“CHIONE MAWSONI sp. nov.
(Plate IV., figs. 47, 48, 49, 50.)
Shell very solid, oblong ovate, umbo at about two-fifths of the length, varying both in contour, sculpture and colour. Externally the colour is a dull white, internally buff or a rich purple which may either stain the margin and the muscular impressions or be suffused over the whole interior. Sculpture ranging from a predominance of radial to a predominance of concentric lines. Usually the surface is comparatively smooth for a distance of about 12mm. from the umbo where it is engraved by about 120 fine, shallow, radiating grooves, parted by rather wider flat interspaces, crowded laterally and spaced medially. External to this area there may be a sudden change to coarse elevated, irregular, close-set, concentric cords, grouped by deeper furrows into bundles of four or five and each composed of an aggregate of smaller fibres. On the posterior dorsal region these cords rise higher. In another case the concentric sculpture in high relief is absent, the valve is comparatively smooth and radial striæ prevail over the whole disk.
Lunule long and narrow, limited by a deeply-incised groove. Sinus short, horizontal, and pointed. Length, 37; height, 29; depth of conjoined valves, 20mm. A second example is 40 × 32 × 19; and a third, 31 × 28 × 18.
Of Mr. H. Suter I inquired if this was the species from the Auckland Islands which he described as Cytherea subsulcata. He replied that the C. subsulcata differed by being more rounded with a more coarse sculpture which extended to the umbo, and that the Macquarie shell was new to him. Venus antarctica Velain, from St. Paul,† is a much rounder shell than this.
Twenty-six specimens were dredged, December 4th, 1913, in 14 fathoms, sandy bottom, in Lusitania Bay, Macquarie Island.
† Velain.—Arch. Expér., vi., 1878, p. 138, pl. v., figs. 21, 22. Vol. IV., Part 1—E.”
(Hedley, 1916: 33)
