Referring back to subject of Felix, ever cryptic! (9)
I believe the answer is:
Here is my best explanation:
'referring back to subject' is the definition.
'felix ever cryptic' is the subsidiary indication.
'cryptic' indicates an anagram.
'felixever' with letters rearranged gives 'reflexive'.
'of' is the link.
(Other definitions for reflexive that I've seen before include "(Of an action) done without conscious thought", "Kind of pronoun like myself, himself etc", "(Of an action) performed unconsciously", "Of word, referring back to subject of verb", "Of a pronoun such as myself" and "Referring back to subject of verb - himself?".)