300 TESTACEOUS CEPHALOPODS 
necessary office during the Tertiary period, 
which is allotted to them in the present ocean. 
We have further evidence to shew, that in 
times anterior to, and during the deposition of 
the Chalk, the same important functions were 
consigned to other carnivorous Mollusks, viz. 
the Testaceous Cephalopods these are of com- 
paratively rare occurrence in the Tertiary strata, 
and in our modern seas; but, throughout the 
Secondary and Transition formations, where car- 
nivorous Trachelipods are either wholly wanting, 
or extremely scarce, Ave find abundant remains 
of carnivorous Cephalopods, consisting of the 
chambered shells of Nautili and Ammonites, 
and many kindred extinct genera of polytha- 
lamous shells of extraordinary beauty. The 
Molluscous inhabitants of all these chambered 
shells, probably possessed the voracious habits 
of the modern Cuttle Fish, and by feeding 
like them upon young Testacea and Crustacea, 
restricted the excessive increase of animal life 
at the bottom of the more ancient seas. Their 
sudden and nearly total disappearance at the 
commencement of the Tertiary era, would have 
caused a blank in the “ police of nature,” 
allowing the herbivorous tribes to increase to an 
excess, that would ultimately have been de- 
structive of marine vegetation, as well as of 
themselves, had they not been replaced by a 
* See explanation of the term Cephalopod, in note at p. 303. 
