Phialopecten tolagaensis (Marwick, 1931)
MARWICK, J. 1931. The Tertiary Mollusca of the Gisborne district. New Zealand Geological Survey Paleontological Bulletin, 13: 177 p. [p. 62, pl. 4, fig. 68]
1931 Chlamys (Phialopecten) tolagaensis Marwick, 1931
«REMARKS: The collection over recent years of good populations of specimens of Phialopecten tolagaensis from Tokomaru Sandstone facies (i.e. shallow-water Kapitean rocks) near Anaura Bay, north of Gisborne, has made the characters of the species much better known than previously. Particularly useful collections are GS13954, Z16/F31, beach at north end of Anaura Bay; GS13956, Z16/f30, mouth of Koronui Stream, north end of Anau¡a Bay; and GS14063, Z16/f37, tributary of Hikuwai River in Waipare Forest, inland from Tokomaru Bay. These and a few better-preserved topotypes than Marwick's type series (from Mangatuna Quarry, main highway north of Tolaga Bay; material from this locality is severely distorted) show that all specimens in the collections that are definitely referable to Phialopecten are no more than 70 mm high (few exceed 60 mm), have prominent and clearly fasciculate radial costae and low, simple commarginal lamellae, and have a significant but shallow byssal notch in adults. The byssal notch is fairly shallow throughout ontogeny. Many, but by no means all, specimens have 4-6 low, very poorly defined plicae near the umbo, fading out over the umbonal third to half of large specimens.
These shells occur, in Tokomaru Sandsone localities, with more regularly and, in some specimens, markedly more strongly plicate specimens that have simple, undivided radial costae of almost square section. These specimens are tentatively assigned to Mesopeplum (Borehamia), as they resemble M. toaense and M. hilli much more closely than they do Phialopecten, but distinction between these two forms is not easy, or certain, in all cases. The variation of P. tolagaensis remains somewhat uncertain; it is possible that some specimens have simple (rather than fascicular) costae. The variation in these collections also suggests the possibility that Phialopecten and a M. (Borehamia) hilli-lke lineage were diverging at this time from a common ancestor, although evolution in weakly plicate M. (Borehamia) species is very far from clear at present and this possibility cannot be evaluated. DISTRIBUTION: Apart from Tokomaru Sandstone localities, records of Phialopecten tolagaensis are very few (localities are listed in Appendix A). Fasciculate-ribbed fragments assigned with confidence to Phialopecten were collected by H.M. Kelsey (Western Washington University) from Kaiparoro Limestone near Mauriceville West, Wairarapa (GS14813, T25/f128, see Appendix A; overlain by sandsone containing the Kapitean índex Sectipecten wollastoni). A very few, poorly preserved specimens assigned here only tentatively were collected from Owhaoko Limestone on the Ngamatea Plateau by Robyn Black (Hawke's Bay Regional Council) (see Appendix A). Specimens are not known from anywhere else in New Zealand, but the Owhaoko Limestone and Kaiparoro Limestone occrurences indicate that this is likely to be due to the scarcity of Kapitean shallow-water facies rather than to a geographic restriction to the East Cape region. AGE: Kapitean.» BEU, A. G. 1995. Pliocene Limestones and their scallops. Lithostratigraphy, pectinid biostratigraphy, and paleogeography of eastern North Island late Neogene limestone. Institute of Geological & Nuclear Sciences Monograph 10. Institute of Geological and Nuclear Sciences, Ltd., Lower Hutt, New Zealand, 243 p. [p. 32, 34]
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Phialopecten tolagaensis (Marwick); A. G. Beu, 1995, Pliocene Limestones and their scallops, figure 14a.
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«Chlamys (Phialopecten) tolagaensis is a small species (height 27-61mm in 10 specimens; mean 44.9mm) with a moderately large number of major radial ribs (26-34 ribs on 10 specimens; mean 29.4). The ribs have relatively narrow crests and narrow interspaces compared with all other Phialopecten taxa, so that the sides of the ribs slope outwards rather than being vertical as in all other taxa. Division of primary radials into two equally high radials occurs irregularly on only about one third to two thirds of the ribs and at about half the height of the disc of average-sized shells. On almost all ribs of other taxa it occurs near the umbo. Secondary rib lets are added between the primary ribs by intercalation at about half the height of the disc and in only about half the interspaces, rather than extending almost from the umbo of all interspaces as in other taxa. The disc is slightly higher than long and slightly oblique, the ventral margin extending further posteriorly than anteriorly, and the umbonal angle is relatively narrow; all other taxa have wide umbonal angles, equilateral and approximately equidimensional discs. Anterior ears are much larger than posterior ears; the right anterior ear retains a marked byssal notch and the left a marked byssal sinus. Most specimens have four or five weak radial folds extending from the umbo which fade out gradually at about half the disc height. Whereas similar but weaker folds are present on a few specimens of C. (P.) triphooki ongleyi, they are absent from later taxa. Therefore, C. tolagaensis, while clearly the ancestral member of the Phialopecten lineage, retains so many of the features of small bysally attached species of Chlamys that it seems best treated as a full species.
TYPE LOCALITY: N89/f464, GS 1244, Mangatuna Quarry, main highway 8 km north of Tolaga Bay, north of Gisborne; grey sandstone, "Ormond Series" (Kapitean; Austrofuses caerulescens (Finlay) reported from the same locality as the synonym A. tuberculatus Marw., by Marwick 1931, p. 33). Holotype (TM4212) in N.Z. Geological Survey. LOCALITIES: N81/f488, GS 69, "Lower Tertiary beds. Akuaku, Poverty Bay, East Cape", A. McKay, 1874; N80/f378, GS 249, "Duncan's, east coast of Auckland, between Tolaga and Tokomaru Bays", A. McKay, 1874 (two poor moulds only); N81/f498, GS 1308, near base Tokomaru Sandstone, behind Tokomaru township, Tokomaru Bay (?poor, with strong radial folds, perhaps related to Mesopeplum crawfordi); N81/f800, GS 8008, junction of Waikirere Stream track north from Anaura Bay, north of Gisborne, several well-preserved specimens; specimens from southern Wairarapa which I identified as C. (P.) tolagaensis (Vella & Briggs 1971, p. 261) are now considered to be Mesopeplum (Borehamia) cf. toaense (Marwick). TIME RANGE: Kapitean Stage (latest Miocene and earliest Pliocene).» BEU, A. G. 1978. Taxonomy and biostratigraphy of large New Zealand Pliocene Pectinidae (Phialopecten and Mesopeplum). New Zealand Journal of Geology and Geophysics, 21: 243-269 [p. 249]
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Chlamys (Phialopecten) tolagaensis Marwick; A. G. Beu, 1978, Taxonomy and biostratigraphy of large New Zealand Pliocene Pectinidae, figures 4-6.
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