136 Hooker. — On Pachytheca- 
the West Malvern Wenlock Limestone ; that he felt certain 
that the fossil was a lycopod, and proposed to have a section 
of one specimen made, but resolved not to do so until I had 
seen it. With Mr. Grindrod’s permission I had sections of 
this specimen made, and these at once revealed to me the fact 
of the algal nature of Pachytheca ; but, as to which, if to any, 
existing order of Algae it should be referred, I was and am 
unable to form any very definite opinion. 
After examining the sections myself, I submitted them to 
various botanists and naturalists who had made a study of 
the lower order of plants, and especially to cryptogamists, 
who all assented to my conclusion as to the algal nature of 
the organism, but whose opinions as to its nearer affinities 
were very much at variance with one another. 
There are three points in the general character of this fossil 
that are especially puzzling. 
First, the perfectly spherical form of so many of the speci- 
mens, whether carbonised or calcified, that I have seen : and 
they are from various localities. This indicates either a density 
of tissues that has withstood compression, or the infiltration 
of a soft tissue by mineral matter during or previous to fossili- 
sation. It further indicates a resistance to decay, for other- 
wise the minute tissues of the periphery would have been 
destroyed. Not only has the spherical form been perfectly 
preserved in all but obviously compressed specimens, but the 
peripheral ends of the radiating filaments, of which the wall of 
the organism is composed, have their lateral walls as perfect as 
are those of the inner cells ; and this, though the apices of the 
peripheral cells are broken away all over the surface of the 
organism : which conditions seem to indicate that the whole 
surface of the latter has been abraded. There can, I think, 
be no doubt but that the substance of Pachytheca was dense 
and resisting to a remarkable degree. 
The second character is the contrast between the tissues of 
the wall or cortical substance, and those of the filaments that 
traverse the central cavity in all directions. From the first I 
have been disposed to regard these latter filaments as having 
