320 



NATURAL HISTORY. 



class has some species that live in fresh water, and some 

 even that live on land. I will notice each of these groups. 



551. Of the Cephalopoda, the only few existing species 

 that have a shelly covering are the Argonauts and the 

 Pearly Nautilus. There are, however, many fossil shells 



found which must have belonged 

 to animals of this group. The 

 Ammonites, commonly called 

 Snake Stones, of which a speci- 

 men is given in Fig. 251, are the 

 most abundant of these, there hav- 

 ing been described over five hund- 

 red species. These are found in 

 various kinds of rocks, and are of 

 various sizes, some reaching a di- 

 ameter of even four feet. 



552. The arms of some of the Cephalopoda are very 

 long. This is the case with the Cuttle-fish, one of the 

 most singular of animals, seen in Fig. 252. Its body is 



Fig. 252. Cuttle-fish. 



soft, and is covered only with a leathery skin. From 

 around its mouth extend eight long arms, which have on 

 them great numbers of little suckers, by which it can 



