  We study the charmless baryonic three-body decays of B mesons: B+ to p
Lambdabar gamma, B+ to p Lambdabar pi0 and B0 to p Lambdabar pi-. The partial
branching fractions as a function of the baryon-antibaryon mass and the polar
angle distributions of the proton in the baryon-antibaryon system are
presented. This study includes the first observation of B+ to p Lambdabar pi0,
which is measured to have a branching fraction of (3.00^{+0.61}_{-0.53}\pm
0.33) times 10^{-6}. We also set upper limits on branching fractions of the
two-body decays B0 to p Sigmabar^{*-}, B0 to Delta^0 Lambdabar, B+ to p
Sigmabar^{*0}, and B+ to Delta^+ Lambdabar at the 90% confidence level. These
results are obtained from a 414fb^{-1} data sample collected near the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+
e- collider.
