Dates of publication of two of Darwin’s volumes on the Cirripedia (barnacles).
The dates of publication of Darwin’s volumes on the Fossil Cirripedia and Living Cirripedia, by the Palaeontographical and Ray Societies, were long considered to be 1851a, 1851b, 1854a and 1854b, or Fossil Cirripedia 1, Living Cirripedia 1, Living Cirripedia 2 & Fossil Cirripedia 2, respectively. It is the purpose of this note to call attention to the fact that the actual publication dates for 1851b and 1854b were found to be 1852 and 1855 (Withers 1928, Newman 1993) as opposed to the dates on their title pages. Dates of publications can be important should matters of priority arise.
1854b = 1855
Withers (1928:1 etc) cites Fossil Cirripedia 1 and Fossil Cirripedia 2 as 1851 and 1855, but he did not indicate how he determined the latter should be 1855 rather than 1854. However, in the references (1928, pp. 114-115), both volumes are accompanied parenthetically by the month as well as year; e.g., "1851 (June)" and "1855 (May)", so he may have had access to the Palaeontographical Society’s records, publishers and/or booksellers announcements, or the like. On the other hand, the two volumes on living Cirripedia were referred to by year alone; e.g., 1851 and 1854, dates likely simply based on the title pages.
1851b = 1852
There is a letter by Darwin apparently written on 30 January  (Calendar 1472a), noting that because of a printer’s 'blunder', publication of Living Cirripedia 1 would be further delayed, and from his subsequent letters it is evident the publication date was likely somewhere between February and April of 1852 rather than in 1851 (Newman 1993, p. 363).
The present author has since noticed in Living Cirripedia 2 that from the onset Darwin cited Living Cirripedia 1 simply as his 'Lepadidæ' rather than by date, at least until he (p. 438) placed "Siphonicella Darwin" in the synonym of Xenobalanus Steenstrup, 1851, where he cites his 'Monograph on the Lepadidæ, p. 156 (1852).' Were it not known publication of Living Cirripedia 1 had been delayed, one might perhaps think this date a slip of the pen. And the same might be said regarding Pilsbry, for while in Pilsbry 1907 he cites Living Cirripedia 1 as 1851, in Pilsbry 1916, p. 12 he writes of Darwin's classification of '1852-1854' (Newman 1993, p. 364). But the date had not been corrected anywhere else, and so from Pilsbry’s synonym of Xenobalanus, it is certain he understood Darwin’s intent was to insure Steenstrup’s priority.
I would like to thank Dr. J. van Wyhe for editorial expertise as well as the opportunity to prepare this note.
William A. Newman
Scripps Institution of Oceanography
La Jolla, CA 92093-0202, USA