— 32 — 
means so well defined as in the larger, and forms occur which 
show only traces of the rings, but I am unable to determine, 
whether this is owing to their non development or to subse- 
quent erosion in these smaller specimens. The simple interior 
canal is shown in the larger forms. Length of an average 
large specimen 2mm, width of shaft 0,247 mm.; width across 
the head 0,45mm. Not very common. 
I have named the spicule in honour of Mr. Joseph Wright 
F. G. S. who first discovered this form in the Irish Chalk 
(List of the Cretaceous Microzoa, Plate II fig. 5). In the 
figures of the Irish specimens, the rings extend quite to the 
extremity of the shaft, and in this respect differ slightly from 
the English forms. I have discovered similar spicules in material 
from Coesfeld and they are also present in beds belonging to 
the Lower Green Sand (Neocomian) in Surrey. Quadrifid spicules 
and also curved cylindrical spicules with similar ring-shaped 
expansions are described by Mr. Carter from the Haldon Green 
Sand under the names of Monilites quadriradiatus and 
M: Haldonensis respectively (An. Mag. N. H. S. 4 Vol. 7 p. 
132 pl. IX, fig. 44—47) but the trifid form does not appear 
to occur in these beds. An annulated quadrifid spicule has 
also lately been discovered by Mr. Carter in an existing sponge, 
Tisiphonia annulata (An. Mag N. H.S. 5 Vol. 6 p. 494 pl. V. 
figs. 28 a. d.) 
In addition to these trifid spicules, I have also found in 
the Horstead flint, a simple annulated acuate spicule similar 
in all respects to the trifid spicules but minus the capitate 
rays. At first I thought it might have been perfect for similar 
acuate forms are common in Chalk Flints in Oxfordshire, and 
also in the North of Ireland, but on examination under the 
microscope, I find that the head of the shaft is not evenly 
rounded off and that therefore the spicule is merely a headless 
trifid. 
