Dear & Honoured Sir

I am much pleased that my Books have been of any use to you:¹ and I take delight in affording any information in my power. Your drawings are quite beautiful. I can explain about Verruca, which has hitherto been quite misunderstood. The cleverest naturalist would never, I believe, make out Verruca, without studying the recent species, and indeed the whole class.² I must premise that Verruca homologically (and indeed to a certain extent really during the earliest youth) is constructed, as in Diagram 1³ (alas I cannot in the least draw) of six valves, 2 scuta, 2 turga,⁴ and a carina and rostrum, all symmetrical; but during development, the carina and rostrum shrink on one side, and the scutum and tergum on that side take a special development, increase in size, and become immovably joined to the carina and rostrum, as in Diagram (2). Hence the shell is formed of 4 valves, viz. a fixed scutum and a fixed tergum, a carina and rostrum. And the operculum of 2 valves, a movable scutum and movable tergum. But it must be specially remarked that in every species, it is a mere chance whether the right side be fixed or the left side be fixed. Now you will understand what I mean by following explanations of your drawings. Fig. 1 is a fixed scutum of an individual in which the right side became fixed. Fig. 2 is either carina or rostrum; for it is not possible to say which, without knowing whether it belonged to a fixed right or left-side individual. Fig 3, Fixed tergum of individual fixed by its right side. Fig. 4, Fixed tergum of individual fixed on left side: So figs 3 and 1 might have been articulated together and belonged to same individual. Fig. 7 is movable scutum of individual fixed by left-side. Fig. 8, movable tergum of d^o. individual. So fig. 4, 6, 7 might have belonged to same individual. The one Chalk specimen which I have seen had shell-valves all articulated together, but no operculum, but I feel no doubt about the identification of your figs 6 and 7: they are intermediate in character between those of V. Strömia of N. Europe, and V. lævigata from S. America.⁵ Will you tell me what name you intend calling it? as you will probably publish first: in my MS. I had called it V. prisca, but will alter it as soon as you choose.⁶ If in your power I should much like to examine the valves 6, 7 and 1. Is not the adductor Plate (I admire the judgment shown by you in recognising its nature) broken? if not, its form is peculiar. Is there any adductor ridge to movable scutum;⁷ such occurs in one recent species? If you require your drawings to be returned, please inform me. I enclose for you a Verruca Strömia. With respect to the Lepas? I somehow doubt, though I can assign no very good reason: I should have expected the lines of growth to have curled a little round the apex of upper corner: a tooth might have been expected at umbo or under side: without inspection I dare hardly offer any opinion, or regarding the carina-like body. The latter certainly resembles the carina of Poecilasma:⁸ if so, the lines of growth should be all upwards, from the knobbed and thicker end. I forgot to remark that you have all the valves of the Verruca except either a Carina or a rostrum which closely resemble each other. I shall be proud to receive a copy of your memoir.⁹ Any specimens, which you could really spare, I should be very glad of, for the sake of giving, with all my own collection, to the British Museum.

With every good wish and much respect. Believe me | Sincerely Yours | C. Darwin

I should be grateful for answers sometime to my questions on Verruca.