The date of Louis Pfeiffer's description of this species
is inconsistently cited in scholarly works as well as on the
Internet. A search of the latter resource for this species
using "kochi Pfeiffer" produced 49 hits for 1821
(when he was a teenager), 46 for 1845, and 0 for 1846.
Refining the search to "kochi L. Pfeiffer" elicited
7, 3, and 6 respectively.
The original description of Helix kochi can be found
(bottom of p. 127). I became suspicious of the date of
publication when I saw, on the last page (143) of this issue
mention of the cancellation December 23  meeting of
the Zoological Society. It seemed a bit unlikely that the
magazine got into print over the holidays.
I finally found evidence of the basis for this anachronism
(Waterhouse, 1893: 438, bottom L column: <http://www.biodiversitylibrary.org/item/97156#page/550/mode/1up>):
February, 1846 was the publication date for Helix kochi
L. Pfeiffer in the PZSL for 1845: <http://www.biodiversitylibrary.org/item/46217#page/209/mode/1up>.
Note this erroneous "antedating" was epidemic in the
mid-nineteenth century, e.g., <http://www.jaxshells.org/0050a.htm>
In the case of the topical species, even the great master,
H.A. Pilsbry (1848: 591), was snookered by it:
no doubt entraining the Internet proponents of 1845 as the
How 1821 entered the mix is presently unexplained, but
there must have been some mindless copy-cating, an Internet
phenomenon we've witnessed on many other occasions.
Having learned my lesson well, I even felt compelled to
verify the publication date of the collation by Waterhouse
in a later issue of PZSL (August 1, 1893); see
and bibliography below!
Duncan, F.M., 1937. On the dates of
publication of the Society's "Proceedings" 1859-1926. With
an appendix containing the dates of publication of
"Proceedings" 1830-1858, compiled by the late F.H.
Waterhouse, and of the "Transactions" 1833-1869, by the late
Henry Peavot, originally published in the P. Z. S.
1893, 1913. Proceedings of the Zoological Society of
London 107: 71-84. [not seen]
Pfeiffer, L.,1846. Descriptions of thirty-six new species of
Helix, belonging to the collection of H. Cuming, Esq.
Proceedings of the Zoological Society of London, for 1845
13(153): 126-133. February.
Pilsbry, H.A., 1948. Land Mollusca of North America north
of Mexico vol. II part 2. Academy of Natural Sciences,
Philadelphia. xlvii + 521-1113. 19 Mar.
Waterhouse, F.H., 1893. List of the Dates of Delivery of the
Sheets of the 'Proceedings' of the Zoological Society of
London, from the commencement in 1830 to 1859 inclusive. In:
May 2, 1893. Sir W.H. Flower, K.C.B., LL.D., F.R.S.,
President, in the Chair. Proceedings of the Zoological
Society of London, for 1893(2): 436-440. 1 August.