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 naereous 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- 

 rialism and N. Sowerbyi. 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 Med way. 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 



