James and Paul are both talking about intellectual assent to theological truths. The difference between the passages lies in the claims they make about what does not save.
James points out that intellectual assent alone is not enough to justify us, as even the demons have that (Jas 2:19) – our faith has to be completed by our works (Jas 2:22), which enliven our faith just as the spirit enlivens the body (Jas 2:26). He is not saying anything about “dead faith” or “mere intellectual assent.”
Paul’s audiences in Romans and Galatians are Jewish Christians who believed that one could only come to Christ by first accepting the Old Covenant. Thus, when Paul contrasts faith with “works of the Law,” he is merely pointing out that the real beginning of our salvation, intellectual assent to God’s Word, is possible for everyone and that the Old Covenant (i.e., circumcision – see Romans 4) is not first necessary. (You can infer that this is what’s going on by carefully examining Rom 3:28-30.)
So, in short: Paul is dealing with people who believe that a certain kind of work is necessary for salvation, and in fact that it merits salvation on its own, while James is dealing with people who believe, on the basis of Paul’s teaching, that intellectual assent alone is responsible for our justification. But at the end of the day, they hold the same view – we need intellectual assent, faith, working through charity (Gal 5:6) to be saved.
As for sources (which you actually asked for – whoops!) I’d recommend, as a starting place, one of Jimmy Akin’s essays on justification in James 2. There are other pieces on that site about justification and the use of terms in the Pauline letters.
Hope that helps.