Group N is the rarer of the two design groups that make up Series Z (Unelli). I cannot say with any certainty if this Group precedes Group O. There is no design evolution. The die engraver, who exhibits very little talent, tries to mimic an evolution of design by mixing certain elements borrowed from Coriosolite coinage. This is perhaps done to decieve his employer Viridovix, or because of religious taboos concerning duplication of design. He uses one early element with a late one in each group.
Group N has beads inside the tail, Group O has them outside the tail.
The Group O coin illustrated by the line drawing is the commonest of Series Z, and is distinguished by the hockey-stick shape of the lower part of the eye. This coin is known from thousands of examples and is probably the commonest of all Celtic coins. For some perverse reason dealers seem to charge more for this coin than many, much rarer coins. It should be viewed as relatively worthless.