We claim the ornamental design for a lantern device, as shown and described.
FIG. 1 is a front perspective view of the claimed design;
FIG. 2 is a front view of the claimed design;
FIG. 3 is a rear view of the claimed design;
FIG. 4 is a left side view of the claimed design;
FIG. 5 is a right side view of the claimed design;
FIG. 6 is a top view of the claimed design; and,
FIG. 7 is a bottom view of the claimed design.
The ornamental design which is claimed is shown in solid lines in the figures. The broken line showing of the lantern device is for illustrative purposes only and forms no part of the claimed design. Broken lines formed by equal length dashes show unclaimed portion of the design.