  The discovery of numerous new charmonium-like structures since 2003 have
revitalized interest in exotic meson spectroscopy. These structures do not fit
easily into the conventional charmonium model, and proposals like four-quark
states, hybrids, and re-scattering effects have been suggested as explanations.
Since 2009, several new structures were reported in the $J/\psi\phi$ mass
spectrum with the following characteristics: they are the first ones reported
decaying into two heavy mesons which contain both a $c\bar{c}$ pair and a
$s\bar{s}$ pair; and their masses are well beyond the open charm pair
threshold. Conventional $c\bar{c}$ states with a mass beyond the $J/\psi\phi$
threshold are not expected to decay into this channel and the width is expected
to be large, thus they are good candidates for exotic mesons. My focus in this
article is to review the recent developments on the structures in the
$J/\psi\phi$ mass spectrum from CDF, Belle and LHCb.
