Mediaeval Lore from Bartholomew Anglicus by Robert Steele

And some men say, that they are fishes of the sea in likeness of women. Some men feign that there are three Sirens some-deal maidens, and some-deal fowls with claws and wings, and one of them singeth with voice, and another with a pipe, and the third with an harp, and they please so shipmen, with likeness of song, that they draw them to peril and to shipbreach, but the sooth is, that they were strong hores, that drew men that passed by them to poverty and to mischief. And Physiologus saith it is a beast of the sea, wonderly shapen as a maid from the navel upward and a fish from the navel downward, and this wonderful beast is glad and merry in tempest, and sad and heavy in fair weather. With sweetness of song this beast maketh shipmen to sleep, and when she seeth that they are asleep, she goeth into the ship, and ravisheth which she may take with her, and bringeth him into a dry place, and maketh him first lie by her, and if he will not or may not, then she slayeth him and eateth his flesh.”

—Excerpted from Mediaeval Lore from Bartholomew Anglicus

I was only interested in the excerpt that mentions mermaids so I don’t intend to read the book by any means but I’m glad there was an English translation available. The book can be found for free in the Gutenberg Project archives.