. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA 215 fastigiate area between the ventrolateral tubercles and the central keel, numer- ous spiral striae occur. In some specimens, SAS Z15 (Fig. 73), these striae also cover the ventrolateral tubercles. The central keel undulates, but the undu- lations do not coincide with ventrolateral clavi. The central keel is bounded on either side by a shallow depression producing slight spiral ridges, but these can hardly be termed lateral keels. On the outer whorls of the
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA 215 fastigiate area between the ventrolateral tubercles and the central keel, numer- ous spiral striae occur. In some specimens, SAS Z15 (Fig. 73), these striae also cover the ventrolateral tubercles. The central keel undulates, but the undu- lations do not coincide with ventrolateral clavi. The central keel is bounded on either side by a shallow depression producing slight spiral ridges, but these can hardly be termed lateral keels. On the outer whorls of the specimens available (nearly all of them are still septate), all ornament weakens and the whorls become nearly smooth. Discussion P. (Zuluiceras) undulatocarinatum continues the trend towards increased involution and compression, forming a link between P. (Z.) henniei and P. (Z.) modes turn. In addition, loss of ornament on the outer whorls is obvious. This is comparable to that found in the transition from Texanites to Submortoniceras (Klinger & Kennedy 1980: 172). Differences between undulatocarinatum, henniei and modestum are grada- tional in some respects. There is no clear-cut boundary between them in respect of umbiHcal diameter: P. (Z.) henniei has an umbilical width of 40 to 45 per cent, P. (Z.) undulatocarinatum between 35 and 40 per cent, whereas P. (Z.) modestum has an umbilical width below 30 per cent. These reductions in umbili- cal width are, however, accompanied by changes in whorl section and loss of or- nament. P. (Zuluiceras) undulatocarinatum, as here interpreted, includes P. (Zuluites) georgemeintjesi van Hoepen and P. (Z.) lettiae van Hoepen. Differ- ences between these latter 'species' and P. (Zuluiceras) undulatocarinatum are minor and restricted to details of the inner Fig. 72. Peroniceras (Zuluiceras) undulatocarinatum van Hoepen, 1955. Suture-line and whorl section of SAS Z185, the holotype of P. (Zuluites) lettiae van Hoepen, 1965. x 1. (
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
