To Wilhelm Bernhard Rudolph Hadrian Dunker¹   20 September 1850

Much honoured Sir

I received this morning your letter of the 6^th of June & a Box of fossil Cirripedia from my friend M^r J. Morris.³ The fossils have arrived quite safely.— I beg to thank you with the utmost cordiality for this act of kindness: I will take the greatest care of the specimens, & return them you in a month or two’s time, when I have completed the engravings for the Fossil Part of my Monograph.— I particularly request you to give my sincere thanks to M^m. Roemer & Philippi.—⁴ I know your drawings & descriptions of P. Hausmanni in the work on the Oolithgebirges,⁵ than which nothing can be better.—

I am making considerable progess in my monograph; I have described 38 fossil Pedunculated Cirripedia; all the recent Pedunculata including the animal’s body, & I have just finished with the 45^th. species of the great & difficult genus of Balanus.— I should esteem it a great favour & most valuable aid if you would entrust me with your collection of recent species; but you will almost certainly object to send me unique specimens, when I tell you that I cannot recognise the species, & will never name any species, without disarticulating one specimen; I can, however, almost always gum together the valves so that they look nearly as well as ever.— I have, also, resolved in hardly any case to name a sessile Cirripede without the operculum.—⁶ I care comparatively little for specimens without their habitats.— I can assure you the genus Balanus is so difficult, that it is folly to attempt describing the species without the opercula; all the species are subject to much variation.—

If you could persuade the distinguished Philippi to send me a specimen (allowing me to disarticulate it) of the Mediterranean species which he has named,⁷ it would be doing me the greatest service; for I earnestly wish to avoid renaming a known species—

I am very sorry to hear that your health has been indifferent; it makes your kind assistance to me the more generous.—

With the utmost respect | Yours truly obliged | C. Darwin

Pray thank Romer & Philippi.—

Any parcel addressed as at the head of this letter, will reach me.— Sept. 20^th. 1850.—