264 POPULAR CONCHOLOGY. 



is but recently that their true origin has been 

 discovered, and their place in creation ascer- 

 tained; in former ages they have been de- 

 scribed as petrified fingers, thunder-stones, 

 stalactites, or as the teeth of an animal. — 

 There are nearly 100 species at present known. 



127. Orthoceras. — Shell straight, with 

 septa regularly concave towards 

 the mouth, perforated by a 

 simple and nearly cylindrical si- 

 phuncle, either in or not far 

 removed from the centre of the 

 disk. 



All fossil? Found in strata 

 mostly below the carboniferous 

 or mountain limestone. 



128. Spirula. — Shell cylindrical, thin, and 

 almost transparent ; partially spiral, 

 the whorls not touching each other ; 

 perforation of the chambers at the 

 side, which are equidistant ; par- 

 titions externally concave. Animal 

 with ten arms, two of which are longer than 

 the others, and nearly conceal the shelL — • 

 1 species, recent. 



