The ornamental design for spherical drum shells, as shown and described.
FIG. 1 is a front view of spherical drum shells showing my new design.
FIG. 2 is a rear view thereof.
FIG. 3 is a top view thereof.
FIG. 4 is a front view of a second embodiment of the spherical drum shells.
FIG. 5 is a rear view thereof.
FIG. 6 is a top view thereof.
FIG. 7 is a front view of a third embodiment of the spherical drum shells.
FIG. 8 is a rear view thereof; and,
FIG. 9 is a top view thereof.
The broken lines showing the foot-pedal-operated baton, securing rim, drumhead, and support stand are included for the purposes of illustrating environmental structure and form no part of the claimed design.