Beak membrane (4)
I believe the answer is:
cere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">beak membrane</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cere that I've seen before include "Wax" , "Waxy covering at base of some birds' upper beak" .)