Dr. G. J. Hinde on Fossil Calcispongie. 193 
due to a partial decomposition of the spicule itself. Some of 
the rays of the larger spicules exhibit a smooth surface and 
even outlines, though in no instance comparable to the exqui- 
site smoothness of the spicules of existing sponges. Under 
polarized light the fossil spicules occasionally exhibit faint 
prismatic tints of the same character, but less distinct than 
those shown by recent calcareous spicules. I have not dis- 
covered any traces of an interior canal in these spicules. 
The spicules forming the outer layer of the sponge are either 
three- or four-rayed, and vary considerably in size. ‘Three 
rays of the spicule are horizontally extended in the same 
plane, radiating from a common centre; in section each ray 
is circular, thick-set at the centre, where it connects with the 
others, and gradually tapering to the extremity, which is 
bluntly pointed. ‘Two of the three rays of the spicule are 
equal or very nearly equal in length, such as are termed by 
Hiackel “lateral” or paired-rayed, whilst the opposing ray, 
the “ basal” ray of Hiackel, is either longer or shorter than 
the lateral rays. Where a fourth ray is present (the “ apical” 
ray of Hickel), it springs from the central point of the three 
rays and at right angles to them. In this species the lateral 
or paired rays of the relatively large dermal spicules are either 
straight or nearly so, asin Pl. XI. figs. 3, 4, or possess a 
slight curve, which may be either towards the basal ray, as in 
figs. 5-8, or away from it, as in figs. 1,2. The angle 
formed by the lateral rays varies from 160° to 180°, whilst 
that on either side of the basal ray correspondingly varies 
between 90° and 100°. ‘The paired rays are usually both 
longer and stouter than the basals. ‘The apical ray, where 
present, appears to be shorter than any of the facial rays. 
There are great variations in the dimensions of these surface 
tri- and guadriradiate spicules. The length of ray in the 
largest which I have been able to measure is °24 millim. by 
054 millim. in thickness, whilst in a small specimen the ray 
is only °05 millim. in length by -015 millim. in thickness. 
The spicules of this surface or dermal layer are disposed 
with their facial planes parallel with the wall, so that the rays 
rest on the surface without spreading over the circular aper- 
tures. In some portions the basal ray of the triradiates is 
directed towards the base of the sponge; but in general no 
regular disposition of the spicules is apparent. The apical 
ray of the quadriradiate spicules appears to penetrate the wall 
at right angles to its surface. The majority of the dermal 
spicules seem to be quadriradiate; but in some no trace of a 
fourth ray can be detected. The largest of these spicules are 
disposed on the surface with their rays nearly touching ; the 
