"The Merman of Aden" in the Red Sea was exhibited in 1939 at the Ripley Odditorium (whose name was an inspiration to Joe Nickell in naming the Skeptiseum). Ripley was the creator of the famous "Believe It or Not!" cartoon series.
The text on the back of this postcard reads:
At RIPLEY ODDITORIUM
48th and Broadway, New York
MERMEN OF ADEN— the dugong, a rare sea mammal with a most human-looking face, probably inspired ancient tales of mermaids. In Aden on the Red Sea, Mr. Ripley found a "merman" which he judges to be a clever oriental fake, half monkey, half fish.
Usually such fakes were the female type, like the "Feejee Mermaid" exhibited by the great showman P. T. Barnum (1810-1891).