The phylogenetic affinity of the fifteen families enumerated, and the morphological relationship based upon it, form a very difficult problem. The whole legion of Phæodaria is probably monophyletic, in as much as all the families may be derived from a single ancestral group, the skeletonless Phæodinida (Phæodina and Phæocolla); but at the same time polyphyletic, in as much as probably many families have been derived, independently one from another, from different branches of Phæodinida; or in other words, the characteristic malacoma of the Phæodaria (the cannopylean central capsule and the calymma with the phæodium) may be a monophyletic product, inherited from a single ancestral form; the manifold skeleton, however, is certainly a polyphyletic product, originating from different skeletonless Phæodinida.
Among the independent families of Phæodaria, derived directly from skeletonless Phæodinida by production of a peculiar skeleton, may be the following: Cannorrhaphida (Pl. [101], probably polyphyletic), Aulacanthida (Pl. [102]-[105]), Castanellida (Pl. [113]), Challengerida (Pl. [99]), Concharida (Pl. [123]-[125]), Circoporida (Pl. [114]-[117]) and Tuscarorida (Pl. [100]). The four families of Phæosphæria (the Orosphærida, Sagosphærida, Aulosphærida and Cannosphærida (Pl. [106]-[112]), may be derived perhaps from the Castanellida; and the Medusettida (Pl. [118]-[120]), have been perhaps derived from the Challengerida. The complicated affinities of these groups are however difficult to explain. The Cœlodendrida (Pl. [121]) are probably derived from the Concharida, and the Cœlographida (Pl. [126]-[128]) from the Cœlodendrida.
The geometrical fundamental form of the shell is in the majority of Phæodaria monaxonial, corresponding to the main axis of the enclosed central capsule; the astropyle of the latter, placed on the oral pole of the main axis, corresponds to the mouth of the shell in all Phæogromia. In the Phæosphæria, where no peculiar shell mouth is developed, the general fundamental form of the shell is usually homaxonial or spherical, often an endospherical polyhedron, rarely ellipsoidal or spindle-shaped (with prolonged main axis), or lenticular (with shortened main axis). The bivalved Phæoconchia have usually either an amphithect shell (with the same fundamental form as the Ctenophora), or a dipleuric, bilaterally symmetrical shell (with a dorsal and a ventral valve, a right and a left parapyle). A small number of Phæodaria (mainly Circoporida) are remarkable on account of the regular polyhedral form of their shell, the geometrical axes of which resemble crystalline axes and are defined by regular radial tubes; as the octahedral Circoporus (Pl. [117], fig. 6), the dodecahedral Circorrhegma (fig. 2), and the icosahedral Circogonia (fig. 1).
The siliceous or silicate bars, which compose the skeleton of the Phæodaria, are in the majority hollow tubes, filled up by jelly; in some other families, however, they are solid rods, as in the Nassellaria and Spumellaria. Such usual lattice-work, composed of solid rods, occurs only in the families Sagosphærida (Pl. [108]), Castanellida (Pl. [113]), and Concharida (Pls. [123]-[125]). A quite peculiar structure, a diatomaceous tracery of extremely fine and regular hexagonal frames, distinguishes the Challengerida (Pl. [99]). The hollow cylindrical tubes, which are found in the other families, appear in three different forms, simple, articulate, and provided with an axial thread. Simple hollow tubes, which are neither articulate nor provided with an axial thread, occur in the Cannorrhaphida (Pl. [101]), Aulacanthida (Pl. [102]-[105]), Cœlodendrida (Pl. [121], [122]), and Cœlographida (Pl. [126]-[128]). In all these families the hollow cylindrical tubes have a very thin wall and contain a wide cavity, filled only by jelly. The Orosphærida (Pl. [106], [107]), differ in the reduction of the cavity, which becomes very narrow (often rudimentary or lost), whilst the walls of the tubes become extremely thickened and stratified, numerous concentric layers of silica being disposed one over the other. The hollow cylindrical tubes contain an axial filament, or a thin thread of silica, placed in its axis, in the families Aulosphærida (Pl. [109]-[111]), Cannosphærida (Pl. [112]), Circoporida (Pl. [114]-[117]), and Tuscarorida (Pl. [100]). Usually the axial filament is connected with the thin wall of the tube by numerous horizontal branches. A quite peculiar structure distinguishes the Medusettida (Pl. [118]-[120]); their hollow tubes, extremely prolonged, are articulate owing to the presence of numerous, regular, equidistant transverse septa; these are pierced by a short tubule, similar to the siphon of the shells of Nautilus; this remarkable alveolar structure also occurs in the peripheral part of their shell-wall (and sometimes in the whole shell), numerous small polyhedral chambers or alveoles which communicate by small openings, being developed; they become easily filled with air in the dry shell (Pl. [120], figs. 11-16).
