  The Born cross section of the process
$e^{+}e^{-}\rightarrow\Lambda\bar\Lambda$ is measured at 33 center-of-mass
energies between 3.51 and 4.60 GeV using data corresponding to the total
integrated luminosity of 20.0 fb$^{-1}$ collected with the BESIII detector at
the BEPCII collider. Describing the energy dependence of the cross section
requires a contribution from the $\psi(3770)\rightarrow\Lambda\bar\Lambda$
decay, which is fitted with a significance of 4.6-4.9$\sigma$ including the
systematic uncertainty. The lower bound on its branching fraction is
$2.4\times10^{-6}$ at the 90% confidence level (C.L.), at least an order of
magnitude larger than expected from predictions using a scaling based on
observed electronic widths. This result indicates the importance of effects
from vector charmonium(-like) states when interpreting data in terms of e.g.,
electromagnetic structure observables. The data do not allow for definite
conclusions on the interplay with other vector charmonium(-like) states, and we
set 90% C.L.upper limits for the products of their electronic widths and the
branching fractions.
