Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . c a-uo \_ •X ^ m i^ ^\ -5^,, ^ \ --. .^--^ -.^ ,\^ ..--* - ,- \ ^^.. , - ^ ^ ^ ^ f o oX ^. CRETACEOUS FAUNAS FROM SOUTH AFRICA 251 flanked by faint, shallow grooves, which subsequently develops low crenula-tions, each of which corresponds to a rib. As size increases, ribbing andtuberculation becomes increasingly differentiated. At a diameter of 36 mm thecoiling has become a little more evolute (umbiUcus is 27,3% of diameter) andhigher-whorled (whorl breadth to height ratio of 0,69). There are fifteenmedium-sized umbil
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . c a-uo \_ •X ^ m i^ ^\ -5^,, ^ \ --. .^--^ -.^ ,\^ ..--* - ,- \ ^^.. , - ^ ^ ^ ^ f o oX ^. CRETACEOUS FAUNAS FROM SOUTH AFRICA 251 flanked by faint, shallow grooves, which subsequently develops low crenula-tions, each of which corresponds to a rib. As size increases, ribbing andtuberculation becomes increasingly differentiated. At a diameter of 36 mm thecoiling has become a little more evolute (umbiUcus is 27,3% of diameter) andhigher-whorled (whorl breadth to height ratio of 0,69). There are fifteenmedium-sized umbilical bullae per whorl. These give rise to pairs of low,relatively broad, flexuous prorsiradiate ribs that sweep forward across the innerflank, are feebly convex across the mid-flank and feebly concave across theouter flank. Occasional intercalated ribs are inserted around mid-flank and allthe ribs develop a small, conical ventrolateral tubercle. These give rise to broadprorsiradiate extensions of the ribs that sweep forward to link with elongatesiphonal clavi borne on the siphonal keel. There are thirty-eight ribs per whorlat this diameter, corresponding to a s
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
