320 



NATURAL HISTOKY. 



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 NautUus. There are, however, many fossil shells 



found which piu^tliave belonged 

 to animals of this group. The 

 Ammonites, commonly called 

 Snake Stones, of which a speci- 

 men is givten^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 

 Fig. 25i.-Ammonite. various sizcs, some reaching a di- 

 ameter of even four feet. 



552. The arms of some of the Cephalopods 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. 



Boft, and is covered only with a leatheiy skin. From 

 around its mouth extend eight long arms, which have on 

 them great numbers of little suckers, by which it can 



