Annali della South African Museum = Annale van die Suid-Afrikaanse Museum . B Fig. 253. Menabites (Delawarella) sp. aff. jeanneti s.l. Collignon, 1948. SAMPCZ5691. X 0,85. Cretaceo faune DAL SUD AFRICA 333 allungato e punto fortemente verso l'interno. Con diametro crescente costolatura e remainsweak prorsiradiate con appena percettibile laterale (2) e submarginal (3),e leggermente più forte marginale (4), ma progressivamente più forte di cordone ombelicale (1) andexternal (5) tubercoli. Numerose intercalazioni e biforcazioni si verificano, generallyat il sito del tubercolo submarginal, ma anche occasionalmente alla

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Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . B Fig. 253. Menabites (Delawarella) sp. aff. jeanneti s.l. Collignon, 1948. SAM~PCZ5691. X 0, 85. CRETACEOUS FAUNAS FROM SOUTH AFRICA 333 elongated and point strongly inward. With increasing diameter ribbing remainsweak and prorsiradiate with barely perceptible lateral (2) and submarginal (3), and slightly stronger marginal (4), but progressively stronger umbilical (1) andexternal (5) tubercles. Numerous intercalations and bifurcations occur, generallyat the site of the submarginal tubercle, but also occasionally at the umbilicaltubercle. This results in there being about twice as many external as internaltubercles. Specimen SAM-PCZ5691 (Figs 252-253) has part of the early bodychamber preserved. Here tuberculation weakens even more, and the ribsbecome wider spaced. The suture is only partially exposed in the present material. The keel, asfar as can be seen, is never very prominent.. Fig. 254. Menabites (Delawarella) sp. aff. jeanneti s.l. Collignon, 1948. SAM-FB. x 1. 334 ANNALS OF THE SOUTH AFRICAN MUSEUM Discussion This species is identified by the fine, dense ribbing throughout, and thevery poor development of the lateral and submarginal tubercles. Collignon (1948: 34-36), in erecting M. {D.)Jeanneti, distinguished betweena typical form and a more compressed form, var. compressa, the difference inwhorl breadth between the two forms being approximately 5 per cent. Thelarger Zululand specimen, SAM-PCZ5691 (Figs 252-253), with a whorl breadthof 39 per cent of the diameter, appears closer to the typical form of M. (D.)jeanneti than to the compressed variety. The main difference between the Zulu-land material and the Malagasy specimens of M. (D.) jeanneti, lies in the factthat, in the adult stage, the latter lose ornament on the venter and take on theappearance of a pachydiscid. In the Zululand specimens the venter remains

Parole chiave associate all'immagine

• bookcentury1800
• bookdecade1890
• booki
• booksubjectnaturalhistory