202 THE TERTIARY AGE, AND 
affinity whatever with the Cephalopods. The sub- 
joined wood-cut represents 
one of these Shells, so nu- 
merous in the Tertiaries 
that large masses of rock 
consist of their remains. 
The Univalve Shells or Gas- 
teropods of the Tertiaries 
embraced all the families 
now living, including land 
and fresh-water Shells as well 
as the marine representatives 
of the type. Some of the lat- 
ter, as, for instance, the Ce- 
rithium, are accumulated in 
vast numbers. The limestone 
quarries out of which Paris is 
chiefly built consist almost 
wholly of these Shells. The 
fresli-water basins were filled 
with Helices, one of which is 
represented in the following 
■ wood-cut, with Planorbis, 
Limnseus, and other Shells 
resembling those now so 
common in all our lakes 
and rivers, and differing 
from the living ones only 
Helix. by slight specific characters. 
Cerithium. 
Nummulite. 
