Mintmark type 5 - eight rayed star rather than 6, indicates newly defined sub-class 3d3 when found on coins from the London mint.
Mintmark type 4, star with blunt ends: rounded or angular.
Also note that coins from these classes often have a colon after REX.
Ten sub-classes are recognised using a combination of features. When the mintmark is clear enough it is a convenient starting point for identification. Four mintmarks are seen in the Class 3 group: types 3, 3*, 4 and 5.
Mintmark type 3* - sharp pointed star, but lower ray pointing down towards central crown ornament.
Mintmark type 3 - sharp pointed star, straddling the central crown ornament.