188 



MAlfdAL or THE MOLLTJSCA. 



but at the bottom lie creeps in the reverse position, with his 

 boat above liim, 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 trooi^s, floating on the water, heing driven 

 up hy the agitation of the luaves. This sailing, however, is not of 

 long continuance ; for having taken in all their tentacles, they 

 upset their boat, and so return to the bottom." 



Fig. 51. Nautilus expauded.* 



Bistrihution, 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, hy Professor Loven, who 

 appears to have taken the details from M. Valenciennes' Memoir in the Archives du 

 Museum, vol. ii., p. 2.57. A, hood ; s, siphon. It is just possible that when tne 

 nautilus issues from im shell, the gas contained in the last, incomplete, air-chambet 

 maj' expand ; hut this could not happen under any great pressure of water. 



