Dactylocalycites callodiscus (An. Mag. N. H. S. 4 Vol. 7 p. 
123) Pl. TX.) fig. 40). » It) seems ito me owever, that Wie 
affinities of these discs is rather with the siliceous globules 
and stellates of Geodia and other genera of Tetractinellid 
sponges than with the Lithistidae. In the surface spicules of 
both recent and fossil Lithistids, im which canals are present, 
they are restricted to three, which afterwards bifurcate in some 
instances. In no known instance of ascertained Lithistid sur- 
face spicule is there the number and disposition of the canals 
as in these isolated discs. Considerable light is thrown upon 
the affinities of these discs from the description which 
O. Schmidt has given of the different stages of growth of 
certain thin oval discs present in the existing sponge S/e/letia 
Euastrum (Spong. d. K. von Algier, p. 20, Taf. IV, fig. 4). 
In the earliest stage of the development of these discs there 
is a granular centre from which a single layer of extremely 
delicate needle-like rays or spicules radiate. More developed 
specimens show these fine ray-like spicules united near their 
bases and deeply notched at the periphery. In the complete 
disc one surface is smooth, flat, or slightly concave, whilst 
the other is convex and thickly covered with small warts. 
The structure of these discs from the Upper Chalk may 
be understood, if we suppose that in a similar manner to 
those of Stel/etta Euastrum, they have been developed by 
the amalgamation of a single layer of very fine spicules ra- 
diating from a centre and that the shorter and longer canals 
which are shown in the discs are those of the spicular rays 
of which they are composed. Although O. Schmidt does not 
mention the presence of canals in the spicular rays of the 
discs of Stelletta Euastrum, he yet states that he has repeat- 
edly noticed a central canal in the similar and equally mi- 
nute spicular rays of the siliceous globules of Geodza canal- 
culata (Spong. d. K. von Algier, p. 21). There appears there- 
fore a probability that these small bodies are the surface discs 
of a species of Stelletta. 
