ARGONAUT A PAPER SAILOR. 137 



other by a small siphunculus ; white or cream 

 colour ; the shell when perfect about an inch 

 in diameter. 



This shell is so exceedingly brittle that perfect 

 specimens are very rare. The last chamber, 

 which the animal inhabits, is a straight cylinder, 

 but it is so fragile that a vestige of it is seldom 

 to be met with. In the broken state in which 

 these shells are found, they resemble a ram's 

 horn, and so they have been described, but when 

 complete they have more the appearance of the 

 crosier. The mouth of the animal is surrounded 

 by ten arms, two being longer than the others. 

 This Nautilus is found in great numbers in the 

 West Indies. 



GENUS. ARGONAUTA.* 



PAPER SAILOR. 



Generic character. Shell univale, involuted, 

 the last turn very large, having a double tuber- 

 culated carina, thin, transparent, delicate, uni- 

 locular; aperture cordate, entire, contracted. 

 This shell has much the appearance of being 

 composed of two pieces united by the keel, and 

 seems to be the link between the univalve ancl 

 bivalve shells. 



* Plate VI. figure 5. 



12* 



