Very interesting. It's like a cross between Optima and Arrow, with a touch of Baker Signet. I think the printing quality (and perhaps phototype technique) has a lot to do with the softness of the contours.
Here’s a bigger view. I’ll check my phototype references later. Closest I found so far is Photo-Lettering’s Perpetua Graphic, an interpretation of Gill’s Perpetua. It has that pointed terminal in a and the flat-bottom d, but seems off in some other details.
Thanks to Florian’s lead, I think I may have tracked it down: neo-Perpetua, Headliners, issued before 1969. Soften these corners and I think that’s it. Of course, there’s always the possibility the book used some other phototype Perpetua that Headliners later copied, but the company did tend to create original designs. Maybe this is why I was thinking about Arthur Baker’s Signet earlier; he drew many of Headliners’ typefaces.