instances the tube apparently commences in the centre of the 
broken end of a spicule, where the canal in the perfect example 
would be situated and from thence it extends forwards in the 
substance of the spicule without any regularity , occasionally 
keeping near the centre or wandering towards different parts 
of the circumference, without however penetrating the outer 
wall of the spicule. The interior is apparently filled with a 
transparent material of a light greenish tint, giving no colour 
under the polariscope and apparently destitute of any granular 
particles. The longest of the tubes noticed is 1,8 mm. and 
the width varies in different specimens between 0,033 mm. 
and 0,067 mm. 
The mineral character of the spicules in which these bor. 
ings occur is precisely similar to the normal ones of this 
material, that is to say, it is now of chalcedonic silica and 
there seems no reason to doubt that the chalcedonic silica 
has been produced from the conversion of the original amor- 
phous silica of the sponge spicule, so that these perforated 
tubes whether made previous or after the change, have been 
constructed in siliceous material. The peculiar form of the 
perforations show that they have been produced by the action 
of some living organism, of which no other traces are left. 
These tubes are larger than those which have been described 
by Prof. Duncan in the substance of Silurian and Tertiary 
corals, and attributed by him to the boring influence of a 
parasitic alga, Palacachyla perforans (Quart. Jour. Geo. Soc. 
Vol. XXXII, p. 205) neither are they branched or filled with 
the dark granules which appear associated with the borings 
in the corals. There is further the peculiarity that they have 
been made in siliceous structures. 
