We present reversible magnetization data of a high-quality

{Bi}_{2} {Sr}_{2} {CaCu}_{2} O_{8 + δ}

single crystal and explore the occurrence of three-dimensional (3D)-

x y

critical behavior close to the bulk-transition temperature

T_{c}

and of Kosterlitz-Thouless (KT) behavior. Below and above the presumed Kosterlitz-Thouless transition temperature

T_{KT}

we observe the characteristic two-dimensional (2D)-

x y

behavior: a downward shift in the crossing point phenomenon toward

T_{KT}

as the field is decreased and sufficiently below

T_{KT}

the characteristic 2D-

x y

relationship between the magnetization and the in-plane magnetic penetration depth

λ_{a b}

. In contrast, the measured temperature dependence of the superfluid density does not exhibit the characteristic KT behavior around the presumed

T_{KT}

. The absence of this feature is traced back to the 2D- to 3D-

x y

crossover setting in around and above

T_{KT}

. Invoking the Maxwell relation, the anomalous field dependence of the specific-heat peak is also traced back to the intermediate 2D-

x y

behavior. However, close to

T_{c}

we observe consistency with 3D-

x y

critical behavior in agreement with measurements of

λ_{a b}

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