Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . OQ 00 i o c. i^fe .^^^ CRETACEOUS FAUNAS FROM SOUTH AFRICA 309 There are sixteen strong, narrow ribs per whorl. These arise as mere striaeat the umbilical seam but strengthen at the umbilical shoulder, developingfeebly defined bullae. They are strong, rounded and narrow on the inner half ofthe flanks, straight and prorsiradiate, and bear a strong, sharp, bullate lateraltubercle. The lateral tubercles usually give rise to pairs of weak, concavesecondaries that are accompanied by a few intercalated secondaries to give a
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . OQ 00 i o c. i^fe .^^^ CRETACEOUS FAUNAS FROM SOUTH AFRICA 309 There are sixteen strong, narrow ribs per whorl. These arise as mere striaeat the umbilical seam but strengthen at the umbilical shoulder, developingfeebly defined bullae. They are strong, rounded and narrow on the inner half ofthe flanks, straight and prorsiradiate, and bear a strong, sharp, bullate lateraltubercle. The lateral tubercles usually give rise to pairs of weak, concavesecondaries that are accompanied by a few intercalated secondaries to give atotal of thirty ribs per whorl on the outer parts of the flanks. These sweepforward across the ventrolateral shoulder where they terminate in low, swollen,oblique ventrolateral clavi. There is a low, broad, rounded undulose siphonalridge flanked by shallow grooves, developing ill-defined siphonal clavi corre-sponding in position and number to the ventrolateral clavi. The sutures are not exposed. Discussion Few Yabeiceras species are known at this diameter but all those that areshow th
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
