  We reconsider entropy arguments which have been previously argued to support
the idea that the dark matter constituents are primordial black holes with many
solar masses. It has recently been shown that QCD axions which solve the strong
CP problem may have masses $m_a$ in the extended range $10^{-3}eV > m_a >
10^{-33} eV$. Ultralight axions provide so many degrees of freedom that their
entropy can exceed that of primordial black holes. This suggests that
ultralight axions are more suited than primordial black holes to be
constituents of dark matter.
