Source: Board of Governors of the Federal Reserve System (US)  

Release: Banking and Monetary Statistics, 1914-1941  

Units:  Number, Not Seasonally Adjusted

Frequency:  Semiannual, End of Period

This series may have irregularities or important features that are not disclosed here. To see whether this is the case, please consult Part 1, Section 1, Table 2 in the original source at https://fraser.stlouisfed.org/scribd/?item_id=6408&filepath=%2Fdocs%2Fpublications%2Fbms%2F1914-1941%2FBMS14-41_complete.pdf&start_page=1

Relevant details can be found in the footnotes of each table as well as the introductory material for Section 1.