CHAP. x.J CONTINUITY OF THE CHALK. 493 



the shallower is the water which it inhabits. The 

 cephalopods are chiefly pelagic and surface things, 

 and their remains are consequently found in deposits 

 from all depths. To this general pelagic distri 

 bution of cephalopods there seem to he two re 

 markable exceptions, and these the two members 

 of their class which are by far the most interest 

 ing in their geological relations. Nautilus pom- 

 pilius inhabits the deep water of the Pacific, while 

 the habitat of Spmda australis is unknown. The 

 shell of Spirilla is thin and light, and, probably 

 after the death of the animal and by the decom 

 position of organic matter, it becomes filled with air, 

 and the emptied shell floats, and is drifted along on the 

 surface of the sea. Tropical shores are strewn with 

 the pearly little coil, which attracts attention by the 

 elegance of its form. It is abundant on all shores in 

 the path of the Gulf-stream. Sysselmann Miiller gave 

 me, a few years ago, a quantity which had been drifted 

 on the south-western shores of different islands of the 

 Pseroe group. Still the structure of the animal of 

 Spirilla may be said to be unknown. One specimen 

 only, which was described by Professor Owen, was 

 found nearly perfect on the coast of New Zealand by 

 Mr. Percy Noel. I suppose there can be little doubt 

 that this is a deep-water form, and I hope that with 

 our deep-sea dredging we shall soon clear up its 

 economy; but in the meantime the evident abundance 

 of the animal and our ignorance of its history are very 

 suggestive. In the London clay one or two examples 

 of a fossil have been found, nearly allied to Spirilla, 

 but differing in this respect that a solid conical 

 rostrum projects backwards, its half-calcified, half- 



