You didn't miss it Frank, it was an error. Scouten posted an update on his FB page acknowledging I was correct.
The problem is that on Wikipedia a picture of a Model 34 was posted to show the linage of the 317, but a lot of people probably didn't read the details.
So that question should be thrown out as the picture is neither a 317 nor an 18, but a M34.
I can rest easy now, I've been vindicated.
I may not be a S&W expert, but I do own The Book.