Borehamia hilli (Hutton, 1905)
HUTTON, F. W. 1905. Three new Tertiary shells. Transactions and Proceedings of the New Zealand Institute, 37: 472-473. [p. 473, pl. 44, fig. 3]
1905 Pecten hilli Hutton, 1905
F. W. Hutton, 1905, plate 44.
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«Large, equivalve, rather compressed, equilateral, suborbicular. Ears large, equal, without any sinus; the posterior with 3, the anterior with 4 slightly undulating ribs. Eight valve with about 30 narrow ribs, many of which are grooved in the ventral half of the shell, and slightly roughened by growth-lines. Interstices broader than the ribs, smooth, simple. The left valve is imperfectly preserved, but what can be seen of it does not differ much from the right valve.
Length, 4·55 in. (116 mm.); height. 4·25 in. (108 mm.); thickness, 1·55 in. (40mm.). Locality.— Napier, in limestone. Allied to P. triphooki, but distinguished from that species by the narrower and more numerous ribs, which are not so scaly, as well as by the simple interstices. The type is in the Canterbury Museum.» FREDERICK WOLLASTON HUTTON, 1905
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«Allan (1941) fully described and figured the holotype of Pecten hilli, which is in the Canterbury Museum (reg. No. M648). The shell is large (up to 108 mm high), has the right valve slightly more inflated than the left, has relatively small, almost square, equilateral ears, and has weak radial folds and relatively widely spaced radial ribs, and thus is referable to Mesopeplum (Borehamia). Mesopeplum hilli differs from M. crawfordi in having more equally inflated valves, much weaker radial folds that fade out at about half the height of the disc, a wider umbonal angle, and fewer, coarser, broader, weakly subdivided radial ribs (27-32 ribs, mean 30· 0, in 3 M. billi; 37-61 ribs, mean 46·6, in 10 M. crawfordi). However, the ribbing of M. crawfordi varies greatly between populations; shells from Patea River mouth and Lower Waipara Gorge have only slightly more numerous ribs than has M. hilli.
LOCALITIES: Only a few specimens referable to M. hilli are known to me. The holotype was stated by Hutton (1905, p. 473) to be from "Napier, in limestone" and may well be from the Lower Scinde Island Limestone (Nukumaruan) at Napier. However, the holotype is so much better preserved than specimens of Phialopecten from the Lower Scinde Island Limestone that it may have come from a soft calcarenite of the Te Aute Limestone (sensu stricto) nearby in central Hawkes Bay. A specimen in NZ. Geological Survey from calcarenite at Pukeora Hill, Waipukurau (Te Aute Limestone sensu stricto) is as well preserved as the holotype. Other localities I am aware of are R21/fl (metric), GS 11 886, Larsen Shellbed, Waitotara Valley (Opoitian); N129/f501, GS 5240, Waihi Beach, Hawera (Waipipian); and N145/f526A, GS 11 480, Hatuma Quarry, Hatuma, east of Takapau (Mangapanian). TIME RANGE: Opoitian, Waipipian and Mangapanian Stages (Pliocene); possibly early Nukumaruan Stage (basal Pleistocene). RELATIONSHIPS: Although Mesopeplum (Borehamia) hilli clearly belongs in the same subgenus as M. crawfordi, it does not appear to belong in the same lineage. A specimen collected by P. A. Maxwell from S68/f1146, GS 9866, "Neotbyris shellbed", Weka Creek, Weka Pass, North Canterbury (Altonian, Lower Miocene), 51 mm high, is possibly ancestral to M. hilli as it has similarly weak radial folds, riblets of square section, and a wide umbonal angle. However, the anterior ear is longer than the posterior and has a marked byssal notch as in Mesopeplum (Mesopeplum) so that, if it is related to M. hilli, it is apparently an early member of the lineage. The Altonian species may well be ancestral also to the lineage of M. crawfordi, which is first known in Waiauan (late middle or early upper Miocene) rocks in the same district.» 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, figs. 1-30. [p. 263]
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Mesopeplum (Borehamia) hilli (Hutton, 1905); A. G. Beu, 1978, Taxonomy and biostratigraphy of large New Zealand Pliocene Pectinidae (Phialopecten and Mesopeplum), figure 7.
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