision of the primary ones, by intercalation in the radial interspaces or by both means on one valve, the costellae remain relatively weak on almost all specimens and, even in those specimens where they develop into regularly fasciculate rib groups, with low secondary costellae on each side of the primary costae, intercostal spaces remain relatively wide and gently and evenly concave. Another character apparently diagnostic for A. corioensis is the relatively wide umbonal angle (c. 110º), particularly obvious on LVs and on the ‘Chlamys stage’. The remaining diagnostic character is the low, ventrally directed scales, forming short transverse ridges on the costal crests, developed on primary costae on the distal portion of the disc and auricles of the ‘Chlamys stage’. The scales develop over the distal quarter to tenth of the disc, leaving the early area of the disc of most specimens sculptured with low, smooth radial costae and wide areas of shagreen microsculpture in the radial interspaces, although secondary and tertiary costellae develop at up to the proximal third of the height in a few specimens. Some specimens in the large, morphologically and sculpturally diverse Bairnsdale Limestone population remain in the regularly shaped ‘Chlamys stage’ until a large size (up to 58 mm height observed; Fig. 10C) and in these costal interspaces become nearly flat, and secondary and tertiary costellae become numerous, complex, and evenly and weakly scaly. Most LVs of A. corioensis we have observed retain moderately regular, scaly primary costae that continue to subdivide fairly regularly across the disc of the cemented stage despite irregularity of shell growth in conformity with the substrate, and a coarse and somewhat irregular version of this sculpture remains on some RVs with a small attachment area. Other RVs, with a larger attachment area and greater distortion of sculpture through the development of irregular cementation lamellae, lack regular radial costae. Specimens we assign to A. corioensis from Tambo River Formation greensand at Swan Reach, PL3110, are the youngest specimens of Austrohinnites in Victoria, other than a single specimen (possibly mislocalised) from ‘Cheltenham’, ie., Beaumaris. From Swan Reach we know only eight Chlamyslike shells with wide umbonal angles, with flat intercostal spaces, with low scales on the primary costae, with irregularly subdivided and intercalated secondary and tertiary costellae, and with interspaces bearing coarse shagreen microsculpture; the largest (Fig. 10A) is 63 mm high. These specimens agree in all characters with the ‘Chlamys stage’ of A. corioensis, and evidently represent a non-breeding population recruited from a nearby population cemented to a hard substrate. Specimens from the Batesford lime quarry, PL3524, include the type material of ‘Hinnites’ mulderi Chapman (1922: 5). The specimen figured by Chapman (1922) is not now present in Museum Victoria and apparently is lost, but one of Chapman’s syntypes, labelled ‘Batesford, pres. J. Mulder’ remains in Museum Victoria (Fig. 8B) and is here designated the lectotype of Hinnites mulderi Chapman, 1922. This specimen and the few collected subsequently from the same locality are abraded, so the hinnitoid stage, in particular, has weak sculpture remaining, but the ‘Chlamys stage’ has costae, costellae and scales indentical to those of A. corioensis. We are satisfied that these are merely abraded specimens of A. corioensis. The lectotype of ‘Hinnites’ tatei Cossmann, 1907 (= figured syntype of Pecten deformis Tate, 1887, a junior homonym of P. deformis Gabb, 1864) (Fig. 9A) is a severely abraded LV from the ‘upper beds’ (Grange Bum Formation) at McDonald’s Bank, Muddy Creek, near Hamilton, western Victoria (Kalimnan, Early Pliocene). However, like many other abraded specimens from the Grange Burn Formation, there is no doubt that this shell has been reworked from the underlying Muddy Creek Formation (Balcombian, Middle Miocene). The specimen has moderately wide, gently concave intercostal spaces, and has costal subdivision and intercalation as in A. corioensis, but lacks scales. There is no doubt that this is merely a small specimen of A. corioensis with its scaly sculpture abraded off.» 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. 45, 47]
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Austrohinnites corioensis (McCoy, 1879); A. G. Beu & T. A. Darragh, 2001, Revision of southern Australian Cenozoic fossil Pectinidae, figure 8B (above); figures 9A-E (middle); figures 10A-E (below).
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