Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . B Fig. 3. Protexanites {Protexanites) cycni (van Hoepen, 1965. A. SAS-Z808. B. SAS-Z832. A, C-E x 1; B x 1,1. 12 ANNALS OF THE SOUTH AFRICAN MUSEUM SAS-Z834 shows details of the ontogeny (Figs 2A-C, 3B). On the innermostwhorls, up to a diameter of c. 6 mm, the whorls are rounded and devoid ofvisible ornament. Beyond that diameter, umbilical (1) tubercles and very weak,bifurcating fold-like ribs start appearing. Microscopic examination of the ribsshows them to be ornamented by numerous radial striae. With
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . B Fig. 3. Protexanites {Protexanites) cycni (van Hoepen, 1965. A. SAS-Z808. B. SAS-Z832. A, C-E x 1; B x 1,1. 12 ANNALS OF THE SOUTH AFRICAN MUSEUM SAS-Z834 shows details of the ontogeny (Figs 2A-C, 3B). On the innermostwhorls, up to a diameter of c. 6 mm, the whorls are rounded and devoid ofvisible ornament. Beyond that diameter, umbilical (1) tubercles and very weak,bifurcating fold-like ribs start appearing. Microscopic examination of the ribsshows them to be ornamented by numerous radial striae. With the onset ofornament, the whorl section changes and becomes rectangular. Traces of thesubmarginal (3) tubercles become visible in the umbilical seam at a diameterof about 14 mm. From then onward, ornament remains basically the same,apart from the fact that the ribs tend to become more prominent on the bodychamber. The external suture is relatively simple with a broad, asymmetrically bifidlateral lobe (Fig. 4).. ,0 ?-0 Fig. 4. Protexanites (Protexanites) cycni (van Hoepen, 1965).SAS-Z832. Scale bar in millimetres. Suture line of Discussion The main characteristics of this species are the subrectangular whorlsection with little-inflated flanks, ornamented by weak, flattened ribs withoccasional bifurcations and intercalations and by the weakly crenulate keel. Van Hoepen (19656: 183) based this species on an immature juvenilespecimen, still fully septate at the largest diameter. On the basis of the presentmaterial, the authors would place this specimen in Protexanites rather than inSubprionocyclus, as suggested by Van Hoepen, although the dividing linebetween the two taxa here becomes indistinct. As far as the crenulate keel is concerned, comparisons may be drawn withP. (P.) bourgeoisi and P. (P.) bontanti bontanti. Both species were recentlyreviewed on the basis of the original material by Matsumoto (1966, 1970).P. (P.) bourgeoisi has more sinuous ribs than P. (P.) cycni and exhi
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Keywords: ., bookcentury1800, bookdecade1890, booki, booksubjectnaturalhistory
