Only part of this cup fragment appears in the photograph of the Exhibition: it seems to have been broken after it was published in the Palace of Minos and then mended after the Exhibition - perhaps it was broken during installation/transit. The light-on dark reed or grass design is typical of Late Minoan Ia pottery.
Bibliography
Evans, Arthur. 1928. The Palace of Minos at Knossos, II, pp. 469-470, fig. 276f
Myres, John (ed.). 1936. British Archaeological Discoveries in Greece and Crete 1886-1936, p. 25