For a semi-popular account of Hilgendorf's and Hyatt's work on this subject, see Romanes' "Darwin and after Darwin," I., page 201.) I have no strength to spare, being much out of health; otherwise I would have endeavoured to have made this letter better worth sending.

I most sincerely wish you success in your valuable and difficult researches.
I have received, and thank you, for your three pamphlets.

As far as I can judge, your views seem very probable; but what a fearfully intricate subject is this of the succession of ammonites.

(254/3.

See various papers in the publications of the "Boston Soc.Nat.