Article: The Cretaceous ammonite Ammonites requienianus d'Orbigny, 1841

Coilopoceras requienianum (d'Orbigny, 1841) is revised on the basis of the types and other material. It shows wide intraspecific variation and dimorphism of the type demonstrated in North American species of the genus. Similar dimorphism is shown in other Old World species, especially Nigerian forms, with Glebosoceras Reyment, 1954, a strongly ornamented genus which is treated as a synonym of Coilopoceras Hyatt, 1903. The Coilopoceras from Algeria described by Pervinquiere (1910) and said to be of Cenomanian age are confirmed as members of the genus, but they are shown to be upper Turonian; so this occurrence does not contradict previous views that the genus arose during the Turonian via Hoplitoides von Koenen, 1898.