The Y here probably refers to the royal tomb of Merneith and to the subsidiary burials arranged around it in the Umm el-Qa'ab at Abydos. Flinders Petrie numbered royal tombs as follows: Aha (tombs B5, B6, B10, B14, B15, B16, and B19), Narmer (B17/B18) and nearby tombs (B1, B2 'Benerab', B9 'Zeser?', B7 Ka), Djer (tomb O), Peribsen (tomb P),Qaa (tomb Q),Den (tomb T),  Semerkhet (tomb U), Khasekhemwy (tomb V), Djet's subsidiary burials (Cemetery W), Andjib (tomb X), Merneith (tomb Y) and Djet's tomb (tomb Z)

UC37020, Courtesy of the Petrie Museum of Egyptian Archaeology, UCL