CONCHOLOGY. 175 



(S. Peronii. Peron's Spirula. PI. 36, fig. 2. 



Answers to the above description ; colour yellowish white. 



2. Nautilus. Two species. 



An elegant, well-known shell, more or less ventricose, dis- 

 coid, slightly compressed, umbilicated or not, but never pa- 

 pillose ; the septa simple, transverse, not visible externally, 

 the last deeply sunk and perforated by a siphon running 

 through them all ; edges entire. 



The N. Pompilius, when dissected, displays its beautiful 

 pearly chambers ; fine specimens are often converted into 

 drinking-cups by the Orientals, who sometimes remove the 

 outer coating, so that its whole appearance is pearly. 



The Nautilis varies in size; some are microscopic; and 

 although they have received diflferent names, and on account 

 of the animal have been made to form different genera, it 

 was deemed unnecessary to treat of them here. 



Nautilus Pompilius. Nautilus umbilicatus. 



N. Pompilius. The Pompilius Nautilus. PI. 36, fig. 3. 



Species not umbilicated ; the back rounded ; aperture 

 round and pearly ; siphon sub-central ; pale yellow, with 

 chestnut streaks and undulations. 



N. umbilicatus. The umbilicated Pompilius. PI. 36, 

 fig. 1. 



Spepies umbilicated, sub-orbicular ; pale fawn colour, with 

 chestnut undated transverse clouds. 



FAMILYXXII. 



Heteropoda. Two genera. 

 1. Argonauta. The Paper Sailor. Three species. 



The shells of this genus are remarkable for their fragility, 

 delicacy, and elegance ; they resemble a scroll, ornamented 

 with various canaliculated grooves from the summit to the 

 margin, which is bicarinated. The colour is usually bluish, 

 but the keel is of a darker hue ; they vary greatly in size. 



Shell navicular, symmetrical, very thin, compressed, bi- 



