UPDATE (3/23/11): George Beccaloni found online an image of this card with names included (and I like how what looks like a monkey at the top right is closest to Darwin):
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This Victorian cabinet card was offered recently on eBay. The seller knew that Charles Darwin was one of the figures, but who are the others?
Top row: ???, ???, Charles Darwin
Bottom row: ???, Herbert Spencer, ???
The Dispersal of Darwin 
I think that the gentleman in the front to the right is Thomas Huxley.
Top row: Old White dude, Slightly Younger White Dude, Charles Darwin Bottom row: Youngish White Guy, Herbert Spencer, Mutton Chopped White Cat.
The muttonchopped man on the lower right might be Fleeming Jenkin.
http://www.clerkmaxwellfoundation.org/html/picture_viewer_38.html
Front right – I just realized that that is probably JD Hooker. Compare:
http://www.google.com/images?q=joseph+dalton+hooker&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1366&bih=643
But Thomas, you are right on with them all!
Oh what fun. May I jump in unceremoniously?
🙂
Shall we say the 2nd chap from the left, standing, is a not very good likeness of T.H. Huxley?
See the 2nd photo here:
http://communicatescience.com/zoonomian/2009/05/04/happy-birthday-thomas-henry-huxley-1825-1895/
I just discovered this site and I shall return!
If it’s even Huxley?
It doesn’t look like a cabinet card to me. Anyone know where the original painting/drawing of this picture was published?
Great game. Not easy. Maybe back left Spencer, back right Huxley, front right Hooker. Presumably remainder other X-Club. Be good to put this to bed properly.
Spencer is definitely the one in dead center, see: http://www.gettyimages.com/detail/3351418/Hulton-Archive
John van Wyhe thinks the gentleman on far left, back row is John Stuart Mill: http://www.utilitarian.net/jsmill.jpg
“…I came across a very curious photograph showing Darwin, Mill, Spencer, Ruskin and two less famous English writers. I could never find out whether such a meeting had actually taken place or whether the photograph had been cleverly assembled by the artist…” see http://darwin-online.org.uk/content/frameset?itemID=F2093&viewtype=text&pageseq=1 Footnote 2.
Wow, George, how did you come across this?
I think top left is John Stuart Mill.