134 BRITISH PALAZOZOIC SPONGES. 
stituted a new genus, Octacium, for spicules in which a vertical axis is present in 
addition to the horizontal rays. But Zittel' 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 Astrwospongia 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 
Hexactinellide. The same features likewise distinguish it from any of the genera 
included in the Heteractinellide, though some of the spicules of Tholiasterella, 
consisting of six horizontal rays and a vertical ray, bear a certain resemblance to 
those of Astreospongia (Pl. VII, figs. 1 ¢,1d). 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 Astrewospongia 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 ; Hifel, Germany ; and in Belgium. 
15. Asrrmosponcia patina, I’. Roemer. Plate I, figs. 7, 7 a—?7 d. 
1861. Asrrmosponata Pattna, F. Roemer. Fossile Fauna d. Silur. Geschiebe 
von Sadewitz, p. 14, pl. ii, figs, 
5 a—5 d. 
1880. _— — — Lethza pal., p. 315. 
1883. —_ — Hinde. Cat. Foss. Sponges, p. 149, pl. 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. 
