This British series, similar to Novello's Octavo Anthems, started about 1880. The choruses were extracts from oratorios and cantatas, such as Haydn's Creation and Elgar's Dream of Gerontius.
Octavo refers to the paper size, which is 10 X 6.5 inches. This size is between modern ISO 216 sizes (adopted in Germany in 1922, in the rest of Europe and U.K. by 1970) B5 (9.84 X 6.93 inches) and A4 (11.27 X 8.27 inches). This is smaller than usual sheet music, which is 31 X 23cm. (12.20 X 9.05 inches). It was chosen by Novello for their cheap editions in the 1850s and has remained the standard for choral music to the present.
Many items were issued additionally in tonic sol-fa notation. A sample of Handel's Halleluja Chorus in this notation can be seen here (section 2.7.1)