Found the following hamletworks.org entries referring to line 552
View Commentary Note for 549
549
Laer. Farwell Ophelia, and remember well
1.3.84
View Commentary Note for 551
551
Ophe. Tis in my memory lockt
1.3.85
View Commentary Note for 552
552
And you your selfe shall keepe the key of it.
1.3.86
View Material Textual Note for 552
552
And you your selfe shall keepe the key of it.
1.3.86