REPORT ON THE RADIOLARIA. 



421 



(as ill many Medusa;) 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 liotli halves of the disk become asymmetrical. If the 

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

 in size ami 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 (PL 32, 

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

 often also pyramidal or deejjly furrowed (PL 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 (PL 33, fig. 9 ; PL 35, figs. 3, 5). 



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

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



The Central Cap.'<ule of the Phacodiscida is everjrwhere circular, lenticular, envelops 

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

 which connei't the latter to the former. 



I. Subfamily 



SethodisciJa. 

 Margin of the disk witliout ^ 



Synopsis of the Genera of the Phacodiscida. 



T.,r . . , .,, , ( Medullary shell .'dimple, 



Margin simple, without ) •' ' ' 



equatorial girdle. | jj^j^,ii^,.y ^^^^y j^^,y^_ 



radial spines. 



TIT ■ 111 ( Medullary shell simiile, 



Margin surrounded by a ) '' ' ' 



^ hyaline equatorial girdle, 'j ^^^^^^^^y.^^.^ ^i^^.^j ^„„,^i^^ 



rr, 1- 7 • / -if Jledullary shell simple, 



iwo radial spmes (opposite ) •' ^ 



in one axis). '^ ^^j^.^j^u^^^.y ^j^^.ji j^^^,^}^,^ 



II. Subfamily 



Heliosestrida. 

 Margin of the disk with 

 two to eight solid radial 

 spines, usually quite regu- 

 larly disposed. (Number 

 usually constant.) 



III. Subfamily 



Heliodiscida. 



Margin of the disk with 

 numerous (ten to twenty 

 or more) radial spines, 

 usually irregulaily dis- 

 posed. (Number variable. ) 



Three radial spines. 



Four radial spines (iu cross 

 form). 



Six radial spines. 

 Eight radial spines. 



Medullary shell simple, 

 Medullary shell simple, 

 Medullary shell double, 

 Medullary shell simple, 

 Medullary shell simple, 

 Medullary shell double. 



■r, ,. 1 . 11 • 1 ( Medullary shell simple, 



Kadial spines all simple, ) ■' 



not branched. ) at i n i n i 1 1 



( Medullary shell double, 



Radial spines all or partly ) -.r i u in- i 



, ,^ , ( '^ledullary shell simple, 



181. Sethodiscus. 



182. Phacodisciis. 

 18.3. Perqjluvna. 



184. Pcrizonn. 



1 85. Sdhosfijhis. 



1 86. Phucostijlus. 



1 87. Tn'acf/6cus. 



188. Sethosfauruf. 



1 89. Phacodaurnt!. 



190. Distruuihs'. 



191. Heliosestrum. 



192. Astrosestruw. 



193. lldiodiscus. 



194. AdrojihaciM. 



19.5. Hi'liudnjnm--i. 



