The ornamental design of a casket, as shown and described.
FIG. 1 is a front elevational view of the casket illustrating my new design.
FIG. 2 is a top plan view of my design.
FIG. 3 is a left side elevational view of my design.
FIG. 4 is a right side elevational view of my design; and,
FIG. 5 is a rear elevational view of my design.
The broken line portions of the casket in FIGS. 1 through 5 which include the shape of the casket lid and casket body, the casket handles, handle supports and lid hinges form no part of the design. The Dotted portions showing of fastener heads in FIGS. 1 through 5 also form no part of the claimed design.