DESCRIPTION. 137 



Specimen white, with undulated, smooth, and 

 bifurcated ribs ; teeth of the keel brown towards 

 the apex, extremely thin and brittle. 



Inhabits the Mediterranean and Indian Ocean. 



Fig. 2. Nautilus Pompilius. 



Shell with a cordate aperture, whorls obtuse and 

 smooth. 



Lister Conch, tab. 550. fig. 1.3. 



Specimen white, with flexuous yellowish tawny 

 rays and streaks : the inner whorls dark brown j 

 interior surface fine mother-of-pearl j umbilicus 

 pervious. 



Inhabits the Indian and African Ocean. 



Fig. 3. N. Spirula. 



Shell with an orbicular aperture, whorls cylin- 

 drical, remote. 



Lister Conch, tab. 550. fig. 2. 



Specimen white, within pearly j whorls gradu- 

 ally decreasing towards the point of the spire 3 the 

 last whorl excentric, continued, in a perfect shell, 

 into a long cylindrical straight tube ; siphunculus 

 lateral. 



Inhabits the American and Indian Ocean. 



