Cassell's National Library was a series issued by Cassell, Petter, Galpin & Co. in London consisting of edited versions of English literature. The series was edited by Henry Morley, and between 1886 and 1890 it issued 209 weekly volumes. These were sold for 3d (paperback) or 6d (hardback).
References
Cassell's National Library Wikipedia(Text) CC BY-SA