. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA. Fig. 5. Plesiotexanites {Eutexanites) sextuberculatus sp. nov. Holotype, BMNH C82427 from the St Lucia Formation, Lower Santonian, locality 86, Zululand. Part of external suture lines. keel, at this diameter, is already well developed and entire. At a diameter of 40 mm the ventrolateral tubercles already show distinct signs of splitting in two, although still joined by a common base. In addition, the umbilical tubercles move outwards from the umbilicus and also sh
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA. Fig. 5. Plesiotexanites {Eutexanites) sextuberculatus sp. nov. Holotype, BMNH C82427 from the St Lucia Formation, Lower Santonian, locality 86, Zululand. Part of external suture lines. keel, at this diameter, is already well developed and entire. At a diameter of 40 mm the ventrolateral tubercles already show distinct signs of splitting in two, although still joined by a common base. In addition, the umbilical tubercles move outwards from the umbilicus and also show signs of splitting in two. At this stage the ventral half of the umbilical tubercle appears strongest. Beyond this diameter, crenulations appear on the keel. With increasing diameter the division of the ventrolateral and umbilical tubercles becomes more and more marked, and at a diameter of about 75 mm the division is completed. Also at this stage faint indications of a lateral row of tubercles appear, situated slightly closer to the submarginal than inner umbilical tubercle. Up to this stage all the ribs are single and more or less radial, but beyond this, slight indications of forward curvature of the ribs develop. The holotype is still septate at a diameter of 102 mm, and at the greatest preserved diameter six distinct rows of tubercles are present, although the lateral row is still weakest. Spacing of the rows of tubercles is virtually equi- distant, each being situated on one-sixth of the flanks. Part of the external suture is shown in Figure 5. It is of the normal col- lignoniceratid type with little-incised elements. Discussion The description of the species is based mainly on the holotype (Figs 1-3, 5, 7). Paratype SAM-PCZ5926 (Fig. 4E-G) is an immature individual, whereas SAM-PCZ5925 (Fig. 4D) differs from the holotype in being slightly more inflated, narrower umbilicate and does not have as distinct outer umbilical tubercles in the adult stage. Both sides of the ho
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
