FIG. 1 is a first perspective view of a spa shell showing our new design;
FIG. 2 is a second perspective view of a spa shell showing our new design;
FIG. 3 is a top plan view of a spa shell showing our new design;
FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3;
FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 3;
FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 3;
FIG. 7 is a cross-sectional view taken along 7-7 of FIG. 3;
FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 3;
FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 3;
FIG. 10 is a cross-sectional view taken along line 10-10 of FIG. 3; and,
FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 3.
The broken-line disclosure in the views represents portions of the article in which the claimed design is embodied, but which form no part of the claimed design.