Calvinism and natural law

I have just received a copy of L. S. Koetsier, Natural Law and Calvinist Political Theory, a small volume published by Trafford, which specializes in "on-demand" publishing. I look forward to reading it. Nevertheless, a perusal of the index indicates the absence of two names I would have expected to see treated in such a study: Johannes Althusius (1557-1638) and Girolamo Zanchi (1516-1590).