134 BRITISH PALAEOZOIC SPONGES. 



stituted a new genus, Octacium, for spicules in which a vertical axis is present in 

 addition to the horizontal rays. But Zittel 1 has pointed out that the spicules, even 

 in the typical species, show indications of a vertical axis, though one or both of 

 its rays may be reduced to a mere rudimentary process, and therefore the fully 

 developed spicules in Astrceospongia may be regarded as possessing eight rays. 



The spicules of this genus are so distinctly marked off from those of any other 

 group of Sponges that in my opinion they characterise a separate sub-order. The 

 constancy and the regular disposition of the six horizontal rays, and the additional 

 rays of the vertical axis, clearly show that the genus cannot be ranked with the 

 Hexactinellida3. The same features likewise distinguish it from any of the genera 

 included in the Heteractinellidse, though some of the spicules of Tholiasterella, 

 consisting of six horizontal rays and a vertical ray, bear a certain resemblance to 

 those of Astrceospongia (PI. VII, figs. 1 c, 1 d). But in Tholiasterella the horizontal 

 rays are very inconstant, varying from five to nine in number, and further, their 

 mode of union with each other also indicates the absence of any real affinity 

 between these groups. 



The genus Astrceospongia makes its first appearance in the Silurian (Niagara 

 group or Wenlock) and passes up into the Devonian. It occurs in North America ; 

 Isle of Gothland, Sweden ; England ; Bifel, Germany ; and in Belgium. 



15. Astf^iospongia patina, F. Roemer. Plate I, figs. 7, 7 a — 7 d. 



1861. AsTEiEOSPONGiA patina, F. Roerner. Fossile Fauna d. Silur. Geschiebe 



von Sadewitz, p. 14, pi. iii, figs, 

 5 a — 5 d. 



1880. — — — Lethaea pal., p. 315. 



1883. — — Hinde. Cat. Toss. Sponges, p. 149, pi. xxxi, 



fig. 5. 



The Sponges are discoid, with rounded, convex bases, and shallow, concave 

 upper surfaces. The type specimen is stated to be 41 mm. in width and 20 mm. in 

 height. 



The skeletal-spicules exhibit well-marked, flattened, central discs ; the rays 

 taper very slightly as a rule, and terminate obtusely. In many, only the six 

 horizontal rays are developed, in others one ray of the vertical axis is present as a 

 small projection from the centre of the disc, whilst more rarely some possess both 

 rays of the vertical axis. In one abnormal spicule only three horizontal rays are 



1 ' Handbuch der Pal.,' Bd. i, 1879, p. 185. 



