This work appears in the Family History Libraray Catalog and WorldCat, but I did not find a version available online.
Did locate an extensive work online as "Boswell Collection GEN MSS 89" via Yale University Library. The Yale material includes a series of "genealogical charts" referencing, in part, the work of the same author.
Link follws. Description includes, "drawn from a variety of published and unpublished sources, including the Dictionary of National Biography, several volumes of the Yale Edition of the Private Papers of James Boswell, and Jasper John Boswell's History and Genealogical Tables of the Boswells (Vol 1, privately printed, 1906; Vol 2, unpublished manuscript photocopy in the files of the Boswell Editorial Project). When information obtained from the papers in the Boswell Collection contradicted the published sources, the primary source was preferred."
See: "Boswell Collection. General Collection, Beinecke Rare Book and Manuscript Library," aka Boswell Collection GEN MSS 89: Overview, Yale University Library. Scroll to "Genealogical Charts" and follow information and links from there.
Hope this helps.