My dear Sir

I am very much obliged to you for your kindness in writing to me on the several curious points, specified in your letter, touching the Cirripedia.

I think I certainly know the large species, attached to turtles’ backs & sometimes penetrating even their bones; it is the Chelonobia of Leach & Astrolepas of Gray.² I have not yet particularly attended to this genus.³ I have dissected with care Coronula & Tubicinella & the only conclusion which I was able to arrive at was, that the cirripedes did not in fact penetrate the skin, but that the surrounding parts of the skin of the cetacea grow upwards, the part immediately under the cirripede not growing or even being absorbed by the action of the downward pressure of the cirripede which grows at its base.—⁴ I always have felt some doubt regarding this, & especially in regard to Chelonobia.—⁵ It is quite new to me that this genus should make burrows or move at all laterally, if I understand you rightly: but I do not think a cast w^d. be worth sending,⁶ though I sh^d. have much liked to have examined the real specimens.

I have a vast number of specimens in the Turtle-shell, & these hereafter I will closely inspect: Lithotrya, Alcippe of Hancock & a nov. genus,⁷ have an undoubted power of mechanical burrowing, but this is different from anything which Chelonobia could possess.—

If you w^d. take the trouble to send me the S. American Balanus, the growth of which is known to have been under 7 weeks, I sh^d be very much obliged in order to measure it & see what species it is.— I have plenty of specimens, which are impressed with the various markings of the shells & other objects to which they have been attached.

Very many thanks for your offers of sending me notes of the occurrence of species of Anatifa on the Irish Coasts; but having had M^r. W. Thompson’s of Belfast⁸ & several other collections for examination, I do not think it likely there would be anything new. Of the six species of Anatifa, I know of 5 as being British; & the 6^th is antarctic.

With my sincere thanks. Believe me | My dear Sir | Yours sincerely | C. Darwin