The substance of the siliceous or silicated shell-wall is, in the majority of Phæodaria, homogeneous and structureless, as in the Spumellaria and Nassellaria; but sometimes it acquires a peculiar structure. The thickened wall of the hollow tubes in the Orosphærida and in several Aulacanthida (Pl. [105], figs. 6-10) becomes distinctly stratified, concentric strata being disposed one over the other. A very remarkable structure, differing from that in all other Radiolaria, is found in the porcellanous shell of the Circoporida (Pl. [114]-[117]), and Tuscarorida (Pl. [100]). The thickened wall of the opaque shell is here composed of a peculiar silicated cement, which encloses numerous very thin and irregularly scattered needles (Pl. [115], figs. 6-9; Pl. [116], fig. 3). Dry fragments of these shells, observed by a strong lens, appear finely punctulate, and probably air, entering into these fine porules of the cement, causes the white colour and the calcareous or porcellanous appearance of the opaque dry shell. Its surface is smooth in the Tuscarorida (Pl. [100]), panelled in the Circoporida (Pl. [114]-[117]).
The hollow or solid spines, which arise from the shell of the Phæodaria, exhibit an extraordinary variety and elegance in the production of different branches, bristles, hairs, secondary spine, and thorns, hooks, anchor-threads, pencils, spathillæ, &c. These appendages are developed similarly to those of many Spumellaria, but exhibit a far greater variety and richness in form. They are organs partly for protection, partly for retention of food. They are much more interesting than in other Radiolaria.
Synopsis of the Orders and Families of Phæodaria.
I. Order PHÆOCYSTINA. Skeleton absent or incomplete, composed of numerous single scattered pieces, without connection. Central capsule placed in the centre of the calymma. |  | Skeleton completely absent, | 1. Phæodinida. | ||
| Skeleton composed of numerous scattered pieces, not of radial tubes, | 2. Cannorrhaphida. | ||||
| Skeleton composed of numerous hollow radial tubes, the proximal ends of which are in contact with the central capsule, | 3. Aulacanthida. | ||||
II. Order PHÆOSPHÆRIA. Skeleton a simple or double lattice-shell, not bivalved, without a peculiar shell-mouth (shell usually spherical, rarely of a modified form, always without peristome). Central capsule placed in the centre of the shell-cavity. |  | Shell composed of a simple non-articulated lattice-plate, without astral septa in the nodal points. |  | Network very robust and coarse, with irregular polygonal meshes; bars very thick, partly hollow, | 4. Orosphærida. |
| Network very delicate and fragile, with subregular, triangular meshes; rods very thin, filiform, always solid, | 5. Sagosphærida. | ||||
| Shell composed of numerous hollow, tangential cylindrical tubes, which are separated by astral septa in the nodal points. |  | Shell articulated, with astral septa, without a simple central shell, | 6. Aulosphærida. | ||
| Shell double, composed of two concentric shells; the outer articulated, the inner simple, | 7. Cannosphærida. | ||||
III. Order PHÆOGROMIA. Skeleton a simple lattice-shell, not bivalved, constantly provided with a peculiar large shell-mouth placed on the oral pole of the main axis; peristome usually surrounded by peculiar feet or teeth. (Shell either spherical or ovate, or of another form). Central capsule excentric, placed in the aboral half of the shell-cavity. |  | Structure of the shell not porcellanous (without needles imbedded in a punctulate cement-substance). |  | Structure of the shell diatomaceous, with very delicate and regular hexagonal pores. No articulate feet, | 8. Challengerida. |
| Structure of the shell alveolar, with hollow alveoles between a double plate. A corona of articulated feet around the mouth, | 9. Medusettida. | ||||
| Structure of the shell of simple lattice-work, neither diatomaceous nor alveolar. No articulate feet, | 10. Castanellida. | ||||
| Structure of the shell porcellanous, with peculiar fine needles imbedded in a punctulate cement-substance (a circle of pores around the base of each tube). | | Surface of the shell panelled or dimpled (spherical or polyhedral). Peristome flat, | 11. Circoporida. | ||
| Surface of the shell smooth, even (ovate or subspherical). Peristome prominent, | 12. Tuscarorida. | ||||
