My dear Darwin

As I sent you a list of the land-shells picked up at Down when we were last there¹ I wish you, in case you have kept it to put ?? to Helix carthusiana which I still think is among them— But the shell which I meant by that name is I find called by Forbes & Hanley Helix Cantiana Mont. as being the prior name—² In my own list & perhaps in the one I sent you I find I had added this name of Montagues³ as a synonym—, for I had made no mistake about the species which I meant—

I also find amongst them another shell which I suppose to be Helix rufescens? and the Bulimus which I left unnamed must I think be B. obscurus— The Clausilia which I called C. plicatula ought to have been C. nigricans, according to Forbes & Hanley.

I have met with such a remarkably conical variety of Helix aspersa from Charing Kent, in Woodward collection⁴ that I cannot regard that shell as quite so constant in England as I told you—& as it is reputed to be. I sh^d. like to show it to you as I have got this variety

I have just heard from Woodward that his friend M^r C. Prentice of Cheltenham caught that large & most powerful of our water beetles Hydrobius piceus with an ancylus fluviatilis adhering to him! & treating him as he would a stone after the beetle was out of the water.—⁵ Here is a new light as to the way by which these sedentary mollusks may get transported from one river basin to another— That species of Ancylus seems to have got into Madeira before Man—⁶ How far can an Hydrobius fly with a favourable gale?

I hear that when you & Hooker & Huxley & Wollaston got together you made light of all species & grew more & more unorthodox— ⁷

Heer of Zurich has given us a capital essay on the old Atlantis in a new paper just out on the fossil leaves of Madeira— ⁸ When I go abroad I will lend it to you for now I am always using it.⁹ He makes out a good case in favour of the old union provided one believes in specific centres. According to any other hypothesis I cannot as yet very well see how to bring the geograph^l. facts to bear one way or the other— I wish you would publish some small fragment of your data pigeons if you please & so out with the theory & let it take date—& be cited—& understood. ¹⁰

With my love to M^rs Darwin & the children ever truly Y | Cha Lyell

To encourage you to get up J. E. Gray’s subdivision of the Genus Helix I may mention that Macandrew brought back from the Salvages a Helix allied to (some think only a var of) Helix pisana a British species¹¹ it was named by some one H. Macandrei & by Lowe who had received it first H. ustulata—¹²

Gray enters into his catalogue diag Nanina ustulata Salvages

N—— Macandrei d^o—ramme making two species, & on being asked why he called them Nanina said, because it is the form which belongs to islands in the Pacific! He had imagined the Salvages to be in the Pacific otherwise he should have certainly had some other subgenus assigned to it—! some Atlantic genus of Helicidæ!¹³

May 2. This letter was not posted yesterday by accident. I went to see poor Curtis the entomologist who being nearly blind by amaurosis was run over 10 days ago by three Cabs & broke a shoulder bone but is doing surprisingly well.¹⁴

He told me that a french entomologist brought him a Dytiscus marginalis the large water beetle (which flies about freely) with a small bag of eggs of a water spider under his wings, evidently put there by the parent. It was not a parasitic insect which had done this— He could not look up the case because of his illness & blindness but some day I will get it perhaps—

What unexpected means of migration will in time be found out—¹⁵

The multiple creation of Agassiz will one day rank with spontaneous generation but Madeira seems to me to favour the single specific birth-place theory & I long to see your application of any modification of the Lamarckian species-making modification system— Representative forms in closely adjoining islands are great puzzles where the conditions are one would think so nearly the same—¹⁶

ever truly yrs | Cha Lyell C Darwin Esq