188 MANUAL OF THE MOLLUSCA. 
but at the bottom he creeps in the reyerse position, with his 
boat above him, and with his head and tentacles upon the 
ground, making a tolerably quick progress. He keeps himself 
chiefly upon the ground, creeping also sometimes into the nets 
of the fishermen; but after a storm, as the weather becomes 
calm, they are seen in troops, floating on the water, being driven 
up by the agitation of the waves. This sailing, however, is not of 
long continuance; for haying taken in all their tentacles, they 
upset their boat, and so return to the bottom.” 
Fig. 51. Nautilus expanded.* 
Distribution, 3 or 4 species. Chinese seas, Indian Ocean, 
Persian Gulf. 
Fossil, about 188 species. In all strata, South and North 
America (Chili). Europe. S. India. 
There are two types of ornamentation in nautili—the smooth 
and the longitudinally striated; the latter are almost exclu- 
sively oolitic, and at present only 1 species is known in Indian 
cretaceous rocks; the smooth type is almost exclusively cre- 
taceous, and is abundantly represented in India. D’Orbigny 
* Ideal representation of the nautilus, when expanded, by Professor Lovén, who 
appears to have taken the details from M. Valenciennes’ Memoir in the Archives du 
Museum, vol. ii., p. 257. h, hood; s, siphon. It is just possible that when tne 
nautilus issues from its shell, the gas contained in the last, incomplete, air-chambet 
may expand; but this could not happen under any great pressure of water. 
