What a range and what a variability in the Cyrena! (50/1.

A genus of Lamellibranchs ranging from the Lias to the present day.) Your list of the ranges of the land and fresh-water shells certainly is most striking and curious, and especially as the antiquity of four of them is so clearly shown.
I have got Harvey's seaside book, and liked it; I was not particularly struck with it, but I will re-read the first and last chapters.
I am growing as bad as the worst about species, and hardly have a vestige of belief in the permanence of species left in me; and this confession will make you think very lightly of me, but I cannot help it.

Such has become my honest conviction, though the difficulties and arguments against such heresy are certainly most weighty.
LETTER 51.

TO C.LYELL.November 10th [1856].
I know you like all cases of negative geological evidence being upset.
I fancied that I was a most unwilling believer in negative evidence; but yet such negative evidence did seem to me so strong that in my "Fossil Lepadidae" I have stated, giving reasons, that I did not believe there could have existed any sessile cirripedes during the Secondary ages.
Now, the other day Bosquet of Maestricht sends me a perfect drawing of a perfect Chthamalus (a recent genus) from the Chalk! (51/1.

Chthamalus, a genus of Cirripedia.