The reference is from Housesteads Roman Fort, Northumberland, by J. G. Crow published by:
English Heritage (http://www.english-heritage.org.uk)
23 Savile Row
London SIS 2ET
First published in 1989 and reprinted several times through 2005
ISBN 1 85074 244 8
The number on the web page that got you here is the page number for this book.