46 NAUTILIDyE. 



from the body, with a great number of cylhidrical, anmi- 

 lated, retractile tentacles, without cups. Gills four. Si- 

 phuncle slit. Foot-like a]3pendage distinct. 



This order is the same as the Tetrabranchiata of Owen ; 

 the only recent genus is Nautilus ; the rest are fossil, and 

 comprise a large number of highly interesting forms, which 

 must formerly have played an important part in the mala- 

 cological history of our planet. 



Fara. NAUTILID^. 



Head retractile within the mantle. Eyes pedunculated. 

 Mandibles calcareous. Body attached to the shell by ad- 

 ductor muscles, and by a continuous horny girdle. 



Shell external, camerated or many- chambered, and 

 siphuncled ; the inner layers and septa nacreous, the outer 

 layers porcellanous ; sutures simple ; aperture simple. 



This family contains the only living representative of 

 the Oephalopods belonging to the present order, the re- 

 mainder, comprising numerous families and genera, and 

 upw^ards of one thousand four hundred species, are now 

 extinct. The generic characters and peculiarities of these 

 forms are well and clearly pointed out in Mr. S. P.Wood- 

 ward"'s valuable "Treatise on Recent and Fossil Shells," a 

 work of which we have frequently availed ourselves. 



Genus NAUTILUS, Breynius. 



Shell involute or discoidal, few-whorled ; siphuncle cen- 

 tral ; septa dividing the chambers simple ; inner surface 

 pearly. 



Ex. N. Pompilius, Linnaus, pi. 5, fig. 4. Shell, N. 

 Pompilius, fig. 4, a. 



