A Marx Sister?

In 1972, 81-year-old Groucho Marx performed at Carnegie Hall. Introduced by Dick Cavett and accompanied by Marvin Hamlisch on piano, Groucho told stories of his life and sang. Out of this show came a two-record album called "An Evening With Groucho," which I still have. It's been a couple decades since I've had a turntable hooked up, so I haven't listened to it for many years. Now, thanks to the internet, transcriptions are available and the recording itself can be downloaded in digital format.

In discussing his family, Groucho said:

Then we had a sister. She wasn't really our sister, she was an adopted sister. The father of that sister had gotten a look at this girl and fled to Canada, and we never saw him again. But the girl stayed with us, and her name was Polly. Polly didn't... She wasn't a bad looking girl, but her rear end stuck a-way out. You could play pinochle on her rear end.

Polly, or Pauline, was the daughter of Groucho's aunt Hannah, who was Minnie Marx's sister. The paternity of Polly is uncertain, but she was probably conceived after the death or disappearance of Hannah's first husband. It is likely that Sam and Minnie Marx adopted Polly, and it appears they fibbed about the date of their marriage to make it look like Polly was was their own legitimate child. The record shows Sam and Minnie were married January 18, 1885, but they moved the date back a year to 1884 in future records, to accommodate the January, 1885 birth of Polly.