Serripecten venosus (Hutton, 1873)
HUTTON, F. W. 1873. Catalogue of the Tertiary Mollusca and Echinodermata of New Zealand, in the collection of the Colonial Museum. Wellington, Government Printer, for Colonial Museum and Geological Survey Dept. xvi + 48 p. [June 1873] [p. 30]
1873 Pecten venosum Hutton, 1873
Chlamys venosa (Hutton); J. Marwick, 1943, Some Tertiary Mollusca from North Otago, pl. 25, figs. 1, 2.
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«104. P. venosum, sp. nov.; Hector, Cat. Col. Mus., 1870, p. 189. Sub-orbicular, inequivalve; right valve with eleven broad rounded scaly ribs, with about two scaly lines in the depressions; left valve with nine narrow scaly ribs, with from four to six scaly lines between them; ears sub-equal, with radiating scaly ribs. Height, 1.5 ; length, 1.5.»
FREDERICK WOLLASTON HUTTON, 1873
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«Small for genus (height 35-40 mm), right valve more inflated than left. Ears prominent, dorsal margins on right valve serrate, divergent, byssal notch well developed; dorsal margins on left valve colinear. Radial sculpture on disc of right valve of 10-13 prominent convex primary costae commencing at or near apex, those near dorsal margins scaly at an early stage of growth, others remaining smooth until 25-30 mm from apex when they become sparsely scaly. From 1-3 finely scaly secondary costellae appearing between costae at 20-25 mm from apex, and "tertiary" ones at a somewhat later stage, some of them arising from flanks of primary costae. Radial sculpture on left valve more variable than on right, some shells with primary costae remaining very prominent throughout growth; in others becoming narrower and of lower relief and even subdividing, and eventually becoming similar in strength to interstitial costellae, so there may be 85 or so subequal scaly costae distally. Ears of both valves with 5 or 6 fine, scaly radial costae.
Runangan, "Oamaru" (type), possibly from Waiareka Volcanic Formation, Bridge Point, Kakanui where it is common; Trig M, Totara; Teschemaker's Quarry.
Serripecten venosus belongs to a complex and poorly understood group of pectens of Late Eocene to Early Oligocene age, particularly well represented in the limestones and associated tuffs of North Otago. It is easily distinguished from the other species, most of which are undescribed, by having relatively few prominent primary costae that remain smooth throughout most of their growth.
Figured specimen (PI. 7i): OS11214, J42/f126, Bridge Point, Kakanui, Runangan (NZOS) x 1.»
BEU, A. G. & P. A. MAXWELL. 1990. Cenozoic Mollusca of New Zealand. New Zealand Geological Survey Paleontological Bulletin, 58: 1-518, pls. 1-57. [p. 115]
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Serripecten venosus (Hutton, 1873); A. G. Beu & P. A. Maxwell, 1990, Cenozoic Mollusca of New Zealand, plate 7, figure i.
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«HOLOTYPE (TM 2842), a right valve. Hypotype (TM 2843), a right valve from G2141, Bridge Point, Kakanui, figured by Marwick (1943, pI. 25, fig. 2).
TYPE LOCALITY: Oamaru. The exact locality is uncertain. "Serripecten" venosus has been collected from several localities in the Oamaru district, all of Runangan age: GS 963, Trig. M, Totara; GS 966, Teschemakers Quarry; OS 3899, Station Road, Kakanui; GS 2141 and 5664, Bridge Point, Kakanui; Maheno Quarry (ex Suter Collection, no. 578); and Aorere Point (ex Suter Collection, no. 496). The preservation of the type specimen, and matrix consisting of buff calcareous tuff with bryozoan fragments, closely matches that of specimens from Trig. M and Teschemakers Quarry.
ORIGINAL DESCRIPTION: "Sub-orbicular, inequivalve; right valve with eleven broad rounded scaly ribs, with about two scaly lines in the depressions; left valve with nine narrow scaly ribs, with from four to six scaly lines between them; ears sub-equal, with radiating scaly ribs. Height, 1.5; length, 1.5."
REDESCRIPTION: (based on the holotype and several specimens from the six localities in the Oamaru district listed above): Shell small, equilateral, right valve more inflated than left, which is often nearly flat. Ears subequal, byssal notch obsolete in adult. On the left valve, the dorsal margins of the ears are smooth and aligned; on the right, they are serrated and meet at an obtuse angle. Sculpture variable, probably not markedly discrepant on opposite valves, but no doublevalved individuals have been seen. Ten to 13 (average 11) rounded major ribs, usually smooth but sometimes with fine scales neaL the ventral margin and on flanks of the disc. On a few specimens the major ribs are each composed of several separate fine, serrated riblets. Relative width of ribs and interspaces variable: the interspaces on right valves, and vice versa on left valves. Major ribs occasionally unequal in strength of development, the fourth and seventh from the anterior end being thicker than the others. Up to five fine, scaly interstitial riblets appear at 20-30 mm from the apex on both valves. Ears sculptured by five or six fine, scaly riblets.
DIMENSIONS: Holotype – height, 36 mm; length, 38 mm; inflation (one valve), 8 mm. The largest specimen collected measures – height, 42 mm; length, 46 mm; inflation (right valve), 10 mm.
REMARKS: "Serripecten" venosus and its allies constitute a small but distinctive group of pectinids, which occur sporadically in Upper Eocene to Lower Oligocene rocks of New Zealand. In the Oamaru district "S." venosus is restricted to Runangan horizons, but in Westland a related species (unnamed) occurs in the Kaiatan at several localities near Brighton (GS 31, 3170, 3184). Four fragmentary specimens of "S." venosus have been collected from Whaingaroan rocks in north Westland (GS 4288, Heaphy River), and one left valve from a Duntroonian-Waitakian limestone in south Canterbury (GS 5323, Hakataramea).
The origin and affinities of "S." venosus and its allies are uncertain. A few specimens of "S." venosus show sculpture of numerous fine, serrated riblets essentially similar to those of small forms of Serripecten including S. enfieldensis (Marwick). The riblets are grouped into fewer, larger ribs with minor interstitial riblets on "S." venosus but are not grouped on S. enfieldensis, except on a few specimens of S. aff. enfieldensis from Teschemakers Quarry, near Oamaru (GS 966, Runangan), which show an incipient tendency towards formation of compound ribs. Inflation of "S." venosus also is like that of Serripecten, the right valve being more inflated than the left, in contrast to Chlamys, which generally has the left valve more inflated than the right. The venosus group could be interpreted as an offshoot from early Serripecten stock - rather than from Chlamys in which the fine, serrated, subequal riblets became amalgamated into fewer, broad major ribs.» BOREHAM, A. U. E. 1965. A revision of F. W. Hutton's pelecypod species described in the Catalogue of Tertiary Mollusca and Echinodermata. New Zealand Geological Survey Paleontological Bulletin, 37: 1-125, pls. 1-20. [p. 32, 33]
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"Serripecten" venosus (Hutton); A. U. E. Boreham, 1965, A revision of F. W. Hutton's pelecypod species described in the Catalogue of Tertiary Mollusca and Echinodermata, plate 5, figure 5.
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