. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. REVISION OF LATE VALANGINIAN CEPHALOPODA 163 of Olcostephanus and possibly O. (Subastieria), and is, therefore, superfluous. The genus Ceratotuberculus is characterized by the appearance, after the third whorl, of high, thick, ventrolateral bullae, as well as by possessing a ventral furrow, whilst retaining the other olcostephanid characters. If, as suggested by Imlay (1938), this genus is of early Hauterivian age, then it is probably descended from Saynoceras. If, however, it is of late Valangi
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. REVISION OF LATE VALANGINIAN CEPHALOPODA 163 of Olcostephanus and possibly O. (Subastieria), and is, therefore, superfluous. The genus Ceratotuberculus is characterized by the appearance, after the third whorl, of high, thick, ventrolateral bullae, as well as by possessing a ventral furrow, whilst retaining the other olcostephanid characters. If, as suggested by Imlay (1938), this genus is of early Hauterivian age, then it is probably descended from Saynoceras. If, however, it is of late Valanginian age, then the differences probably warrant at most subgeneric separation from Saynoceras. Spath (1924) erected the genus Subastieria for Olcostephanus sulcosus Pavlow, differentiated from Olcostephanus by its younger age and highly coronate whorl section. According to Wright (in Arkell et ah 1957), Subastieria closely resembles the inner whorls of some Rogersites which, as just shown, is a synonym of Olcostephanus Moreover, Wiedmann & Dieni (1968) have recently shown Subastieria to range into the Upper Valanginian, whilst Olcostephanus is common in the Lower Hauterivian of the Swiss Jura (Debehnas & Thieuloy 1963). Consequently, not only do Subastieria and Olcostephanus have the same stratigraphic range, but they are also morphologically very similar. However, in Subastieria the whorl section is coronate at all growth stages, whereas microconch forms of Olcostephanus become coronate only with the egression of the umbilical seam on the body chamber. This appears to be a subtle but distinct difference, and consequently Wiedmann & Dieni (1968) are provisionally followed in treating it as a valid Fig. 9. Olcostephanus {Olcostephanus) cf. atherstoni (Sharpe). The holotype of Taraisites bosei Cantu Chapa, from the Taraises Formation of northern Mexico (after Bose 1923). x 1. Cantu Chapa (1966) erected the genus Taraisites for the specimen of Astieria
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
