Boyal Microscopical Society. 
103 
which, in 1845, I made the remarkable discovery of the existence 
of Xanthidia and Polythalamia in the grey chalk of Folkestone, a 
bed below the common white chalk. It is well known that the 
white chalk is chiefly made up of the debris of the shells of Fora- 
minifera — a fact first brought to my notice by the late Dr. Pereira 
— and that the layers of flints, supposed with strong reason by Dr. 
J. S. Bowerbank to be the fossilized condition of ancient sponges, 
contained a great variety of the organisms called Xanthidia and 
Polythalamia. I looked carefully in the chalk itself for the 
Xanthidia without success, but found them freely distributed in 
some portions of the grey chalk in which flint in layers, like those 
of the white chalk, do not exist, but in which occur occasional 
masses of chert, showing abundant evidence of the structure of 
sponges without, so far as I could detect, any evidence of Xanthidia. 
The Polythalamia in this grey chalk were in a very remarkable 
condition, showing what appeared to be the investing membrane of 
the shells and the bodies in a truly fossilized but not silicified con- 
dition. The species seemed to be identical with those found in the 
white chalk. Another curious fact seemed to me to be brought 
out, namely, the mode of distribution of the silica in these two kinds 
of chalk. In the white chalk it chiefly exists in the form of layers 
of flints ; in the other it is distributed in minute grains or crystals. 
I also discovered in a fucus (?) prepared as an article of diet in 
China or Japan, an abundance of a beautiful siliceous organism 
occasionally found in Ichaboe guano, and which, in a notice read to 
the Society, I named Arachnoidiscus Jajoonicus, forming the basis 
of a genus of great beauty, and deservedly popular amongst amateur 
observers with the microscope." 
" The distribution and exchange of these and other objects of 
interest with members of the Society led to the most friendly inter- 
course with many excellent men, to whom I am greatly indebted 
for kindly feeling and for hints in the art of observing and mounting 
objects, thousands of which I have had intense pleasure in distri- 
buting. It is almost invidious to name one good friend without, 
naming others, but it would be unjust not to mention Mr. Bower- 
bank's open weekly evening meetings at Islington, where anyone 
with a desire for knowledge was ever welcomed, with or without 
personal introduction. Frederick Bell and I went thus, were 
kindly welcomed, and had our first lesson in observing with a good 
microscope. So began what little skill I possess in the use of an 
instrument which for full thirty years has afibrded me an in- 
exhaustible source of elevating and unalloyed pleasure. My micro- 
scope led to a most friendly intercourse with the late Dr. Pereira, 
and some of the illustrations in the edition of his * Materia Medica,' 
in progress and unfinished at his decease, were made from objects 
prepared and mounted by myself." 
