discussed the meaning of the relation between representative species before
I did, and, as I suppose, Wallace did in his paper before the Linnean
Society. Von Buch's is the nearest approach to such discussion known to
me.


LETTER 400. TO W.D. CRICK.

(400/1. The following letters are interesting not only for their own sake,
but because they tell the history of the last of Mr. Darwin's
publications--his letter to "Nature" on the "Dispersal of Freshwater
Bivalves," April 6th, 1882.)

Down, February 21st, 1882.

Your fact is an interesting one, and I am very much obliged to you for
communicating it to me. You speak a little doubtfully about the name of
the shell, and it would be indispensable to have this ascertained with
certainty. Do you know any good conchologist in Northampton who could name
it? If so I should be obliged if you would inform me of the result.

Also the length and breadth of the shell, and how much of leg (which leg?)
of the Dytiscus [a large water-beetle] has been caught. If you cannot get
the shell named I could take it to the British Museum when I next go to
London; but this probably will not occur for about six weeks, and you may
object to lend the specimen for so long a time.

I am inclined to think that the case would be worth communicating to
"Nature."