Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 21q): Mt Harris, South Canterbury, Otaian-Altonian (hypotype of Marwick 1926a, pl. 62, fig. 8) (GNS)
Beu & Maxwell (1990): Chapter 11; p. 205; pl. 21 q.
Synonymy: Lapparia parki Suter 1907a, p. 207; Lapparia corrugata "(Hutton)" of Suter 1914, p. 27 (in part - not Voluta (Lyria) corrugata Hutton 1873b, p. 7, a nomen dubium not now used); Cymbiola (Miomelon) corrugata "(Hutton)" of Suter 1917, p. 87 (in part); Spinomelon otaioensis Laws 1932, p. 193; S. evelynae Laws 1933, p. 326
Type species of Spinomelon Marwick, 1926
Classification: Volutidae: Zidoninae
Description: Moderately large for subfamily (height 105-135 mm), fusiform, spire 0.3-0.4 total height. Protoconch highly variable, mamillate to cylindrical, of 2-3 whorls with feeble spiral ridges, those with 2 whorls having a prominent apical spike, those with 3 with a very bulbous initial whorl. Teleoconch of 5-6 whorls, typically weakly shouldered near middle on spire with gently concave sutural ramp and convex sides, but more distinctly shouldered on some shells, particularly on last whorl. Last whorl contracted gradually with little or no excavation. Axial sculpture of distant, rounded costae reaching from suture to suture on early whorls, but becoming obsolete on ramp on later whorls, and extending onto upper part of base of last whorl, distinctly tubercular on shoulder on those shells with a definite angulation; 12-15 costae on penultimate whorl. Aperture large, constricted to a prominent channel posteriorly; anterior notch moderately deep, fasciole distinct, depressed in some shells, slightly projecting in others. Columella with 5 prominent plaits, the lowest usually much weaker than the others, some shells with a 6th, weak plait at posterior end. Inner lip with thin callus smear spreading well onto last whorl; outer lip broadly convex, thickened internally, in some specimens weakly reflected.
Comparison: The holotype of Lapparia parki is a juvenile shell consisting of the protoconch and only two teleoconch whorls, but it compares closely with larger shells from its probable type locality and with numerous specimens (including adults) from coeval beds at Bluecliffs, Otaio River, the type locality of Spinomelon otaioensis and S. evelynae. S. otaioensis was alleged to differ from S. parki in having angulated whorls with a strongly concave sutural ramp, and in having sharply nodulated axial costae, whereas S. evelynae was supposed to have a more slender shell and a higher spire than S. parki. However, the reasonably large series of specimens now available shows that S. parki varies considerably in shell form, relative spire height and whorl shape, and that the holotypes of Laws' species fall well within the observed range of variation of S. parki. S. speighti (Otaian or Altonian, Mt Harris) is probably another synonym of S. parki; Marwick (1926a, p. 284) distinguished it on the basis of its supposedly broader shape and in having more strongly angled teleoconch whorls with strongly tubercular axial costae, but these differences are unlikely to be important in view of the variability noted in Bluecliffs shells. Marwick (1926a, p. 284-285) described a second species of Spinomelon, S. mira, from the foot of Mt Horrible, Pareora River. It differs from S. parki in having only very fine axial sculpture on the spire whorls but quite prominent costae on the last whorl, and in having a distinctly concave zone below the shoulder angle on the last whorl. Similar specimens have been collected from Bluecliffs, lower Tengawai River, Awamoa Creek and Ardgowan Shellbed and indicate that this is a distinct species rather than a variant of S. parki. Even more distinctive is S. benitens (type locality Trig Z, Otiake (Waitakian), also recorded from Awamoa Creek and Target Gully Shellbed) this has axial sculpture confined to the first three or four whorls, a very shallow anterior notch, and an inconspicuous fasciole.
Species of Spinomelon and Alcithoe are of similar adult size, and some closely resemble one another in sculpture. Most protoconchs of Spinomelon, however, have an apical spike, although this is not present in a few individuals where the normally deciduous initial whorl has not been shed, but Alcithoe lacks such a spike. In addition, species of Spinomelon typically have a shallower anterior notch and a less prominent fasciole than Alcithoe. Eocene species formerly assigned to Waihaoia are now assigned to Spinomelon, so this genus has an Eocene (Bortonian) to Recent range, and some Eocene to Recent species have very fine spiral sculpture. The genus is best-represented in faunules of Waitakian to Altonian age, particularly in North Otago and South Canterbury, but an unnamed species is present in Tongaporutuan faunas at Palliser Bay, S. awaterensis King, 1934 is an Opoitian-Waipipian reprentantative from the Awatere Valley, S. kingi Marwick, 1965 occurs in Waipipian-Mangapanian rocks in northern Hawke's Bay, and "Alcithoe" benthicola Dell, 1963 and "A". flemingi Dell, 1978 have proved to be Recent species of Spinomelon on the basis of molecular evidence (S. Hills, Massey University, pers. comm.).
Distribution: Otaian-Altonian; "Lower Gorge of Pareora River" (type locality of L. parki probably Mount Harris Formation, foot of Mt Horrible, Otaian); Bluecliffs, Otaio River, Otaian (type locality of S. otaioensis and S. evelynae); Mt Harris; Dyer's Run, Waihao Valley; Awamoa Beach; Ardgowan Shellbed.
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)