53 -- 



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 Lyidium torquilla 

 O. Schmidt, he has noticed (An. Mag. Nat. Hist. S. 4, Vol. 7, 

 p. 1 1 8, PI. VIII). Judging from the figures, these green sand 

 spicules are of a greater thickness than those from Horstead. 

 Spicules resembling those of Lyidium are figured by Mr. Wright 

 from the North of Ireland (op. cit. PI. Ill, 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 d R. Pattrick 

 of Warbro' Lastly, they are figured by Zittel from the Chalk 

 Formation of Westphalia (Ueber Coelop. Taf. VII, fig. 38 



