Penguin's Peregrine Books were thick dense soft cover books. I come across them quite often. They were academic books published by Penguin and the series began in January 1962.
I collect these when I come across them and only pick up first published books.
Y11 Aubrey's Brief Lives
Y12 Milton by E. M. W. Tillyard
Y18 A Critical History of English Poetry
Y25 The Rise of the Novel by Ian Watt
Y30 The Growth and Structure of Elizabethan Comedy by M. C. Bradbrook
Y35 The Englishness of English Art by Nikolaus Pevsner
Y37 The Elizabethan House of Commons by J. E. Neale
Y39 D.H. Lawrence / Novelist by F. R. Leavis
Y44 Poetry and Experience by Archibald MacLeish
Y64 Opinions and Perspectives by The New York Times Book Review
Y68 Milton's Epic Poetry (Essays on Paradise Lost and Paradise Regained) Edited by C.A. Patrides
Y70 Beyond Culture by Lionel Trilling