Noli manere in memoria!
It's en memoria. not in memoria. D=
*shot*
Uhhh... nope, it's 'in'. And I'm just saying that because it's an preposition taking an ablative in Latin, and is used the exact same way as our word 'in'. Ie. 'in memory'... only memory must go into the ablative case in Latin. In Latin en would be... hmm... can't quite recall. But it's actually ancient Greek that has 'en' for this particular preposition.
By the way, what gave you the idea that it was 'en'?