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Darwin Correspondence Project

To William Thompson   [1 March 1849]

Down Farnborough Kent


My dear Thompson

I shd. have answered your note by return of Post, but I was in bed all the day before yesterday & was incapable of doing anything yesterday morning. The enclosed diagram will show difference between Chthamalus & Balanus.—1 You will with great difficulty recognize the genus externally in the British species: internally (when cleaned) there is a conspicuous difference.— I send some good British specimens & a N. American species, in Blotting Paper which shows the characteristic difference much better— Look with lens at inside of the cleaned Brit. spec. & compare with a cleaned Balanus & look at diagram & you will understand difference.— It is curious that the British B. punctatus & Chthamalus are so alike externally, as they belong to different sub-families.— The British Chthamalus has never been named as a Chthamalus; I suspect it is the B. punctatus of Montague; but the nomenclature of the sessile Cirripedes is all guess-work.— As I thought it wd be satisfactory to you, I have looked through your whole collection & cannot see any Chthamalus; I suspect cause is that you have collected generally those on shells & wood, crabs &c. & not so often on rock.— (NB The walls in Chthamalus are not cellular or tubular as is always case with Balanus)— I have been delighted at going over your collection again to see what an admirable one it is: it will be invaluably useful to me.—2

I have gone through 45 of your Book3 & found much to interest me— The accounts of the Hawks & Corvidæ,—in short wherever you treat much of habits, will, interest, I shd. think, everyone.— The discussions on the rarer species being deservedly Irish, will tend to make the Book heavy for the general reader; but I know that you intended your work not as one of amusement, but of instruction.— Why do you & others separate English & Latin Index.— does the English hurt the Latin? Many a time in such cases has something very like an oath come very near my lips, when I have found that I have been looking in a hurry in the wrong index.—

Have you seen Rev. E. S. Dixon (not Dickson) work on Poultry;4 it is very good & amusing.

I quite forget whether I told you, that I have quite lately made up my mind to go before the end of this month to Malvern for two months to see if there be any truth in the water cure.— It will lose me two months but if I can partly regain my health, it will indeed answer in every respect, for I am sure I have not worked more than 1 out of the 3 last months. I fear we shall not meet this Spring, without you remain till June in London.—

I am tired so no more— If you are in doubt about any Irish Chthamalus, pray send it me.

Your’s most sincerely | C. Darwin

What labour your Book must have cost you!

Horizontal section through upper part of shell.

you will see that carina & second latera are the same in Balanus & Chthamalus— whereas Rostrum & 1st latera materially differ.— The Rostrum & carina have a similar structure in Chthamalus.—


The diagram is at the end of the letter, and is on the verso of what appears to be the cover of Thompson’s letter to CD, postmarked 27 February. A similar diagram appears in Living Cirripedia (1854): 39 and depicts these and three other genera in the Balanidae.
Thompson sent CD ‘his very large collection’ of Balanus balanoides and also provided information concerning the range, habits, and growth rate of this species (see Living Cirripedia (1854): 272–3, and letter from William Thompson, 29 September 1848).
CD is referring to the first volume of W. Thompson 1849–56. CD’s annotated copies of the first three volumes of this work are in the Darwin Library–CUL. CD recorded having read them on 5 March 1849 (DAR 119; Correspondence vol. 4, Appendix IV).
E. S. Dixon 1848. CD’s annotated copy is in the Darwin Library–CUL. See letter to J. D. Hooker, 6 October [1848], for CD’s opinion of Edmund Saul Dixon.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Dixon, Edmund Saul. 1848. Ornamental and domestic poultry: their history and management. London: Office of the “Gardeners’ Chronicle”.

Living Cirripedia (1854): A monograph of the sub-class Cirripedia, with figures of all the species. The Balanidæ (or sessile cirripedes); the Verrucidæ, etc. By Charles Darwin. London: Ray Society. 1854.

Thompson, William. 1849–56. The natural history of Ireland. 4 vols. (Vol. 4 edited by Robert Patterson.) London.


Encloses diagram illustrating difference between Chthamalus and Balanus. Specimens sent. Finds no Chthamalus in WT’s collection.

Has read with much interest WT’s book [The natural history of Ireland, vol. 1 (1849)].

Recommends E. S. Dixon’s book [Ornamental and domestic poultry; their history and management (1848)].

Letter details

Letter no.
Charles Robert Darwin
William Thompson
Sent from
Source of text
Trinity College Library, Cambridge (Add.L.b.1: 24)
Physical description
ALS 5pp & CC 1p inc

Please cite as

Darwin Correspondence Project, “Letter no. 1232,” accessed on 25 September 2023,

Also published in The Correspondence of Charles Darwin, vol. 4