Dear Sir

By the same post with this, I have the pleasure of sending you a copy of my “Ventriculidæ”—of which I beg your acceptance.¹ When you have a little leisure, I think you will find in its contents some matters more than usually illustrative of your views on the development of species. Not to take up, now, too much of your time, I will note two points:—first, here is a group of fossils entirely distinguished, by a very remarkable structure, from any other. We find them running thro’ all the Chalk formation—but with a difference. Indeed, when I opened your plate of graduating species,² I immediately remarked—“this is a table of the Ventriculidæ”. There is both the change & branching off of many, & the retention of single forms, just as you have pictured. (Let me refer to pp. 41–43, 55, 73, 88).

Second, there is the difficulty of structure—a structure unapproached by any known structure, recent or fossil. This is a more difficult point than any of the modifications of parts. But no doubt you will see the way, from your vast stores of comparison, to illustrate it. I can thus far illustrate it:—that, for years, I have lost no opportunity of pointing out to visitors to my collection, the “imperfection of the geological record”, as illustrated by the Chalk fossils, & the beds above & below them. I could enlarge much on this,—but will only add, that two flints, compared, are enough to satisfy the most sceptical,—while we have, between the chalk & the London clay, the distinct & unquestionable marks of a lost record—of which all the details are gone; & what is left is only enough to tell us how much is wanting. I compare it to Livy’s History. We have some chapters tolerably complete. Of others we have the mere heads—but enough to know that they once existed.³

If it will be agreeable to you, at any future time, to see my collection, I shall have pleasure in showing it to you—& pointing out the illustrations to which I have alluded.

Apologising for the length at which I am troubling you, | I am Dear Sir | Yours faithfully | Toulmin Smith

C. Darwin Esq