The ornamental design for a cathetersheath, as shown and as described.
FIG. 1 is a top, three dimensional view of a catheter sheath;
FIG. 2 is a bottom, three dimensional view of the catheter sheath;
FIG. 3 is a top plan view of the catheter sheath;
FIG. 4 is a bottom plan view of the catheter sheath;
FIG. 5 is an end view of the catheter sheath; and,
FIG. 6 is a side view of the catheter sheath.
The broken line representation of the bores in the catheter sheath illustrate that these edges form no part of the claimed design. The design is shown broken away in order to indicate that a specific length of catheter sheath forms no part of the claimed design.