See, for list of abbreviations and explanations, p. Iv.
I_ _ I
United States. Superintendent of Documents. Checklist of United States Public Documents, 1789-1909, Third Edition Revised and Enlarged, Volume 1, Lists of Congressional and Departmental Publications. Washington. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc1029/. Accessed April 25, 2015.