REPOET ON THE RADIOLAEIA. 583 



Genus 258. Stylotrochus} Haeckel, 1862, Monogr. d. Radiol., p. 463. 



Definition. — S p o n g o d i s c i d a with numerous solid radial spines on tlie margin 

 of the disk (five to ten or more), all situated in the equatorial plane. 



The genus Stylotrochus comprises those Spongodiscida in which the margin of the 

 circular disk bears numerous radial spines. All these spines lie in the same equatorial 

 plane, whilst in the following genus they are disposed over the whole surface of the disk. 

 Stylotrochus corresponds to Astrocyclia among the Coccodiscida, to Stylodictya among 

 the Porodiscida. The spongy framework of the disk is either quite irregular 

 (StylotrochiscKs), or includes in the middle part some concentric circular rings 

 (Stylospongia). 



Subgenus 1. Stylotrochiscus, Haeckel. 



Definition. — Spongy framework of the whole disk irregular, without concentric 

 circular rings or spiral convolutions. 



1. Stylotrochus arachnius, Haeckel. 



Spongotrochns arachnius, Haeckel, 1862, Monogr. d. Radiol, p. 464. 



Spongy framework of the whole disk irregular. Eight to twelve marginal spines very long and 

 thin, bristle-shaped, twice to four times as long as the diameter of the disk. (Very similar to the 

 common Stylodictya arachnia, but without concentric circular rings and sieve-plates, with quite 

 irregular network of fine bars.) 



Dimensions. — Diameter of the disk 012 to Olo ; length of the radial spines 0'2 to 0'6, basal 

 breadth 0-001. 



EaMtat. — Cosmopolitan ; Mediterranean, Atlantic, Indian, Pacific, surface ; also fossil in 

 Tertiary rocks of Barbados and the Mediterranean. 



2. Stylotrochus craticulatus, Haeckel. 



Spongotroehus craticulatus, Stohr, 1880, Palaeontogr., vol. xxvi. p. 118, Taf. vi. fig. 12. 

 t. Spongodisam aculeatus, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. "Wiss. Berlin, 

 p. 246. 



Spongy framework of the whole disk irregular. Sixteen to twenty short marginal spines (twice 

 to four times as long as the diameter of one mesh of the framework), free prolongations of internal 

 radial beams which arise from the darker centre of the disk. (The interruption of the disk-margin 

 on one point of its circumference, figured by Stohr as osculum or " Miindungs-Oeffnung," is probably 

 an accidental abnormality ; I did not find it in other specimens.) 



1 .S(!/to?roc/iiis = Wheel with styles ; cTu}\as, r^oxos- 



