nautiliDjE. 5T 



SUBCLYMENIA, d'Oi'b, 1850. 

 Diiitr. — S-evoluta^cVOrh (xxxi, 12, 13\ Devonian; England. 

 Shell spiral, planorbiform ; sutures of septa sinuous, not 

 angular on the sides, but with a single dorsal lobe. 



Trococeras, Barr., 184Y. 



Distr. — 60 sp. L. Silurian to Devonian ; Bohemia, France, 

 North America. 



Shell depressed, spiral, nautiloid or nearly discoidal ; whorls 

 free ; septa simple. Very closely related to Lituites. 



Nautilus, Breyn,, 1732. 



Syn. — Angulites, Montf., 1810 ; Omphalia, De Haan. 



Distr. — 6 living species, tropical seas ; and nearly 300 fossil 

 species, commencing with the Silurian. N. Pompilius, Linn, 

 (iv, 62, 63; xxvii, 54). 



Shell involute or discoidal, few-whorled ; septa concave, simple ; 

 siphuncle nearlj^ central. 



Outer surface smooth in the recent species, but corrugated in 

 some of the fossil ones. 



Animal placed with its ventral face to the convex (dorsal) wall 

 of the shell. 



They are divided into the following groups : 



1. Lsevigati. Shell smooth. Permian — Living. 



2. Radiati. Shell transversely ribbed. Principally cretaceous. 



3. Striati. Shell longitudinally striate. Oolite of Europe, 

 and Lower Chalk, India. 



Respecting the habits of the Nautilus very little is known : 

 the specimen dissected by Prof. Owen had its crop filled with frag- 

 ments of a small crab. Rumphius states that " when the Nau- 

 tilus floats on the water, he puts out his head and all his tentacles, 

 and spreads them upon the water, with the poop of the shell 

 above the surface ; but at the bottom, he creeps in the reverse 

 position, with his boat above him, and with his head and ten- 

 tacles 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, how- 

 ever, is not of long continuance ; for having taken in all their 

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



The shell is composed of two layers — the outer one porcellanous, 

 the inner pearly ; and the Chinese avail themselves of this circum- 

 stance to produce elegant relieved carvings upon the pearly 

 layer. Specimens are frequently imported for sale. 



During the voyage of the Challenger, a living N. Fompilius 

 was dredged in three hundred and twenty fathoms, off" Matuka 



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