The map is reproduced in
Eaton, Richard M. The Rise of Islam and the Bengal Frontier, 1204-1760. Berkeley: University of California Press 1993;
reference given are:
Barrie M. Morrison, Political Centers and Cultural Regions in Early Bengal (Tucson: University of Arizona Press, 1970), esp. ch. 4, and Susan L. Huntington, The “Pala-Sena” Schools of Sculpture (Leiden: Brill, 1984), 171. For a discussion of Bengal’s physical subregions, see O. H. K. Spate and A. T. A. Learmonth, India and Pakistan: A General and Regional Geography, 3d ed. (London: Methuen, 1967), 571–73. Where to search?