The bennettitalean trunk genera Cycadeoidea and Monanthesia in the Purbeck, Wealden and Lower Greensand of southern England: a reassessment
The history of the discovery of the Lower Purbeck dirt-beds on the Isle of Portland and the silicified bennettitalean trunks occurring within these fossil soils is reviewed and discussed. In the absence of the original type material, neotypes are selected for the two poorly-defined Purbeck species Cycadeoidea megalophylla Buckland and Cycadeoidea microphylla Buckland. A third cycadeoid trunk species, Cycadeoidea gigantea Seward, from higher in the Portland Purbeck sequence, is reassigned to the genus Monanthesia Wieland ex Delevoryas, the use of which is discussed in relation to the genus Cycadeoidea Buckland. Synonymies are presented for both genera and for all the more or less recognisable named species from the English Lower Cretaceous. Newly collected specimens from the Isle of Wight support the view that loose beach specimens of Cycadeoidea and Monanthesia trunks, formerly considered to be from the Wealden, are actually from the Lower Greensand. It is suggested that additions to our knowledge of English cycadeoid trunks can only be achieved by the use of invasive techniques, which are recommended for the further study of type specimens.