From the Robin Catalogue:
A. MS., G-1919-4, pp. 1-20, with 2 pp. of variants; plus 10 pp. of an untitled earlier draft (9/11/10)
Published, in part, as 1.568-572. Unpublished (pp. 11-20): The classification of the animal world is continued. CSP’s admission of his slight acquaintance with zoology and, in spite of his study of classification under Agassiz for six months (1860), his “incapacity” for this kind of work. An examination of Huxley’s classification of fish. Also unpublished (pp. R9.1-9.8): Artificial things are classified, with a view toward establishing trichotomies.

CP, Cross-reference index: “On trichotomies. [CP] 1.568 572. See [CP] 1.568n for a reference to a book of which this may have been a part. Several more pages of the ms. have been found since [CP] 1.572n* was written.”