perisporium

from The Century Dictionary.

• noun A genus of pyrenomycetous fungi of the order Perisporiales, having black superficial perithecia and elongate, dark-colored, 4-celled spores. About 10 species are included in the genus.

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

• noun mycology the outer part of a spore wall which often disappears in older spores.