. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 208 ANNALS OF THE SOUTH AFRICAN MUSEUM. Fig. 52. Olcostephanus {Olcostephanus) irregularis (Wegner) (?). The holotype, by monotypy, from the Lower Hauterivian of Marignac (Drome) (after Wegner 1909). x 1. Parabolae are lacking but there is a prominent apertural constriction. This species resembles O. atherstoni but may be distinguished by its more compressed form, fewer umbilical bullae and its younger (mid-Hauterivian) age. Olcostephanus fascigerus Spath (Figs 92-97) differs from O. atherstoni in it
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 208 ANNALS OF THE SOUTH AFRICAN MUSEUM. Fig. 52. Olcostephanus {Olcostephanus) irregularis (Wegner) (?). The holotype, by monotypy, from the Lower Hauterivian of Marignac (Drome) (after Wegner 1909). x 1. Parabolae are lacking but there is a prominent apertural constriction. This species resembles O. atherstoni but may be distinguished by its more compressed form, fewer umbilical bullae and its younger (mid-Hauterivian) age. Olcostephanus fascigerus Spath (Figs 92-97) differs from O. atherstoni in its finer, thread-like secondary ribs with more intercalatories between bundles, its more prominent bullae, and its constant rate of inflation which gives Spath's (1939) species a cylindrical aspect in ventral view. The microconch of O. baini baini (Sharpe) (Fig. 114) diners from that of O. atherstoni in being smaller with somewhat fewer secondary ribs per whorl, and in possessing parabolae. The O. baini var. sphaeroidalis (Spath) microconch (Figs 145-146, 149) diners from O. atherstoni ($) in possessing parabolae. Within the Uitenhage fauna, O. atherstoni macroconchs are rather rare and only five further specimens, one of which is fragmentary, are without hesitation assigned to Sharpe's species. However, very common are large macroconchs which differ from the holotype of O. atherstoni in the greater inflation of their middle whorls and their more depressed whorl section (Fig. 118). Whilst the differences may appear slight, the holotype of O. baini. 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
