Seymour de Ricci Bibliotheca Britannica Manuscripta Digitized Archive contains the notes of the bibliographer Seymour Montefiore Robert Rosso de Ricci (1881-1942) for his unfinished Bibliotheca Britannica Manuscripta. Intended as a companion to his Census of Medieval and Renaissance Manuscripts in the United States and Canada (1935-1940).
Census of Medieval and Renaissance manuscripts in the United States and Canada, by Seymour de Ricci ; with the assistance of W.J. Wilson. New York : H.W. Wilson, 1935-1940. 3 v.
HOLLIS Record with online version
Census of medieval and renaissance manuscripts in the United States and Canada: Supplement, by C. U. Faye, continued and edited by W. H. Bond. New York, Bibliographical Society of America, 1962, xvii, 626 p.
HOLLIS Record -- HOLLIS Record
Directory of collections in the United States and Canada with pre-1600 manuscript holdings, by Melissa Conway and Lisa Fagin Davis. Papers of the Bibliographical Society of America, vol. 109 (3 ): 273-428, 2015.
-- Gives current location of the collections listed in the Census, and lists additional 282 North American repositories.
Schoenberg Database of Manuscripts tracks the movement of pre-1600. Compiled from chiefly UK and North American book and auction catalogues.
Iter: Gateway to the Renaissance (U. Toronto) offers P.O. Kristeller's listing of uncataloged, or incompletely cataloged, humanistic manuscripts in Italian and other libraries around the world, and the Iter Bibliography of articles, essays, books and reviews, and related databases.