REPORT ON THE RADIOLARIA. 



1541 



The substance of the siliceous or silicated shell-wall is, in the majority of 

 PH.-EODARIA, homogeneous and structureless, as in the SPUM ELL ARIA and NASSELLARIA ; 

 but sometimes it acquires a peculiar structure. The thickened wall of the hollow tubes in 

 the Orosphaerida and in several Aulacanthida (PI. 105, figs. 610) becomes distinctly 

 stratified, concentric strata being disposed one over the other. A very remarkable 

 structure, differing from that in all other Eadiolaria, is found in the porcellanous shell 

 of the Circoporida (PI. 114-117), and Tuscarorida (PI. 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; PI. 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 (PI. 100), panelled in the Circoporida (PI. 114-117). 



The hollow or solid spines, which arise from the shell of the PILEODARIA, exhibit 

 an extraordinary variety and elegance in the production of different branches, bristles, 

 hairs, secondary spine, and thorns, hooks, anchor-threads, pencils, spathillse, &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. 



I. Order 



PH^OCYSTINA. 



Skeleton absent or in- 

 complete, composed of 

 numerous single scattered 

 pieces, without connec- 

 tion. Central capsule 

 placed in the. centre of 

 the calymma. 



II. Order 



Synopsis of the Orders and Families of PHJEODARIA. 



Skeleton completely absent, .... 



Skeleton composed of numerous scattered pieces, not 

 of radial tubes, ..... 



Skeleton composed of numerous hollow radial tubes, the 

 proximal ends of which are in contact with the central 

 capsule, ...... 



Skeleton a simple or double 

 lattice-shell, not bi valved, 

 without a peculiar shell- 

 mouth (shell usually < 

 spherical, rarely of amodi- 

 fied form, always without 

 peristome). Central cap- 

 sule placed in the centre 

 of the shell-cavity. 



Shell composed of a simple, 

 non-articulated lattice- 

 plate, without astral 

 septa in the nodal points. 



Shell composed of numer- 

 ous hollow, tangential 

 cylindrical tubes, which 

 are separated by astral 

 septa in the nodal 

 points. 



[ Network very robust and 

 coarse, with irregular 

 polygonal meshes ; bars 

 very thick, partly hollow, 



Network very delicate and 

 fragile, with subregular, 

 triangular meshes; rods 

 very thin, iiliform, always 

 solid, 



Shell articulated, with astral 

 septa, without a simple 

 central shell, 



Shell double, composed of 

 two concentric shells ; 

 the outer articulated, the 

 inner simple, 



2. CANNORRHAPHIDA. 



3. AULACANTHIDA. 



4. OROSPHJSRIDA. 



5. SAGOSPHJ3RIDA. 



6. AULOSPH^ERIDA. 



7. CASNOSPH^RIDA. 



