HYALOSTELIA. 159 
proximal ray of the vertical axis penetrated into the interior of the Sponge (PI. VI, 
fig. 1). 
The spicules of the body of the Sponge are regular and modified hexactinellids. 
In the simplest form, the rays are straight and gradually taper from the central 
node to an obtuse point; the vertical axis is also considerably longer than the 
transverse axes of the spicule. In other spicules the rays are very unequally 
developed, and sometimes curved. In some, probably abnormal, forms, five of the 
rays are reduced to small knobs. In other spicules the distal ray is not developed. 
There are great variations in the dimensions of the skeletal- and dermal-spicules. 
In small examples the principal axis is ‘64 mm. in length by ‘1 mm. in thickness, 
whilst the main axis in large forms attains to 9 mm. in length by °54 mm. in 
thickness. 
The spicular rods belonging to the anchoring appendage of the Sponge, occur 
either in detached fragments, or as broad compressed bands, in which the 
component rods are parallel to, and in contact with, each other. The rods are 
smooth, cylindrical, and with a well-developed axial canal, and not infrequently 
show traces of the concentric layers of which they are composed. In some, if not 
in all cases, the rods terminate in four short, blunted, more or less recurved rays 
(Pl. VI, figs. 2e—2h). No complete bundle of rods has been discovered ; Messrs. 
Young have traced them to a length of 300 mm. (12 inches). The longest fragment 
which has come under my notice has a length of 170 mm. by 38 mm. in width, and 
from 5 to 10 mm. in thickness. There is also great variation in the size of the rods 
in the same bundle; the majority vary from *95 to 1°35 mm. in diameter, but there 
are smaller ones intermingled, which are not more than *15 mm. in thickness. 
The skeletal-spicules of this species occur for the most part independently 
detached from each other, and mingled with spicules of other kinds of Sponges in 
beds of decayed chert in the Lower Carboniferous strata of Scotland, Yorkshire, 
North Wales, and Ireland. They also occur in close association with the ropes or 
bundles of anchoring-spicules, but not infrequently these latter are met with in beds 
which do not apparently contain the hexactinellid skeletal-spicules. This fact, 
however, may be explained by the greater chance of preservation of the anchoring- 
spicules owing to their penetration in the bottom ooze during the existence of the 
Sponge. It may be assumed that the anchoring and the skeletal-spicules belong 
to the same species. Further, the small fragments of the dermal layer of the Sponge 
which have been met with afford a clue to the character of the skeletal-spicules of 
the species, since they consist exclusively of simple and modified hexactinellids, and 
thus justify excluding therefrom those peculiar forms which were originally supposed 
to belong to this same species. 
The spicules of this species in the decayed cherts and limestones of the West of 
Scotland are of a porcelain-white tint, the larger forms are opaque, but the smaller, 
