_The Central Capsule_ is in the two observed genera either ovate or nearly spherical, usually slightly tapering towards the basal mouth. Its transverse section is constantly circular. The membrane of the capsule is usually rather thick and double-contoured, and bears on the truncate basal pole a circular "porochora" or area porosa, through which the pseudopodia are protruded. The _porochora_ is either quite simple, circular, or in some species trilobed, with three equal circular lobes, each of which is surrounded by a girdle of small granules. The _podoconus_, or "pseudopodial-cone," arising vertically from the horizontal basal porochora, is half as long as the central capsule, or longer, simply conical and finely striped longitudinally. The _nucleus_ lies usually in the uppermost part of the central capsule, above or behind the podoconus, and is either spherical or ovate, sometimes kidney-shaped. It includes one or more nucleoli. _Synopsis of the Genera of Nassellida._ Calymma hyaline, without alveoles, 382. _Cystidium_. Calymma foamy, with numerous large alveoles, 383. _Nassella_. {897}Genus 382. _Cystidium_,[1] R. Hertwig, 1879, Organismus d. Radiol., p. 87. _Definition._--#Nassellida# with hyaline calymma, without extracapsular alveoles. The genus _Cystidium_ is the simplest and most primitive among all NASSELLARIA, and may be regarded as the common ancestral form of this legion, for which it has the same high importance as _Actissa_ for the SPUMELLARIA. The central capsule is quite simple, ovate or nearly spherical, and included in a voluminous hyaline calymma, which contains no large alveoles. _Cystidium_ differs from _Actissa_, its probable ancestral form, in the possession of the "podoconus" and its basal "porochora," characteristic of all NASSELLARIA or MONOPYLEA. 1. _Cystidium princeps,_ n. sp. (Pl. 91, fig. 1). Central capsule ovate, one and a third times as long as broad. Podoconus with simple circular porochora, about half as long as the capsule, surrounded at its base by red granules of pigment. Nucleus spherical. Three equal oil-globules in the endoplasm. No pigment in the voluminous calymma, which includes numerous xanthellæ. _Dimensions._--Length of the central capsule 0.1, breadth 0.075; nucleus 0.035. _Habitat._--Indian Ocean, Maldive Islands (Haeckel), surface. 2. _Cystidium lecythium,_ n. sp. Central capsule ovate, one and a half times as long as broad. Podoconus with simple circular porochora, three-fourths as long as the capsule. Nucleus ellipsoidal. No oil-globules in the endoplasm. No pigment and no xanthellæ in the calymma. _Dimensions._--Length of the central capsule 0.12, breadth 0.08; nucleus 0.04. _Habitat._--Central Pacific, Station 271, surface. 3. _Cystidium inerme,_ R. Hertwig. _Cystidium inerme,_ R. Hertwig, 1879, Organismus d. Radiol., p. 87, Taf. vii. figs. 1-1_b_.