McCarthy, John; Abrahams, Paul W.; Edwards, Daniel J.; Hart, Timothy P.; Levin, Michael I. (1985), LISP 1.5 Programmer's Manual (second ed.), Cambridge, Massachusetts: MIT Press, ISBN978-0-262-13011-0, page 36, describes cons cells as words with 15-bit "address" and "decrement" fields.
See, for example, Mitchell, John C. (2003), Concepts in Programming Languages, Cambridge University Press, pp. 28–29, ISBN9781139433488, Section 3.4, Innovations in the Design of Lisp. The reference identifies the IBM 704 and correctly explains the address and decrement part of a cons cell, but then it omits the "part of" in McCarthy's explanation.