Order xiii. STEPHOIDEA.—Skeleton with a sagittal ring continuous with the branched spicule, and sometimes other rings or branches. (Families 48-51.) _Lithocercus_ Théel (Fig. 26, A). Order xiv. SPYROIDEA.—Skeleton with a latticed shell developed around the sagittal ring (cephalis), and constricted in the sagittal plane, with a lower chamber (thorax) sometimes added. (Families 52-55.) {79}Order xv. BOTRYOIDEA.—As in Spyroidea, but with the cephalis 3-4 lobed; lower chambers, one or several successively formed. (Families 56-58.) Order xvi. CYRTOIDEA.—Shell as in the preceding orders, but without lobing or constrictions. (Families 59-70.) _Theoconus_ Haeck. (Fig. 25, B). D. PHAEODARIA. Order xvii. PHAEOCYSTINA.—Skeleton 0 or of distinct spicules; capsule centric. (Families 71-73.) _Aulactinium_ Haeck. (Fig. 26, B). Order xviii. PHAEOSPHAERIA.—Skeleton a simple or latticed sphere, with no oral opening (pylome); capsule central. (Families 74-77.) Order xix. PHAEOGROMIA.—Skeleton a simple latticed shell with a pylome at one end of the principal axis; capsule excentric, sub-apical. (Families 78-82.) _Pharyngella_ Haeck.; _Tuscarora_ Murr.; _Haeckeliana_ Murr. (Fig. 28). Order xx. PHAEOCONCHIA.—Shell of two valves, opening in the plane ("frontal") of the three openings of the capsule. (Families 83-85.) We exclude Haeckel's Dictyochida, with a skeleton recalling that of the Stephoidea, but of the impure hollow substance of the Phaeodaria (p. 84). They rank now as Silicoflagellates (p. 114). The Radiolarian is distinguished from all other Protozoa by the chitinous central capsule, so that its cytoplasm is separated into an outer layer, the _extracapsular_ protoplasm (ectoplasm), and a central mass, the _intracapsular_, containing the nucleus.[88] The _extracapsular_ layer forms in its substance a gelatinous mass, of variable reaction, through which the plasma itself ramifies as a network of threads ("sarcodictyum"), uniting at the surface to constitute the foundation for the pseudopodia. This gelatinous matter constitutes the "calymma." It is largely vacuolated, the vacuoles ("alveoli"), of exceptional size, lying in the nodes of the plasmic network, and containing a liquid probably of lower specific gravity than seawater; and they are especially abundant towards the surface, where they touch and become polygonal. On mechanical irritation they disappear, to be formed anew after an interval, a fact that may explain the sinking from the surface in disturbed water. This layer may contain minute pigment granules, but the droplets of oil and of albuminous matter frequent in the central layer are rare here. {80}The "yellow cells" of a symbiotic Flagellate or Alga, _Zooxanthella_, are embedded in the jelly of all except Phaeodaria, and the whole ectosarc has the average consistency of a firm jelly.