REPORT ON THE RADIOLARIA. 



575 



(among the Porodiscida), bearing on the disk-margin two, three, or four spongy arms, 

 commonly disposed reguLarly in the equatorial plane. Here also occurs the peculiar 

 formation of a "patagium," or of an interbrachial spongy framework different from that 

 of the arms, which connects the arms like a web-membrane in the equatorial plane. 



The spongy framework exhibits in all these Spongodiscida no remarkable 

 differences, being everywhere comjjosed of fine branched solid siliceous threads, inter- 

 woven in all directions, with irregular meshes of very different size. 



The central capsule of all Spongodiscida is filled up with the same spongy 

 framework which covers also both its sides. It grows according to the enveloping 

 skeleton, but remains constantly smaller. The form of the central capsule is circular 

 (lenticular or discoidal) in the Spongophacida and Spongotrochida, whilst in the 

 Spongobrachida it enters into the radial spongy arms, developed from the margin of the 

 spongy disk. 



Synopsis of the Genera of the Spongodiscida. 



I. Subfamily 



Spongophacida. 

 Spongy disk without radial 

 appendages. 



II. Subfamily 



Spongotrochida. 

 Spongy disk with solid 

 radial spines on the 

 margin (in the equatorial 

 plane). 



Spongy disk with simple margin (without peculiar 

 equatorial girdle), .... 



Spongy disk with a peculiar (solid or porous) equatorial 

 cru-dle, ..... 



Few (two, three, or four) 



radial spines regidarly -l Three marginal spines, 

 disposed. 



Two opposite sjiines. 

 Three marginal spine 

 Four crossed spines, 



III. Subfamily 



Spongobrachida. 



Spongy disk with spongy 

 radial arms on the 

 margin (in the equatorial 

 plane). 



Numerous (five to ten or 

 more) radial spines, 

 often irregularly dis- 

 posed. 



Two arms, opposite in one 

 axis. 



Three arms on the margin. 



Four arms in cross form. 



Sjjines only on the 

 margin (equatorial). 



Spines on both sides of 

 the disk, 



Without a patagium. 



With a patagium, 



Without a patagium, 



With a patagium, 



Without a patagium. 



With a patagium. 



2.53. SjMngodiscus. 



254. Spongopliacus. 



255. Spongolonclie. 



256. Spongotripus. 



257. Spongostaurits. 



258. Stylotrochus. 



259. Spongotrochus. 



260. Spongolena. 



261. Spongobrachium. 



262. Rhopalodidyum. 



263. Dictyoeoryne. 



264. Spongasteriscus. 



265. Spongaster. 



Subfamily 1. Spongophacida, Haeckel, 1881, Prodromus, p. 461. 



Definition. — S p o n g o d i s c i d a with a simple cii'cular disk, without radial 

 appendages on the margin (neither solid spines nor chambered arms). 



