Why doesn't the tag filter appear when I send to part of a list?

Apologies if this has been asked before:

I Have a list and on occasion I want to only send my next email to a part of that list. I have tagged the individual contacts that I want to filter out but when I get to the options of lists to choose from for that email send, the filter by tags ie 

AND

Do not appear. This is pretty fundamental

Any help much appreciated. Thank you.