Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 23k): GS2938, D45/f8471, shellbed, Cucullaea Point, Third Bay, Clifden, Southland, Lillburnian (GNS)
(Pl. 23l): GS2938, D45/f8471, shellbed, Cucullaea Point, Third Bay, Clifden, Southland, Lillburnian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 216; pl. 23 k,l.
Synonymy: Perna sp. Hutton 1873b, p. 26; Perna zealandica Hutton 1873b, pp. xiii, 47 (nomen nudum); ? Perna quadrata Park 1887, p. 53 (nomen nudum); Melina zealandica Suter 1917, p. 68; Pedalion zealandicum; "Isognomon" cf. zealandicus, Beu & Maxwell 1990, p. 216, pl. 23k, l.
Description: Moderately large to very large (height 90-100 mm in Middle Miocene specimens, 160 mm and more in middle Pliocene ones), almost as long as high, subquadrate, with small anterior ear and long, almost square posterior wing set off from disc only by shallow concavity in both valves; hinge and umbonal area extremely thick and massive (more than 20 mm thick on large Pliocene shells) but ventral area of disc very thin and exceedingly fragile (few complete Pliocene shells are known). Moderately thick (2-3 mm) prismatic calcite outer layer, missing from most specimens; inner layer and hinge-umbonal area brightly nacreous aragonite. Ligamental plate wide (15 mm wide on Middle Miocene shells, 42 mm and more wide on large Pliocene ones), with 4 or 5 deep, wide, somewhat irregular resilial pits (a few pits spread laterally or split into 2 in some shells), deeply sinuating the otherwise smooth hinge line; the 2 ligamental areas of each articulated specimen diverge dorsally at 85º. Below anterior ear, valve edge with wide, moderately deep embayment forming large byssal gape, oval in anterior view in articulated shells. Exterior smooth apart from weak growth ridges. Adductor scar large, oval, with roughened surface of anastomosing wrinkles; an elongate, oblique (?byssal retractor) scar in front of anterior edge of adductor. Pallial line a row of widely separated small muscle impressions, ascending into deep umbonal hollow; small impressions are deep enough to form prominent nodules on some large Pliocene internal moulds.
Comparison: An unusually complete Clifden Miocene specimen of Panis n. sp. aff. zealandica is illustrated here, but the species is much more abundant in many Pliocene to early Pleistocene localities in shellbeds and near-shore sandstone or mudstone (Waipipi shellbeds, South Taranaki; Nukumaru Brown Sand, Wanganui; Hawke's Bay Nukumaruan successions). The smaller Miocene shells and larger Pliocene shells apparently represent distinct species. Their relationship to the Early Miocene "Pteria" oneroaensis also needs investigation. Similar specimens from Brydone, Mataura River, Southland (Waitakian) have thinner, narrower, more obliquely angled shells and narrower hinges and belong in another unnamed species.
Although there previously had been no apparent doubt that this species group belongs in Isognomon Lightfoot, 1786 (= Melina Retzius, 1788, = Pedalion Dillwyn, 1817, = Perna of many authors) before Beu & Maxwell (1990), comparison of specimens with the holotype of "Pedalion" fortissimum (Tongaporutuan) and with New Zealand and European Mesozoic species of Isognomon showed that I. fortissimus is the only named mid-Cenozoic species correctly referred to Isognomon (although other early Cenozoic species were named by Crampton 1988). Isognomon species have nearly vertical ligamental areas (almost parallel in articulated shells) with a large number of regular, narrow, parallel resilial pits, no hollow beneath the hinge plate and umbo, and no anterior ear. The widely diverging ligamental plates, few wide resilial pits, prominent anterior ear, and deep umbonal hollow of "I." zealandicus are most similar to Panis Stephenson (1952, p. 67) (type species: P. cuneiformis Stephenson, 1952, Cenomanian (Late Cretaceous), Texas). Beu (2004, p. 156) pointed out that Panis has only a slight byssal gape, whereas Neopanis zealandica has a deep, widely open, almost cylindrical byssal tube, reaches a much larger size, and has a more equidimensional shell shape than Panis species. Other species occur in Pliocene rocks in southern Australia, and in Oligocene-Miocene rocks in Chile and Argentina. The family position is in doubt as, although Neopanis resembles Panis and some other genera attributed to the Bakevelliidae, it seems nearest in most characters to Isognomonidae, and it is unclear whether the two should be maintained as separate families in any case.
Suter (1917, p. 68) clearly attributed the species name to Hutton, in the designation "Melina zealandica (Hutton) nov. sp.", and the specific epithet was first proposed (as a nomen nudum) by Hutton (1873b, p. xiii). However, according the current International Code of Zoological Nomenclature, the name should be attributed to Suter, who first made the name available.
Distribution: (Waitakian?-) Lillburnian-Nukumaruan; "Shrimpton's", i.e., Kikowhero Stream, Matapiro Station, north side of Ngaruroro River, central Hawke's Bay, Nukumaruan, smaller syntype Melina zealandica of Suter (1917, pl. 8, fig. 4); Scinde Island Limestone, Napier, Nukumaruan, larger syntype (internal mould) of Suter (1917, pl. 13, fig. 2); "Castle Point" and "Taipo marls", Wairarapa, "chirotype" of Hutton (1873b, p. xiii, 26) [but bears a shelly, dark grey, coarse sandstone matrix, clearly that of the Waipipi Shellbeds, Waverley Beach, west of Wanganui, Waipipian], all in GNS. Common at some Middle-Late Miocene localities in near- shore sandstone (shellbeds high in the Lillburnian at Clifden, Southland; Te Araroa, East Cape, Kapitean).
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)