James B. Riding, Susan L. Matthews, Nicholas H. Miles, Anton Wolfard; Metaridium solidispinum gen. et sp. nov., a polygonomorph acritarch from the Lower Cretaceous of Europe. Palynology ; 22 (1): 57–66. doi:
A new morphologically distinct polygonomorph acritarch, Metaridium solidispinum sp. nov. occurs in the Hauterivian-lowermost Barremian (Lower Cretaceous) strata of eastern England and the southern North Sea Basin. This morphotype is small and rectangular with a simple, long and solid process emanating from each corner and a large pylome. This species is persistent, relatively common and confined to the Hauterivian-lowermost Barremian, and hence is deemed to be a reliable stratigraphic maker. Metaridium solidispinum is, however, most characteristic of the upper Hauterivian.