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Genus Murexsul Iredale, 1915.
The name Murexsul was originally proposed as a sub-generic division of Murex by Iredale (Trans. N.Z. Inst., vol. 47, 1915, p. 471), but was given full generic significance by Finlay (Ibid., vol. 57, 1926, p. 487).
Murexsul echinophorus n. sp. (Figs. 91, 92).
A spinose approximately fusiform shell of moderate size, ornamented by prominent spinose varices.
Spire-whorls small, rapidly increasing in size to a large body-whorl. Height of spire (incomplete) is estimated as about equal to that of aperture without canal. Whorls angled a little above their middle, the shoulder relatively free from spines near the suture Outlines of whorls convex, body-whorl contracting gradually at base.
The sculpture is of axial varices (10 or 11 per whorl) and of strong spiral ridges (7 primary ones on body-whorl; apparently 3 on spire-whorls) produced into prominent spines where they cross the varices. Spines elongated, not hollow as in octogonus, but filled during growth. Interspaces between major spirals locally indicate subsidiary spirals.
Basal portion of body-whorl worn, but has less prominent ornamentation than octogonus.
Aperture ovate, apparently narrower than in octogonus, but outer lip is a little crushed. Outer lip also descends more steeply from suture as body-whorl is less inflated; imperfect near suture;
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furnished with prominent spines at the spirals. Aperture narrows gradually below to a somewhat short, very narrow, apparently shallow, almost closed canal, oblique to the left and apparently not bent back below. Columella almost vertical; faintly excavated.
Inner lip with thin callus on parietal wall descending as a moderately thick narrowing projecting plate over the fasciole, forming a false umbilicus over excavated portion, which is not so open as in octogonus owing to more vertical descent of plate.
A narrow elevated convex fasciole-ridge with coarse imbricating lamellae ascends at a small angle with columella from basal notch of anterior canal; excavation on its inner side furnishes false umbilicus beneath callus-plate of inner lip.
Dimensions of holotype (A.U.C. collection): Height (incomplete), 45.5 mm.; diameter, 25.5 mm.
The Oneroa shell differs from M. octogonus (Q. & G.), in having a shorter and straighter canal, a less inflated outer lip and a more vertical lower inner lip. In addition it has stronger sculpture of close - spaced axial varices, with much stronger, solid and not hollow spines. M. echinophorus approaches M. cuvierensis Finlay (Trans. N.Z. Inst., vol. 57, 1927, p. 487), but differs noticeably in having a prominent spiral row of spines between the shoulder and suture.
An undescribed species from Target Gully, Oamaru, in the N.Z. Geological Survey collection is more closely allied to the Recent octogonus than to the Waiheke shell.