— 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 2 mm, width of .shaft 0,247 nim.; width across 

 the head 0,45 mm. Not very common. 



I have named the spicule in honour of Mr. Joseph Wright 

 F. G. S. who first discovered this form in the Msh 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 pi. 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, 

 TisipJionia annidata (An. Mag N. H. S. 5 Vol. 6 p. 494 pi. 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 P"lints 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. 



