SHELLS. 221 



2. Genus Loligo. — The species known here is the 

 Loligo punctata. The body is generally lengthened, 

 more or less flattened, with the skin dilated on each 

 side, so as to form a pair of wings or fins. Its usual 

 mode of swimming is by dilating its body and filling 

 it with water. The body is then suddenly contracted, 

 and the water forcibly ejected, so as to propel it 

 backward with great rapidity, shooting like an arrow 

 through the water. 



The animals comprising this genus hare been 

 celebrated from the earliest times for their singular 

 property of surrounding themselves with an inky 

 fluid, with which they envelop themselves to evade 

 pursuit. They are carnivorous, destroying many 

 fish and crabs. 



II. Cephalopoda monothalama : — 



This division contains only one genus, viz. Argo- 

 nauta ; but we have seen no species to represent it. 



III. Cephalopoda polythalama : — 



The greater portion of the shells of this division 

 are fossils, and many of them very minute. 



Only one species is known here of the genus 

 Spirula, viz., Spirula peronii : shell white, fragile, 

 about a quarter of an inph in diameter, with two or 

 three spiral turns, which do not touch each other. 

 The place of the partitions of the chambers within 



