Ox Dr. G. J. Hinde on Fossil Calctspongie. 
smaller forms appear to be disposed beneath and between the 
rays of the larger. 
Beneath this surface-layer of tri- and quadriradiates the 
wall-fibre of this sponge is composed of spicules of a very dif- 
ferent form. These latter are in reality triradiates also, 
though at first sight scarcely to be recognized as such. They. 
are mostly elongated, curved, filiform bodies, with a small 
projecting knob. in the middle (Pl. XI. figs. 18-23) ; many 
are nearly straight or geniculate (figs. 14, 15), also provided 
with a similar central projection, which represents the basal 
ray of a triradiate spicule, on either side of which are the late- 
ral or paired rays. The rays are nearly of an even thickness 
throughout their length; im some they slightly diminish — 
towards the extremities. ‘The minute basal ray is in the same 
plane with the lateral rays, and, in the case of the curved 
forms, always springs from the outer or convex side of the 
curve. From their extreme delicacy it is rare to obtain these 
filiform spicules entire; the rays are usually fractured, and 
the broken portions might be mistaken for uniaxal spicules ; 
but I have not detected simple uniaxal spicules anywhere in 
this sponge. The largest which I have been able to measure 
is °3 millim. from end to end, or ‘15 millim. of a single lateral 
ray, whilst the thickness is 006 millim. The knob or basal 
ray is only ‘009 millim. in length, and is, I believe, complete. 
The fibre of the sponge is built up of these filiform spicules 
(figs. 18-23) disposed close together, though not absolutely 
parallel with each other; for many rest across the others, 
though generally in the same direction. The curved spicules 
are mostly disposed round the margins of the canals which 
penetrate the wall. The geniculate spicules (figs. 14, 15) are 
rare forms; so also is the spicule represented in fig. 16, which 
appears in form to be intermediate between the spicules of the 
dermal layer and those of the interior fibre. ‘he triradiate 
(fig. 24) with all the rays unequal is also arare form. I have 
carefully searched all the fragments of the fibre without dis- 
covering other than these filiform spicules in it. The inner 
or cloacal surface of the fibre, which faces the interior cavity 
of the sponge, appears to be unprovided with any special 
layer of spicules similar to those of the dermal surface. 
The spicules met with in this sponge are in form so dis- 
tinctly typical of calcareous sponges, that it would seem hardly 
necessary, but for the great doubt which has been manifested 
respecting the affinities of the Pharetrones, to point out in 
detail their close resemblance to those of existing Calcisponges. 
We have only to turn to the beautiful fgures in Hickel’s 
monograph to find a resemblance in form, and, as regards 