IV. Order PHÆOCONCHIA. Skeleton a bivalved lattice-shell, composed of a dorsal and a ventral valve which are completely separated (rarely connected by a ligament on the aboral pole). Central capsule enclosed between the two valves. |  | The two valves of the bivalved shell thick and firm, regularly latticed, without a galea or cupola on their apex, and without hollow tubes, | 13. Concharida. | ||
| The two valves of the bivalved shell very thin and fragile, scarcely latticed, each with a conical cupola or a helmet-shaped galea on its sagittal pole or apex, and with hollow tubes. |  | Galea without rhinocanna or nasal tube, without frenula, | 14. Cœlodendrida. | ||
| Galea with a rhinocanna or nasal tube, both connected by an odd or paired frenulum, | 15. Cœlographida. | ||||
I. Order PHÆOCYSTINA. Skeleton absent or incomplete, composed of numerous single scattered pieces, without connection. Central capsule placed in the centre of the calymma. | ||||||
| Skeleton completely absent, | ||||||
| 1. Phæodinida. | ||||||
| Skeleton composed of numerous scattered pieces, not of radial tubes, | ||||||
| 2. Cannorrhaphida. | ||||||
| Skeleton composed of numerous hollow radial tubes, the proximal ends of which are in contact with the central capsule, | ||||||
| 3. Aulacanthida. | ||||||
II. Order PHÆOSPHÆRIA. Skeleton a simple or double lattice-shell, not bivalved, without a peculiar shell-mouth (shell usually spherical, rarely of a modified form, always without peristome). Central capsule placed in the centre of the shell-cavity. | ||||||
| Shell composed of a simple non-articulated lattice-plate, without astral septa in the nodal points. | ||||||
| Network very robust and coarse, with irregular polygonal meshes; bars very thick, partly hollow, | ||||||
| 4. Orosphærida. | ||||||
| Network very delicate and fragile, with subregular, triangular meshes; rods very thin, filiform, always solid, | ||||||
| 5. Sagosphærida. | ||||||
| Shell composed of numerous hollow, tangential cylindrical tubes, which are separated by astral septa in the nodal points. | ||||||
| Shell articulated, with astral septa, without a simple central shell, | ||||||
| 6. Aulosphærida. | ||||||
| Shell double, composed of two concentric shells; the outer articulated, the inner simple, | ||||||
| 7. Cannosphærida. | ||||||
III. Order PHÆOGROMIA. Skeleton a simple lattice-shell, not bivalved, constantly provided with a peculiar large shell-mouth placed on the oral pole of the main axis; peristome usually surrounded by peculiar feet or teeth. (Shell either spherical or ovate, or of another form). Central capsule excentric, placed in the aboral half of the shell-cavity. | ||||||
| Structure of the shell not porcellanous (without needles imbedded in a punctulate cement-substance). | ||||||
| Structure of the shell diatomaceous, with very delicate and regular hexagonal pores. No articulate feet, | ||||||
| 8. Challengerida. | ||||||
| Structure of the shell alveolar, with hollow alveoles between a double plate. A corona of articulated feet around the mouth, | ||||||
| 9. Medusettida. | ||||||
| Structure of the shell of simple lattice-work, neither diatomaceous nor alveolar. No articulate feet, | ||||||
| 10. Castanellida. | ||||||
| Structure of the shell porcellanous, with peculiar fine needles imbedded in a punctulate cement-substance (a circle of pores around the base of each tube). | ||||||
| Surface of the shell panelled or dimpled (spherical or polyhedral). Peristome flat, | ||||||
| 11. Circoporida. | ||||||
| Surface of the shell smooth, even (ovate or subspherical). Peristome prominent, | ||||||
| 12. Tuscarorida. | ||||||
IV. Order PHÆOCONCHIA. Skeleton a bivalved lattice-shell, composed of a dorsal and a ventral valve which are completely separated (rarely connected by a ligament on the aboral pole). Central capsule enclosed between the two valves. | ||||||
| The two valves of the bivalved shell thick and firm, regularly latticed, without a galea or cupola on their apex, and without hollow tubes, | ||||||
| 13. Concharida. | ||||||
| The two valves of the bivalved shell very thin and fragile, scarcely latticed, each with a conical cupola or a helmet-shaped galea on its sagittal pole or apex, and with hollow tubes. | ||||||
| Galea without rhinocanna or nasal tube, without frenula, | ||||||
| 14. Cœlodendrida. | ||||||
| Galea with a rhinocanna or nasal tube, both connected by an odd or paired frenulum, | ||||||
| 15. Cœlographida. | ||||||