Australiceras is a genus comprising mostly large heteromorph ammonites characterising the upper Aptian of the Austral biogeographical realm. The phylogenetic relationship between Australiceras and Proaustraliceras is still obscure, thus the generic concept remains provisional to some extent. Apart from the well documented occurrence of juvenile fragments (Casey, 1961: p. 55), Australiceras spp. are hitherto known with certainty only from the Austral Realm. Australiceras simpsoni sp. nov. is the first adult example of this genus from the Boreal Realm, whilst Australiceras dubium is assigned to this genus with reservation. Confirmation that the two genera overlapped geographically sheds new light upon the possible phylogenetic relationship between them. Regarding Proaustraliceras gigas the designation ‘holotype’ applied by Casey (1961) to the depicted syntype of Sowerby (1828, in Sowerby 1826‒1829) is invalid, we designate it as lectotype. Our recognition of Ammonitoceras chalense sp. nov., a large heteromorph previously attributed to A. sowerbyi Casey, adds to the species of that genus already known from the upper Aptian, with additional material clarifying the morphology of the latter species. A poorly known species from the upper Aptian of North West Germany, clearly related to the specimens from South East England, is described as Ammonitoceras ochtrupense sp. nov. The morphology of a little-known upper Aptian species, Caspianites boughtonensis , is revealed by the availability of new specimens.
Lehmann et al. (Fri,) studied this question.