up from the Atlantic, off the Coast of Cuba, at a depth of 
270 fathoms, on which O. Schmidt, on account of the highly 
characteristic form and arrangement of the spicules, constituted 
the genus. I have had the opportunity of examining a frag- 
ment and also mounted slides of the original specimen, which 
were presented by O. Schmidt to Prof. Zittel, and have thus 
been able to compare the fossil Chalk spicules with those of 
the existing sponge. The spicules of the existing sponge 
have the same diversity of form and are attached together by 
the close fitting expanded extremities in a similar manner 
to the Horstead flint spicules, but the mesh is of a more open 
character and the thickness of the spicules is considerably 
less, in a word, to continue the simile, the strand of wire is, 
in this case, of a different thickness having an average diameter 
of 0,045 mm. but little more than one-third the thickness of Ly- 
idium Zitteli. It is on this difference of thickness of the spi- 
cules and on the closer character of the openings of the mesh 
that I venture to constitute these fragments and spicules into 
a distinct species, which it gives me great pleasure to name 
in honour of Professor Dr. Karl Zittel. 
Though first noticed as an existent sponge, the genus 
Lyidium appears to have had a wide distribution in the past. 
Mr. Carter has figured a number of spicules from the Haldon 
Green Sand whose similarity of form to Lyzdium torquilla 
‘O. Schmidt, he has noticed (An. Mag. Nat. Hist. S.4, Vol. 7, 
p. 118, Pl. VIII). Judging from the figures, these green sand 
spicules are of a greater thickness than those from Horstead. 
Spicules resémbling those of Lyidium are figured by Mr. Wright 
from the North of Ireland (op. cit. Pl. III, figs. 2 a, b, 3 a, b) 
and are referred to by Dr. Bowerbank as «singular and _pro- 
bably abnormal form of dermal spiculum of a. siliceo-fibrous 
sponge» I have also seen Lyidium spicules from the Chalk 
of Oxfordshire which were discovered by the Rev? R. Pattrick 
of Warbro’ Lastly, they are figured by Zittel from the Chalk 
Formation of Westphalia (Ucber Coelop. Taf. VII, fig. 38 
