104 Proceedings of the Royal Physical Society. 
had lost the whole of the outer or inhabited chamber, but the 
triangular shape of the aperture was distinctly shown by the 
compressed ventral margin of the remaining part of the shell. 
The position of the siphuncle — said to be close to the dorsal 
margin — seemed to be indicated by a small deposit of iron 
pyrites, probably caused by the organic matter having been 
longer retained in that canal. The interior of the shell was 
filled with a ferruginous clay, containing a large proportion of 
carbonate of lime, a stalagmitic layer of which was seen en- 
crusting a portion of the mass. Defoliation of the outer 
porcellanous coat of the shell had taken place, but what 
remained of the inner nacreous layer showed the striae of 
growth bending sharply backwards in well-marked undula- 
tions. If the proportions of the fossil specimen were similar 
to those of the recent Nautilus pompilius, the shell, when 
entire, would have measured about fifteen inches in diameter. 
Dr M'Bain stated that the Nautilidse were in some respects 
the most interesting family in the molluscan sub-kingdom. 
They formed the type of the second order, Tetrabranchiata of 
Owen, in the class Cephalopada, of which upwards of 1400 
fossil species have been disinterred from the Palaeozoic and 
Mesozoic rocks. Of all the genera constituting the Tetra- 
branchiate order of mollusca that existed in the ancient seas, 
the nautilus was the only one that had been found to pass into 
the tertiary formations, and there were at least two species 
still existing in the seas of the tropics. Six fossil nautili 
were stated by Mr Edwards to have been found in the older 
Eocene deposits of England, and four of these had been ob- 
tained from Sheppy — the N. centralis, N. urbanus, N. impe- 
rialis, and N. SowerhyL That island was well known to 
palaeontologists as a rich depository of organic remains. It 
was situated on the south side, at the mouth of the Thames, 
and separated from the county of Kent by the East Swale, 
and estuary of the river Medway. The greatest length of 
the island, from the garrison at Sheerness to Warden Point, 
the easternmost extremity, was about ten miles, and it was 
from five to six miles in breadth. The geological structure 
consisted of a vast deposit of dark gray or brownish clay, 
rising to the height of nearly 500 feet above the sea, with 
