THEIR DISTRIBUTION AND FUNCTIONS. 299 
Transition lime to the Lias, belongs to the herbi- 
vorous genera; and that the herbivorous class 
extends through every stratum in the entire 
series of geological formations, and still retains 
its place among the inhabitants of our existing 
seas. On the other hand, the shells of marine 
carnivorous Univalves are very abundant in the 
Tertiary strata above the Chalk, but are ex- 
tremely rare in the Secondary strata, from the 
Chalk downwards to the Inferior oolite ; beneath 
which no trace of them has yet been found. 
Most collectors have seen upon the sea shore 
numbers of dead shells, in which small circular 
holes have been bored by the predaceous tribes, 
for the purpose of feeding upon the bodies of 
the animals contained within them ; similar 
holes occur in many fossil shells of the Tertiary 
strata, wherein the shells of carnivorous Tra- 
chelipods also abound ; but perforations of this 
kind are extremely rare in the fossil shells of any 
older formation. In the Green- sand and Oolite, 
they have been noticed only in those few cases 
where they are accompanied by the shells of 
equally rare carnivorous Mollusks; and in the 
Lias, and strata below it, there are neither perfo- 
rations, nor any shells having the notched mouth 
peculiar to perforating carnivorous species. 
It should seem, from these facts, that in the 
economy of submarine life, the great family of 
carnivorous Trachelipods, performed the same 
