  A quark model which includes both scalar and vector contributions to the
reaction mechanism is used in a DWBA calculation of total and differential
cross-sections, polarizations, and spin correlation coefficients for the
reaction $\bar p p \rightarrow \bar \Lambda \Lambda$ at laboratory momenta from
threshold to 1.92 GeV/c. The free parameters of the calculation include the
scalar and vector strengths, a quark cluster size parameter, and six parameters
in the unknown $\bar \Lambda \Lambda$ interaction. Excellent agreement with
experiment is found for a constructive interference of scalar and vector terms,
and for a $\bar \Lambda \Lambda$ potential which differs from that suggested by
several authors on the basis of SU(3) arguments. The fit to the data is better
than that obtained by other quark models, which use only scalar or vector
annihilation terms. The agreement with experiment is as good as that found in
meson-exchange models, which use more parameters than the present calculation.
