The ornamental design for a shellshapedtub, as shown and described.
FIG. 1 is a perspective view taken from the top left of the shell shaped tub;
FIG. 2 is a left side elevation view of the shell shaped tub;
FIG. 3 is a front elevation view of the shell shaped tub;
FIG. 4 is a right side elevation view of the shell shaped tub;
FIG. 5 is a back view of the shell shaped tub;
FIG. 6 is a top plan view of the shell shaped tub;
FIG. 7 is a perspective view taken from the top left of the shell shaped tub in an open positon;
FIG. 8 is a left side elevation view of the shell shaped tub in an open position;
FIG. 9 is a front elevation view of the shell shaped tub in an open position; and,
FIG. 10 is a top plan view of the shell shaped tub in an open position.
The broken lines and the unshaded areas immediately adjacent to the broken lines depict portions of the shell shaped tub that form no part of the claimed design.