In the Superintendent of Documents (SuDocs) classification system, the call number is divided into two parts: the class number, or stem, and the individual book number.
A colon separates the class number from the book number. If the colon is followed by a letter, the publication is a monograph. If the colon is followed by a number, it is a serial.
Monographs
Civil War Manuscripts LC 4.2: C 49
LC Library of Congress
4 Manuscript Division
.2 type of publication (General Publications)
: C 49 individual book number
Serials
Monthly Labor Review L 2.6: 26/9
L Department of Labor
2 Labor Statistics Bureau
.6 type of publication (journal)
:26 volume 26
/ 9 issue 9