Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . U I. (50 CRETACEOUS FAUNAS FROM SOUTH AFRICA 299 Dimensions D Wh Wh Wb: Wh U c 64,0(100) 26,5(41,4) 18,5(28,9) 1,43 29,3(45,8) ic 64,0(100) 23,8(37,2) 18,5(28,9) 1,29 29,3(45,8) Description The earliest stage visible is at a diameter of 20 mm (Fig. 41C-D). Thecoiling is evolute with a deep umbilicus, the whorl section depressed, with thegreatest breadth low on the flank intercostally and at the lateral tuberclecostally. There are thirteen to fourteen strong primary ribs per whorl, arisingon the umbilical shoulde
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . U I. (50 CRETACEOUS FAUNAS FROM SOUTH AFRICA 299 Dimensions D Wh Wh Wb: Wh U c 64,0(100) 26,5(41,4) 18,5(28,9) 1,43 29,3(45,8) ic 64,0(100) 23,8(37,2) 18,5(28,9) 1,29 29,3(45,8) Description The earliest stage visible is at a diameter of 20 mm (Fig. 41C-D). Thecoiling is evolute with a deep umbilicus, the whorl section depressed, with thegreatest breadth low on the flank intercostally and at the lateral tuberclecostally. There are thirteen to fourteen strong primary ribs per whorl, arisingon the umbilical shoulder. They develop into strong buUate to conical umbilico-lateral tubercles that increase rapidly in strength as size increases. At thesmallest diameter visible these tubercles give rise to pairs of strong prorsiradi-ate ribs that terminate in oblique ventral clavi. A shallow depression separatesthese from a corresponding number of siphonal clavi. This same style ofornament continues to 20 mm but the ribs become broader and lower. Beyondthis the whorl section becomes very depressed, th
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
