Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 20n): GS11283, J39/f9500c, Bluecliffs, Otaio River, Otaian (GNS)
Beu & Maxwell (1990): Chapter 11; p. 194; pl. 20 n.
Synonymy: Xymene n. sp. (?), Beu & Maxwell 1990, p. 194, pl. 20n
Classification: Muricidae: Ocenebrinae?
Description: Small for family (height 9-14 mm), fusiform, spire slightly less than half total height. Protoconch conical, of 2.5 smooth convex whorls. Teleoconch of 5-5.5 whorls, shouldered at or near middle on spire, with 2 less prominent angulations between shoulder and lower suture; last whorl excavated, base convex, neck moderately long, straight, slightly left-deflected. Axial sculpture commencing as narrow costellae, on later whorls consisting of prominent raised costae of rounded or broadly triangular section with broad, concave interspaces, reaching from suture to suture on spire whorls, dying out on base or upper part of neck of last whorl; later whorls typically with 1 or 2 previous varices retained; 9 or 10 costae (including varices) on penultimate whorl. Other axial sculpture of growth ridges of variable development, weak on some shells, forming scaly lamellae on others, particularly on axial costae. Spiral sculpture commencing as 2 or 3 cords, 1 on shoulder angle, the other 2 below, penultimate whorl with 3 subequal, rather prominent cords on sides, some shells with a 4th margining lower suture, and 1-3 weaker cords on sutural ramp. Last whorl with 11-13 additional cords, becoming obsolete on neck. Aperture ovate-trigonal, columella slightly concave, bent to left just above inception of moderately long, narrow, weakly notched siphonal canal. Inner lip moderately callused; outer lip angled at periphery, with a heavy varix, inner face with a shallow channel at shoulder angle and 6-7 narrow lirae below.
Comparison: The taxonomy of Oligocene and Early Miocene Xymenella species and related genera is in an unsatisfactory state. Ponder (1972a) lumped too many genera together in Xymene, and Beu (2009) began the recognition of narrower, more realistic genera by raising Xymenella, Axymene and Zeatrophon to genera again, seperating them from Xymene. Houart (2004) also removed some small "Xymene" species to the genus Gemixystus Iredale, 1929, although correspondents have expressed doubt since whether all these species really belong there, as paucispiral, smooth protoconchs, paucispiral, strongly keeled protoconchs, and conical, multispiral, in many cases medially keeled protoconchs all were included in one genus. The species with conical, multispiral protoconchs tentatively are retained here in Xymenella, whereas those with pauicspiral ones are included in Gemixystus. The one New Zealand specimen now referred to Gemixystus, therefore, is the single specimen from Beach Road, South Oamaru, collected by P. A. maxwell and identified as G. cf. rhodanos Houart, 2004 (a Recent eastern Australian species) by Houart (2004, p. 22, fig. 19). However, it is conceivable that the other small New Zealand fossil species with conical protoconchs, Xymenella apipagoda (Ponder, 1972), X. comes (Maxwell, 1992), and X. zebra (Houart, 2004), require a further genus. The classification proposed here clearly is still unsatisfactory in other respects, as "Zeatrophon" huttoni (Murdoch, 1900) (Nukumaruan-Recent) does not sit comfortably in Zeatrophon, it is unclear whether the other small species referred there are congeneric with the type species, Z. ambiguus (Philippi, 1844), the relationship between Z. ambiguus and typical South American-Antarctic Trophon species is unknown, and other species such as "Terefundus" aipipagodus Dell, 1956 (Recent) and "T." murdochi (Marwick, 1924) (Nukumaruan, Hawke's Bay) are much larger than Terefundus species and require a new genus near Ingensia Houart, 2001. This unnmed genus also is represented in Waitakian-Altonian rocks of North Otago and South Canterbury.
Ponder (1972a, p. 480-481) identified Otaian shells and very similar shells from Awamoa Creek and other North Otago Altonian localities as Xymene (now Xymenella) lepida, but the holotype (from Target Gully Shellbed) differs from the Otaian species in its relatively broad shell and in having evenly convex teleoconch whorls and a rounded aperture. It seems unlikely to be conspecific with the species described here, which is much more like X. minutissima in shape, but not in size. Specimens of X. minutissima from the Southburn Sand at White Rock River (type locality) and from Sutherlands are indeed minute (height 2.7-4.7 mm), have a much smaller protoconch than the Otaian shells and have less prominent axial sculpture with costae becoming obsolete on the last whorl of some shells. Ponder (1972a, pp. 482, 484) recorded X. minutissima from several other localities, including Pukeuri where he noted that it seemed to intergrade with "lepida". The large shells from Awamoa Creek and Ardowan Shellbed resemble the Otaian shells in most respects but typically have only two spiral cords on the sides of the penultimate whorl (although an additional cord may appear at a later stage of growth), and only five lirae on the inside of the outer lip. They are probably conspecific with shells from Target Gully Shellbed assigned by Ponder (1972a, p. 490) to X. chattonensis . The latter species (described from Shell Gully, Chatton, Duntroonian) is poorly known, and its relationship to the Altonian shells must remain uncertain until more material is available. Maxwell (1992, p. 122, pl. 17e-i) also named a second, small species, X. comes, which occurs with X. apipagoda at McCulloch's Bridge, Waihao River (Kaiatan), and probably several other species remain unnamed.
Distribution: Otaian; Mount Harris Formation, Bluecliffs, Otaio River; Mt Horrible, Pareora River (common).
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)