slender tapering arms, spread out in a plane at right angles 
to the shaft and united together near the shaft by a solid 
siliceous membrane. The angle embraced by the four arms 
varies between 80° and 135° in different specimens. Only 
traces of canals are shown in the Horstead specimens but in 
similar spicules from Coesfeld, they are present both in the 
rays and shaft, and unite at the junction of these. I have 
not yet met with a complete specimen, but the arms appear 
to have been of equal length; the longest which I have seen 
is 0.9mm. The longest shaft met with is 0,787 mm. with a 
thickness of 0.056mm. In all the specimens the connecting 
membrane between the arms is only developed but a short 
distance from the shaft. The spicules are somewhat rare. 
No spicule at all resembling this has been met with 
in any recent sponge and its affinities are very doubtful. 
The number of the rays remove it from relationship with 
Tetractinellid sponges as also with surface spicules of the 
known Lithistids. It is possible however that it may be the 
surface spicule of a Lithistid sponge as there is a great 
diversity known to prevail in the outer spicules of this group. 
This spicule was first noticed in the Chalk of the North of 
Ireland (Wright: op. cit. p. go, Plate III, figs. 1 a, b.) and 
Dr. Bowerbank expresses the opinion that it is ‘from the 
expansile dermal system of a siliceo-fibrous sponge’. Professor 
Zittel has also figured several examples of the same _ spicule 
from the Upper Chalk Formation of Coesfeld (Ueber Coelop. 
p. 46 Pl. V. fig. 47—50). 
Order Hexactinellidae, Oscar Schmidt. 
The sponges of this order are built up of spicules com- 
posed of six rays which form three axes crossing each other 
at right angles. In each ray there is a distinct canal which 
unites with those of the other rays in the centre of the 
spicule. ‘There is an enlargement, in many instances, inthe 
