Here are books that include information on the South African angulate / angulated / bowsprit tortoise (Chersina angulata). Most of them only have brief descriptions and photos of angulates, but some offer more. For example, the "Turtles: Proceedings: International Turtle & Tortoise Symposium, Vienna 2002" book includes a whole chapter about keeping and breeding angulates. Books are listed in no particular order.
Tortoises, Terrapins & Turtles of Africa
* by Bill Branch / Struik Publishers, 2008 / 128 glossy p., color photos / ISBN-10: 1770074635, ISBN-13: 978-1770074637
The Southern African Tortoise Book
* by Richard C. Boycott, Ortwin Bourquin / 2nd revised ed., 2000 / color and b/w photos, 228 p. / limited availability / ISBN-10: 0620265361, ISBN-13: 978-0620265362
Turtles: Proceedings: International Turtle & Tortoise Symposium, Vienna 2002
* by H. Artner, B. Farkas, V. Loehr / Edition Chimaira, Mar 2006 / incl. angulates / color photos, 621 p. / limited availability / ISBN-10: 393061278X, ISBN-13: 978-3930612789
Terralog: Turtles of the World: Africa, Europe and Western Asia, Vol. 1
* by Holger Vetter / revised 2nd edition, 2011 / Aqualog Verlag / 152 pages / ISBN-10: 3930612275, ISBN-13: 978-3930612277
What's That Reptile?
* by Johan Marais / Struik Nature, Nov 2010 / descriptions, color photos, 160 p. / ISBN-10: 1770077715, ISBN-13: 978-1770077713
Cape tortoises: Their identification and care
* by Ernst H.W. Baard / Cape Nature Conservation, 1994 / descriptions, general care, 68 p. / out of print / ISBN-10: 0798401958, ISBN-13: 978-0798401951
A Guide to the Reptiles of Southern Africa
* by Graham Alexander, Johan Marais / Struik Publishers, Jan, 2008 / color photos, 408 p. / ISBN-10: 1770073868, ISBN-13: 978-1770073869
The Wildlife of Southern Africa: A Field Guide to the Animal and Plants of the Region
* Vincent Carruthers / Struik Publishers, 2008 (updated ed.) / descriptions, color illustrations, 320 p. / ISBN-10: 1770077049, ISBN-13: 978-1770077041
Tortoises, Terrapins and Turtles Drawn from Life
* by James de Carle Sowerby & Edward Lear / H. Sotheran, J. Baer & Co, 1872 / you can read this book online at the Biodiversity Heritage Library
or Internet Archive / text and color plate for Testudo angulata