The ornamental design for a spiralarchtrellis, as shown and described.
FIG. 1 is a front view of the spiral arch trellis;
FIG. 2 is a left side view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof; and,
FIG. 5 is a perspective view thereof.
The rear side view of the design is the same as the front side view shown in FIG. 1, and the right side view of the design is a mirror image of the left side view shown in FIG. 2.
The design consists of the features of shape, pattern, ornament and configuration of a spiral arch trellis shown in the drawings.