Can you give some examples of ones beginning with 'C'? (and what's the derivation?)

Cotter=MacOttar. I can't remember any more C's right now, but there are G's and K's to choose from, like Guinness=MacInness and Keane=MacEane (I'm not going to attempt Irish spellings, which would go on for miles of alternating vowel and consonant and look unrecognisable as the modern name)

Then there are all the O's, like O'Neill, that I forgot to mention.