ASTRAOSPONGIA. 133 
Sub-Order.—OctactinELLIpm, 
Genus.— AstRmosPonata, Ff. Roemer. 
1860. Silur. Fauna Tennessee, p. 14. 
Syn.—Blumenbachium, I’. Roemer (non Koenig) ; Astreeospongium, F. Roemer ; 
Octacium, Schliiter. 
Generic Characters.—Sponges discoid or shallow cup-shaped in form, and 
without stem or any surface of attachment. No special canal-system indicated in 
the skeleton, which is composed of spicules having six rays extending in a plane 
from a common centre, at equal angles from each other, and with a vertical axis. 
One or both rays of the vertical axis may be reduced or not be developed. The 
spicules are irregularly arranged, with their horizontal rays generally parallel to 
the surface of the Sponge ; they are quite free from each other. 
Though the spicular elements of the skeleton in this genus do not appear to 
have been organically attached together, entire Sponges are of not infrequent 
occurrence. In these the spicules are now cemented together by the matrix, and 
they are best preserved on the weathered surface of the Sponge. The rays insome 
of the larger spicules show, when weathered, longitudinal open furrows, indicating 
the presence of canals. Many of the examples of this genus are now composed of 
carbonate of lime, and even the detached spicules met with in the rocks consist of 
the same mineral. In some, however, the exterior is of carbonate of lime, whilst 
the interior is a mass of chalcedonie silica, in which the spicular structure has 
been obliterated. The frequent occurrence of these calcitic specimens has given 
rise to the belief that the Sponges originally consisted of this mineral, and Ferd. 
Roemer' supports this view by the statement that other Sponges, as Astylospongia 
for example, occurring, with Astr@ospongia in the same beds in Tennessee, are com- 
pletely silicified. But it does not thereby follow that this latter genus is a Calci- 
sponge, since we know that many of the Silurian examples of Aulocopiwm, a 
generally recognised siliceous Sponge, are partly of calcite and partly of chal- 
cedonic silica, like some of the Tennessee specimens of Astrwospongia. The form 
and general character of the spicules of this genus, moreover, do not indicate any 
affinity with recognised Calcisponges, and I therefore regard the calcareous 
specimens as replacements after silica. 
The spicules of Astraospongia have been described by F. Roemer as consisting 
only of six horizontal rays, and Schliiter,” maintaining the same opinion, has con- 
1 « Lethea paleozoica’ (1880), p. 314. 
2 *Sitzungsb. d. niederrhein. Gesellsch. in Bonn,’ 1885, p. 151. 
