  Vortex phase diagram under tilted fields from the $c$ axis in
Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+y}$ is studied by local magnetization
hysteresis measurements using Hall probes. When the field is applied at large
angles from the $c$ axis, an anomaly ($H_p^\ast$) other than the well-known
peak effect ($H_p$) are found at fields below $H_p$. The angular dependence of
the field $H_p^\ast$ is nonmonotonic and clearly different from that of $H_p$
and depends on the oxygen content of the crystal. The results suggest existence
of a vortex matter transition under tilted fields. Possible mechanisms of the
transition are discussed.
