REPORT ON THE RADIOLARIA. 1593 



the diameter of the shell ; they are longitudinally striped in the basal part, spinu- 

 late or reticulately dimpled in the distal part ; sometimes they are straight, at other 

 times curved or undulate (PI. 106, figs. 1-4 ; PL 107, figs. 4-6). The slender rod- 

 shaped spines are usually longer than the diameter of the shell, cylindrical, more or less 

 curved or even undulate, smooth or thorny, sometimes irregularly branched, and often 

 the branches are all or partly connected (PI. 106, fig. 3 ; PI. 107, fig. 1). In the 

 majority of the shells observed the radial spines were found to be partly broken off. 

 Their structure is the same as that of the bars of the network ; but the central axial 

 canal and the surrounding concentric lamellae are usually more distinct than in the latter. 

 The central capsule of the Orosphserida lies in the centre of the spherical lattice- 

 shell, surrounded by the voluminous calymma, which fills up its cavity. The form, 

 structure, and size of the central capsule are the same as in the closely allied Aulosphserida 

 (PI. Ill, fig. 2). Its diameter is usually about 0'2, or between 0'15 and 0'25, rarely 

 more than 0'3 or less than T2. The dark pha3odium is of about the same volume as the 

 central capsule, and envelops its oral half with the radiate operculum and the proboscis 

 of the astropyle. The two opposite parapylse are small. 



Synopsis of the Genera of Orosphcerida. 



I. Subfamily f Surface smooth, without radial spines, . 671. Orona. 



Oronida. 

 Surface of the shell without pyramidal or 1 Surface studded with simple or branched radial 



tent-shaped elevations. [ spines, ..... 672. Orosphcera. 



TT o T_* -1 f Pyramids of the surface free, without spongy 



11 ^SLid, 



Surface of the shell with numerous pyra- p ^ of ^ ^^ connected b a 



midal or tent-shaped elevations. ^ envelope or an external lattice-shell, 674. Oroplegma. 



Genus 671. Orona, 1 n. gen. 



Definition. rosphaerida with a simple spherical or slightly ellipsoidal shell, 

 without pyramidal elevations and radial spines. 



The genus Orona is the simplest of the Orosphaerida, and probably the common 

 ancestral form of this family. The lattice-shell is a simple fenestrated sphere, some- 

 times slightly ellipsoidal, with prolonged main axis, and bears on its surface neither 

 tent-shaped elevations nor radial spines. It may be confounded with some big forms 

 of Cenosphcera ; it differs, however, in the possession of hollow central canals in the thick 

 bars of the very coarse lattice-plate. 



1 Orona Hilly or tuberculate shell; fas, ">"! 

 (ZOOL. CHALL. EXP. PART XL. 1886.) Rr 200 



