40 



minute pointed spines. They average 0,18 mm. in diameter. 

 In existing sponges a somewhat similar form of globo-stellate 

 is present in Stelletta lactca, Carter. (An. Mag. Nat. Hist. 

 S. 4, Vol. VII, p. 9, PL IV, fig. 21 a) and also in Tethya 

 robusta, Bowerbank. (Mon. Brit. Spong. Vol. I, PL VI, 

 fig. 165) and it is probable that these Horstead examples be 

 long to one or other of these genera. O. Schmidt has 

 also noticed the similarity of the globo-stellates of Tethya and 

 Stelletta. (Spong. d. Kiiste von Algier. p. 21). Globo-stel- 

 lates precisely similar to those from Horstead are also pre- 

 sent at Coesfeld. (Ueber Coelop. Taf. IV. figs. 28, 30). 



In the remaining form of globo-stellate (fig. 27) the spi- 

 cule is larger and the rays are proportionately longer and 

 not so thickly set on the surface as in the form just described. In 

 an average specimen, the diameter, including the rays, is 0,29 mm. 

 and the rays have a length of 0,0675 mm. Varied forms of 

 these globo-stellates appear to be present in the same specimen 

 of sponge and these spicules probably belong to the same 

 species as the preceding. A similar body is figured by Rutot 

 from the Eocene of Brussels, (op. cit. PL III, fig. 35). 



Free Siliceous Discs of Stelletta? 



(Plate I, figs. 23, 24, 28). 



Besides the minute globates and globo-stellates, there are 

 present in the Horstead flint, two forms of small, flattened 

 disc like spicules. One of these (fig. 23) is an extremely 

 delicate, thin disc, circular in outline, with a well defined 

 smooth border and an apparently smooth outer surface. 

 Arranged at regular distances round the border of the disc 

 is a series of about 18 extremely delicate flask-shaped canals, 

 having their narrow end directed to the edge of the disc, which, 

 however, they do not reach, and extending somewhat more 

 than one third of the distance to the centre. Between each 

 of these canals, there are two, and occasionally three, still 



