. Bulletin of the British Museum (Natural History), Geology. . Fig. 24 Sutures in Forbesiceras obtectum (Sharpe). A, at diameter of 165 mm; B, Material and occurrence. Seven specimens (, , , , , ) from the Odukpani Formation (Middle Cenomanian) can be definitely referred to this species. is from a horizon exposed 29-3 km from Calabar, and from 30-3 km from Calabar: the remainder cannot be precisely localized. In addition two fragmentary specimens (, UIN ) from 30-1 km from Calabar probably belong i
. Bulletin of the British Museum (Natural History), Geology. . Fig. 24 Sutures in Forbesiceras obtectum (Sharpe). A, at diameter of 165 mm; B, Material and occurrence. Seven specimens (, , , , , ) from the Odukpani Formation (Middle Cenomanian) can be definitely referred to this species. is from a horizon exposed 29-3 km from Calabar, and from 30-3 km from Calabar: the remainder cannot be precisely localized. In addition two fragmentary specimens (, UIN ) from 30-1 km from Calabar probably belong in this species. Dimensions. D 205 155 92 Wb 46 (22-4) 36 (23) 20 (22) Wh 125 (61) 100 (64-5) 55 (60) U Description. The present material falls into two groups. Up to a diameter of some 80mm development in both groups is similar, the ornament consisting of prorsiradiate ribs on the dorsal part of the flanks terminating in a row of bullate swellings or discrete tubercles in the middle of the flanks, while the ventral half of the flanks bear rursiradiate ribs terminating in fine clavate tubercles at the ventrolateral shoulder. The venter is narrowly fastigiate with dense nodate to bullate siphonal tubercles. The ornament at this stage is usually fairly pronounced. At diameters in excess of 80 mm, however, development in the two groups differs markedly. The first group, represented by (Fig. 29a, b), reaches full adult size at a diameter of some 110 mm, at which stage the sutures are simplified and approximated and the umbilicus is egressing, and the ornament is reduced in strength. The ribs are continuous from umbilicus to venter and are only slightly prorsiradiate on the dorsal part of the flanks and only slightly rursiradiate on the ventral part. The venter becomes broadly rounded with only a slight keel evident on the internal mould. The last third of the final whorl on this specimen is body chamber. It bears a broad deep pre-oral constriction swept forwards on t
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