Mr. Broad’s interesting article in the July  Mind on “A General Notation for the Logic of Relations” attributes to me (for what reason I cannot guess) a number of notations employed in Principia Mathematica. As far as my memory serves me, all these were invented by Dr. Whitehead, who, in fact, is responsible for most of the notation in that work. My original notation, before he came to my assistance, may be found in Peano’s Revue de Mathématiques, vols. vii and viii.
The articles by Russell in Peano’s journal that Russell refers to are:
“Sur la logique des relations avec des applications à la théorie des series,” Revue de mathématiques 7, nos. 2-3 (1901), 115-36, 137-48. Repr. in English translation with original notation as “The Logic of Relations” in Logic and Knowledge, Robert Charles Marsh (ed.)
“Théorie générale des séries bien-ordonnées,” Revue de mathématiques 8, nos. 1-2 (1902), 12-24, 25-43. Repr. CPBR3 with original notation
Marsh refers the reader interested in Peano’s symbolism to Jorgen Jorgensen’s A Treatise of Formal Logic (1931), 1: 176ff.
(source: Kenneth Blackwell, email transmission to russell-l, the online Forum for Bertrand Russell Studies.)
Broad himself had published the following note in the October 1918 Mind (p.508):
I see, in looking through my paper in Mind N.S., No. 107, that although I at first speak of ‘Whitehead and Russell,’ I later generally refer to pieces of notation contained in Principia Mathematica as ‘Russell’s’. I did not mean by this to ascribe them to Mr. Russell rather than to Dr. Whitehead. I have no idea which of the authors is responsible for any given part of the book, and I only used ‘Russell’ as an abbreviation for ‘Russell and Whitehead’. I should be sorry indeed to appear unfair to Dr. Whitehead, and my only excuse is the extreme difficulty of putting a phrase like ‘Russell and Whitehead’ into the possessive in English. Perhaps Dr. Whitehead will provide me with a suitable notation for this purpose, and Mr. Russell will guarantee it to be ‘ethically neutral’.