Article: Distinction between sympatric species of Micraster (Echinoidea) from the English Chalk
Robert B. Stokes
Sympatric species of Micraster recorded from the upper Cretaceous Chalk of England are most easily distinguished from one another by the relative height of their periprocts measured from the base of the test. The observation of Gauthier (1887) and Melville (1954) that Micraster species with a high conical aboral surface (so-called 'gibbous' forms) have a lower periproct than the associated non-gibbous forms is confirmed by numerical analysis of samples from the Santonian of Kent (M. gibbus and M. coranguinum) and the upper Campanian of Norfolk (M. stolleyi and the M. schroederi-glyphus lineage). The nomenclature of the gibbous species M. gibbus and M. stolleyi is discussed.