Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . ma pronounced sinus over the siphonal area. As size increases, the flexure of thestriae increases and they become very concave on both flanks and venter. There are five or six collar-like ribs and associated constrictions per whorlin smaller specimens; adults bear seven to eight, with some crowding on the bodychamber. Collars are faint on the flanks, but strengthen considerably on the CRETACEOUS FAUNAS FROM SOUTH AFRICA 159 shoulder and venter. They are rounded, with a gentle adapical and steep adaper-tural slope. The
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . ma pronounced sinus over the siphonal area. As size increases, the flexure of thestriae increases and they become very concave on both flanks and venter. There are five or six collar-like ribs and associated constrictions per whorlin smaller specimens; adults bear seven to eight, with some crowding on the bodychamber. Collars are faint on the flanks, but strengthen considerably on the CRETACEOUS FAUNAS FROM SOUTH AFRICA 159 shoulder and venter. They are rounded, with a gentle adapical and steep adaper-tural slope. The constrictions parallel growth striae; they arise at the umbilicalseam, are deep across umbilical and ventrolateral shoulders, but relatively weakon flank and venter. The internal mould is smooth, save for the constrictions, which are far moreprominent than on the test. They arise at the umbilical seam, pass straight up theumbilical wall and forwards across the umbilical shoulder, where they arestrongly marked. They are concave and strongly prorsiradiate on the flanks and. Fig. 4. Tetragonites subtimotheanus subtimotheanus Wiedmann. A-C. BMNH C78834, fromthe Mzinene Formation, Albian II, on the farm Izwehelia, north north-east of Hluhluwe,Zululand. D-F. BMNH C78836, from bed 4 of the Mzinene Formation, Albian V, at locality71 on the southern tributary of the Munywana Creek, Zululand. This specimen shows a well-preserved septal lobe, x 1. 160 ANNALS OF THE SOUTH AFRICAN MUSEUM flex backwards over the shoulder with a striking ventral sinus. The constrictionsbecome broader and more strongly flexed as size increases. The adult aperture shows features very similar to the collars associated withconstrictions, being marked by a thickened lip. None of the present specimens shows the external suture, but the septal faces
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Keywords: ., bookcentury1800, bookdecade1890, booki, booksubjectnaturalhistory
