THE SILURIAN BEACH. 
49 
Of tlie Silurian Univalves or Gasteropods there 
is not much to tell, for their spiral shells were so 
brittle that scarcely any perfect specimens are 
known, though their broken remains are found 
in such quantities as to show that this class also 
was very fully represented in the earliest crea- 
tion. But the highest class of Mollusks, the 
Cephalopods or Chambered Shells, or Cuttle- 
Fishes, as they are called when the animal is un- 
protected by a shell, are, on the contrary, very 
well preserved, and they are very numerous. Of 
these I will speak somewhat more in detail, be- 
cause their geological history is a very curious 
one. 
The Chambered Nautilus is familiar to all, 
since, from the exquisite beauty of its shell, it is 
especially sought for by conchologists ; but it is 
nevertheless not so common in our days as the 
Squids and Cuttle-Fishes, which are the most 
numerous modern representatives of the class. 
In the earliest geological days, on the contrary, 
those with a shell predominated, differing from 
the later ones, however, in having the shell per- 
fectly straight instead of curved, though its in- 
ternal structure was the same as it is now and 
has ever been. Then, as now, the animal shut 
himself out from his last year’s home, building 
his annual wall behind him, till his whole shell 
was divided into successive chambers, all of 
3 
