peridium

Plant small, spherical, having a double shell or peridium, the inner one white and the outer one smooth and greyish lead-color or bluish-grey, and shelling off at maturity.

From Student's Hand-book of Mushrooms of America, Edible and Poisonous by Thomas Taylor

The author hesitated about the generic reference, finally referring it to Diachaea despite the lack of calcium, because it was sessile and had a peridium rather more persistent than is usual in comatrichas.

From The North American Slime-Moulds A Descriptive List of All Species of Myxomycetes Hitherto Reported from the Continent of North America, with Notes on Some Extra-Limital Species by Thomas H. (Thomas Huston) MacBride

The peridium, except a small part below, all falls away, leaving the capillitium apparently intact, crowded with spores.

From The North American Slime-Moulds A Descriptive List of All Species of Myxomycetes Hitherto Reported from the Continent of North America, with Notes on Some Extra-Limital Species by Thomas H. (Thomas Huston) MacBride

The fructification is a delicate netted plasmodiocarp, the tubule about .5 mm., bright red; the peridium simple, cartilaginous, dehiscent from above, and flecked with just here and there a red calcareous scale.

From The North American Slime-Moulds A Descriptive List of All Species of Myxomycetes Hitherto Reported from the Continent of North America, with Notes on Some Extra-Limital Species by Thomas H. (Thomas Huston) MacBride

In some instances the peridium is almost smooth, and sometimes cracks in areas, inner peridium thin and tough.

From Student's Hand-book of Mushrooms of America, Edible and Poisonous by Thomas Taylor