"Here ends the Epistle" is an alternative form approved in Rite II, which is what we do, so I was wrong, a little. OTOH, "Here endeth the Epistle" is in fact an alternative form in Rite I.
To me, "Here ends the Epistle" would only make sense if you were reading a whole Epistle (and Corinthians is pretty long!) or a passage that happened to be at the end of one.