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Volume 54, 1923
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Art. 11.—The Occurrence of the Genus Lahillia in New Zealand.

[Read before the Wanganui Philosophical Society, 27th October, 1921; received by Editor, 15th December, 1921; issued separately, 8th February, 1923.]

Plate 16.

Lahillia is a genus of pelecypods that has a restricted geographical occurrence as well as a restricted range in geological time. It is therefore a genus of considerable importance, both in regard to former geographical conditions and also in connection with the correlation of geological formations in different countries. Up to the present time Lahillia has been recorded only from the Upper Cretaceous and Lower Tertiary formations of South America and Antarctica, where it is of quite frequent occurrence. The record of the occurrence of this genus in New Zealand seems to be of such great importance that we take the opportunity of transcribing remarks that have been made about it by geologists in South America.

Wilckens makes the following remarks about the genus: “Die gattung Lahillia die sich in Obersenon von Quiriquina (Chile) und Südpatagoniens und in Tertiar von Patagonien und Chile findet ist auch in Antarctischen Senon vertreten so dass sie als eine für diese ganze Region besonders kennzeichnende Versteinerung betrachtet werden kann.” (Otto Wilckens, “Die Anneliden, Bivalven, und Gastropoden der Antarctischen Kreideformation,” Schwed. Sudpolar Exped., Bd. iii, Lief. 12, Stockholm, 1910.)

Von Ihering, in his work “Les mollusques fossiles du Tertiaire et du Crétacé superieur de ľArgentine” (Annales del Museo Nacional de Buenos Ayres, ser. iii, tome vii, p. 83, 1907) makes the following remarks: “Le genre Lahillia bien developpé dans les faunes Supracrétacé et Éocene de la Patagonie et du Chili, n'a pas été trouvé dans la Nouvelle-Zélande.” This remark is repeated on page 90. On page 499 he says, “Le genre singulier Lahillia dont la distribution a été restreinte au Chili et à la Patagonie, se trouve aussi bien dans la Crétacé superieur et dans la patagonien. On voit que les relations faunistiques entre le Crétacé superieur et le patagonien sont les plus intimes possibles, et ce fait pour fixer ľàge Éocene de la formation patagonienne, me parait bien plus important que ne ľest le nombre restreint ďespéces vivantes qui s'y sont trouvées.” On page 492 he says, “Un genre specialement caracteristique du Tertiaire chileno-patagonien est Lahillia.” Further on page, 498, “En général le nombre de genres qui sont caracteristiques pour cette ancienne faune antarctique et qui lui sont exclusifs est tres restreint et presque reduit à Struthiolaria, Malletia, et Lahillia: ce dernier genre ne parait pas avoir atteint la Nouvelle-Zélande.”

In 1917 Woods described the Cretaceous faunas of the north-eastern part of the South Island of New Zealand, and amongst the species that are recorded is a doubtful Mactra (N.Z. Geol. Surv. Pal. Bull. No. 4, p. 30, plate xvi, fig. 8, 1917). In a critical reference to this publication Wilckens makes the following statement: “Diese muschel ist keine Mactra, sondern eine vertreterin der für das patagonische und antarctische Obersenon so beseichnenden Gattung Lahillia die sich auch in den Quiriquinaschichten

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findet und ausserdem in patagonische und antarctische Altertertiar wiederkehrt” (O. Wilckens, Cen. f. Min., &c., Jahrg. 1920, No. 15 u, 16, p. 264). The specimen was too imperfect for Woods to write any description of it, but its form in the figure he gives is certainly different from that of the present species.

Lahillia neozelanica n. sp. (Plate 16, figs. 1–3.)

Mactra crassa Marshall non Hutton, Trans. N.Z. Inst., vol. 49, pl. xxxvii, fig. 49 (figure only).

Shell of moderate size; height 72 mm., length 78 mm; another specimen, height 37 mm., length (imperfect) 33 mm. Shell thick, rather swollen, umbo curved forward, beak median, posterior margin regularly curved, descending rapidly, the ventral margin gently rounded, anterior margin in front of the beak somewhat concave, descending less rapidly than the posterior, the anterior end broken off. Surface nearly smooth, marked with a large number of concentric lines in larger and smaller series, the latter from six to ten between each pair of the larger lines, on the posterior margin they are sharply raised and closely crowded together. Hinge of right valve with a large, deep, and very marked pit below the beak, slightly oblique and the posterior margin longest, outside of this a narrow groove followed by a long somewhat narrow tooth coalescent above; anterior to the pit the hinge-plate is large, thick, and somewhat curved, with no distinct tooth-like projection; the whole hinge, however, is corroded.

Specimens have been found at Wangaloa only.

Type to be presented to the Wanganui Museum.

The specimen originally figured by Marshall as Mactra crassa is not at present available, and the larger measurements given are taken from the figure of that specimen. The above description has been drawn from a smaller right valve (imperfect), and the interior filled with hard matrix, while the hinge is that of a fragment of a much larger right valve with the beak eroded.

This species approaches Lahillia luisae Wilckens, from the Upper Senonian of Seymour Island, in sculpture, but is wanting in the subangular separation between the posterior and dorsal margins. It differs from L. larseni Wilckens, from the Tertiary of Seymour Island, in form and sculpture. It is higher in proportion to length when compared with specimens from the Upper Senonian of South Patagonia. The hinge and, as far as can be seen, the form, resemble those of L. veneriformis Hupé from Quiriquina, but no description of the form or sculpture or of the dimensions of this species are available.

It will be understood from the above that the genus Lahillia has previously been restricted, so far as its occurrence is concerned, to the Cretaceous and older Tertiary of Chile, Patagonia, and Seymour Island. Wilckens's reference which has been mentioned above is the only suggestion of its occurrence in New Zealand. Its inclusion in the New Zealand fauna obviously provides further proof of the former connection of New Zealand and South America, through the Antarctic continent, in the Cretaceous and early Tertiary. It is interesting to remember also that this Wangaloa fauna contains species of Heteroterma and Perissolax which are very closely allied to species from the Tejon fauna of California.

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Fig. 1.—Lahillia neozelanica n. sp. Right valve. Height, 37 mm.; length in profile, 33 mm.
Fig. 2.—Lahillia neozelanica n. sp. Same specimen. Profile.
Fig. 3.—Lahillia neozelanica n. sp. Fragment of a large right valve to illustrate the hinge.