The Spanish-American philosopher, George Santayana, was a close friend of Frank Russell, the second Earl, elder brother of the now-more-famous Bertrand, and, it seems, a man with much more than his allocated lifetime quarter-hour of drama and fame.  In the second volume of his memoirs (The Middle Span, pp. 50-52), Santayana mentions their first encounter, at Harvard in October 1886, where they seem to have connected instantly and deeply, meeting just once but talking for hours.  Reading this account, I was reminded of Bertie’s account in his autobiography of his first meeting with Joseph Conrad, which also (at least, according to BR) went deeper, and deeper faster, than any previous or subsequent encounter he had with another person.
Santayana says that following their initial meeting, upon his return to England Frank Russell sent Santayana a gift:

I received through the post a thin little book bound in white vellum, The Bookbills of Narcissus, by Richard Le Gallienne, inscribed “from R.” ” (page 52).

Santayana next saw Russell on his trip to England in March 1887, when they spent significant time together, and they continued to meet and travel together periodically.
Something is amiss in this report, since that book by Richard Le Gallienne was not published until September 1891, by Frank Murray in Derby.   I thought perhaps that Russell had sent Santayana a pre-publication copy, but checking a biography of Le Gallienne (Whittington-Egan & Smerdon 1960),  I find, first, that Le Gallienne seems only to have written this book during winter 1890-91 (p. 125), and, second, that Le Gallienne wrote to his parents around February 1892 that he had heard that Lord Russell “raves” about Narcissus (p. 185).   So clearly, Frank Russell knew and liked the book, and told others this following its publication; he also quite possibly gave an inscribed copy to his friend Santayana.   But he could not have done so in the winter of 1886-7.  Le Gallienne’s first volume,  My Ladies’ Sonnets, was only published in August 1887, and circulated only in Merseyside, so it is unlikely that Russell would have had a pre-publication copy of that to give to Santayana.
Did Russell send some other book to Santayana in 1886, which Santayana’s memory has forgotten and confused with Narcissus?  Or was perhaps the book Russell sent Santayana something he would prefer not to mention, a book that might reveal more of their relationship than Santayana desired to be revealed?  Certainly, reading the urbane, enthralling and smoothly-written three volumes of Santayana’s memoirs, one would not be led to think he had a poor memory; he seems to have recalled every person he ever met or Harvard student he ever taught, and every soap-operatic life-incident in his two Faulkneresque extended families, one Spanish, one American.
I doubt this mystery will ever be resolved; on the other hand, nothing momentous rests on its resolution.
POSTSCRIPT (2013-10-22):  I wonder if the book of verse sent by Russell to Santayana in late 1886 was one of the works by poet Marc-Andre Raffalovich (1864-1934).
References:
M-A. Raffalovich [1884]: Cyril and Lionel, and other poems. A volume of sentimental studies. London, UK: Kegan Paul & Co.
M-A. Raffalovich [1885]: Tuberose and Meadow-Sweet. London, UK: D. Boque.
M-A. Raffalovich [1886]: In Fancy Dress.  London, UK: Walter Scott.
George Santayana [1947]:  The Middle Span.  London, UK:  Constable.
Richard Whittington-Egan & Geoffrey Smerdon [1960]: The Quest of the Golden Boy:  The Life and Letters of Richard Le Gallienne.  London, UK:  The Unicorn Press.