Gaster (1924, 1927, 1929, 1932, 1937, 1941, 1944) - Micraster cortestudinarium Zone
Biostratigraphical correlation: Equates with an interval from within the top of the S. plana Zone to between the top of the M. cortestudinarium Zone and the basal part of the M. coranguinum Zone of current usage. Gaster therefore followed Rowe's interpretation of this zone rather than that of Griffith & Brydone (1911) (Wood, WH/95/31R).
Lithostratigraphical correlation: Equates with the upper part of the Lewes Nodular Chalk Formation and possibly basal part of the Seaford Chalk Formation of southern England.
Age: Latest Turonian & Coniacian