class="sc">Nassellaria which have not yet secreted a skeleton, or older Nassellaria which have lost their original skeleton.

We distinguish in this small family two genera only: Cystidium with hyaline, not foamy calymma, without extracapsular alveoles, and Nassella, with a very voluminous foamy calymma, including numerous large alveoles; the former corresponds to Actissa and the latter to Thalassicolla among the Colloidea or the skeletonless Spumellaria. But in these two latter genera, as in all Peripylea, the central capsule is perforated everywhere by innumerable small pores; the two former genera, however, exhibit the same characteristic podoconus in the central capsule, and the same porochora at its base, as all the other Monopylea. The pseudopodia are protruded from the central capsule through the porochora only.

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.

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.

Central capsule subspherical, a little longer than broad. Podoconus about two-thirds as long as the capsule, with trifid porochora, which is composed of three equal circular lobes. Nucleus spherical. Numerous oil-globules in the endoplasm. The calymma includes numerous xanthellæ and brown pigment around the mouth.

Dimensions.—Length of the central capsule 0.06, breadth 0.05; nucleus 0.03.

Habitat.—Mediterranean, Messina (R. Hertwig), surface.