peritreme

from The Century Dictionary.

• noun In entomology, a small circular sclerite, or ring of hard chitinized integument, often surrounding the spiracle or breathing-hole of an insect.
• noun In conchology, the circumference of the aperture of a univalve; a peristome.

from the GNU version of the Collaborative International Dictionary of English.

• noun That part of the integument of an insect which surrounds the spiracles.
• noun The edge of the aperture of a univalve shell.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun zoology That part of the integument of an insect which surrounds the spiracles.
• noun zoology The edge of the aperture of a univalve shell.