Dear and much respected Sir

I received your last valuable letter only the day before leaving home for a month with my whole family for the sea-side, and therefore could not give up time enough to consider the several points in your letter. But in truth you seem to have so thoroughly gone into the subject of Cirripedes, that any opinion of yours is quite as good, if not better, than mine. I had time to compare carefully the valve you were so good as to send me, with the rostro-lateral compartment of Sc. rutilum,² and you are perfectly right there is a very close resemblance between them: that this valve is the rostro -lateral compartment of Sc. rutilum I think there can be hardly any doubt, for the manner in which the several valves fitted, and especially from its very considerable curvature. I am quite prepared to be proved wrong about the number of the valves in Sc. quadratum:³ but when I concluded that there were only 3 pairs of Lateral valves, my attention had been called by M^r. Sowerby’s figures of M^r. Dixon’s specimen,⁴ to the possibility or probability of there being 4 pairs and yet I thought that there were only 3 pairs: it should not be forgotten that in Sc. Peronii⁵ there are certainly only 3 pairs: yet upon the whole, after your discoveries, I agree in the probability of there being in Sc. quadratum 4 pairs. I will only further remark that in Pollicipes, which is so closely allied to Scalpellum (and indeed in Sc. villosum) no one could possibly distinguish the Rostral from the medial or carinal compartments; and therefore I do not think it at all surprising, that you should be puzzled in attributing to fossil species, the several valves to their right places. I heartily wish you success in your labours,—and indeed with such industry and penetration as yours, success in whatever you undertake is certain.— and with much respect I remain

Dear Sir | Yours sincerely | C. Darwin

P.S. In my volume now preparing which will complete the Cirripedia; I will insert a Synopsis in Latin of all the species of the Sub-Class; and I shall be very glad to have (or copy) a short character of your new species.⁶ My volume will not be printed till the Autumn, and I suppose before that time yours will be published.