. Bulletin of the British Museum (Natural History). MID-CRETACEOUS AMMONITES OF NIGERIA. Fig. 19 Sutures in: A-D, Nigericeras gadeni (Chudeau), Gadeni Zone, Pindiga Formation. A, , basal limestone bed, Ashaka Quarry. B, , north-east of Biu plateau. C, , Teli. D, , Teli. E, Eotissotia simplex Barber, , upper Dukul Formation. Dukul. F-K, Hoplitoides ingens (von Koenen), upper Dukul Formation, Dukul. F, ; G, ; H, ; I, ; J, C. 91248; K, L, Coilopoceras discoideum Barber, , Pindiga Formation, Bularaba. M, Wrigh
. Bulletin of the British Museum (Natural History). MID-CRETACEOUS AMMONITES OF NIGERIA. Fig. 19 Sutures in: A-D, Nigericeras gadeni (Chudeau), Gadeni Zone, Pindiga Formation. A, , basal limestone bed, Ashaka Quarry. B, , north-east of Biu plateau. C, , Teli. D, , Teli. E, Eotissotia simplex Barber, , upper Dukul Formation. Dukul. F-K, Hoplitoides ingens (von Koenen), upper Dukul Formation, Dukul. F, ; G, ; H, ; I, ; J, C. 91248; K, L, Coilopoceras discoideum Barber, , Pindiga Formation, Bularaba. M, Wrightoceras munieri (Pervinquiere), , upper Dukul Formation, Dukul. All specimens are housed in the British Museum (Natural History), London, x 2-4 dissection of several adult V. nigeriense failed to reveal juvenile whorls with the highly bullate umbilical tubercles which are common in these forms. Vascoceras cf. evolutum (Schneegans 1943: 130; pi. 8, fig. 2) is common in the Cauvini Zone at Ashaka and Pindiga; it occurs associated with Pseudaspidoceras pseudonodosoides (Choffat). At Dukul the stratigraphically lowest ammonite collected belongs to the latter genus (Fig. 22). This form is conspccific with the "Pseudaspidoceras ; of Barber (1957: 11; pi. 25, fig. 8) which, while losing all but the umbilical ornament early in ontogeny, shows the robust, rectiradiate ribbing of P. pseudonodosoides in its juvenile and middle growth stages. The Dukul specimen occurs below scree levels containing ammonites typical of the Proprium and Nigcricnsis Zones (Fig. 28), suggesting a stratigraphical position high in the Cauvini Zone. Barber's material, how- ever, came from Bularaba, where the ammonite-bearing beds begin in the Proprium Zone (see below), indicating that Pseudaspidoceras of pseudonodosoides type extend into this part of the sequence. Popoff et al. (1986) proposed a 'Zone of Vascoceras tavense' for beds at Pindiga and Ashaka making up the lower part of the Cauvini
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