REPORT ON THE RADIOLARIA. 



421 



(us in many Medusse) four larger perradial spines alternating with four smaller inter- 

 radial spines. Often in one and the same species occur abnormalities in number and 

 disposition of the radial spines, three or five spines instead of four, or also seven or nine 

 .spines instead of eight ; often both halves of the disk become asymmetrical. If the 

 number of the marginal spines exceed eight to ten, they commonly become very variable 

 in size and irregular in disposition ; these variations characterise the third subfamily, 

 Heliodiscida, Commonly also here all spines lie in the equatorial plane ; but sometimes 

 they become crowded in several parallel circles on both sides of the margin (PI. 32, 

 fig. 1). The form of the marginal spines is commonly conical or flattened triangular, 

 often also pyramidal or deeply furrowed (PI. 31, figs. 6-9). Very rarely the spines are 

 fenestrated (PL 35, fig. 1) ; only in one genus (Heliodrymus) they are all or partly 

 branched (PI. 33, fig. 9 ; PI. 35, figs. 3, 5). 



The peculiar development of the phacoid shell has been already described by J. 

 Miiller (compare my Monograph, 1862, pp. 156, 438). 



The Central Capsule of the Phacodiscida is everywhere circular, lenticular, envelops 

 the medullary shell, and is enclosed by the phacoid shell, perforated by the radial beams, 

 which connect the latter to the former. 



L Subfamily 



Sethocliscida. 



Margin of the disk without j 

 radial spines. 



Synopsis of the Genera of the Phacodiscida. 



Margin simple, without / Medullary shell simple, 

 equatorial girdle. | Medu , lary ghell doubl6) 



II. Subfamily 



Heliosestrida. 



Margin of the disk with 

 two to eight solid radial 

 spines, usually quite regu- 

 larly disposed. (Number 

 usually constant.) 



I Margin surrounded by a j Medullary sh ' n sim P le > 

 I hyaline equatorial girdle, j Medullary ghell doubl(lj 



Two radial spines (opposite J Medullarv she11 sim P le ' 



Medullary shell double, 



Medullary shell simple, 

 Medullary shell simple, 

 Medullary shell double, 

 Medullary shell simple, 



in one axis). 

 Three radial spines. 



Four radial spines (ill cross 

 form). 



Six radial spines. 

 Eight radial spines. 



Medullary shell simple, 

 Medullary shell double, 



III. Subfamily 



Heliodiscida. 



Margin of the disk with 

 numerous (ten to twenty - 

 or more) radial spines, 

 usually irregularly dis- 

 posed. (Number variable. ) 



r i- i 11 i ( Medullary shell simple, 



Radial spines all simple, ) 



not branched. ) , , , ,, 1.111 1 1 



( Medullary shell double, 



Radial spines all or partly ) -, T , ,, in- i 



branched. } Med llar y slle11 slm P le - 



181. Selhodiscus. 

 . 182. Phacodlscun. 



183. Periphaina. 



184. Perizona. 



. 185. Sethostylus. 



186. Phacostylus. 

 . 187. Triactiscus. 

 . 188. Sethostaurus. 



189. Phacostaurux. 

 . 190. Distriactis, 



191. Heliosestrum. 

 . 192. Astrosestrum . 



193. Heliodisais. 

 . 194. Asfrophacutt. 



195. 



