. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. UPPERMOST CENOMANIAN-BASAL TURONIAN AMMONITES FROM SALINAS, ANGOLA 113 towards the very narrow venter (Fig. 30). On the flanks, initially straight, later slightly flexuous, ribs arise at the umbilicus from very weak umbilical bullae and broaden markedly towards the venter. The ribbing on the inner portion of the flanks, closest to the umbilicus, is very faint and indistinct on the adoral half of the outer whorl. Between all long ribs there are almost invariably 1-2 ribs inter- calated at about mid-fl
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. UPPERMOST CENOMANIAN-BASAL TURONIAN AMMONITES FROM SALINAS, ANGOLA 113 towards the very narrow venter (Fig. 30). On the flanks, initially straight, later slightly flexuous, ribs arise at the umbilicus from very weak umbilical bullae and broaden markedly towards the venter. The ribbing on the inner portion of the flanks, closest to the umbilicus, is very faint and indistinct on the adoral half of the outer whorl. Between all long ribs there are almost invariably 1-2 ribs inter- calated at about mid-flank. At the venter there are about 30 ribs on the outer whorl, with rib terminations broader than the interspaces. All ribs bear strong upper and weak lower ventro-lateral clavi, the latter weakening noticeably with age. Broad low ribs connect the upper ventro-lateral tubercles across the venter on the adoral portion of the outer whorl. The narrow venter is distinctly concave on the adapical portion of the outer whorl, but as tuberculation weakens it becomes tabulate. The greatest width is at mid-flank. Measurements No. D H W H/W U SAM-PCA2714 84 51 (61) 29 (35) 1,76 7 (8,3) 55 57 28 (49) 20 (35) 1,40 ? Discussion The following ontogenetic features are apparent in the Angolan example before the writer: the shell becomes more compressed with age, the tuberculation weakens (especially the lower ventro-lateral clavi) considerably, the venter is showing the tendency, so typical amongst described forms, to round with. Fig. 30. Metoicoceras gibbosum Hyatt, SAM-PCA2714. Whorl section, x Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original South African Museum. Cape Town : The Museum
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
