Gislebert / Gilbert le Goz

In "Les Barons du Cotentin", Alan Davies lists four sons as the children of Turtain Gotz (Thurstan le Goz) and Judith de Monterolier:

• Renouf (mort avant 1090)
• Turstin (Turtain) Haldup, ancestre des barons de La Haye-du-Puits
• Gislebert d'Avranches
• Richard Gotz, dit RIchard d'Avranches (1024-1082), vicomte de lieu en 1050, epousa Emma de Comteville demi-soeur du duc Guillaume

Les barons du Contentin (2009) by André Davy is out of print (ISBN: 978-2914541961) and not available online. WorldCat.org shows six libraries in the United State that have this book:
University of Chicago Library
University of Notre Dame Hesburgh Library
University of Michigan Library
Princeton University Library
Yale University Library Orbis Library
Harvard University Hollis Library