Excellent.  Thanks very much.  I had not thought of Professor Royce's seminar.
I have the book you provided a link to.  The reference evidently starts on page 72.  On December 9, 1913 Royce introduced this question to the seminar;  "Is the proposition 'There are values' a primitive proposition?".  During the discussion Eliot seems to lead the discussion astray by talking about primitive religion and in a footnote Grover Smith directs the reader's attention to Eliot's introduction to his mother's poem "Savonarola: A Dramatic Poem".   In this introduction Eliot refers to the paper he gave on "The Interpretation of Primitive Ritual". 
The paper itself is, unfortunately, not part of the book. 
Thanks again
Rick Seddon
McIntosh, NM