Interesting. Is there good documentation anywhere of their family
connection (Cyril & SLC)?

On a quick search I found this --

"Mr. [Cyril] Clemens said his great-great-grandfather and Samuel Langhorne
Clemens' great-great-grandfather were brothers—and therefore, he and the
famous writer and humorist were third cousins, twice removed."
http://www.genealogy.com/ftm/s/c/o/Mery-B-Scott/WEBSITE-0001/UHP-0151.html

Cyril's father was James Ross Clemens, and apparently SLC referred to him
as "a cousin of mine" in the 1897 mixup:

http://www.twainquotes.com/Death.html  (Image of the "report of my death"
statement at the link.)

A 1929 writing from James Ross Clemens himself, on topic, is included in
Gary Scharnhorst's "Twain in His Own Time" (2010) on p. 222-224


(But I have never thought about it before today, so I don't claim to know
anything. I bet others do.)


DDD