18
2
May
275
283
RAWSON, P. F. 1975. The interpretation of the lower Cretaceous heteromorph ammonite genera Paracrioceras and Hoplocrioceras Spath, 1924. Palaeontology, 18, 2, 275–283.
Peter F. Rawson Ammonites (Crioceras) occultum Seeley and Hamites phillipsi Phillips, the type species of Paracrioceras and Hoplocrioceras Spath, 1924, are redescribed and the original concept of the genera is reviewed. The 'Tethyan' forms Emericiceras and Aspinoceras are regarded as junior subjective synonyms of Paracrioceras and Hoplocrioceras respectively. As defined by Spath, Hoplocrioceras embraces small forms with weakly aspinoceratid coiling together with larger, crioceratitid species; this definition cuts completely across existing generic classification of related Tethyan forms. The significance of shell coiling in the classification of some Lower Cretaceous heteromorphs is discussed briefly, and it is suggested that forms with aspinoceratid/ancyloceratid coiling may be dimorphs of larger, crioceratitid forms. The Palaeontological Association (Free Access)