Help please
Two clues I think I've solved but can't understand logic.
19a. Beasts hold back short grey element (6) O?Y?E?
I have ORYXES and E affects first letter of 20d (I believe OS is derived from element Osmium and oryx is a beast)
20d. One after another (6) E?E?E?N
First letter E dependent on 19a being correct
I have ELEVEN but can't understand why or the logic of the clue