My dear Sir

The only evidence on the existence of living land Mollusc in England is the Helix labyrinthica Say, of the eocene Hordwell deposits & considered by Mr. Wood¹ to be identical with the American species of Say.²

The identity of the Melaniopsis buccinoidea of the Woolwich (lower eocene) series is probably doubtful with the Nile form. although I believe considered so by Ferrussac & Deshayes.³ So that is but little evidence of many existing forms in the older tertiary period.

Nor is there much evidence respecting the greater duration of life of the fresh water-testaceæ to the marine gasteropoda none of the eocene species ranging into the upper strata

I can only call to mind at present the genus, Strophostoma or Ferrusina of the miocene which is an extinct genus—

The relation of the gasteropoda found in the Mammalian beds at Grays⁴ &c &c to the marine deposits, is not definitely settled—ie whether they are equivalent to or superior to some of the deposits of the glacial or pleistocene epoch

There is a notice (I think in the journal (geological)) of some deposits in which I believe it is mentioned that a stratum of extinct freshwater shells, cover a deposit of marine mollusca of still existing species. I believe it is alluded to to by Sir R. Murchison in his Alps paper, but I have not the reference.⁵ I will look for it & others and write you again—

The best evidence is (as you are aware) that the freshwater genera as genera have survived many mutations of the surface, and outlived many of the marine genera, of course I allude to the still living genera of Physa Planorbis, Melanopsis, Cyrena, Paludina, &c in the Purbeck & Wealden—so in the lower and middle tertiary, &c

Yours sincerely | John Morris C Darwin Esq