Fig. 36.--Perpendicular section through the capillitium, columella, and stipe of Diachæa Thomasii, Rex. NOTE.--The figures of the objects are drawn as they appear under a magnifying power of about 100 diameters. [Illustration: The Journal of the Cin. Soc. Natural History. VOL. XVI. PLATE XI.] ORDER VII.--DIDYMIACEÆ. Sporangia simple and subglobose, or plasmodiocarp, rarely combined into an æthalium. Wall of the sporangium a thin membrane with an outer layer composed of minute stellate crystals, or of minute roundish granules of lime; these either lie singly upon the surface, or are compacted into a crustaceous coat. Stipe present or often wanting; the columella usually conspicuous and well-developed. Capillitium consisting of very slender, often sinuous threads, which extend from the base of the sporangium or from the columella to the walls, either simple or outwardly branching a few times at a sharp angle, combined into a loose irregular net by a few transverse branchlets, which are situated chiefly at the extremities. Spores globose, violaceous. This order is readily distinguished from the Physaraceæ by the absence of lime from the threads of the capillitium. TABLE OF GENERA OF DIDYMIACEÆ. _a. The lime on the wall of the sporangium in the form of minute stellate crystals._ 1. DIDYMIUM. Sporangium simple, subglobose and stipitate, the base commonly umbilicate, or sometimes sessile and plasmodiocarp. 2. SPUMARIA. Æthalium composed of numerous elongated irregularly-branched sporangia, closely compacted together and confluent. _b. The lime on the wall of the sporangium consisting of minute roundish granules._ 3. DIDERMA. Wall of the sporangium with the outer calcareous layer usually compacted into a smooth continuous crust. 4. LEPIDODERMA. Wall of the sporangium with an outer layer of large scales, consisting of bicarbonate of lime. I. DIDYMIUM, Schrad. Sporangium simple, subglobose and stipitate, the base commonly umbilicate, or sometimes sessile and plasmodiocarp; the wall a thin membrane with an outer layer of minute stellate crystals of lime. Stipe present or sometimes wanting; the columella mostly conspicuous, sometimes thin or obsolete. Capillitium of very slender threads, straight or often sinuous, stretching from the columella to the wall of the sporangium, simple or outwardly sparingly branched at a sharp angle. Spores globose, violaceous. Didymium, together with Spumaria, is to be distinguished from all other genera of the Myxomycetes by the covering of stellate crystals, like hoar-frost, upon the outer surface of the sporangium. §1. CIONIUM. Columella prominent, subcentral, globose, obovoid, or turbinate; the threads of the capillitium radiating in all directions to the wall of the sporangium. _A. Sporangium stipitate._